Manual hyperbaric welding in a dry hyperbaric environment is now a well established technique for underwater pipeline tie-ins and repairs Over 600 hyperbaric tie-ins have been performed to date, and manual procedures have been successfully qualified down to simulated depths of 450 msw
Despite the obvious success of manual welding, considerable resources have been invested in the development of automatic hyperbaric welding systems The advantages of automatic welding will offer the following technical and economic advantages
improved weld quality and properties
improved assurance of weld quality during offshore operations through increased process control and monitoring
reduced costs for qualifying procedures and personnel
lower costs for diving personnel
improved working conditions for the habitat personnel
This chapter describes the Thor-1 system developed by the Comex Group and used on the North Alwyn Export Pipeline in August 1986 to perform the first commercial automatic weld on a submarine pipeline The chapter concludes with a brief review of the future of automatic hyperbaric welding and the development of the second generation Thor-2 system which will permit diverless tie-ins
Thor-1 was designed as an autonomous ‘stand alone’ system which can be used with any suitable welding spread1 The system is suitable for deep water work and therefore the welding power source, weld head motors, and camera container were developed for use at 500 msw
Important features incorporated into the design of Thor-1 include the following considerations
The entire welding procedure can be pre-programmed so that the offshore(Fig. 1 is available in full paper) welds are made with parameters identical to those used for welds made onshore during the welding procedure qualification tests
The welding operation can be initiated, monitored and supervised from the surface and the surface operators can intervene at any moment during the cycle to make modifications, etc. as required within pre-qualified/approved parameters ranges
The habitat personnel are responsible for installing and servicing the equipment under the supervision and at the request of the surface operators, but they do not intervene during the welding cycle itself
The system used on the North Alwyn Pipeline tie-in consisted of:
A lightweight track which is readily installed on the pipe by the habitat Personnel
A modular orbital weld head which is rapidly assembled on the track and connected to a short umbilical from the subsea module
The weld head consisting of a motorized module (or ‘engine’) carrying the torch, etc. which pushes/pulls around the track a number of unmotorized modules (or ‘wagons’) carrying ancillary equipment such as wire feeders. This system permits ready modification of the weld head to include new equipment, for example NDT head
A simple pendant control which permits the habitat personnel to perform function tests for the weld head under the supervision of the surface personnel
A subsea module, installed beside the habitat and which houses the welding power source, weld head drive cards, teletransmission terminals, power transformers, etc.
