Welding steel hull below the water line 1

[ztug]

We are installing new engine beds in a tug. What is the proper procedure of welding to the hull while in the water. Some people say this causes cracking. Others say clean and dry will be fine. What is SOP?

Thanks

 

[metengr]

I can't provide SOP, but I could give you some advice. The answer to your question depends on the thickness and material of the hull, and water temperature. The ABS provides a listing of various hull materials.

If the hull is ordinary-strength steel (per ABS specification), you should be ok for welding with water backing (hull in the water) at a water temperature above 50 deg F. The ordinary-strength hull material has a carbon equivalent similar to an A 36 structural steel material and, as such, can be welded with minimal problems.

If the hull is classified as high-strength steel you may need to dry dock to avoid affecting the strength and low temperature impact properties of the steel.

If you do not know the chemical composition of the hull because of the age of the vessel, have someone perform a positive material identification of the hull using a portable alloy analyzer. It is cheap and will confirm your approach for welding. Specifically check for Chromium, Nickel, and Vanadium contents. If any combination of these alloying elements is greater then 0.02% it could indicate a high-strength steel hull material.