Hyperbaric Welding at 300 MSW

ABSTRACT Hyperbaric welding and diving capabilities down to 300 m.s.w. were the contingency techniques required to support the laying of a sea-bed pipeline across the Norwegian Trench. Two welding methods were defined to meet stringent weld property specifications. Welding, diving equipment and diving procedures were developed m simultaneous programmes involving extensive unmanned tests and three manned simulated dives. An offshore demonstration of a full scale tie-in 300 m.s w. following identification of a "damaged" pipe section was performed from a D.S.V. assigned from conventional construction activities. Destructive testing of the actual welds confirmed the suitable of the equipment and procedures to provide insurance for deep field development projects. INTRODUCTION The development of the STATFJORD field and the decision to export its gas via the EKOFISK-EMDEN network necessitated the laying of two pipelines across the Norwegian Trench in depths ranging down to 300 m.s.w. a 30" line from STATFJORD to the gas treatment plant in KARSTO and a 28tf "export" line out to the EKOFISK area. Production tie-in operations were planned for maximum depth of 145 m.s.w. but demonstration of repair capabilities in the deepest sections of the trench was an obvious necessity. Routine construction operations seldom exceed 200 m.s.w. although single open sea dives as deep as 50 m. (JANUS N, 1977) have been proved possible. Welding procedures were previously qualified at 300 m.s.w. with some manual welding test performed at 400 m.s.w. An extensive programme was compiled jointly by STATPIPE and CCMEX SERVICES. The project was identified as the Deep Dive Development Project (3DP). The objective was to develop equipment and procedures and to, verify that they could be used safely at 300 m for a pipeline repair by hyperbaric welding. Welding procedures had to be refined from previous knowledge and qualified, followed by welder team qualification. Parallel manned and unmanned development programmes were to be launched to test equipment items, validate saturation procedures and evaluate short and long term effects of repetitive welding and diving tasks. Human factor aspects were to be observed during these routine deep work activities. In addition, a diving support vessel was to be prepared and a new welding spread constructed for use at 300 m.s.w. and beyond. The programme was scheduled for completion With in 15 months (by August 1983) with a demonstration dive in a Norwegian Fjord and performance of a full scale hyperbaric welding tie-in. The methods described in this paper, not only confirm that manned hyperbaric welding is a routine pipeline repair and pipeline connection method at 300 m.s.w., but also indicate that similar techniques could be extended to even greater depths. DEFINITION OF PARAMETERS AND PREVIOUS WORK Welding Two different welding process methods were required to be defined, one for qualifying welding procedures for each of five different pipes and for a minimum of twelve welder qualifications, and the second method as a back-up system.