A bad influence. WP_C&C2014_44-49.indd 44 09/10/ :54

Transcription

1 A bad influence 44 WP_C&C2014_44-49.indd 44 09/10/ :54

2 Alex McCarthy, Dan Huslig and Rob Floria, American Innovations, USA, discuss how surrounding structures can interfere with a pipeline operator s carefully planned and executed cathodic protection system. Pipeline operators know what they have in the ground. However, some may be unaware of what is positioned near their infrastructure, which could potentially influence or interfere with their assets. Because the days of the lone operator and his pipeline are long gone, this information is crucial. Today, rights-of-way (ROWs) are all too often crowded with multiple cathodically-protected pipes; nearby railroads; waterlines; light rail; telecommunications, television and electrical power lines; and other potential sources of interference. According to the US Department of Transportation, Residential and commercial development in once-rural areas is encroaching on pipeline ROWs with increasing frequency. Encroachment implies safety concerns for local residents and for the physical integrity of the pipeline itself. 1 In an ideal world, an effective cathodic protection (CP) system controls corrosion on a pipeline by making it the cathode of an electrochemical cell. This is accomplished by connecting it to a more easily corroded sacrificial metal that acts as an anode. Metal loss occurs on the anode and not the protected structure, for example, the pipeline. 45 WP_C&C2014_44-49.indd 45 09/10/ :54

3 However, an impressed current cathodic protection (ICCP) system can potentially trigger accelerated corrosion by causing interference on nearby metallic structures not intended as part of the ICCP system. Interference occurs when stray current, as the name implies, flows from an ICCP system through an unintended metallic path and then back to the protected pipeline. Any submerged metallic structure represents a low resistance current path and, consequently, is susceptible to the effects of stray currents. When a stray current flows onto a nearby pipeline in one area (the current pickup location) it helps polarise the area (Figure 2). The stray current continues moving along the metallic path of the pipeline system to another area (the current drain location) where it then leaves the pipe, with the potential for resulting corrosion. The stray current moves back through the electrolyte and returns to the current source, thereby completing the circuit. In a worst case scenario, an interfering ICCP system could reverse a nearby operator s painstakingly planned and executed CP system, and effectively cause the area of discharge on their pipeline to corrode. Influence studies The most effective way to determine whether or not a CP system is being compromised by stray current is to conduct influence studies along the pipeline where stray currents are suspected. Large unaccounted deviations of P/S potentials are indications that stray currents may likely be effecting the integrity of a pipeline. All pipeline and facility operators in the testing area should be included in the study and have access to the findings. Influence studies help determine the influence of nearby CP systems and other stray current sources on an operator s CP measurements. Basic pipe-to-soil (P/S) potential measurement techniques are applied to establish whether one or more of the recommended CP criteria are met. By taking P/S potential readings along the pipe operators can determine: ) If an interference condition exists. ) Magnitude of the stray current influence. ) Source of the influence. ) Point of maximum exposure or discharge. Additionally, interference study results identify: ) Which surrounding CP systems need to be included when conducting future CP measurements. ) Locations requiring additional focus or resolution to maintain required CP protection levels. Criteria for establishing the effectiveness of a CP system to mitigate corrosion are outlined in the NACE International Recommended Practice SP , Control of External Corrosion on Underground or Submerged Metallic Piping Systems. 2 The criteria has been adopted, in part, in US Department of Transportation (DOT) regulations CFR 49, Parts and If one or more of the recommended criteria is met, the CP system is assumed to be applying an adequate cathodic current to prevent corrosion. Figure 1. A crowded pipeline infrastructure means the potential for interference from stray current is significant. Source: Energy Information Administration, Office of Oil & Gas, Natural Gas Division, Gas Transportation Information System. Conducting effective influence studies To truly understand what is happening underground, operators need to de-energise all current sources that could influence their structure pipe-to-soil potentials. This can only be accomplished Figure 2. Corrosion caused by stray current. Figure 3. Voltage waveform at current pickup location shows potential exceeds the volt criteria for proper corrosion mitigation. 46 World Pipelines / COATINGS & CORROSION 2014 WP_C&C2014_44-49.indd 46 09/10/ :54

4 by working with other operators in the vicinity so that operatorowned and foreign current sources are interrupted simultaneously. Innovative products that are now on the market, such as American Innovations Bullhorn RM4150 and RM4010 remote monitors and MicroMax GPS300 portable interrupters make the testing much easier than traditional methods. Clay Martin, Corrosion Specialist at NuStar Energy in El Paso, Texas, claims that using new, reliable technologies to synchronise interruption shaves off approximately 90% of the time and manpower it used to take to conduct a typical test point influence test. Martin is an active member of the Texas New Mexico Corrosion Correlating Committee, a group that was established about 10 years ago out of a need to understand the influence and impact of CP currents on pipelines throughout Arizona, South Central New Mexico and West Texas. Represented on the TXNMCCC are corrosion professionals from about a dozen area pipeline operators. The group typically meets five times a year to discuss CP improvement projects, including construction, testing and maintenance that may affect area pipeline systems. Martin cites a particular 6 mile segment of parallel pipelines in El Paso on which he has conducted numerous influence studies in conjunction with other affected pipeline operators. Because of proximity and influence, 57 rectifiers have to be interrupted to Figure 4. Voltage waveform at current drain location shows potential does not meet the volt criteria for corrosion mitigation increasing possibility of metal loss. get a true instant off P/S potential at test points on these two pipelines. There were 45 foreign CP rectifiers and 12 belonging to Martin s company. Done manually, this test requires one or more technicians to visit each rectifier with phones and/or two way radios to co-ordinate and document the influence of each rectifier at each test point. All told, a manual test could take about 8-10 labour intensive days to set up, conduct and then return all equipment back to normal operating mode. Using a combination of remote monitors and portable current interrupters with interference mode, Martin says this same test, co-ordinated through the committee, takes just one day. The interference parameters on remote monitors are configured using a secure web application. The portable current interrupters are programmed via built-in keypad or a USB cable, which reduces common errors during field installations for influence studies. As these RMUs and portable interrupters are GPS based, the foursecond on, one-second off configuration, for example, is precisely synchronised down to the millisecond. Martin says once the testing begins, he knows within 30 minutes if there is a problem, where it is and how he might approach mitigation. Martin also finds this equipment to be valuable when conducting influence tests on his own pipeline system. On a 60 mile stretch with two parallel pipes, he can programme a specific set of interrupters, then restore them to normal, then programme the next set of interrupters, and so on, as he progresses down the line. This ensures he is not depolarising his pipelines unnecessarily. When conducting influence studies, Martin also uses a data logger or field data PC to capture voltage waveforms (potentials recorded over time), date, time and GPS location at each test point (Figures 3 and 4). It then sends this information to compatible pipeline compliance software for operators to organise, manage and analyse the data. The software can also ensure necessary follow up testing is scheduled, routed and completed. Why are influence studies important? There are numerous benefits to co-operating with surrounding pipeline operators to conduct influence studies. According to Martin, it opens up lines of communication and helps build relationships between other corrosion professionals. In addition, conducting co-ordinated influence studies: ) Gives you a much clearer understanding of what s taking place on your pipeline. ) Rules out or pinpoints the possibility of CP interference on your system. ) Narrows the target area if interference is present. ) Removes the possibility of errors in your individual P/S potential readings. ) Helps determine corrective actions. Figure 5. Stray current can adversely affect underground metallic structures in a matter of months. 6 Corrosion rate of steel is 20 lbs/amp/yr. Paul Sedlet, President of Accurate Corrosion Control (ACCI), and his team have been conducting approximately two to three influence studies annually over the past decade. According to Sedlet, influence studies are the only way for operators to get a clear, thorough picture of what is happening underground. During the first influence study in which he was involved, stray current corrosion was detected. 48 World Pipelines / COATINGS & CORROSION 2014 WP_C&C2014_44-49.indd 48 09/10/ :54

5 Sedlet was commissioned by a pipeline operator in West Texas after it discovered a leak in the middle of a field. Stray current was suspected due to positive potentials at the site, and the operator wanted to determine the extent of the interference and the exact cause. The ACCI team sought co-operation from the other five operators in the area and installed GPS based portable current interrupters on 18 rectifiers across all operators. They established an interruption plan and then conducted the test. Starting at the leak site, they gathered waveforms every 50 ft upstream and downstream. From the waveforms, they could immediately see the influence of each of the 18 rectifiers to the potential every 50 ft for the half mile under test. Right away, says Sedlet, they knew who and what was causing the suppression to his client s P/S potentials and the full extent of that suppression. Waveforms were then recorded to measure current flow on the pipeline towards the leak site and positively identify all sources and magnitude of foreign current on the pipeline. If undetected, stray currents can cause serious damage (Figure 5). A case in point occurred in November 2004, when a liquid natural gas pipeline leaked in Ivel, Kentucky. A vapour cloud was released and ignited, causing an explosion and ensuing fires in the Rolling Acres Estates subdivision in Floyd County. Five homes were destroyed or partially damaged, at least 15 people were injured and more than 30 residents had to be evacuated. A number of lawsuits ensued, with the final arbitration award stating, The Tribunal finds by a preponderance of the evidence that there were two inter-related causes of the explosion that led to the losses: (1) stray current interference which caused localised corrosion that weakened the pipeline wall at the point where the rupture occurred allowing liquid natural gases to escape, and (2) the negligence of MarkWest employee (name withheld). 5 Take proactive steps The potential for stray current interference to quickly corrode buried pipelines should be widely known and understood across the industry. Federal pipeline safety regulation, 49 CFR, Part specifically states, For pipelines exposed to stray currents, you must have a program to identify, test for and minimise the detrimental effects of such currents. In NACE Paper No , author Jeffrey Didas says the avoidance of problems caused by stray current can be done several ways: ) Become active with the local Corrosion Co-ordinating Committee and/or NACE section. This is a good location to become aware of new current sources being installed or reporting ones that you have installed. ) During the design process for the new or additional CP systems, perform an assessment of underground utilities that are in the vicinity and perform preliminary interference testing with those utilities. ) Utilise sound engineering judgment during the design process to minimise any stray current effects. 7 As pipeline and facility construction continues to rise, ROWs become more crowded, and operators add new and additional cathodic protection to aging infrastructures, the potential for stray current interfering with CP systems will only escalate. Operators can avoid being the bad influence by taking an active role in industry efforts to understand stray current, where it goes, how it returns and who it is impacting. References 1. Briefing: Pipeline Rights-of-Way Final Award, CPR Arbitration, RE: Incident at Ivel, Kentucky, 8 November 2004, issued 25 th August, EDINGER, Jerome. DC Interference Detection and Confirmation, 2014 American Innovations Users Group Meeting. 7. DIDAS, Jeffrey L. Interference Testing and Case Histories, Colonial Pipeline Company, NACE Paper No , 2003 by NACE International VgnVCM ed07898RCRD&vgnextfmt=print Home of the World's Largest Corrosion Control Website FarwestCorrosion.com Products & Materials C.P. Anodes Power Supplies Test Stations Pipe Wraps Casing Fillers Instruments Reference Electrodes Inspection Equipment Cable Coatings Isolators Seals Sealants Engineering & Design C.P. Design A/C Mitigation Remote Monitoring Field Testing Current Mapping Voltage Potential Readings Close Interval Surveys Contractor Training Installation Services A/C Mitigation Services Solar Power Systems Deep Well Drilling Shallow Well Anodes Under-Tank Systems We use our own equipment Total DOT Compliance Call (888) O ce/warehouse Locations Providing Nationwide Service WP_C&C2014_44-49.indd 49 09/10/ :54