As a follow up to a previous massage I would appreciate info on acceptable rejection rates for the following scenarios:
Both cases are in a petrochemical environment using GTAW and SMAW, with rejection rates calculated as butt’s rejected vs. butt’s tested for pipe welding (butt rate). We weld mostly carbon, low alloys and stainless steels. Please note that we are using radiograph (X-ray) results only for our calculations. (We realize that in using radiograph results only we are not painting the complete picture, but this is the only inspection technique we have reliable data for)
1. What will be the benchmark for rejection rates, using radiographs only, for new fabrication under shop conditions using ASME B31.3 as inspection criteria for radiographs?
2. What will be the benchmark for rejection rates, using radiographs only, for maintenance welding under field conditions using ASME B31.3 as inspection criteria for radiographs? Where mostly old and new material are joined.
Thank you for your inputs.
Joe
Hi Joe,
I'll throw my 2 cents in on this...this subject has come up several times here.
1. RT rejection rates for B31.3 shop fab should not exceed 5%.
2. RT rejection rates for B31.3 field fab should not exceed 15%.
The variables that you did not mention are wall thickness & OD. These rates may be conservative if you deal with thinner pipe, since the acceptable size of rounded indications is determined by wall thickness. Also smaller pipe is more difficult for many welders. I'm thinking that any rejects due to joint configuration (pipe to pipe, pipe to fitting and fitting to fitting will average out and not be a big factor.
I'm looking forward to seeing other input on this.
An adder to my post above:
Many times it's the tail that is the contributing factor in those rounded indications on the thin wall pipe.
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