The International Marine Contractors Association’s (IMCA) newly published ‘Guidelines for Oxy-Arc Cutting’ (IMCA D 003 Rev 1) has five main aims – to improve safety and efficiency; to consider the selection of subsea cutting methods; to place more emphasis on risk assessment prior to commencing a job; to provide operational considerations; and to provide preventative maintenance guidance for equipment.

“Oxygen-arc cutting is an oxygen cutting process in which metal is severed by means of the chemical reaction of oxygen with the base metal at elevated temperatures,” explains IMCA’s Technical Director, Jane Bugler. “The heat of the arc brings the metal to its kindling temperature and then a high velocity jet of pure oxygen is directed through a tubular cutting electrode at the heated spot. The metal oxidises and is blown away. The tip of the electrode, which is exposed to both heat and oxidation, is consumed in the process and needs to be replaced by the diver at regular intervals.”

Oxy-arc cutting is typically used to cut steelwork in the underwater environment, some examples of which are structure removal; removal of redundant steelwork from a worksite to provide access for installation activities; removal of damaged tubulars and caissons; cutting of seized bolts subject to removal or replacement; and major abandonment operations.

“Divers who perform underwater cutting and welding should have greater skill and stamina than those doing the same work topside,” says Jane Bugler. “The success and speed of operations depend upon the conditions under which the diver must work because the underwater environment imposes numerous limitations and restrictions on the operator and equipment. The diver is often restricted to working for only a short time on the bottom, particularly at deeper depths. The use of correct techniques and equipment becomes extremely important in terms of work accomplished per hour. Diving apparel, great depth, adverse currents, low temperature, lack of visibility and unstable footing are all factors which make underwater cutting and welding difficult.”

The guidance includes a section on the selection of subsea cutting methods identifying that when confronted with an underwater cutting operation, there should be a review of the advantages and disadvantages of all forms of cutting (mechanical, explosive, electrochemical and thermal) prior to identifying the appropriate method to use.

The new guidance addresses the basics of oxy-arc cutting. It includes general points that should be considered when deciding if oxy-arc cutting is indeed the correct solution, and it places great emphasis on safety, risk assessment, planning and general equipment maintenance. The risk assessment covers underwater explosion. These have occurred in industry, and some explosions have been fatal. They occur due to the simultaneous presence of explosive gases (e.g. oxygen and hydrogen), heat (from the electrode) and possibility of gas guild up.

Tags: IMCA