In order to address the above-mentioned risk factors, the pipeline industry is dedicating a lot of effort to prepare and standardise the construction and operation of pipelines in mountain regions.
The International Pipeline and Offshore Contractors Association (IPLOCA) presents ten different pipeline construction environments in its recently released recommended construction practices for onshore pipelines, Onshore Pipelines: The Road to Success. Three of these environments directly describe mountain areas – the side slope, ridge and rock RoW scenarios. Another two refer to arctic conditions and the environmentally sensitive area often encountered in mountain terrain. In all the scenarios, one of the most efficient ways of mitigating the pipeline construction and operating risks is to protect the steel pipe against mechanical damage from impact and penetration.
The need for supplementary mechanical protection
Mechanical damage to the pipe can occur during all phases of the pipeline construction and operation, for example during transportation, handling (loading in and out), storage, lowering-in, backfilling, and during pipeline’s service life. Impacts and penetration damage can be caused by many factors:
* Other pipes or pipe handling equipment;
* Lowering-in; and,
* Rocks in the trench bottom or impact from the backfill material.
Steel pipe is impact resistant by itself and some of the external coatings applied on steel increase this basic mechanical protection. However, in order to ensure an incident-free service life for the pipeline, the steel pipe and the anti-corrosion coating have to be intact during construction and operation. This cannot be guaranteed by the basic mechanical protection of the steel and anti-corrosion coatings. Therefore, the industry has developed supplementary mechanical protection systems that are aimed at reducing or eliminating the risk of mechanical damage.
As the industry uses a wide range of supplementary mechanical protection systems, this article will focus on the systems that protect the entire diameter and length of the pipe, and which are the most efficient in protecting the pipe and its coating against impact and penetration. Today, most pipeline projects use the following supplementary mechanical protection system: concrete coatings, sand padding and select backfill (mechanical padding), as well as non-woven geotextiles and rockshield materials.