Dimensional Control During Welding

[Genetix]

Good afternoon respected members of this forum,

We had an LL (Lessons Learned) discussion for one of our previous project. One of the LL is about the lateral discrepancy of the interconnecting nozzle (on channel head) of stacked heat exchangers (2 BEU type). Lateral discrepancy is out of tolerance and was due to poor dimensional control during repair of channel head luckily hydrotest was conducted successfully and client accepted use-as is as disposition. My question is, as a contractor, prior to vessel construction, how would we verify the dimensional control capabilities of vendor specially for critical vessel construction such as HEX. My idea is to check the experience list of vendor whether they have provided similar equipment before. Vendor without experience of fabricating similar equipment will most likely have similar mistake. Are there any other means to verify dimensional control prior to construction.

Thank you.

 

[shamino]

Hi Genetix,
Good question and very important. I really think it comes down to audits. Before you approve a vendor, I would do a good audit of their QC and fabrication departments and get an idea how they tackle this type of issue. You want to go with the shop that has the years and experience in handling the distortions that come with welding. The new guys usually have no clue.

Also, inform the shop of the critical dimensions. Put the dimension right on the drawing as a "hold" or "jig-set." Having a PSV nozzle bent a bit out of tolerance won't affect the functionality of the part, but what about inlet nozzles on a suction scrubber that fit onto a compressor? You basically need to get it perfect.

A lot of times companies will actually go down and check up on the shops themselves to verify that this is being done, or will hire third party inspectors. Might be something to consider. Having something get to the field that doesn't fit up right can mean big $$$$