Inline Inspection, Pigging Methods For Managing Pipeline Integrity

March 2015, Vol. 242, No. 3

Paul Otway, Senior Subsea Engineer, Jee Ltd. Aberdeen, Scotland

Corrosion, erosion and other forms of material degradation can cause critical damage to steel pipelines and riser systems, potentially resulting in health and safety hazards and costly repairs for oil and gas operators. Inspection technologies are available to evaluate pipeline integrity, and as a result, maximize the economic recovery of oil and gas reserves.

In regions with maturing oil and gas reserves it has become increasingly common for operators to adopt the method of inline inspection (ILI) to verify the status and integrity of aging pipelines. This is particularly common in the North Sea where the method allows for the operational lives of oil fields to be extended.

ILI uses tools called intelligent pigs, which are sent through pipelines to collect data on the pipeline wall thickness and to detect defects. This data is then used to assess the pipeline condition and establish if repair, maintenance or a change to the operating conditions is required.

Inline inspection is valuable throughout the life cycle of a project. Early in the pipeline’s life, particularly prior to start up, it can be used to detect manufacturing defects. This provides an original record against which future inspections can be correlated to show which features were already present and which were subsequently developed.

ILI may also be used on pipelines that did not originally envisage pigging. In mature fields, for example, increasing water cut, not present at the start up, may change conditions within the pipeline.

Although ILI is important, it can be a high-risk activity and should be treated accordingly. Pig traps, for example, are ostensibly pressure vessels that need to be operated with care. Debris brought back from a pigging run can be toxic or radioactive. From a commercial perspective, running anything through the bore of a pipe carries the risk of a stuck pig, which can potentially stop production flow.

As a result, prior to the commencement of an ILI operation, it may be necessary to clean the pipe with foam or brush pigs, to ensure any restrictions are removed that may obstruct the inspection tools.

It is important that debris is picked up in a controlled manner, especially in pipes requiring multiple cleaning runs. If too much debris is gathered, it can create a blockage in front of the pig, causing it to stick. The best way to manage this is by a progressive cleaning campaign. The application of increasingly aggressive tools gives greater confidence that the line is clean while minimizing the risk of getting a pig stuck.

Following pipeline cleaning, gauge pigs and calliper pigs are used to ensure that inline inspection tools will fit through the pipeline diameter.

The diameter of a pig must be matched to pass through the pipe. However, some pipelines consist of sections with different diameters, so a pig has to be able to pass through the smaller bore and not get stuck, as well as being able to travel through the larger bore and maintain the seal.

ILI Case Study

Pipeline integrity is extremely important in offshore projects and is becoming increasingly critical as assets age. To detect corrosion and improve the corrosion management systems to extend the lifespan of these pipelines, pigging is crucial, and choosing the right technology can save operators valuable time and money.

Jee recently managed a pipeline integrity project from inception to completion for a major operator in West Africa. The contract saw Jee take a lead role in the tool development, inspection, offshore deployment and overall management of the project. It required technical management and campaign design of the baseline inline inspections of two deepwater, high-pressure flowline loops located on a floating production, storage and offloading vessel (FPSO).

Development Stage

The campaigns, which included the inspection of the clad pipe sections and flexible risers, represented a new challenge as it was the first time either pipeline had been pigged during operation. Jee was tasked with identifying any internal or external defects in the pipeline, with the operator particularly concerned about small defects which had the potential to grow.

With a water depth of 1,500 meters it was critical that the tools chosen were fully operational at high pressure. Jee carried out a full pipeline geometry review from pig launcher to receiver, specifying the tooling requirements for the pipeline cleaning, gauging and inspection. This ensured that the pig vendors had complete pipeline information in order to design tools for the range of internal diameters, bend radii, etc. The team then managed the procurement of the tools and ensured it was fully compliant with industry certifications and regulations.

This project required a detailed campaign and tool development stage. Jee designed the pre-ILI cleaning strategy prior to the campaign, defining the level of cleaning and types of tools required, based on the anticipated debris in the pipeline. This was accounted for in the pre-ILI cleaning strategy to ensure cleaning was sufficient so that the ILI tool sensors would not become obscured, and there would be no interference with the data collected. The flowlines also exhibited a wide bore range and the pigging tools that were chosen had to be designed to pass through and operate in all bores within the system.

To give the client full assurance that high-quality results could be achieved using the tools chosen, Jee oversaw loop testing of the tools to check geometric and functional performance, and analyzed the data generated, as well as completing independent pig design assurance checks.

Project Management

One key element of the project management scope was the preparation and tracking of costs and time schedules to ensure the campaign was completed on time and within budget. The team met regularly with the vendors to identify, manage and resolve any issues, so that they did not affect completion of the project.

The team visited the offshore site to assess the facilities and equipment ahead of the campaign and to ensure that the site was ready for the pipeline inspection. During the offshore execution of the cleaning and inspection runs, Jee worked with the client’s team for the duration of the ILI campaigns, oversaw the vendor activities, independently reviewed recommendations and managed the interface between the pigging team and the offshore management team.

One of the offshore campaigns was completed on time and the other ahead of schedule, minimizing the production losses associated with shutting down each pipeline during a pigging campaign. The shutdown time from the original estimate fell from 21 days to 12 days. This resulted in a saving of about $100 million for the client in otherwise lost production.

Following the campaigns, a close-out meeting to review lessons learned was arranged and chaired. A detailed report was compiled and issued to the client, summarizing all onshore and offshore activities during the project and key data recovered by the inspection.

The complex ILI campaigns were managed and executed successfully, giving the client a first run inspection success and significant cost savings. As a result of this success, Jee went on to secure a further two contracts with the same major operator in West Africa and the North Sea, due for completion in 2015.

Author: Paul Otway is the senior subsea engineer at Jee Ltd., where he has worked since 2009. He specializes in in pipeline pigging and management of pipeline in-line inspection campaigns.

A cleaning pig prior to its run.

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