In this era of increased market competitiveness and the need for cost reduction strategies, natural gas pipeline and local distribution companies will soon be able to better control the growth of their cathodic protection (CP) pipeline maintenance costs with the emergence of a new productivity enhancement instrument.

Driven to become more cost-effective, Southern California Gas Company (SoCalGas) and Pacific Gas & Electric Company (PG&E), with Gas Research Institute in the mid '90s, partnered with Radiodetection Corp. in the research and development of a new CP fault-finding device known as the Pipeline Current Mapper (PCM).

In the early '90s, corrosion control engineers at SoCalGas were encouraged to find new methods to reduce maintenance costs associated with the company's approximately 173 million feet of cathodically protected pipelines, mains and services. Mindful of how maintenance problems in their CP systems were typically being resolved and the annual dollars associated with these efforts, an intriguing concept was conceived that could potentially reduce these costs or increase productivity by at least 25 percent.

Cathodic protection of an electrically isolated steel structure is achieved when a prescribed amount of direct electrical current (DC) is applied to the structure's external surface via an anode(s) through an electrolyte such as ground or water in which the facility is immersed. Occasionally, foreign metallic structures come in contact (fault or short) with the cathodically protected facility and draw enough protective current away from it to cause the CP system to become ineffective in controlling corrosion. When a pipeline network or area becomes shorted, present-day methodologies used to find and clear these anomalies can be time-consuming. Operators of CP systems worldwide have long sought for a way to quickly and accurately determine the location of CP shorts.

When a CP area is found "down" or below the established area protection criteria during the required scheduled routine monitoring program, the normal approach is to send a technician into the area with a file information package detailing the location and extent of the area, number and type of protective devices, a history of past pipe-to-soil potential reads, and the current output history of the system's anodes, etc. If, after a cursory check, the CP area is deemed to be shorted, the ordinary practice of most technicians is to set up a Pearson-type audio AC oscillator device/detector and "go hunting" for shorts. Due to technical limitations, this can be time consuming, expensive, frustrating and far from a perfect means in providing a solution for all CP-area shorting problems.

Another approach, or typically the next step in resolving difficult CP problem(s), is to conduct a current-span or line-drop survey. A current-span or the measurement of DC in a lateral pipeline segment is analogous to measuring current in an electrical circuit using a shunt. This standard method often requires a team of two technicians but is almost always successful in establishing the location of a short(s). However, this highly dependable method of locating CP shorts is infrequently used for the following reasons: (1) the number of available electrical contacts to the protected pipeline system is inadequate, (2) concerns for safety due to traffic congestion and terrain, (3) the significant time required to conduct a quality survey, (4) the often arduous nature of the survey, (5) the number of repetitive hand calculations, (6) the preparation of good field notes, and (7) the high skill levels required to make the proper data interpretations needed for success.

In a traditional line-drop analysis, the CP system's anode(s) are often used to impress a somewhat higher than normal magnitude of DC onto the area's pipelines on a time-interrupted basis. This current distributes itself on the gas piping via coating holidays or defects and returns to the power source via the steel pipeline conductor. Knowing the conductance of the main between two contact points, the voltage difference between the two points when the test DC is turned on and off, and the distance between the contact points (which are typically at the risers of steel service lines), a determination of the average magnitude of current flow and its direction in the subject pipeline span can be calculated. If larger-than-expected amounts of current are found in a segment of the shorted CP area's piping network, the process is continued until the short's location is resolved (the degree of resolution depending on the number of contact points that are available).

Positioned above the target pipeline segment, the PCM receiver's flux gate magnetometer module, shown being operated by technical consultant Kris Keas, measures the magnetic field from which a corresponding current magnitude is electronically calculated.

The success of the PCM system lies in its ability to emulate and quickly quantify the attributes and magnitudes of current flows that could be obtained from a comparable line-dropping analysis without the inherent procedural complications and the all-to-frequent restrictions of limited contact points. By impressing and therefore distributing a given amount of near DC signal onto a protected pipeline system, the PCM can non-intrusively (without contacting the pipeline) and accurately measure the magnitude and direction of this current anywhere within the piping network.

The receiver portion of the unit is packaged in two parts consisting of a unique hand-held pipe locating receiver that can be used as a Pearson-type detector along with an attachable magnetometer module. The transmitter component is a stand alone 0.1 to 3 ampere current output device and locating signal generator – powered from a variety of sources.

To remove the Earth's magnetic field and other static fields from the PCM's current measurement function, an alternating current signal of 4 Hz is transmitted onto the pipeline. The receiver's flux gate magnetometer module, using specialized signal processing techniques, is positioned directly above the target pipeline segment and accurately measures the 4 Hz magnetic field from which a corresponding current magnitude is electronically calculated. During the research portion of this development, it was confirmed that this alternating signal was sufficiently low in frequency to suffer negligible effects from the capacitance of the protected structure. In other words, the electrical characteristics of current attenuation and distribution on typical natural gas piping systems are virtually the same for this near DC signal as they would be for a comparable magnitude of DC.

At each measurement point in a typical PCM survey, the location of the pipeline is determined via either a 98 Hz or 512 Hz signal, within specifications the depth of the pipeline's center is indicated, and an accurate measurement of current strength and direction is provided—both of which are displayed on the receiver. Knowing the magnitude and direction of the near DC current flow on the structure, a field technician can then easily pinpoint the location of the foreign contact (place or places where relatively large amounts of this current should not be) often with one equipment set-up and usually within less than a couple hours of testing.

Once a CP area is cleared of all foreign contacts, and if it is deemed desirable for historically troubled areas, the area can again be current mapped using the PCM at selected locations. This current distribution data can later be downloaded from the unit's receiver into a personal computer for future reference. This reference information will show the normal current distribution of the then non-shorted area and with more refinement identify small areas of relatively high-current demands resulting from possible coating deterioration or defects.

The demonstrated productivity gains through the use of the PCM system are impressive. Using the labor-intensive techniques and procedures of the past, corrosion technicians often spent days in search of difficult foreign contact(s).

During the winter of 1996-97, CP specialists from PG&E and SoCalGas involved in the prototype PCM evaluations requested, from their venous operating regions, notification of shorted CP areas that had proven difficult to resolve using traditional troubleshooting methods. The following case studies document some of these findings:

Case # 1

The CP potential reads in an extremely large distribution network of coated pipe had been reported "down" the prior month. After at least one week of extensive field investigative work by two technicians using traditional troubleshooting techniques, the problem failed to be resolved. Within three hours of the PCM equipment set-up, an evaluation team member determined that a two-inch main was shorted in the middle of a paved intersection. Excavation found that the main had come into parallel contact with a previously abandoned gas pipeline.

Case # 2

The subject CP area consisted of approximately 45,000 feet of 2-, 3-, and 4-inch mains and 15,000 feet of service piping. System piping was in a compounded multiple loop configuration and coating conditions were fair to poor Pipe-to-soil reads were below the established criteria. Approximately 100 hours had been spent trying to resolve the problem. Line-dropping techniques had not been used to determine the problem. Instead, extensive Pearson detector surveys were performed without success.

The PCM transmitter was connected to the power supply and groundbed of the rectifier supplying current to the area. Due to the size of the area, the transmitter was set at its maximum output of three amperes. Using a systematic current mapping approach, an uninsulated meter set was found in approximately two hours. Protective levels were reestablished.

Case # 3

The subject CP area consisted of approximately 18,000 feet of 2-, 3-, and 4-inch mains and 6,000 feet of service piping. Area piping was in a multiple loop configuration and coating conditions were generally only fair. Pipe-to-soil voltage reads were found to be below the established criteria. After approximately 80 hours of investigation using traditional troubleshooting methods, a missing meter set insulator was located and corrected. Subsequent tests showed that even with the installation of another 20-pound magnesium anode, the potential reads were still low. Use of a Pearson detector had been difficult due to the high noise levels of alternating current interference from overhead electrical lines. Close interval line-dropping of the main was not economically feasible due to the lack of adequate contact points - a result of the area's large number of plastic replacement services .

Using an existing magnesium anode bank located near the middle of the area as a ground, the PCM transmitter was set at an output of one ampere. Using a systematic current mapping approach, an underground contact was pinpointed. A subsequent excavation at this location found that a 6-inch diameter cast iron water main had come into contact with a 3-inch gas main. The time to locate this contact with the PCM was approximately 2.5 hours. Pipe-to-soil measurements after the contact was cleared were higher than at any previous time.

Case # 4

The subject CP area contained approximately 22,000 feet of 2-inch main and 15,000 feet of 3/4-inch service piping. System piping contained one loop and pipe coating conditions were good. Potential reads were below criteria. Approximately 60 hours had been spent mobile surveying the area using a Pearson device with a bumper probe. During the investigation, the Pearson system's transmitter had been moved at least five times.

The PCM was connected to a magnesium anode located in the parkway and to a longside service line located in the middle of the subject area. The transmitter's output was set at one ampere. Current measurements over the main on either side of this service-to main connection were approximately equal with a total magnitude of approximately 600 milliamps. An additional measurement over this service line, on the other side of the transmitter's pipe connection, showed approximated 380 milliamps coming from the downstream portion of the longside service and specifically a downstream cross-lot branch service. No insulator was found at the meter set of the branch service. Total time to resolve this problem with the PCM was approximately 40 minutes.

Case # 5

A rural townsite's cathodically protected natural gas distribution system consisting of approximately 80,000 lineal feet of fair to poorly coated 2-, 3-, and 4-inch mains and associated services was found to be below protective levels. Numerous attempts to locate the problem over a three-week period using a Pearson detector were unsuccessful. Technicians found that if they increased the output of the rectifier providing the protection by 50 percent, the problem could be adequately masked and all routine read points in the area would be in the marginal, but acceptable, range.

Because this was not an acceptable solution, technicians using a prototype PCM unit later resumed to the townsite and within two hours determined that an old and poorly coated steel gas service line was shorted in a customer's front yard. A remedial excavation cleared the contact, which was found to be an inactive metallic waterline.

The ability of the prototype PCM system to quickly, non-intrusively and accurately measure the distribution of an impressed test current on a natural gas piping network is a quantum improvement in the methodology of troubleshooting CP areas. Feedback has been extremely positive:

"The technology to be able to quickly measure pipeline current flow and know its direction is unquestionably a major breakthrough in the approach to troubleshooting cathodic protection systems," said R.C. Shelton, cathodic protection consultant.

Klaus Jeppesen, cathodic protection specialist Farwest Corrosion Control Co., said "The PCM provides a higher level of confidence than a conventional signal locator. The current direction feature has enabled me to quickly resolve problems that previously required calibrated current span work. The PCM has quickly become my troubleshooting tool of choice."

Midway through the field evaluation phase, it became clear to SoCalGas and PG&E that the performance of the prototype PCM units had far exceeded developmental and productivity expectations. After PG&E and SoCalGas's initial and significant equipment orders, Radiodetection delivered the first production PCM units in April 1997.

The original objective of developing a new CP device that could increase troubleshooting productivity by a least 25 percent was met. It has also been found that use of the PCM system significantly increases field technicians' working knowledge of cathodic protection, reduces safety and liability considerations inherent with previous troubleshooting techniques, and allows for other operating cost reductions, i.e. the reduction in the current outputs of many urban impressed current systems (set high in the past to mask existing shorts) thereby also reducing the potential of stray current interference. Based on the current retail price of the production PCM unit, various economic analyses have shown that a simple payback period of less than one year is a reasonable expectation for a PCM system.

Additional Efforts

Once it became clear to the partnered companies that the capabilities demonstrated by the PCM's prototype devices would exceed original project expectations, other practical spin-off applications for this technology were explored. Additional financial partners are already joining in another R&D agreement to develop a device known as the Stray Current Mapper (SCM). If successful, this system will be able to determine if and where stray current interference is being forced onto a metallic piping system, the magnitude of this interference, and most important, the location(s) and magnitudes where this often detrimental current leaves an interfered-with system The SCM concept demonstrator unit should be ready for extensive field evaluations later this year.

Reprinted from / Pipeline & Gas Journal / October 1997