All Gas Distribution Networks (GDNs) in the United Kingdon (UK) have high pressure gas pipelines that are sleeved (the carrier pipe which the live pipe sits in) to protect them in locations where they cross third-party infrastructure such as railways, rivers and roads. These sleeves were installed in accordance with IGEM/TD/1 (Steel pipelines and associated installations for high pressure gas transmission) to protect pipelines from any point loads or conditions which could potentially impact their integrity; however, with the implementation of IGEM/TD/1 edition 3 these were no longer permissible.

The condition of these sleeves has been problematic to quantify, and it has been envisaged that sections of sleeved pipeline could be exhibiting significant levels of corrosion. Due to the age of the pipeline, pipeline coating and end seals, water ingress can occur inside the sleeve and external corrosion on the gas pipeline can initiate and accelerate. It has been identified that there is a higher risk of external corrosion on the pipeline located in a sleeve.

SGN has approximately 600 Air Filled Sleeves currently in operation on Scotland’s Local Transmission System (LTS).  Within this population, approximately 116 of these are on pipelines that Inline Inspection (ILI) cannot be performed but require inspection (condition assessment) as a regulatory requirement, these are a known as OLI/4 Pipelines. Moreover, a further 484 OLI/1 sleeved pipelines with limited condition data.

Current inspection methods require extensive excavation works to dig out the pipe, remove the sleeve and visually inspect it, which are often costly, time-consuming and a resource burden on the GDNs.  In June 2003 Advantica Report R6196 was produced which provided a risk assessment methodology for OLI4 pipelines contained within Air-Filled Sleeves. This report made a number of recommendations as to how potentially make a desktop assessment to select which pipelines should be exposed and inspected. Since this time sleeves have undergone a limited number of condition assessment since this was published and recommended as the overall cost is extremely prohibitive.
A means of inspecting the sleeves without the need to excavate would greatly simplify the process of assessing these sleeves, limit interference and inform any future action taken by the networks.

Benefits

All Networks follow Pipeline Safety Regulations Compliance & UKOPA Guidelines the learning from this project will be shared across the relevant parties. The savings for a single sleeve inspection utilising current techniques equates to £120,000 it is envisaged that if this project is successful the cost of a single inspection will be approximately £4,200 giving a saving of £115,800 per inspection.
Current method inspection costs pipeline danger zone- hand dug excavation £30,000 plus standardised engineering costs to access the pipe & expose seals / make cuts £90,000 total £120,000.
New project inspection method costs total £4,200 therefore single saving of £115,800