In this era where pipeline infrastructure is badly needed to bring liquid products from new plays to market—ﬁnding a path to build new pipelines has been increasingly difﬁcult. Politics aside, there is no question that environmental, health and safety are the main concerns when it comes to permitting and building pipelines, and we’ve seen many major projects stalled or cancelled over the past five years. The good news? Pipelines remain the safest and most efﬁcient way to transport liquid product, which ultimately bodes well for the industry as expansion is needed. However, the industry needs to make a much better case in the court of public opinion if it ever hopes to quell the fears prevalent in the discussion.
The even better news is that technology exists today to ensure that leaks are detected accurately, and quickly, and that procedures are in place to mitigate and even halt any negative impacts of a leak event. In this regard, the industry has done great work with the newly published API recommended practice 1175, and there is likely more to follow as new PHMSA rules come into play.
Most leak detection systems are fail-safe, very sensitive, and as such produce frequent false alarms.
While this sensitivity keeps major events from occurring, it can drive operating costs extremely high and interrupt service as the alarm events are investigated. These false alarms are usually caused by changing conditions within the pipeline, resulting from a myriad of different situations. For example, batch interfaces, pumps, and valves, as well as more seemingly benign things such as temperature ﬂuctuations through the day, can all cause transient changes within a pipeline. At the heart of the leak detection system are the instruments constantly monitoring these conditions, which can have trouble dealing with changing conditions. In particular, the ﬂow meters used in leak detection systems can be the root cause of 20% or more of the false alarms produced on a yearly basis.
Many different ﬂow meter technologies exist—which meter technology is best for leak detection?
Traditional mechanical based technologies, such as turbine and positive displacement (PD) meters, do a fantastic job achieving repeatable results under normal operation. The inertia produced as the meter internals spin generates very smooth performance. However, these technologies have very limited diagnostic capabilities, which translates into having only the basic beneﬁt of ﬂow measurement. There is virtually no way for these meters to distinguish the difference between normal and transient conditions. Also, these meters are mechanical and require maintenance as the internals wear, and the resulting measurement errors lead to false alarms.
Coriolis meter technology is fast becoming a dominant technology across many industries, but for leak detection systems, Coriolis meters are often not applicable due to size limitations (maximum of 12-inch pipes in many cases). These meters also cannot be pigged, which limits their ability to be applied in situations where a bypass isn’t available. Unlike the older mechanical technologies, Coriolis meters do have advanced digital diagnostic capability, which can be applied to infer parameters for uses like batch identiﬁcation.
Ultrasonic ﬂow meters are the most widely applied meter technology for pipeline leak detection, mainly due to their ﬂexibility (size and turndown) and digital diagnostic capability. Ultrasonic ﬂow meters can be used in pipelines from one-half inch to over 72 inches, and can also be applied in both inline and clamp-on (external) installations. The ultrasonic meters of today are both very accurate and repeatable, and most multi-path ﬂow meters provide a digital snapshot of the ﬂow proﬁle, which is a leading indicator of pipeline transient conditions. The newest multi-path meters, like GE's Sentinel LCT8, are designed to compensate for changes in ﬂow, and can also be very efﬁciently heat blanketed for applications where buildup is a concern. For existing pipelines, clamp-on ultrasonic meters can be installed without cutting into the pipe, avoiding up front capital expenditure for operators. And advanced diagnostics, like GE's Predix platform, give operators predictive insight as conditions change within the pipeline.
- Technology is available today to ensure safe operation of pipelines. And more regulations are coming, so consult those in the industry who provide leak detection systems and evaluate what is laid out in API recommended practice 1175.
- Get down to the instrumentation layer. The leak detection system is built upon a foundation of instrumentation. If the instrumentation is lacking, then the system will not operate to its fullest potential.
- For ﬂow meters, choose ultrasonic. It’s the best and most widely applied technology. Manufacturers of today’s ultrasonic ﬂow meters have made signiﬁcant advances speciﬁcally for leak detection purposes.
- Go digital. There is a wealth of information available for operators. The diagnostic data available alone is valuable and can work to improve pipeline system performance and of course—the bottom line.