Corrosion Allowance - Effect on butt-weld joint
Corrosion Allowance - Effect on butt-weld joint
(OP)
Code of Construction: ASME VIII-1
I'm probably overthinking things, but I'm wondering if there are any interpretations that discuss this topic (I may have to convince another engineer, and interpretations are often handy...)
We have two sections of a pressure vessel that will be butt welded together, each with different specified corrosion allowances as follows (customer specs - long story):
Plate 1: 1/8" internal / 0" external
Plate 2: 0" internal / 1/16" external
At this point we are planning for the vessel to be 3/4" thk plate / 60" ID.
Based on these corrosion allowances, the corroded thickness of the two plates would be:
Plate 1: 0.625" thk
Plate 2: 0.6875" thk
Right at the weld joint however, the minimum thickness would be: 61.375" OD x 60.25" ID = 0.5625" thk (under code required thickness). Am I overthinking this small region corrosion allowance step change, or do I really need to consider a 9/16" thickness for the vessel design?
In reality, there will be some excess weld material deposited in this area that would provide additional material for corrosion...
I'm probably overthinking things, but I'm wondering if there are any interpretations that discuss this topic (I may have to convince another engineer, and interpretations are often handy...)
We have two sections of a pressure vessel that will be butt welded together, each with different specified corrosion allowances as follows (customer specs - long story):
Plate 1: 1/8" internal / 0" external
Plate 2: 0" internal / 1/16" external
At this point we are planning for the vessel to be 3/4" thk plate / 60" ID.
Based on these corrosion allowances, the corroded thickness of the two plates would be:
Plate 1: 0.625" thk
Plate 2: 0.6875" thk
Right at the weld joint however, the minimum thickness would be: 61.375" OD x 60.25" ID = 0.5625" thk (under code required thickness). Am I overthinking this small region corrosion allowance step change, or do I really need to consider a 9/16" thickness for the vessel design?
In reality, there will be some excess weld material deposited in this area that would provide additional material for corrosion...





RE: Corrosion Allowance - Effect on butt-weld joint
RE: Corrosion Allowance - Effect on butt-weld joint
It must have been a long and painful story to get into that mess.
Also if the customer is stupid enough to come up with a spec like that they won't pick up any issues at the connection point.
A wholly artificial problem IMHO.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Corrosion Allowance - Effect on butt-weld joint
I'd not consider a step change in the thickness, but some reasonable transition between surfaces, 1:3, 45 deg, whatever, and check that the resulting thickness including weld reinforcement along the transition is not less than tmin.
If I had to. I guess. :)
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Corrosion Allowance - Effect on butt-weld joint
RE: Corrosion Allowance - Effect on butt-weld joint
General Blr. CA,USA