This paper reviews the recent development of a stressed grouted clamp as a permanent repair technique for subsea pipelines and describes test results of a prototype clamp The clamp is designed to reinstate the strength of defective pipelines and to contain localised leaks The defects to be repaired include shallow buckles, dents, cracks, slowly weeping holes, pitted areas or any other localized areas that have been damaged or weakened by corrosion, fatigue or accidental impact. The great advantage of using such a clamp is that a pipeline can be repaired without shutting down its operation or using an expensive by-pass Substantial cost savings may result from this repair technique as compared with a hyperbaric welded repair Four basic clamps, covering 14"/16", 18"/20", 22"/24" and 34"/36" pipelines, have been designed and one prototype clamp has been fabricated and tested underwater. The tests were witnessed by the Certifying Authority and the clamp design has been certified


A major economical consideration In repairing defective pipelines IS to reduce the shutdown time while the repair is being carried out. Other considerations include the ability to restore the strength of a weakened pipeline and minimise the requirements for precise positioning. Existing techniques such as hyperbaric welding, mechanical end coupling or mechanical spilt sleeves suffer in one or other of these areas The welding technique requires the shutdown of the pipeline that IS to be repaired Mechanical techniques may also require shutdown and, in addition, they do not necessarily have the ability to reinstate the strength or provide a permanent repair

Recognizing the irnplicatlons of reducing shutdown time and the need for permanent repair, SLP Engineering London (formerly Wimpey Offshore) started work to extend the stressed grouted clamp concept to subsea pipeline repair In the early eighties, but lack of funding forced the work to be put on hold

Meanwhile, Phillips Petroleum Company Norway (PPCoN) had continuously been evaluating their Emergency Pipeline Repair (EPR) philosophy and the readiness to fulfil the emergency repair requirements The need to be fully prepared for any incidental pipeline repair cannot be overstressed as the company operates some 1100 km of pipelines including the 442 km gas trunk line to Emden, the 354 km oil trunk line to Teesside and numerous pipelines In the Greater Ekofisk Area as shown in Figure 1. In addition to a resultant Pipeline Incident Repair Manual (PIRM), which covers all repair aspects ranging from inspection, classification to engineering, repairing and recommissioning, a need was also established to upgrade and maintain the emergency repair stock. The stressed grouted clamp was identified as a suitable means for permanent repair of defective pipelines with limited damage

As a result, PPCoN commissioned SLP to develop and design four stressed grouted clamps as part of their emergency repair systems The main objective is to ensure rapid permanent repair of a range of defects, with minimum Impact on production, for the pipeline system in general and the vital trunk line to Emden and Teesside in particular.

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