The goal of the project is to develop technology that will enable remote interrogation of the internal corrosion of pipelines.
SouthWest Research Institute
Metal Strategies Inc. (MSI),
Pipeline Research Council International (PRCI)
San Antonio, Texas 78238
According to the Department of Transportation Office of Pipeline Safety (OPS), internal corrosion caused about 15 percent of all gas transmission pipeline reportable incidents over the last several years, leading to an average of $3 million in annual property damage and several fatalities. As a further complication, a significant portion of the pipeline system is “unpiggable;” a pipeline pig with corrosion sensors cannot be used to inspect the pipe due to geometric restrictions of the pipeline. Internal corrosion direct assessment (ICDA) can be a viable option for such lines, but it has uncertainties with respect to the location and extent of the internal corrosion, requiring extensive digs. The objective of the proposed project is to develop an independent and complementary technology that will enable remote interrogation of the internal corrosion of pipelines through miniaturized sensor packages introduced into the gas stream.
This sensor system will be composed of a wireless network backbone, an environmental corrosivity sensor, and a sensor to measure the corrosion rate. The wireless network for communication employs a microprocessor that is on-board powered and has a nominal signal transmission range of 1,500 feet. These sensors will be encapsulated in a polymeric sheath whose surface properties can be manipulated to range from hydrophilic to hydrophobic. By doing so, the sensors can flow in the gas stream and move to the locations of water accumulation. Preliminary flow modeling has demonstrated the feasibility of such a concept. Once at these locations, the corrosivity and corrosion rate sensors can provide information regarding the condition of the pipeline, which can be used to guide the appropriate mitigating actions. Because the powered sensors will be introduced into the natural gas stream, pipeline operations issues and fire hazard considerations will also need to be evaluated. The completed sensors will nominally be on the order of five to fifteen mm in diameter.
A 2002 workshop sponsored by NETL identified several important natural gas infrastructure enhancement goals, including the development of innovative technologies to address internal corrosion problems. The solution of these problems could help to avoid $3 million in annual property damage and potential loss of life associated with corrosion-caused damage.
In order to better assess the integrity of pipelines, in-line inspection (ILI) devices have been developed, based on a wide range of technologies, to determine the remaining pipe wall thickness. ILI is typically conducted by passing sensing devices through the pipeline on a mobile platform called a pig. A key limitation with ILI technologies is that they only provide an instantaneous snap shot of the condition of the pipe and cannot be used for in-situ monitoring because the pig cannot be retained in the pipe, and aligning successive pig runs is difficult at best. The primary limitation with pigging, however, is that over 30 percent of the nearly 1.3 million miles of gas transmission and distribution piping is unpiggable because of geometric restrictions, such as gate valves and bends. ICDA is a methodology based on fluid dynamics modeling that predicts the locations along the pipeline where entrained water and other fluids are likely to drop out of the gas phase and accumulate, thereby prioritizing the locations for direct excavation. Though ICDA holds promise to prioritize the locations for pipeline excavation, it does not provide a direct indication of active corrosion and further, it cannot provide information on the lateral distance over which corrosion is likely. Thus, there exists a significant need to develop a complementary technology that can be used on both piggable and unpiggable pipelines to remotely detect and monitor the extent of corrosion, thereby enhancing pipeline integrity.
This proposed project provides a significant complimentary advantage to the ICDA methodology currently under development. The introduction of sensors to the gas stream that can be used in non-piggable lines will allow remote detection and monitoring of corrosion and the presence of water. If no water is detected, even though water is predicted by ICDA, pipe excavation can be avoided. Furthermore, just because water is detected does not necessarily mean it is highly corrosive. This technology will incorporate the means to measure corrosion in addition to detecting water. In addition, corrosion inhibitors may also be introduced to mitigate any corrosive water found, again minimizing the need for pipe excavation. If the proposed project is successful, the technology will be commercialized and developed into a new inspection service once field validation studies have been completed (not part of this project).
Work has primarily been focused on several aspects of wireless data transmission and corrosion sensor identification and development. The results obtained have clearly demonstrated that wireless data transmission within a pipeline is technologically feasible. Several potential corrosion sensors have been identified and the interdigitated galvanic couple sensor and the magic angle spinning (MAS) probe both show significant promise for use in the proposed sensor concept.
Transmission along distances within a pipe was shown to be feasible, and more efficient within the pipeline than in the case of open-air transmissions. Communication from within the pipe to an external receiver occurs at any gap in metallic continuity in the pipe (e.g., non-metallic discontinuities are provided to prevent long-line telluric currents). Alternatively, corrosion coupon locations in a pipeline can be used to extract signals from within the pipe. Communicating the location of the sensor from within the pipe is still a challenge. Ultra Wide Band transmission does not appear to penetrate the pipe consistently. Low frequency signal (e.g., AM radio type signal) can penetrate steel and ground cover and should be explored as an alternative.
Several sensors were evaluated for use as corrosion sensors on a wireless platform. The interdigitated galvanic couple sensor made of silver-graphite couple was successful at quickly determining general environmental corrosivity, but not actual corrosion rates. The multielectrode array sensor (MAS) probe showed good correlation to corrosion rate of steel. A thin-film flexible version of the MAS probe (TMAS) was developed and shown to function properly. However, the TMAS does not last long in a corrosive environment because of the small thickness of the sensor element. A miniature version of conventional MAS will be used in the resident sensors.
Sensor Power Needs
Battery power, while a readily available solution, is not a long-term solution. One method of actively powering the sensor is to harvest the energy of moving gas to charge a battery. Several wind mill concepts using small motors were examined. A theoretical analysis indicated that wind driven power transformation is possible. Limited wind tunnel testing showed that wind velocity typical of that expected in a pipeline can generate adequate power for charging the battery. The design of such a power system has to be completed.
Sensor Flow Characteristics
The effect of gas velocity, sensor density, and pipeline inclination angle on the ability of sensor to move or deposit at a given location was analyzed. The calculations provided a method to develop sensor parameters to enable deposition at a location of water hold-up.
This effort ended in September 2005.
Recommended future activities include: