Editorial comment
High capital expenditure, and lifelong financial and other risks associated with pipelines, can make it important to contain or reduce operating expenditure while keeping revenue-earning oil and gas flowing.1 Zero downtime is therefore important, and ‘live repairs’ enable this. They can improve cost efficiency while maintaining acceptable standards, reliability and safety levels.
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Live repair can eliminate or reduce disruption or financial liabilities that could otherwise result from removing and replacing pipes. Delivery disruption can have large consequences if a pipeline operator has a contractual obligation to keep gas flowing. Shutting down supply to an LNG facility could cost such a plant around a hundred million dollars, for example.
DNV GL is a technology leader for live repair. The company has lately been involved in many live repair projects both for on- and offshore pipelines, using various techniques such as welding, epoxy grouted sleeves, grouted tees, welded or mechanical sleeves, and pipeline clamps.
Epoxy grouted sleeves involve installing a steel sleeve around a non-leaking pipeline, then introducing a quick-drying end seal before injecting epoxy grout between sleeve and pipe. Grouted tee is a similar technology but has a branch connection and seal, enabling pipeline contents and high pressure to be contained. A single grouted tee can isolate a minor leak or encapsulate a damaged or deteriorated branch connection. Multiple grouted tees can provide a flow-stop and bypass arrangement to enable the replacement of larger sections of pipeline.
Grouting is simple and does not require onsite welding, so full flow can be maintained during repair or intervention. Usage of grouted tees has expanded to include repairs on thin-walled and cast iron pipelines, and on subsea pipelines in up to 200 m of water depth.
The total cost of grouted tee connections is usually less than traditional, welded tees at larger diameters, and they also benefit from a 40 year minimum design life compared with the 20 - 30 years that is common for a pipeline.
Tees and sleeves may be welded rather than grouted to a live pipeline, but this requires flow reduction and can increase safety risks. Simple clamps can be used for temporary seals while permanent repairs are designed.
Design standards usually specify heavy wall pipe for sections subject to higher external forces, at road and rail crossings for example. Replacing standard with heavy wall pipe is very expensive if a pipeline has to be decommissioned during repairs, and could even be hazardous when flow is stopped while a bypass is welded into place to isolate a leaking section.2
An epoxy grouted sleeve involves zero downtime, can address most onshore pipeline defects, and is one of few repairs suitable for defects in girth welds that join pipes end-to-end around their circumference. Production downtime for pipeline repairs offshore can cost millions of dollars per day in lost revenue, so live repair is attractive here too, even though it is technically challenging.3
When a 32 in. natural gas pipeline leaked offshore earlier in this decade, there was concern that 25% of homes and businesses in a large Asian city could suffer partial power blackouts. The pipeline operator engaged DNV GL to help assess the situation. The pipeline was temporarily repaired within a week by using an off-the-shelf leak clamp.
However, the operator wanted a permanent repair that could be done with the pipeline live, which would last 20 - 30 years. DNV GL recommended using a type of sleeve (welded stand-off) developed by DNV GL, and used during projects in Russia and China. A more familiar solution at the time would have been to install a temporary bypass pipeline to allow the damaged section to be cut out and replaced in a hyperbaric (dry) environment. However, both the pipeline and leak locations in Asia meant this would be too complex, risky, entail a long lead time, and would involve disturbance to gas flow. As part of the project organisation, DNV GL contributed technical solutions and added barriers to ensure safety of the live welding operation that enabled use of welded stand-off sleeves.
The project used resources from DNV GL’s large global network of pipeline experts to support the local project management and site team to develop, qualify, design, test and follow up the repair at site. There was no supply disruption over the 18 months that this novel solution took to complete, and flowrate and pressure were maintained.
To further assist customers such as the Asian operator, DNV GL recently launched EC-Pipe, an internally-funded project to help the industry reduce capital and operational expenditure, and to increase efficiency, while maintaining acceptable reliability and safety standards. Read more about EC-Pipe at: www2.dnvgl.com/ECPipe.
