Q: When pipe inspection gauges (PIGs) travel through steel pipelines that are routed on the bottom of the ocean or are buried underground, the information they collect concerning cracks and leaks is just placed in the solid state memory of the PIG and this "memorized" data travels with the PIG until it is retreived and the information is downloaded.
I think the safety of the pipelining industry could be much improved if this data, which could require the shutdown of pumping or compressor stations, could be acted upon immediately. How would you approach solving this problem?
A: At today's state of the art, this instant information is not available, not only because signals would be impeded by the steel pipe walls and their water or earth covering requiring unavailable battery power, but also because today's PIGs are not reliable enough to initiate automatic shutdown that can result in excessive pressure surges. PIGs today are good only to detect gradual phenomena, such the decrease of pipe thickness. Information obtained from pigging is used only for operator warning. Events requiring immediate action, such as pipe damage due to earthquakes, ship anchors or terrorist action, have to use other techniques. What is feasible, though, is to transmit the data collected as soon as the PIG is retrieved from the pipe (Figure 1), and use computer software to speed the evaluation of and response to that data.
A: I am not an expert in the use of PIGs, but I would say it's situational. Use of real- time telemetry depends on many factors; e.g., depth of the pipe and substrate above the pipe; the type of media (behind or in front of the PIG) in the pipe; length of pipe; number of bends, etc. Acoustic or RF telemetry, fiber-optic or copper spools at the launcher and on the PIG are just a few examples of how data can be transported in real time. Bottom line: We need more data to provide a solution. Budget, timeline and performance requirements (bandwidth, data rates, etc.) are an obvious consideration as well.
A: I don't know that I would agree with Mr. Crowney's statement at all. Corrosion and ultimate failure of a pipeline is a rather slow process that usually takes months (if not years) to occur. In most cases, a degrading pipe will be inspected many times before it ultimately fails, providing many opportunities to identify a developing problem and correct it prior to disaster. (Of course. this assumes that the pipeline is inspected at all.)
It seems highly unlikely that a PIG sensor would detect an impending failure that had never been sensed in any of the previous inspections, and so the ability of the pig to shut down the pipeline immediately rather than waiting for the inspection team to interpret the data and notice the problem would markedly improve safety.
On the flip side, Mr. Crowney does not mention the innumerable false shutdowns that would invariably occur every time a PIG sensor malfunctioned or sensed a pipeline abnormality. It seems that the resulting pressure surges of stopping and restarting the pipeline for needless interruptions would cause far more safety issues than the PIG shutdown system would avert.
P. Hunter Vegas
A: Intelligent PIGs nowadays collect all relevant pipeline data. "Pigging" is a process which is deterministic and used on an "as when required" basis. Pipeline leakage or cracks are random phenomenon. Moreover, PIGs often acquire incorrect or garbage information.
Any ESD executive action shall be based on a proven system (leak detection or pipeline integrity system). Therefore, for shutting down a block valve station or compression station, in my opinion, an intelligent PIG should not be used. However, operator alerts can be generated for further action/investigation.
A: Although I am not an expert in pigging systems, pipeline integrity and continuous leak detection is best performed by specialized software programs. Intelligent PIGs are used to collect and store data in their memory because transmitting data while they travel through the pipeline requires a lot of battery power. PIG-tracking transmitters and receivers are available from a number of vendors. However these are restricted to information about the PIG's location rather than data transmission. If Harry is interested, he can contact PPSA and get more information on the latest developments from PIG manufactures and end users.