DC-Voltage Gradient (DCVG) Surveys
Contents
1. The choices are On Off Pairs DSP mode and On Off Pairs GPS Sync On Off Pairs DSP mode In this mode the voltmeter uses digital signal processing to determine the voltage during the ON portion of the rectifier current cycle and the voltage during the OFF portion of the current cycle For these measurements to be successful the data probes reference electrode canes must remain in good electrical contact with the soil for at least one rectifier current cycle With this voltmeter reading mode selected the next step is to select the particular rectifier current interrupter cycle that will be employed during your DCVG survey As can be seen by tapping on the pull down list arrow in the ON OFF Cycle box on the above screen 5 industry standard cycles are available for selection 32 0 7 0 3 Means current is ON for 0 7 sec and OFF for 0 3 sec 0 8 0 2 Means current is ON for 0 8 sec and OFF for 0 2 sec 1 5 0 5 Means current is ON for 1 5 sec and OFF for 0 5 sec 3 0 1 0 Means current is ON for 3 0 sec and OFF for 1 0 sec 10 2 0 Means current is ON for 10 sec and OFF for 2 0 sec There are actually 10 choices since if the Off gt On box in ticked the above waveforms would be reversed For example the 0 7 0 3 waveform would become Current OFF for 0 7 sec and ON for 0 3 sec By tapping on the OK button on the screen after making your waveform cycle selection the active Survey screen would appear2. DCVG Anomaly DCVG Max On Off 0 0219 0 0 0000 Cathodic Cathodic 35 78533 DCVG Anomaly DCVG Max Total 0 0165 0 24 3292 35 78571 DCVG Anomaly DCVG Max On Off 0 0174 0 0 0000 Cathodic Cathodic 35 78571 DCVG Anomaly DCVG Max Total 0 0164 0 25 7984 35 78606 DCVG Anomaly DCVG Max On Off 0 0144 0 0 0000 Cathodic Anodic 35 78606 DCVG Anomaly DCVG Max Total 0 0193 0 24 2513 35 78624 DCVG Anomaly DCVG Max On Off 0 0117 0 0 0000 Cathodic Anodic 35 78624 DCVG Anomaly DCVG Max Total 0 0214 0 31 0009 35 78707 DCVG Anomaly DCVG Max On Off 0 0106 0 0 0000 Cathodic Anodic 35 78707 02703 See Field Notes 0 0000 O 0 0000 PCM indication 35 78707 Line Crossing 0 0000 0 0 0000 ML3TK xing 35 78723 DCVG Anomaly DCVG Max Total 0 0165 0 22 1451 35 78728 DCVG Anomaly DCVG Max On Off 0 0096 0 0 0000 Cathodic Anodic 35 78728 DCVG Anomaly DCVG Max Total 0 0172 0 30 9754 35 78734 DCVG Anomaly DCVG Max On Off 0 0169 0 0 0000 Cathodic Anodic 35 78734 02704 See Field Notes 0 0000 0 0 0000 PCM indication 35 78734 DCVG Anomaly DCVG Max Total 0 0190 0 15 7253 35 78789 r DCVG Anomaly DCYG Max On Off 0 0278 0 0 0000 Cathodic Cathodic 35 78789 lt lu The above Device Readings window displays data for a number of different defects that were marked during this example survey The data presented for each defect occupies 2 rows and is as follows Row 1 Max mV Total mV IR Row 2 Max mV ON Max mV OFF 0 0000 In addition based
3. Also place a tick in the box labeled Copy to Local Folder and identify the Folder s location in your hard drive in the box underneath This is the Folder that you set up previously to save all of your survey files uploaded from your DA Meter see Section VI 2 Pre step 2 If you named the Folder Surveys the Folder s location would be C Surveys E DA Meter Driver Pipeline Survey Data Type Pipeline Survey Get PLS from DAMeter Surveys If you have already moved your survey data to the desktop computer check Use Local Folder and select the folder where it is located Use Local Folder C Surveys e ML2TK 6 17 03 2694 78 2 frank2 Refresh Connection ONEOK 4052 03 29 04 EM LINE 1 001 o anma Select the survey to upload then click on Go gt Go Ready Version 1 9 8 9 Minimum DAMeter Version 1 0 1 52 As an example the Driver window would appear as shown above if the survey named EM 004 was selected for uploading to your PC and if the Folder to which the survey file was to be sent was named Surveys in your hard drive Of course the actual survey names appearing in this box will depend on the filenames of the surveys that have been performed using your own DA Meter In our example the Driver will have located survey file EM 004 in our DA Meter s memory and when the Go button on the Driver Window is clicked the survey named EM 004 will be saved in
4. Management System Step 1 Double click on the ProActive icon on your PC s desktop screen This will open up ProActive s main menu window A window labeled Entire Database will also be seen here The suggested organization of your Entire Database which will represent a hierarchical structure of all of your survey data within ProActive is discussed in the ProActive Manual Step 2 Click once on the Surveys button on the main menu bar at the top of the screen This will open a window labeled Data Logger Get Pipeline Survey By clicking on the pull down list arrow on the Data Logger box you can select the data logger from which you are uploading survey data As shown in the pull down list the various data loggers currently supported are offered as choices including the DA Meter Step 3 Select DA Meter Option 51 Highlight DA Meter in the pull down list and click on the Go button This will open up a window labeled Driver Pipeline Survey Note It may take a few seconds for the Driver Window to appear Step 4 Select the Survey to be Uploaded and Upload Survey Select Pipeline Survey in the box labeled Data Type The Survey box in the DA Meter Driver window will list all of the survey files currently stored on your DA Meter s CompactFlash memory card Click on the file survey name that you would like to be uploaded onto your PC
5. Port in order that the position of items such as DCVG Anomalies flags devices and geo features can be recorded during the performance of a DCVG survey either manually by tapping on the Log GPS button on the survey screen at each critical location or automatically by pre programming the DA Meter as described in Section III Step 10 IV 2 How to Attach Cables and Accessories to the DA Meter The terminals on the top side of the DA Meter for the various connections described above are illustrated in Figure 10 below 38 5 Pin Data Probe Connector GPS Connector Positive Terminal Negative Terminal 9 Pin Communication z 7 Port ib WN Figure 10 Connection terminals on rear of the DA Meter The 5 pin Data Probe Connector is shown above as Terminal 1 As discussed above the reference electrode canes are connected to this terminal via the dual probe adapter Again the reference electrodes are effectively connected to the positive green handled cane or negative red handled cane sides of the voltmeter with this connection Consequently the red and black banana plug terminals Terminals 3 and 4 are not used in this application Terminal 5 is a GPS receiver terminal A GPS receiver capable of outputting NMEA data such as a Trimble Pathfinder unit or the MCM unit would be connected to Terminal 5 9 pin terminal Terminal 2 is currently earmarked for future use Finally Terminal 5 is also used after perfo
6. You can also use either cane button when recording voltages at D C P s data collection points devices to accept or accept and save a device reading as opposed to tapping on the accept or the save buttons on the screen For example with the selection as indicated on the above screen device readings would be recorded automatically by triggering either cane button which is the accept and save option If you prefer to tap buttons on the screen at devices then select the none option in the D C P box Step 9 Select Walking Direction 24 Finally on the Setup 1 of 5 screen you should indicate whether station numbers will be increasing or decreasing as you proceed in the survey direction by tapping once on either Increasing or Decreasing in the Survey Walking Direction box Step 10 Select GPS Receiver Type and GPS Options Tap once on the Next button The Setup 2 of 5 screen will appear as shown below Survey Survey Options Heip 7 AN il AC System eon v GPS Type im id _ Differential GPS Required M Use GPS for Altitude GPS Port Comi v V Log GPS at Flags V Log GPS at DCP Feature M DCVG Anomaly Max my 1st reading for Tot m Log GPS at Side Drain Anomaly BI DAMeter_PLS F Ta 2 49 AM By tapping on the pull down list arrow in the GPS Type box you can select the type of GPS unit you will be using if any from the list shown belo
7. and the left hand electrode is connected to the negative side of the voltmeter If we continue walking past the location of the defect the difference between the soil potentials at the reference electrode positions will begin to decrease in magnitude and eventually will be zero again as we exit the voltage gradient field Consequently a profile such as that shown below in Figure 5 will be observed in the case of Perpendicular DCVG surveys as a coating defect is encountered gt m Electrode Position Survey Direction y Along Pipeline Defect Location Figure 5 DCVG Voltage as a Function of Electrode Position along Pipeline in the vicinity of a Coating Defect as measured with electrodes in perpendicular configuration see Figure 4 11 II 3 Definition of DCVG Voltage DCVG surveys are performed in the rectifier current ON OFF mode ie the rectifier current is switched ON and OFF in a cyclic fashion This allows soil to soil potential differences to be recorded during the ON portion of the current cycle and also during the OFF portion of the current cycle For DCVG surveys the MCM data logger s software calculates the difference between the soil to soil potential difference recorded during the ON part of the cycle delta V ON and the soil to soil potential difference recorded during the OFF part of the cycle delta V OFF The polarities of both delta V ON and delta V OFF are also recorded at defect sites more
8. conditions of the particular survey about to be performed and identifies the section of pipeline that is about to be examined by the DCVG application The set up process and this is very important also establishes a file in which the voltage recordings survey data will be stored At the completion of the survey DCVG survey data can then be retrieved by a PC that is in communication with the DA Meter by accessing the file in which the survey data is stored The uploading process of transferring survey data to a PC following completion of a DCVG survey is discussed in Section VI The software program required to upload or transfer the survey data to a PC is part of an MCM proprietary software package known as ProActive As discussed in Section VI the ProActive software package is a critical component of MCM s Integrated Test Equipment and Database Management Package Step 1 Switch on the DA Meter by pressing the power button Assuming that the battery pack is charged the screen will light up and will display the Windows desktop screen as shown below assuming that the operating system running your DA Meter is Windows Handheld PC 2000 My Handheld C P Meter 75S DAMeterSS E Recycle Bin Ze 9 12 PM q Handheld PC 2000 20 Step 2 Double tap using the special pen stylus provided with the DA Meter on the DA Meter PLS icon This will open the software program that will run the DA Meter in pipe
9. current flowing OFF state If net current is flowing to the defect the potential at the defect will be negative relative to remote earth however the maximum delta V recording will have a positive value due to the positioning of the positive and negative reference electrodes This is a cathodic condition If net current is flowing away from the defect into the soil the potential at the defect will be positive with respect to remote earth however the maximum delta V recording will have a negative value This is an anodic condition Since we are able to record the polarity of Max mV ON and Max mV OFF we can determine the corrosion condition of the defect both when the CP current is impressed and when the CP current is not flowing to the defect The best case scenario is cathodic cathodic however cathodic anodic is also acceptable since in this case the CP system s impressed current is doing its job ie it is preventing corrosion taking place 16 at the defect site The worst case scenario would be anodic anodic since in this case the defect is not protected even with CP current flowing II 10 In Line Parallel DCVG Survey Technique There is a second method of performing DCVG pipeline surveys known as In Line or Parallel mode DCVG surveys In this case DCVG voltages are recorded in a close interval fashion by placing the reference electrodes in line with the pipeline directly over the pipeline as op
10. in uploading DCVG survey data to a PC for data management SECTION II PHYSICAL PRINCIPLES II 1 Potential Voltage Gradients As discussed in our CIS Training Manual when a buried pipeline is under cathodic protection the DC rectifier current that flows to and in the pipeline impressed current causes the pipeline to be negatively charged with respect to the surrounding soil In fact as illustrated in Figure 1 below a potential gradient exists between the pipeline and the surrounding soil the potential being largest at the pipe itself largest negative value and dropping off rapidly with distance away from the pipe The potential at remote earth is zero and the potential gradient is the potential difference between the pipe potential negative potential at the pipe and remote earth Line of Constant Potential Cathodically Protected Buried Pipeline Figure 1 Potential Gradient Associated with a Cathodically Protected Pipeline Equipotential Lines are closer together near the pipe indicating that the potential drops quickly initially with distance away from the pipe In the case of a well coated section of pipeline the potential at ground level in the vicinity of the pipe will be close to zero close to remote earth potential However when coating defects holidays are present the local potential at the defect locations increases significantly since the impressed current flows through the soil primar
11. on these polarities later Since delta V ON represents the soil to soil potential difference with current contributions from the pipeline s CP system as well as from all other sources stray interference foreign pipelines etc and since delta V OFF represents the soil to soil potential difference with only the other current sources contributing a DCVG recording will represent the soil to soil potential difference with only the pipeline s CP system contributing to the current flow to the defect For the remainder of this manual the term DCVG voltage will be taken to mean the difference between the CP current ON soil to soil voltage reading and the CP current OFF soil to soil voltage reading II 4 Definition of Total mV The so called Total mV is the difference between the maximum potential at a defect location and the potential at remote earth arising due to the CP system s contribution to the current flow to the defect Since as shown in Figure 4 a typical electrode spacing is 4 to 5 feet and the voltage gradient field associated with a defect typically extends a significant distance beyond the right hand reference electrode location several measurements are actually required in order to determine the total voltage gradient Total mV associated with a defect 12 II 5 Procedure to determine Total mV When the defect location has been identified as described above ie the location w
12. on this screen The DA Meter s software will calculate the difference between the High and the Low voltage recordings which is the IR drop and use this quantity in future calculations However for this to happen you must place a tick in the box labeled Use reading for DCVG signal strength The IR drop is also referred to as the signal strength You should then tap once on the Accept button and then once on the Save button to save this data 44 Note You should perform pipe to soil measurements at each test station you encounter in order that the DA Meter s software can perform the linear interpolation calculation described in Section II 7 when necessary to determine an average signal strength IR drop to apply at each defect location between test stations V 5 How to Locate and Mark Defects When possible the CP system should be adjusted to provide a signal strength IR drop on the order of 5 00mV This will make it easier to find the smaller defects as well as the larger ones Once you have recorded the pipe to soil voltages and observed the magnitude of the signal strength IR drop you should disconnect the test cable from the DA Meter s red banana plug terminal and reconnect the positive green handled cane to the dual probe adapter You are now ready to record DCVG voltages down the length of the pipeline For Perpendicular DCVG surveys you would place the reference electrodes ca
13. selecting Survey Filenames Critical information should be included in the filename such as pipeline company s name city or state in which the pipeline is located pipeline number and section of pipeline number under survey The protocol developed should be applied consistently for each survey For example let s assume that pipeline company XYZ has a pipeline located in Texas and that the pipeline is identified as pipeline 12 and a survey is being performed on section 085 of this pipeline A good filename for this survey would be XYZ TX 12 085 DCVG When this survey file is later accessed with this filename we know the name of the pipeline owner we know the state in which the pipeline is located we know the pipeline number we know the section of the pipeline that was surveyed and we know that it was a DCVG survey 22 Step 5 Tap once on the OK button The window shown below will appear depending on previous settings This is the first of 5 so called setup windows Survey Survey Options Help vm E E Survey Type Continuous cIs z Cane Button s Allowed To Rectifier Mode cycle ON OFF v D C P None Survey Walking Direction Accept Flag Pause increasing O Decreasing Accept gt Save set once during initial setup Pstart eevameterpis te 4 01 AM Step 6 Select Survey Type Tap once on the pull down list arrow in the Survey Type box to
14. the Survey screen will always point back to the pipe in the perpendicular survey case If you selected automatic logging of GPS position data at Sidedrains Anomalies back at Step 13 Section III the DA Meter will automatically log the GPS position data for this DCVG Anomaly If you did not select this option you should tap on the Log GPS button at this time to log the defect location if you are using a GPS receiver If you are satisfied that you are reading the maximum DCVG voltage value for this defect you should record the Max mV reading by tapping on the circle labeled Read Max mV and tapping on the Accept button do not tap on the Save button at this time The screen show below will appear Mark DCVG Anomaly Accept 5 1 mv DCVG Max mV 65 1 J 104 7mY Oni39 7m Off Clear Total mV 65 1 Notes 8 DAMeter_PLS Ro 11 27 PM 46 In the above example the Max mV reading was 65 1mV delta V ON was 104 7mV and delta V OFF was 39 7mV and the difference between these values is 65 1mV this was a cathodic cathodic situation since both polarities were positive You will also notice that the software has automatically applied the Max mV value to the Total mV determination since we selected this option back at Step 13 Section III If this were not the case you would Accept the Max mV reading a second time and this would become the first voltage used in the Total mV d
15. voltage drop in the soil due to the CP current flowing is a quantity known as the IR IR Total mV IR drop x 100 In order to determine the IR drop value to use in the above equation pipe to soil voltages are recorded at the test stations bracketing a defect location The data logger s software then calculates the difference between the ON and the OFF pipe to soil voltages IR drop values at each of the test stations If the IR values recorded at both test stations are essentially the same the data logger uses this IR drop value to calculate the IR value for the defect using the above equation If on the other hand the IR drop values recorded at the two test stations bracketing the defect are significantly different the data logger s software will generate an average IR drop value to use in the equation based on the defect s location relative to the locations of the two test stations For example if the two test stations bracketing a defect are 1 mile apart and the defect is located as shown below and if the IR drop values are lt 1 3 mile gt lt 2 3 mile gt TS1 Xnn92 22222 0022 22 202 2222 22022 22 0222 2 TS2 300mV Defect 500mV IR drop IR drop recorded as shown at the two test stations 300mV and 500mV the data logger will determine the IR drop value for the IR calculation to be 300mV 1 3 x 500mV 300m
16. which will be placed on the soil above the pipeline in either the Perpendicular or the In Line configuration see Section II have push buttons on top of the handles so that the operator can trigger voltage recordings on his command at each of the pipeline survey measurement locations as well as at Devices and Geo Features See Section III Step 8 for a discussion on cane button functionality Step 8 of the DA Meter s Set Up Process The canes data probes are connected as shown to the input terminals of the dual probe adapter and the output terminal of the adapter is connected to a 5 pin Data Probe Connector socket on the top side of the DA Meter NOTE The left hand reference electrode red handled cane is connected to the dual probe adapter via a black band cable while the right hand reference electrode green handled cane is connected to the dual probe adapter via a red band cable This is important since the right hand reference electrode connects to the positive side of the data logger s voltmeter while the left hand reference electrode connects to the negative side of the voltmeter The red band and the black band cables can be b oe connected to either one of the dual probe adapter s input terminals A GPS receiver is also illustrated in Figure 9 Such a unit can be connected to the DA Meter via the 9 pin serial data terminal on the top side of the DA Meter COM 1
17. you are working on pipeline ABC within valve segment 45 and you are about to begin a DCVG survey at station number 12 00 0 your Setup 3 of 5 screen would be as shown below Survey _ Survey Options Help ANS il Flag Dist Error Limit 20 Name of P L of Feet Per Reading a bd ft Valve Segment of Feet Between Flags 100 ft 45 Starting Station Auto Pacing Mode V 12 00 0 set once during initial setup BiDaMeter PLS J Ta 3 18 AM Step 22 Tap once on Next button on Setup 3 of 5 screen The Setup 4 of 5 screen will appear as shown below Survey Survey Options Hee N il Set up 4 0of5 Work Order j Technician Name Comments Description File Name Compact Flash DAMeter_DATA t10 t10 mem x a cear date time system data Clear E ca 7 8 2004 3 21 35 set once during initial set once during initial setup at the Control Panel Astart peeDaMmeter_PLs J Ta 3 21 AM 30 Step 23 Provide the Work Order Number for the DCVG survey By tapping once on the box labeled Work Order you can type in the work order number for the DCVG survey Step 24 Provide Your Name By tapping once on the box labeled Technician Name you can type in your name Step 25 Provide Comments By tapping once on the box labeled Comments Description you can enter any comments you might have regarding the survey perhaps w
18. DC Voltage Gradient DCVG Surveys Using MCM s Integrated Pipeline Survey Test Equipment and Database Management Package DCVG Training Manual DA Meter Version MAA M6 MILLER co M C Miller Co Inc 11640 US Hwy 1 Sebastian FL 32958 Telephone 772 794 9448 Website www mcmiller com MANUAL CONTENTS Page SECTION I INTRODUCTION 4 SECTION II PHYSICAL PRINCIPLES II 1 Potential Voltage Gradients cece cece ccc e eee nee e eee ee es 5 II 2 Perpendicular DCVG Survey Technique cece ee eens 9 II 3 Definition of DCVG Voltage cece cece eee e eee eee e ence 12 II 4 Definition of Total MV ariencdtedce ish ec thia ePe Peep ee ieee aaa 12 II 5 Procedure to Determine Total MV cece cece cee eee e ee eens 13 II 6 Defect Size Considerations csiss wd ita ee nagon es wie nieedan 14 I 7 Definitionof IR sp c cs cehcartal nt Petatagete mete elect Sum does 14 II 8 Summary of DCVG Parameters at Defect Locations 16 II 9 Polarity Considerations 2 5 0 ssceesseaeecabdeseeter tes tacweee tar on 16 II 10 In Line Parallel DCVG Survey Technique 0068 17 SECTION III HOW TO SET UP THE DA METER FOR DCVG SURVEYS 20 SECTION IV TEST EQUIPMENT HOOK UPS FOR DCVG SURVEYS IV 1 How to Make Cable Hook Ups for DCVG Surveys 37 IV 2 How to Attach Cables and Accessories to the DA Meter 38 SECTION V HOW TO PERFORM DCVG SURVE
19. Manual for specific information 57 APPENDIX 1 How to Delete Survey Files from the DA Meter Once you have uploaded your survey files to your PC and have saved the files on your hard drive see Section VI copy to local folder step you can if you wish delete the files from your DA Meter if you need for example to create space in the data logger s file storage memory to make room for future survey files Your survey files are stored in the DA Meter on a non volatile CompactFlash card Since this memory is non volatile your survey data will be safe even if all power is lost to your DA Meter Please note however that the DA Meter s program files the files that actually run the DA Meter are stored in a volatile memory and so if all power was lost ie the battery pack and back up battery were fully discharged you would need to re install the DA Meter s software application package see DA Meter User s Manual Since your survey files are stored on the CompactFlash card you will have to access this memory in order to delete selected survey files The procedure would be as follows Double tap on the My Handheld PC icon Double tap on Compact Flash Double tap on DA Meter_Data Tap once on the Survey File you wish to delete Tap once on the Delete button x symbol on the menu bar 58
20. Ohm are Status EEJ Data Be DAMeter_PLS BF 3 57 AM In the above active DCVG survey screen the direction of the arrow pointing to the left or pointing to the right depends on the polarity of the DCVG voltage being measured In the above case the voltage being measured was positive which produced an arrow pointing to the left The opposite would be true if the DCVG voltage reading had been negative ie the arrow would point to the right With the reference electrodes properly positioned the polarity of the DCVG voltage will always be positive in the case of perpendicular DCVG surveys see Section II 2 In the perpendicular case the arrow on the Survey screen will always point back to the pipe However a change in arrow direction will be evident when performing parallel or in line measurements in the vicinity of a DCVG anomaly coating defect In this case the arrow will always point in the direction of the defect location on the pipe with respect to where you are currently standing As you approach the defect the arrow will point towards the upcoming defect location and when you are past the defect the arrow will point back to the defect location Consequently performing in line measurements in the vicinity of a defect can be a good way to pin point its precise location by monitoring the arrow s polarity switches When you are actually straddling a defect location with the refere
21. S data at any location on your survey by tapping once on the Log GPS button Alternatively as discussed in Section II Step 11 you can pre program the DA Meter to automatically log record GPS position data at items such as DCVG Anomalies Flags Devices and Geo Features Obviously with automatic logging of GPS data you do not have to remember at each critical location to go through the GPS logging step 49 SECTION VI HOW TO UPLOAD SURVEYS TO MCM s DATABASE MANAGEMENT SYSTEM VI 1 Introduction As surveys are performed as described in the previous sections the readings are stored in the data logger s memory in separate files one for each survey under the survey filenames that you assigned to them during the DA Meter loading setting up process described in Section III The data stored in each of the data logger s survey files representing each separate survey can be uploaded independently to a PC for further analysis and data management The software required to upload survey data from your DA Meter to your PC and to subsequently manage your survey data is the final component of MCM s Integrated Pipeline Survey Test Equipment and Database Management Package This software package known as ProActive is an extremely powerful database management system the full functionality of which is described elsewhere VI 2 Pre Uploading Procedures Before survey data can be uploaded to a PC the following pre
22. V 366 67mV Consequently if the Total mV has been determined by the data logger s software and the IR drop has been determined a value for the size of the defect ie the IR can be calculated by the data logger s software For example if the Total mV for the above defect was determined to be 100 mV the IR for the defect would be calculated as follows by the data logger s software IR 100mV 366 67mV x 100 27 27 15 I 8 Summary of DCVG Parameters at Defect Locations Assuming that IR drop recordings were properly made at bracketing test stations and that the appropriate DCVG voltages were recorded at a defect location with reference to Figure 6 above the MCM data logger calculates and stores for future retrieval the following important quantities in addition to storing all regular DCVG survey data For each marked defect site gt Maximum delta V ON or Max mV ON Magnitude and Polarity gt Maximum delta V OFF or Max mV OFF Magnitude and Polarity gt Max mV Max mV ON Max mV OFF Magnitude always positive gt Total mV Magnitude gt IR Magnitude II 9 Polarity Considerations By noting the polarities of the maximum soil to soil potential difference recorded with rectifier current ON and rectifier current OFF at a defect site we can determine the corrosion condition of the defect with the CP system current flowing ON state and without the CP system s impressed
23. YS V 1 How to Carry Test Equipment During a DCVG Survey 40 V 2 Readings to Take at the Beginning of a DCVG Survey 40 V 3 How to Record the Pipe to Soil Voltage Waveform 4 V 4 How to Record the Pipe to Soil Voltages at a Test Station 43 V 5 How to Locate and Mark Defects cece ee eee ence nee ee eee 45 V 6 How to Use the GPS Buttons if Active on the Survey Screen 48 SECTION VI HOW TO UPLOAD SURVEYS TO MCM s DATABASE MANAGEMENT SYSTEM MEI Mine OORT iO sds lp sess O buh ealace areas E T A sleet sene Bes 50 VEL 2 Pre Uploading Procedures sis cccsnctemrnec dade cn 50 VI 3 How to Upload Survey Files to Database Management System 51 APPENDIX 1 How to Delete Survey Files from the DA Meter 58 SECTION I INTRODUCTION This manual is the sister training manual to MCM s Close Interval Potential Survey CIS or CIPS Training Manual DA Meter Version herein referred to as the CIS Training Manual In the CIS Training Manual our concern was recording the potential difference between a catholically protected buried pipeline and the soil above it at ground level as a function of distance down the length of the pipe In the case of DC Voltage Gradient DCVG surveys however our concern is recording soil to soil potential differences at ground level above a buried pipeline as a function of distance down the length of the pipe S
24. adi Voltmeter Response p otential Difference Increasing and Positive O Potential Difference zero when straddling defect ES RAM Se bah Bsa Potential Difference Decreasing and Negative lt _ SS SSR er Sea Figure 7 In Line DCVG Survey Technique Consequently the DCVG voltage profile recorded in the vicinity of a defect will be considerable different in appearance from that observed in the case of a Perpendicular DCVG survey see Figure 5 18 Figure 8 represents an illustration of the type of DCVG voltage profile that is recorded during an In Line DCVG survey when a defect is encountered Position along Pipeline of Center Point between Electrodes Survey Direction gt Defect Location Figure 8 DCVG voltage in the vicinity of a coating defect as a function of the position along the pipeline of the center point between the electrodes with the electrodes configured as shown in Figure 7 In Line or Parallel It should be noted that once a defect has been located during an In Line DCVG survey the critical parameters noted above in Section II 8 for defect size determination need to be determined using the Perpendicular DCVG technique illustrated in Figure 6 19 SECTION HI HOW TO SET UP THE DA METER FOR DCVG SURVEYS The following section outlines the steps required in setting up the DA Meter to participate in DCVG pipeline survey applications The set up process establishes the
25. and you would be ready to proceed with your DCVG survey On Off Pairs GPS Sync This voltmeter mode would be selected if you were using an MCM GPS receiver on your DA Meter and current interrupter switches equipped with GPS units were being employed on the rectifiers In this case voltage readings High Low readings are synchronized with the current interrupter switching timing Again you would make your selection of ON and OFF cycle times Also in this case you would tap on the GPS Settings button which would bring up the screen shown below Survey Survey Options Help Setup 5 of 5 Voll GPS Sync OnjOff Settings On Delay fiso mg GPS Port Comi v ON OFF Cycle sec Off Delay iso ms GPS Type Em Downbeat Each Minute w M Cycle Start On gt Off Read Mode F ibe 3 41 AM pigDAMeter PLS You are being asked here to make several selections 33 First select the type of GPS unit you will be using the MCM unit is currently the only choice for GPS Sync applications Next enter your On Delay and your Off Delay selections by tapping in the appropriate box and typing in the requested delay time in milliseconds These delay times are employed so that any spiking in the voltage waveform that might occur as the rectifier current is switched from ON to OFF and from OFF to ON does not become a factor in the voltmeter s determination of the tr
26. buried pipelines please refer to our CIS Training Manual Left Hand Electrode to Negative Side of Data Logger 5 10 4 or 5 feet Spacing Right Hand Electrode to Positive Side of Data Logger Direction of Survey Remote Earth Figure 4 Reference Electrode Positioning for a Perpendicular DCVG Survey Potential difference measured at the green line will represent the maximum voltage recorded As can be seen from Figure 4 prior to encountering the coating defect the potential difference measured between the reference electrodes will be essentially zero since we are currently outside the voltage gradient field As we enter the voltage gradient field walking towards the defect the difference between the soil potentials at the reference electrode positions will begin to increase in magnitude and reach a maximum value when we are level with the defect the green line location in Figure 4 As an example if the maximum potential at the defect is 100mV with respect to remote earth the potential difference measured by the data logger s voltmeter at the green line location defect location would be 80mV since the right hand reference electrode would be positioned on the 20 constant potential line 10 The 80mV reading would occur since the voltmeter would subtract 100mV from 20mV to give 80mV 20mV l00mV 80mV Remember that the right hand electrode is connected to the positive side of the voltmeter
27. cordings to be uniformly spaced between survey flags in cases where the actual number of recordings made between flags deviates from the projected number flag separation recording interval By tapping on the box labeled Auto Pacing Mode and inserting a tick in the box you will enable the DA Meter to automatically adjust the actual recordings and space them evenly over a 100 feet span distance between survey flags regardless of the actual number of recordings made This selection is highly recommended Step 19 Provide the Name of the Pipeline By tapping once on the box labeled Name of P L you can type in the pipeline name Note This is not the same as the filename for the DCVG survey that was selected back in Step 4 This is the actual name of the pipeline Step 20 Provide the Valve Segment Identification Number or Name By tapping once on the box labeled Valve Segment you can type in the valve segment number or name if known Step 21 Provide the Starting Station Number 29 By tapping once on the box labeled Starting Station you can type in the number of the starting station if known For example if you are starting the survey at a location 1200 feet from the reference zero location usually the beginning of the pipeline you would type in 12 00 0 If you do not know the station number distance from reference zero where you re beginning your survey type 0 00 0 As an example if
28. e ms 300 0 898 _ Voltage Range 0 00 Sec 1 00 Sec 5 7 W DC 400 MOhm X Notes Josssassecscnesseaseeg Load View Data As can be seen from the above screen the voltage reading is High for 0 7 sec and Low for 0 3 sec which is the prescribed cycle for the rectifier current It can also be noted by examining the above voltage waveform that the transitions from High to Low and from Low to High readings are quite sharp as opposed to being step like This means that all rectifiers having an affect on this section of pipe are being switched ON and OFF in a synchronized fashion which is the ideal case To record this waveform tap once on the save button on the above screen 42 The window shown below will appear on the screen BJ Compact Flash DAMeter_DATA comb 1 Ow t10 Gaz fa DAMeter_DS amp TA vi Name Type waveform Files wfm z 1 00 Sec BM DaMeter PLS 9 Be 12 09 am You are being asked here to establish a file in which the waveform data will be stored saved The name of this file will be the name you type into the Name box on the above screen For ease of future retrieval when you have uploaded your survey to the Data Management software package ProActive see Section VI it is recommended that you use the same name as your survey filename with the addition of something like Wave TS 1 to the file name This wou
29. eather conditions soil conditions etc Also shown on the Setup 4 of 5 screen are the File Name and the date time Note Do not attempt to change the File Name indicated here as this identification will be required by the ProActive software to transfer your DCVG survey data to your PC or server Step 26 Select Voltmeter Reading Mode Tap once on the Next button on the Setup 4 of 5 screen The Setup 5 of 5 screen will appear as shown below 31 Survey Survey Options wee N ll Setup 5 of 5 Voltmeter Setting Read Mode on off Pairs DSP mc z Range 5 7 Y DC 400 MOhm on Off ON OFF Cycle sec 0 7 0 3 v Doon puDaMeter_PLS Pte 3 26 AM First you can select the Voltmeter s Range full scale value and its input impedance value The recommended settings for the voltmeter for DCVG surveys are 5 7 Volts full scale and an input impedance value of 400MOhm These settings provide a relatively fast response time 80 ms which is important in rectifier current interrupted applications and also a relatively sensitive scale with regard to the magnitude of the DCVG voltages that you ll be measuring Next you can select the Read Mode DCVG surveys are performed with the CP system s rectifier current switched ON and OFF in a cyclic fashion and as can be seen by tapping on the pull down list arrow there are two choices available for the DA Meter s voltmeter Read Mode
30. edrain Anomaly If this box is ticked GPS position data will be logged automatically when DCVG defects anomalies are marked Step 12 Select Max mV Reading to be First Reading in Total mV Determination The last box in the above screen is actually not related to GPS Options If this box is ticked the Max mV voltage value recorded at an anomaly location will automatically become the first voltage value used by the DA Meter s software to calculate the Total mV total voltage gradient Otherwise if this box is not ticked you will have to repeat the Max mV recording a second time as part of the Total mV determination process Step 13 Finally on the above screen select the electricity supply operating frequency of the country in which you are performing the surveys 60Hz or 50Hz For the U S select 60Hz Step 14 Tap once on the Next button The Setup 3 of 5 screen will appear as shown below 27 Survey Survey Options Hein NTE il Flag Dist Error Limit ail Name of P L of Feet Per Reading of Feet Per Reading 25 ft acca of Feet Between Flags 100 ft Starting Station Auto Pacing Mode V set once during initial setup Dla 3 10 AM Step 15 Select Voltage Recording Interval Distance Between Recordings By tapping once on the box in the Setup 3 of 5 screen labeled of Feet Per Reading you can type in the voltage reading inte
31. etermination You should then proceed to move the electrodes to their second positions see Section II 5 and you should Accept the second reading You should proceed in this fashion until you are outside of the defect s voltage gradient field ie the DCVG voltage reading is essentially zero typically DCVG voltages less than about 5mV would be considered essentially zero The screen will be as shown below Mark DCVG Anomaly Accept mv DCVG Max mv 65 1 104 7m Onl39 7m Off Clear Total mv 199 9 Opesimacmy Read Town Read Max mv Read Total mw Notes I Ro 11 27 PM pigDAMeter_PLS As can be seen from the above screen the software has generated a sum of the voltage recordings required for us to reach remote earth ie be outside of the voltage gradient field associated with this defect This represents the Total mV value which in our example is 199 9 mV At this point you should tap on the Save button which will save all of the data associated with this defect 47 You would then pick up the survey where you left off and continue triggering DCVG voltage recordings until you encounter the voltage gradient field of another defect V 6 How to Use the GPS Buttons if Active on the Survey Screen If you selected a GPS receiver type during your set up process Section III step 10 the two GPS button will be active on the survey screen as shown below
32. here a maximum DCVG voltage reading has been observed a set of DCVG voltage recordings is made by moving in a straight line perpendicular to the pipeline direction Left Hand Electrode to Negative Side of n Data Logger 5 10 4 or 5 feet Spacing Right Hand Electrode to Positive Side of Data Logger Direction of Survey Remote Earth Figure 6 Reference Electrode Positions black dot locations along green line for Total mV Determination With reference to Figure 6 above a recording is first made with the left hand reference electrode positioned over the defect and the right hand reference electrode positioned at the first black dot location along the green line The DCVG voltage recorded here is known as the Max mV recording as this is 13 the maximum DCVG voltage that will be recorded for this defect This Max mV value becomes the first component of the Total mV determination Once the Max mV has been recorded a DCVG voltage recording is made by placing the left hand reference electrode in the previous position of the right hand electrode and moving the right hand electrode to the location of the second black dot along the green line all black dots shown in Figure 6 are spaced at 4 to 5 feet intervals Once a DCVG voltage recording has been made with the electrodes in this position the electrodes are moved in the same fashion to the next measurement positions and a third DCVG voltage recording is made This process
33. ily to the defects This situation is illustrated schematically in Figure 2 below Large Impressed Current Flowing Directly to Rectifier Anode Holidays Defects Figure 2 The Influence of Coating Defects on Impressed Current Flow Distribution along a Pipeline locally high potentials occur at defect locations due to locally large currents flowing to the defects A small amount of current will also flow to the pipeline through the coating the coating will not be a perfect electrical insulator however this current will be negligible compared to that flowing to the coating defect areas Since the pipe potential can be high at the site of a defect due to large impressed current flow to the defect the potential at ground level above the pipe above the defect site can be significantly higher than zero the remote earth potential Consequently the measurement of a significant above the defect soil potential voltage with respect to remote earth is a good indication that a coating defect has actually been located especially if the soil potential above the pipe away from the defect location is essentially zero with respect to remote earth Since the defect site is surrounded by soil a voltage gradient will exist between the defect site and the soil A voltage gradient will actually exist in 3 dimensions Consider the defect site as being the center of a series of concentric spheres with the surface of each sphere being a
34. ing potential problem areas Excel Spreadsheet Option Another option exists at this point particularly if you do not plan to bring 56 the survey file into the Database Management Section of ProActive and that is to export the survey file back out of the Driver in the form of spreadsheets This can be done by clicking on the Export to Excel button on the DA Meter Driver window and selecting the Exported Surveys Folder in the Save As window Remember that you previously set up an Exported Surveys Folder on your hard drive during the Pre Uploading Procedures Section VI 2 pre step 2 By accessing your Exported Surveys Folder you can view the survey information survey readings and DCP Feature readings in spreadsheet form Step 6 Make Decision to Bring Survey File into Database Management Section of ProActive At this point in the uploading process having examined your survey data you can decide whether or not to bring the survey file into the Database Management Section of ProActive where the particular survey that you are uploading can be integrated with any other surveys you might have in your ProActive Database After importation you can manage the data associated with all of your surveys in a whole host of ways inside ProActive The data management functions available within ProActive are beyond the scope of this particular guide however you are referred to the ProActive Training
35. is continued typically 3 or 4 measurements are required for a significant defect until the soil to soil potential difference is basically zero ie you have reached remote earth The MCM data logger s software will calculate the sum of these DCVG voltage recordings to generate the Total mV This will represent the voltage gradient on the surface of the ground associated with this defect II 6 Defect Size Considerations Since Total mV represents the voltage gradient on the surface of the ground associated with CP current flowing to a defect if we can relate the Total mV to a measure of the magnitude of the CP current we can obtain a measure of the size of the defect Since the CP current is being switched ON and OFF we can measure the IR drop associated with the CP current flowing in the soil primarily to the defect which is just the difference in the pipe to soil voltage measured during the ON portion of the cycle and the pipe to soil voltage measured during the OFF portion of the cycle Consequently we can have a measure of the current flowing to the defect through the IR drop determination which we can relate to the voltage gradient Total mV II 7 Definition of IR The magnitude of the voltage gradient on the surface of the ground Total mV arising as a consequence of current flowing to the pipe in the vicinity of the defect CP current magnitude I expressed in relationship to the IR 14
36. ld represent the waveform data recorded at Test Station 1 at the beginning of your survey You should then tap once on the OK button This process will save the waveform data in the DA Meter s CompactFlash memory for future reference Tap once on the Exit button on the waveform screen and this will bring you back to the survey screen V 4 How to Record the Pipe To Soil Voltages at a Test Station In order to record the High and the Low voltages also known as the ON and the OFF voltages tap once on the Device button on the survey screen The Device Readings screen shown below will appear 43 Device Readings Consumer Purchase Sales Tap POD IR Drop Coupon single Test Station C Known Station 2 00 0 Astat eepameter_Pis Pte 12 43 AM As can be seen from the above screen you can choose from a number of Devices In this case you would tap once on Single Test Station to highlight this selection You should then tap once on the Next button The screen shown below will appear Device Readings x Sinale Test Station Pipe To Soil nte Reading Mode ON OFF X Reading Range 5 7 DC 400 MOhm x Voltmeter Read on 4 0089 ON T ccep aaa OFF 0 8993 OFF 7 Use reading for DCVG signal strength Voltmeter i Previous ABC Cancel As shown above the average High and Low voltage readings measured at the starting test station will be displayed
37. les increases with distance from the defect indicating a less rapid drop off rate with distance as the remote earth potential is approached In order to illustrate this point the constant potential circles have been labeled as percentages It is assumed that the potential on the surface of the ground directly above the defect is 100 of the maximum potential ie the largest potential measurable for this defect 5 10 40 a0 Buried X Pipeline l Remote Earth Figure 3 Potential Voltage Gradient at the Surface of the Ground associated with a Coating Defect on a Buried Pipeline concentric circles represent constant potential lines The X symbol represents location of coating defect If we imagine pushing a pole vertically from the surface of the ground directly above the defect down to the defect itself and then walking on the surface of the ground away from the pole we ll encounter lower potentials with respect to our maximum potential at the pole as we move further and further away from the pole The percentages indicated in Figure 3 would represent percentages of the maximum potential measured at the pole location Since such surface potential voltage gradients exist above pipeline defects we can perform soil to soil potential difference surveys to detect the defects Such surveys are know as DCVG surveys Direct Current Voltage Gradient surveys DCVG surveys can be performed in two different ways Perpendic
38. line survey mode The window shown below will appear Note It may take a few seconds for this window to appear Station r Dist From Start Dist From Known Station Range None Selected Geo Feat Device Read GPs Log GPS Unido Flag FLag DAMeter_PLS Re 10 52 am x This is the Main Survey Window At this point a survey has not been set up the set up process is what we are going through here and so no information is currently displayed in this window Step 3 Tap once on the Survey button situated in the Menu Bar in the top left hand corner of the window The window shown below will appear EE Survey Options Help vn Hj New Survey Ctrl4N Continue Previous Survey Ctrl C Finish Surve tri F Exit CtrH X Dist From Known Station Range None Selected Geo Feat Device Read GPS a Log GPS Unidto Flag Flag DAMeter_PLS Re 11 12 aM Is 21 Under Survey there are several options If this is a new survey not a continuation of a previous survey tap once on New Survey The window shown below will appear Enter New Survey Filename Step 4 Enter a filename for the Survey using the keyboard Note This is an important step as the filename is used to identify the survey and also recorded data voltages will be stored in this named file for future retrieval It is highly recommended that a protocol be established for
39. nce electrodes in line with the pipe the DCVG voltage will be zero ie neither positive nor negative see Section II 10 35 Also with respect to the above active survey screen as DCVG voltages are recorded by the DA Meter the Total Distance total distance from the start of the survey parameter will increase in increments of 5 0 feet or whatever the feet per reading value was that was entered back at Step 17 Also the Distance From Flag parameter will increase in the same increments as voltages are recorded The difference in this case however will be that when each survey flag is registered this distance parameter will begin again at zero In other words this will show the distance you are assumed by the DA Meter to have traveled from the last flag that you encountered and registered You are now ready to perform a DCVG survey 36 SECTION IV TEST EQUIPMENT HOOK UPS FOR DCVG SURVEYS IV 1 How to make Cable Hook Ups for DCVG Surveys The cable connections for DCVG surveys employing MCM test equipment are illustrated in Figure 9 DA Meter and Equipment Hook up Right Hand Left Hand Pipeline Figure 9 Cable Connections for Hook Up of MCM s DCVG Survey Test Equipment 37 As can be seen from Figure 9 a pair of canes reference electrodes see CIS Training Manual is illustrated the left hand cane RED handled cane and the right hand cane GREEN handled cane These canes
40. nes about 4 to 5 feet apart as indicated in Figure 4 Section IT with the left hand cane negative cane directly over the pipe and the right hand cane positive cane off to the right hand side If you set up the cane push button functionality as indicated in Section III Step 8 ie with the right hand cane set to trigger voltage recordings and the left hand cane set to designate the location of survey flags you would trigger the right hand cane every 5 feet or whatever recording interval you set up in Step 12 of the set up process see Section III As discussed in Section II 2 if you are outside the voltage gradient field of a coating defect the DCVG voltages will essentially be zero However as you enter a defect s voltage gradient field you will observe an increase in the DCVG voltage values displayed on the DA Meter s survey screen see Figure 5 in Section II 2 When you observe a peak maximum value in the DCVG voltage readings you should interrupt your walking and Mark the location of the maximum DCVG reading This will represent a defect location In order to mark the defect location you should tap on the mark button on the Survey screen The screen shown below will appear 45 Mark DCVG Anomaly 6 5 1 Accept a m DCVG Max mi Clear Total mi Log Pos Read Max my Read Total mv Notes PAstart Heespameter PLS oF 11 27 PM As discussed in Section III Step 24 the arrow on
41. nt hook up arrangement shown in Figure 9 By temporarily disconnecting the positive green handled cane from the dual probe adapter and connecting a test cable from the red banana plug terminal on the top side of the DA Meter to the test station you can record pipe to soil voltages during the ON and the OFF cycles which will allow the software to determine the IR drop at this test station location For the pipe to soil measurements the negative cane red handled cane should be positioned over the pipe As described below Section V 4 a device reading can then be taken by tapping once on the Device button on the survey screen and proceeding as indicated It is also recommended that you examine and record the pipe to soil Voltage Waveform at this location as described below Section V 3 V 3 How to Record the Pipe To Soil Voltage Waveform To examine the pipe to soil voltage waveform tap once on the WAVE button on the menu bar at the top of the screen The screen shown below will appear 41 Waveform Dis Wareco a Mode On off On Time rms 700 Off Time rms 300 Voltage Range T ooo 5 7 V DC 400 MOhm Notes View Data By tapping once on the Read button on the above screen you can view the actual ON OFF voltage waveform A typical waveform would be as shown in the following screen Waveform Untitled x Display Mode 1 012 On off v On Time ms 700 Off Tim
42. o in this case we do not make electrical contact with the pipe itself other than to determine IR drop values see later DCVG surveys are typically performed on coated pipelines with a view to determining the location of holidays coating defects or other defects As discussed in subsequent sections such surveys can be used to not only pin point the location of defects but they can also be used to provide a measure of the size severity of a particular defect Since DCVG surveys are close interval in nature they can be considered complementary to pipe to soil close interval surveys CIS and both types of surveys are typically performed on the same pipeline sections as part of the ECDA External Corrosion Direct Assessment protocol regarding Indirect Inspections With regard to the ECDA protocol at least 2 types of close interval Indirect Inspection surveys are required to be performed on all sections of a buried pipeline and typically DCVG and CIS surveys are employed to satisfy this requirement on coated pipelines The physical principles associated with DCVG surveys are discussed in Section II and the set up procedures of MCM s data loggers for the performance of DCVG surveys are described in Section III Section IV details the equipment hookup requirements for DCVG surveys and information on how to actually conduct a DCVG survey is presented in Section V Finally Section VI describes the procedures involved
43. on the polarities of Max mV ON and Max mV OFF the corrosion states of the defect both with CP current ON and with CP current OFF are presented in row 2 in the comment column as shown above For example for the defect located at station 2699 the data are as follows Row 1 19 3mV 44 7mV 24 25 Row 2 11 7mV 7 7mV 0 0000 Also the corrosion states are Cathodic Anodic which means that the CP current is protecting the defect site however in the absence of CP current the defect site would be a corrosive site 55 Finally by clicking on the PLS pipeline survey Graph tab the window shown below is displayed E DA Meter Driver Pipeline Survey Download Survey Settings Readings Device Readings PLS Graph amp SI cl ajal gt Stat V Points 7 5 D 2 X 5 a i 3 iret Voltage V Voltage V 2700 00 2702 50 Station DCVG 5 20 2004 12 35 14 PM The above window shows a graphical representation of the DCVG survey data for our example survey Since this was a Perpendicular DCVG survey the defect locations show as peaks in a plot of DCVG voltage versus distance traveled see Figure 5 Section II The locations on the survey where defects were marked and the defect parameters determined are indicated on the graph as DCVG Anomalies As can be seen from the above window a graphical representation of the survey data is extremely useful with regard to immediately identify
44. our PC s hard drive ready for import into the data management section of ProActive Click on the Go button Step 5 Examine Survey Data Prior to Bringing Survey File into Database Management Section of ProActive It is recommended that you examine your survey data prior to bringing the survey file into the Database Management Section of ProActive currently you are in the Driver Section of ProActive To do so click on the cancel button on the window that is currently showing Data Logger Get Pipeline Survey Window The DA Meter Driver window will be shown but this time there will be a selection of tabs on the window labeled as follows Survey Settings Readings Device Readings and PLS Graph By clicking on these tabs you can view information on the Survey conditions or you can view actual survey readings either in spreadsheet form or displayed graphically By clicking on the Survey Settings tab on the DA Meter Driver window you can view a listing of all the selections that you made for your DCVG survey during the DA Meter s loading setting up process as described in Section III By clicking on the Readings tab the window shown below is displayed for the case of an example DCVG survey 53 E DA Meter Driver Pipeline Survey Download Survey Settings Readings Device Readings PLS Date DCVG Voltage DCVG Voltage On DCVG Voltage Off DCP Feature DCVG Latitude Longitude Al
45. posed to placing the reference electrodes perpendicular to the pipeline direction This technique is illustrated in Figure 7 below As can be seen from Figure 7 as the operator enters the voltage gradient field associated with the defect and places the reference electrodes as indicated with the right hand electrode connected to the positive side of the data logger s voltmeter and the left hand electrode connected to the negative side of the voltmeter the DCVG voltage measured will begin to increase and have a positive polarity As the defect location is approached the DCVG voltage will increase more sharply since the circles of constant potential are spaced closer together A maximum DCVG voltage will be measured when the left hand reference electrode is directly over the defect As indicated in Figure 7 however the DCVG voltage will drop to zero when the operator is straddling the defect since in this position the reference electrodes will be measuring the same potential and hence the potential difference between them will be zero Continuing down the line with the right hand electrode directly over the defect the DCVG voltage will again have a maximum value however this time the polarity will be negative Finally as the operator continues down the line the magnitude of the DCVG voltage measured will decrease quickly near the defect and then decrease more gradually moving further away from the defect 17 A
46. reveal the 5 choices shown in the screen below Survey Survey Options _ Heip NS il Rectifier Mode cycle ON OFF Surface Potential Accept Pause Pause v Survey Walking Direction Increasing Decreasing Accept gt Save set once during initial setup Pstart pameter PLS ey 4 03 AM Right By tapping once on DCVG the screen shown below will appear 23 Survey Survey Options Help v 1 2 Bl Survey Type Deva z s Rectifier Mode cycle ON OFF z Cane Button s Allowed To D C P Survey None Left Right Survey Walking Direction Accent Flag Read __ Increasing O Decreasing Accept gt Save set once during initial setup start P DAMeter_PLS OF to 2 41 AM Step 7 Select Rectifier Mode By tapping once on Cycle ON OFF in the Rectifier Mode box pull down list you will be selecting the appropriate mode for DCVG surveys Step 8 Make Cane Button Functionality Choices Typically for DCVG surveys you would trigger DCVG voltage recordings using the right hand positive reference electrode and the left hand negative reference electrode would be used to designate the location of survey flags For this case your Survey selection for canes would be Flag Read as shown in the above screen The other options can be viewed by tapping once on the pull down list arrow in the Survey box
47. rming a DCVG survey and removing the GPS unit if used to connect a serial data communication cable to a PC in order that the survey data recorded by the DA Meter can be uploaded to a PC See Section VI for information on how to transfer upload DCVG survey data to a PC for database management 39 SECTION V HOW TO PERFORM DCVG SURVEYS V 1 How to Carry the Test Equipment During a DCVG Survey With the equipment connected as shown in Figure 9 Section IV and the DA Meter set up as described in Section II you are now ready to perform a DCVG survey To make a pipeline survey more manageable MCM has developed a special harness which allows the DA Meter to be carried around the waist area in a hands free fashion allowing the individual to be able to position the reference electrodes canes on the ground every 5 0 feet or so down the length of the pipeline and to be able to trigger the push button canes when appropriate to do so With the harness assembly the DA Meter sits on a tray at waist level allowing the operator to view the screen at all times and to make any selections required by tapping on the screen Also the dual probe adapter shown in Figure 9 is attached to the underside of the tray allowing convenient 5 pin cable connection of the adapter s output to the DA Meter Again this will effectively connect the green handled reference electrode cane to the positive side of the data logger s vol
48. rval distance in feet expected between recordings for the DCVG survey Typically in DCVG work this expected interval distance is 5 0 feet Step 16 Select Survey Flag Interval Distance Between Survey Flags By tapping once on the box in the Setup 3 of 5 screen labeled of Feet Between Flags you can type in the survey flag interval distance between survey flags for the section of pipeline being measured Typically survey flags are located at 100 feet intervals Step 17 Select the maximum permissible error between the actual number of recordings made between 2 survey flags and the expected number of recordings By tapping on the box labeled Flag Distance Error Limit you can type in the maximum permissible error For example the maximum permissible error is indicated as 20 on the above screen If the recording interval is expected to be 5 0 feet and the survey flag separation is 100 feet that means 28 that 20 recordings are expected If however only 15 recordings are actually made between survey flags an error window will appear on the screen since there is a 25 difference between the expected and actual number of recordings made No error window will appear if the difference is less than 20 for this example ie you could have a minimum of 16 recordings and a maximum of 24 recordings between survey flags to stay within the 20 max error allowance Step 18 Select whether or not you would like the re
49. s box is ticked only GPS data that has been derived using a correction message signal in real time will be logged by the DA Meter If this box is left unticked it means that you will allow the DA Meter to log either standard GPS data or differentially corrected GPS data depending upon what is being output by your receiver at any given time Please note that if this box is checked ticked GPS data will not be logged unless a real time correction signal has been received by the correction message receiver component of your GPS unit In most instances logging standard ie uncorrected GPS data would be preferable to not logging any GPS data Use GPS Altitude If this box is ticked altitude data will be included with the position data whenever GPS data is logged Note Altitude data on some GPS units is not particularly accurate in survey applications 26 Log GPS at Flags If this box is ticked GPS position data will be logged automatically at flags when either the flag button is tapped directly on the Survey screen or when the push button on the designated flag cane is pressed Log GPS at DCP Feature If this box is ticked GPS position data will be logged automatically at Devices or Geo Features when either the Device button is tapped on the Survey screen and a Device reading is logged or when the Geo Feat button is tapped on the Survey screen and a geo feature is registered Log GPS at Sid
50. saen 12 00 0 25 9 lav ccs Dist From kkkk Start Dist From Known Station Range 5 7 V DC 400 MOhm GPS Status No Data BMIDAMeter PLS I a 3 57 AM If you have a GPS receiver attached to your DA Meter via the COM 1 Port and the receiver has been properly configured to output NMEA data strings in the GGA format see your DA Meter User s Manual Appendix 1 if you are using a Trimble GPS Pathfinder receiver you will be able to conveniently examine position data in real time at any given location on your survey using these GPS buttons By tapping once on the GPS Data button you can view a summary of the GPS data associated with your current location You can also see how many satellites Sat In Use were used in the determination of the position data for your present location Ideally a minimum of 5 satellites should be involved for good position accuracy 48 GPS Data x Latitude N 27 64737 Longitude W 90 41517 N o Stop Altitude 65 feet View NMEA Dat al Sat In Use O GPS Mode Standard GPS GPS Fix Time 19 18 51 You can also view the NMEA data output by the GPS receiver by tapping once on the View NMEA Data button on the above window New NMEA data will stream into the DA Meter every second You can freeze this data by tapping once on the Stop button which will allow you to examine the NMEA data strings You can also log record GP
51. surface of constant potential Near the defect the concentric spheres will be closely spaced which means that the potential will drop off quickly with distance from the epicenter the defect site The spheres constant potential surfaces will be spaced further and further apart implying a slower potential drop off rate with distance away from the defect site If we consider the surface of the ground above the pipeline to be a plane the ground will have an in plane potential gradient in the region above the site of the defect Imagine taking a slice through the ball of concentric spheres spherical surfaces of constant potential The slice would represent the surface of the ground with the distance from the epicenter of the concentric spheres to the slice being the distance from the defect to the ground ie the depth of the pipeline Figure 3 illustrates the in plane potential gradient voltage gradient associated with the surface of the ground in the vicinity of a coating defect on a buried pipeline The defect location is indicated by the X symbol on the buried pipeline and the voltage gradient on the surface of the ground arising as a consequence of the defect is represented by the concentric circles of constant potential The separation between constant potential circles is small in the vicinity of the defect indicating a rapid drop off in potential near the defect while the separation between constant potential circ
52. titude Single Test Station 35 78506 91 16557 261 0236 DCVG Anomaly 35 78524 91 16545 261 679 Flag 35 78529 91 16542 261 384 x The above screen displays the first 22 sets of readings for the example DCVG survey The first column far left hand column lists the DCVG voltage data which was obtained by subtracting the delta V OFF values from the delta V ON values The delta V ON voltages are presented in the second column from the left which is labeled as DCVG Voltage ON data while the delta V OFF voltages are presented in the third column from the left which is labeled as DCVG Voltages OFF data A defect location is indicated in the above window at the number 18 data row and is labeled as a DCVG Anomaly This means that a defect was marked at this location as described in Section V 5 The DCVG Anomaly is noted in the column which also lists Devices and Geo Features More details on this defect and all other defects marked during this example DCVG survey can be viewed by clicking on the Device Readings tab as shown below 54 E DA Meter Driver Pipeline Survey telex Download Survey Settings Readings Device Readings i PLS a Station DCP Feature DCVG Anomaly Latitude 02694 45 2798 7 0000 35 78506 02695 0 0177 0 33 5750 35 78524 DCVG Anomaly DCVG Max On Off 0 0216 0 0 0000 Cathodic Cathodic 35 78524 DCVG Anomaly DCVG Max Total 0 0188 0 31 9356 35 78533
53. tmeter and the red handled reference electrode cane to the negative side of the voltmeter In addition a GPS receiver together with its battery pack and antenna can also be attached to the waist band of the harness typically on the operator s back at waist level with the antenna rising to above head height V 2 Readings to Take at the Beginning of DCVG Survey It is important to begin your DCVG survey at a test station or at some other device that allows you to make electrical connection temporarily to the pipeline Connection to the pipeline is required so that an IR drop value can be determined for use in the DA Meter s software calculation of IR see Section I 7 40 Note A significant IR drop value is necessary in order to be able to detect DCVG anomalies A minimum IR drop value of 200mV is suggested If it is assumed that you would like to mark defects having as a minimum a 10 IR size the minimum Total mV value in this case would be 20mV This means in turn that the minimum Max mV value that you d be measuring would only be 10mV or so Given that the noise level will be around 5mV or you can see why 200mV would be a suggested minimum IR drop value An IR drop value around 500mV would make anomaly detection easier With the CP system s current being switched ON and OFF in a prescribed cyclic fashion you can make pipe to soil voltage recordings with a slight adjustment to the equipme
54. ue ON and OFF voltage values for each DCVG measurement For example if 150 ms was selected for the Off Delay the data logger would record the voltage value sampled 150 ms after the rectifier current was switched from the ON to the OFF state Also if 150 ms was selected for the On Delay the data logger would record the voltage value sampled 150 ms after the rectifier current was switched from the OFF to the ON state Finally select your rectifier s Downbeat timing As indicated by tapping on the pull down list arrow in the Downbeat box there are 3 industry standard selection choices Each Minute Each Hour and Midnight If Each Minute is an option for your rectifier we suggest making this selection Also if your rectifier cycle starts with the current in the ON state the first transition is from ON to OFF place a tick in the Start Cycle box remove the tick if the opposite is true After making your GPS Settings selections tap on the OK button which will return you to the Voltmeter Settings screen By tapping on the OK button on the Voltmeter Settings screen the active Survey screen would appear and you would be ready to proceed with your DCVG survey An example starting active Survey screen is shown below 34 Survey Survey Options Help Station 12 00 0 i 25 9 mv pcve Dist From kkkk Start Dist From Known Station Range 5 7 V DC 400 M
55. ular Mode and In Line or Parallel Mode In the case of Perpendicular DCVG surveys an imaginary line drawn between the reference electrodes on the surface of the ground would be perpendicular to the direction of the pipeline and in the case of In Line DCVG surveys an imaginary line drawn between the reference electrodes on the surface of the ground would ideally be in line with the center of the pipeline directly above the pipeline II 2 Perpendicular DCVG Survey Technique As illustrated in Figure 4 below this technique involves placing a matched pair of reference electrodes canes on the surface of the ground perpendicular to the pipeline direction with the left hand cane red cane positioned ideally over the centerline of the pipe and the right hand cane green cane spaced typically 4 or 5 feet from the left hand cane With this cane spacing maintained the operator walks down the length of the pipeline section triggering voltage recordings every 2 5 feet or some other length interval typically 5 to 10 feet Since the left hand cane connects to the negative side of the voltmeter data logger s voltmeter and the right hand cane connects to the positive side of the voltmeter the voltage recorded at each triggering location is the difference between the soil potentials at the two reference electrode positions in each case For a detailed discussion on the design and operation of MCM s reference electrodes used for surveys on
56. uploading procedures need to be performed These procedures suitably configure your PC and enable two way communications between your data logger and your PC Pre step 1 Install MCM s ProActive software package and Microsoft s ActiveSync software program on your PC The ActiveSync program will enable two way communication between data logger and PC Pre step 2 Create a Folder on your PC s hard drive that you ll use to permanently save survey files uploaded from your data logger You might choose to name this Folder something like Surveys If you are only interested in viewing survey data in the form of excel spreadsheets you should also create a Folder within the Surveys Folder that can be used for this purpose and name this Folder something like Exported Surveys More on this later 50 Pre step 3 Connect a serial data communications cable between the DA Meter s 9 pin communication terminal see Section IV 2 Figure 10 and the serial data communications port on your PC and switch on your DA Meter With Microsoft s ActiveSync installed the ActiveSync window will appear on your desktop and the program will confirm that two way communication has been established VI 3 How to Upload DCVG Survey Files to MCM s Database Management System ProActive Performing the following steps will permit the uploading of DCVG survey files saved in the DA Meter s memory to ProActive MCM s Database
57. w Survey Survey Options Hote 7 MN il AC System 60Hz v GPS Type wm F Differential GPS Required V Use GPS for Altitude van V Log GPS at Flags NMEA V Log GPS at DCP Feature M DCVG Anomaly Max mW 1st reading for Tot m Manual V Log GPS at Side Drain Anomaly PEEDAMeter_ PLS F a 3 01 AM As can be seen from the above screen there are 4 choices for GPS Type GPS Port 25 None This means that a GPS receiver is not being used MCM This means that an MCM GPS receiver is being used NMEA This means that a GPS receiver other than the MCM receiver that is capable of outputting NMEA data is being used Manual This means that location data will be entered manually when the GPS button is pressed on the survey screen during a DCVG survey Select the appropriate choice by tapping on your selection Step 11 Select GPS Options After selecting the GPS Receiver Type choices need to be made regarding GPS Options see screen above If a GPS receiver has been selected for use with the DA Meter for a particular DCVG survey all or some of the functions available can be enabled box ticked A box can be ticked or unticked by tapping inside the box The GPS options available are as follows Differential GPS Required This box should be ticked if you only want differentially corrected real time corrected GPS data to be logged by the DA Meter If thi
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