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Pipeline Walking Mitigation

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Pipeline walking is unique challenge for industry caused by thermally driven cyclic expansion resulting in the pipeline walking progressively away from or toward fixed end terminations.

Walking is typically arrested by either applying anchor piles clamped to the pipeline, conventional concrete mattresses or rock dumping. One disadvantage of rock-dumping and concrete mattresses is that the bulk of the additional mass applied is wasted because this is transferred straight to the seabed instead of the pipeline. Approximately 80% of the weight transferred subsea is wasted meaning logistics and and installation effort is also wasted.

Piles typically have to be applied at the pipeline end point, increasing the total restraint load required with a proportional increase to installation and material costs.

In response to these disadvantages, Subcon and Shell Global Solutions (Shell) developed a new walking mitigation method, the “Pipe Clamping Mattress” (PCM). PCMs address all the challenges faced by operators implementing conventional methods with one simple solution that can be retrofit using common light construction vessels and without removing coatings.

FAQ’s

The key design driver of the PCM is to mobilise 100% of the anchoring weight into the pipeline and using the seabed – pipeline friction coefficient to provide the walking restraint load.

This greatly reduces the material required for restraining the pipeline, providing significant cost savings in materials, transport and installation. In addition to this, the PCMs can be installed at the virtual anchor point, which requires the least amount of restraint load to mitigate / arrest the pipeline walking.

There is significant increase in the shear strength of the soils as it consolidates under cyclic loading.

This in turn provides a high friction factor and reduced quantity of PCMs to be deployed. This engineering provides the client with a very economical design to arrest or mitigate their walking issues.

Subcon’s walking mitigation methods are not depth limited.

Not every pipeline will experience walking and pipeline walking is a gradual process.

PCMs can be applied after the first signs of pipeline walking appear. Alternatively, they can be deployed during pipeline installation.

Shell holds a patent on the PCM technology and retains the intellectual property. Shell has granted Subcon with the sole global license to supply the PCMs to market.

PCMs can be deployed not only on Shell projects, but are available to all operators. Subcon pays a royalty to Shell for the license, and as such, on Shell projects (either as Operator or JVP) a discount on the royalty fee is given.

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Pipe Clamping Mattress (PCM)

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