L51401 Hyperbaric Shielded Metal Arc Welding

It is common knowledge that the welding arc is affected by the surrounding atmosphere (gas and pressure) and it was believed, prior to starting the present work, that metallurgical problems could also occur under hyperbaric conditions. These were mainly associated with the belief that some atmospheres could increase the heat extraction and consequently the cooling rates of the weld metal and heat affected zone (HAZ). Other potential problems were alteration of the bead shape and slag cover, due to a change in the balance of surface tensions, variation in the chemistry of the weld metal and variation in the weld metal hydrogen content.

A research program was undertaken by the Materials Department, (Underwater Welding Group) of the Cranfield Institute of Technology to assess the performance of different makes of shielded metal arc welding electrodes under hyperbaric conditions and to identify potential metallurgical problems associated with welding in different gases at high pressure. All welds were carried out in unmanned hyperbaric chambers which were adapted and developed from pre-existing equipment in order to satisfy the needs of the present project. The most important feature was the use of remotely controlled welding torches which had the capability of simulating closely the movements of direct manipulation by a welder and, in these circumstances, the results can be directly extrapolated to a real situation. The workplace was bolted to a table which could be moved longitudinally by a motor, allowing an accurately controlled welding speed. Other features of the hyperbaric chambers included a powered wire brush for deslagging and atmosphere filtration equipment required to maintain good visibility inside the chamber, systems for providing and monitoring pre and post welding heat treatment and for controlling and monitoring humidity. This report is intended to present the results of the tests carried out during the final stages of the project and to give an overall view of the work.