INTRODUCTION

The aim of any hyperbaric welding operation must principally be to provide the client with a weld which satisfies the client's requirements and standards. A habitat is only provided to enable a weld of the right quality to be made and to provide a safe working environment for the welders.

The technology of producing a weld to the required standard is well documented and is not discussed here. I will examine some of the conflicts which arise from the need to satisfy both the production of a satisfactory weld and the provision of a safe environment.

To do this I intend to examine two typical welding operations. One is a structural repair/strengthening operation and the other a pipeline tie-in operation. Both are based on actual North Sea operations and both are in relatively shallow waters.

Shallow waters provide some specific problems which are not apparent in deeper operations. Both examples have been altered to protect the actual operators from the public gaze and neither is used to imply any critiscism but to enable discussion based on real rather than theoretical conditions.

OPERATION A

This task is a node strengthening exercise undertaken in about 30 feet of water. The operation consisted of welding large steel chord wraps to each of the nodal members. It was a very complex welding operation requiring very high levels of pre-heating and very large weld deposits to be made.

Because of the-structural limitations and time constraints the habitat was small and very congested. With the chord wrap material, the myriad of pre-heating mat tails, the divers' equipment, the welding equipment and other necessary tools the inside of the habitat resembled a tropical jungle. The atmosphere was compressed air supplied from the surface support vessel. The temperature and humidity were very high, approx. 150°F, when pre-heat was being applied.

Compressed air was used because of its simplicity and because of the welding pre-qualification procedures previously agreed and tested.

The diving procedures used were that the divers were deployed in a cage wearing dry suits and helmets. They swam to the habitat and entered through the bottom habitat entrance. Inside they would remove their diving equipment and don flameproof overalls. When pre-heating was being applied the divers also wore tube-suits and plugged these into a cold water supply piped to inside the habitat. This enabled the welder/divers to operate in shifts of up to 8 hours. Without it they were becoming exhausted after a very short time. (See Fig. 1.)

Habitat atmosphere was controlled by flushing through as necessary and gas samples were analysed at the surface. The welding used was the conventional Manual Metal Arch technique. A considerable amount of grinding was required but the(Fig. 5.1 is available in full paper) divers wore lightweight breathing masks during the welding operations when noxious gases were being generated.

The selection of the welding procedures and the choice of a compressed air habitat atmosphere were based largely on economics and satisfactory precedents in offshore operations.

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