NDTnet 1998 Aug, Vol.3 No.8

Abstract

Manual welding in dry hyperbaric environments is now well established for underwater pipeline connections and repairs. Although hundreds of welds have been produced successfully by skilled welder divers, there is considerable incentive to develop automatic hyperbaric welding to eliminate variability in quality and properties and reduce the cost of qualifying personnel under simulated hyperbaric conditions, while improving working environments.

STOLT COMEX SEAWAY (SCS) has designed, build and tested THOR 2 representing a second generation automatic hyperbaric welding system with associated integrated pipe preparation module, for use in advanced diver assisted or future diverless tie-ins.Since the majority of the new structures will be situated in deep seas a significant increase in the problem of inspecting offshore structures is foreseen. A very considerable increase in the demand for underwater inspection of all types will occur over the next ten years.In order to reduce safety hazards and the risk of damage, and therefore minimise the high cost that could be involved in the repair of underwater pipelines, welds must be inspected by a suitable underwater non-destructive testing technique, the most common of these being radiography. The most current method, using radioactive isotopes, involves taking radiographs once the weld is completed. This method is slow due to the time needed to expose and process films could be dangerous because of the radioactivity level involved and could lead to administrative problems.

The use of radioscopy can facilitate this task and reduce inspection time. That is why SCS and Institut de Soudure have developed in partnership a radioscopic system capable to be operated from the surface up to 350 m water depth. The system allows the inspection of pipeline welds in hyperbaric habitat. It is designed to operate with the X-ray source and the X-ray detector (6" image intensifier and a camera head) positioned outside the pipe. The system consists of a control station designed to work surface and X-ray, scanner and power and control unit modules designed to work subsea under 30 Bar external pressure.

The Control Station, based on a PC computer, drives the General Control Unit and the Image processing system featuring frame grabber and frame processor boards. Software has been designed by Institut de Soudure and allow to work on real time with Windows.
Test pieces have been inspected with this system and the conventional hyperbaric method using -RAY source and films. The Real-time Radiography system provides significantly better results up to 20 mm pipe wall thickness. For a 20" weld, the inspection time (excluding scanner installation) is expected to be less than 4 mn.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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