With assets beginning to age, the need for integrity solutions strongly increases; upstream natural gas assets are no exception in this regard. However, what is challenging about inspecting those type of pipelines is that most of the time they operate at lower pressures, making it difficult to run conventional in-line inspection (ILI). Thus, the most commonly asked question we receive from customers in the upstream gathering sector is, "How low of a pressure can you run at?". Finding an answer to this question mostly depends on parameters such as number of fittings and bends in the pipeline as well as the actual size of the pipeline. Usually, the line to be inspected is 8" or less in diameter.
Compact low-pressure-capable tools
When it is impossible to increase pressure on a pipeline with normal production, it is common practice – though often cost-prohibitive – to add supplemental natural gas or nitrogen. This has created a need for conventional in-line inspection tools with more compliant specifications. Our solution is our set of compact low-pressure-capable tools with the ability to go as low as 1,800 kilopascals (kPa) of line pressure. Catering to pipelines from 6" to 20" in diameter, ROSEN's Upstream Diagnostics Service is a new solution for a growing challenge.
Taking on the challenge
Challenging 6" to 8" natural gas pipelines with a standard operating pressure of 2,500 kPa or less are addressed in this article. The lines are 25 km or less in length and frequently have multiple areas of heavy wall thickness and tight radius bends. Our experts have completed several inspections that included increasing pressure with supplemental gas or cutting the pipeline into sections and tethering with a bidirectional tool. However, using standard free-swimming tools during inspection has resulted in overspeed or tools getting stuck due to pipeline operating conditions. In most of the pipelines inspected with 2,500 kPa or less, line pressure will have an effect on velocity, as the tool is passing through tight radius bends (3.0D or less). There is not enough head pressure in the pipeline to act as a brake for the in-line inspection tool, which results in a loss of useable data. The standard MFL-A tool will need to operate at a maximum of 5.0 m/s, with an ideal range of less than 3.0 m/s.
Combining technologies
Our approach included conventional MFL-A, caliper and XYZ (high-resolution mapping) technologies built into a smaller and more compact form factor with less weight and high compliance. The technique of combining MFL-A/MD and XYZ technologies on one tool has been used for a number of years in a fast turnaround application with a robust design and small form factor. Coupled with hydrogen-sulfide resistance and rechargeable batteries, the combined tools are an ideal fit for this environment.