Intelligent pigs: broadening the remit

Jon Lawson

Martin Bluck discusses today’s intelligent pigs and how technology can be leveraged to provide improved confidence to pipeline operators striving for zero pipeline failures

In the past, different types of inline inspection tools were developed, each for a single, specific purpose. Magnetic flux leakage (MFL) pigs were developed for metal loss inspection, while caliper pigs were designed to look for dents and geometric features and mapping systems were used to investigate pipeline positioning. Within each of these three types of pig, there were multiple variants, each designed and developed to meet specific industry requirements. At one time, PII had seven different types of MFL systems in operational use, each delivering inspection results to subtly different specifications.

From an operational standpoint, having multiple types of inline inspection tool presents an unwelcome dichotomy. Although the pipeline operator has a fundamental need for confidence in the quality of the inspection, they must balance this against the downtime caused by every inspection run. For a clean bill of health covering metal loss, dents and pipeline positioning, a minimum of three inspection runs would have had to be completed. This need for three runs increases downtime & the likelihood of a failed run. However, this could be compounded by the need to re-run with one of the other MFL or caliper system variants if the pipeline condition was not as anticipated, further increasing the downtime and costs suffered by the pipeline operator.

Faced with this problem, one of the goals for PII in developing its fourth generation MFL technology was to reduce the range of pigs in its inventory while enhancing inspection quality, safety and delivering first run success.

As a result of the smart application of this latest technology, PII’s next generation of intelligent pig now incorporates MFL, caliper and inertial measurement unit (IMU) mapping in a single, compact yet flexible multi-mission system. What used to need three runs can now be completed in a single inspection while offering enhanced levels of accuracy and the flexibility to meet individual client needs, cost effectively.

This has been achieved by optimising the design of each of the three core components of the inline inspection system to gather more data to provide a higher resolution inspection. By reducing the size of the MFL sensors, configuring them in a triax array, while increasing their volume and the sampling frequency, an impressive level of inspection accuracy can be achieved. The same is true for the caliper and IMU modules. By running every inspection with the same set-up at maximum resolution, the probability of first run success can also be improved, whatever the customer’s specific requirements. However, to make the service cost-effective for the customer, only the datasets necessary to meet the required specification are analysed.

For instance, a customer with a clean pipeline with only isolated areas of corrosion might only need a very simple metal loss inspection, so only a fraction of the MFL data would be used while the caliper and IMU data would be recorded and stored, but not analysed. However, because the entire data set has been collected at the highest resolution on the initial run, it is possible to revisit the analysis with a revised higher specification and scope without having to re-run the tool. This flexibility allows PII to work with the customer and run a whole range of different analysis options depending on their specific concerns about their pipeline. Because the analysis can be tailored to the pipeline, its age, location, type of product transported and history, it is a very cost effective way of protecting the integrity of assets.

In parallel with the hardware development, PII has invested in analysis software and tools that look at metal loss, geometry and mapping data as one homogenous dataset so that the combined effects can be assessed. With this information readily available, PII’s analysts can make a far more informed call on the level of threat and advise the client so they can take the necessary mitigation measures further enhancing pipeline safety and security.

Current PII technology can detect, identify size and locate metal loss as shallow as 0.2mm deep and features as small as 2mm in diameter. With the same tool, PII can identify dents as shallow as 2mm deep and 25mm circular diameter which are barely visible to the naked eye. IMU mapping can now identify movement in the pipeline of less than the width of the pipeline itself with offsets of as little as 150mm being detectable.

The improvement in resolution has also delivered some unexpected benefits. The capability to detect pinholes down to 2mm diameter was formally validated by one of the largest publicly traded international oil and gas companies through a blind test followed by in-field dig verification. Its interest was not only in pin holes arising from typical corrosion mechanisms but also from illegal tapping by third parties for product theft. To better address this specific threat, PII enhanced its ‘Pinhole’ offering to include identification of unauthorised connections to live pipelines where there is the possibility of product being stolen. The issue of pilferage is becoming a major commercial threat to pipeline operators around the world and being able to identify where new fixtures and fittings have appeared in a line particularly when coincident with deep small diameter metal loss has already proved effective in mitigating this threat.

Circumferential cracking in the girth weld is another major concern for oil and gas pipeline operators around the world. The capability to detect metal loss in the girth weld area with magnetics technology has been understood since the early 1990s. However, it is only now with the latest high resolution data and algorithms that it has become possible to detect circumferential cracks open by as little as 0.25mm and discriminate from metal loss. This was proven in collaboration with a major Chinese operator in both girth and spiral welds using the latest triax sensor array.

There are implications associated with gathering multiple data-sets at high resolution, the main one being the size of the data files involved. An inspection can now generate up to a terabyte of data that is an order of magnitude more than what was typical in the past. PII has invested heavily in order to build the IT and infrastructure support required to transport, analyse and store such large quantities of data. Another challenge is the complexity of the new multi-mission tools. With up to 10 times the level of sensing technology seen on previous tools the complexity of the system has increased by an order of magnitude, but there is still the requirement to deliver maximum reliability and first run success. PII currently delivers first run success of around 95% beating the industry benchmark of 90%. However, a 5% failure rate is still too high and the company has taken on the challenge to reduce it through operational enhancements and reliability improvements at sub-system component level while remaining cost effective.

All MFL4 development and investment is focused on delivering added value to PII’s customers. First run success is key: ensuring that the pig completes its run in one piece, within the allocated working window, gathering all the data necessary to provide the report specification that is required contractually. Once the inspection is complete it is incumbent on PII to undertake the analysis and deliver the report to the customer within agreed timescales so they can act on it in a timely fashion. The ultimate measure of success is when the customer exposes a pipeline in an operational environment and finds the specific feature or area of corrosion at the precise location noted in the analysis report. This sort of accuracy in delivery gives customers confidence, reduces abortive or false digs and repair activity and helps deliver a cost-effective asset management programme.

Zero pipeline failures is what the client is looking for and achieving this is the goal that PII is constantly striving towards. The more accurate and reliable the data is, the more benefit can be derived from both an asset management and a commercial standpoint. High levels of confidence in inspection results mean that clients can afford to put less contingency around PII’s accuracy and undertake remediation only when strictly necessary.

As inspection technology has enabled traditional threats to pipeline integrity to increasingly be taken care of, the focus moves to less prevalent threats and new failure modes as pipelines continue to age. Matching inspection system signal data to unusual features found during dig verification, and performing pull-through tests in client pipeline spools are two methods by which PII works with customers to identify and optimise inspection system capability to address these new challenges.

Looking to the future, PII will continue to invest in technology utilised in pipeline inspection. With the introduction of MFL4, magnetics, calliper and IMU hardware are now at, or close to entitlement. However, further investment in software, algorithms and data mining offer the potential for further exciting developments. In the longer term it is conceivable that there may be a new approach to measuring the threat to a pipeline using a sensing technology that we don’t recognise today. Whatever that technology might be, PII will continue at the cutting edge of industry research, working with its customers to give them peace of mind and helping protect the integrity of their assets.

Martin Bluck, Magnetics Product Manager at  PII Pipeline Solutions (PII).

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