Forum Re: Semi Automatic Welding tank floor/roof plates
From: CNT [492]
Date: Tuesday, February 02, 2010
Time: 11:14:01 AM
Remote Name: 146.146.4.2
Comments
I was recently reading about some welding processes and it mentioned that FCAW is not a low-hydrogen process, therefore, it may not be acceptable in some shell to floor corner weld situations see API 650 7.2.1.10.I recently had a contractor that used a Goat SAW process on a 120 ft dia. tank. I suppose they saved some time over all, but they spent a lot of time repairing welds, setting up the machine, and addressing areas that the machine couldnt get to. Overall, I think it would have been better to just have stick welded everything. We require a 2 - pass system with either a 6010 root and 7018 top pass, or preferably 7018 all the way out. I require a vac-box between passes. On the surface that sounds ridiculous as the 2nd pass should, in theory, catch any holes in the 1st pass, but sometimes even the 2nd pass fails the vac box. In the tank industry, putting product on the ground is the biggest sin I know of.
Im not a fan of the 7024 Jet rod. It makes a really pretty weld, but weve found too many pin holes in the welds. I think the welders get to moving along too fast and leave pin holes. So, due to quality control issues, we dont allow contractors to use jet on the floor. 7018 takes longer, but I get better results. It doesnt matter how much money you saved building the tank if it leaks the first time you fill it.
