Weld Defect Rate

[qclarry2601]

Good day all,
Currently we are tracking our weld defect rate for our shop piping (ASME B31.3 piping and shop AWS D1.1Structural welding)by linear inches, which is giving us a very low repair rate and a. We recently changed from counting linear inches to counting butt welds, the repair rate immediately went up, like from 0.5% to 10%. Is there an industry standard or best practice for tracking weld defect rate?

 

[DekDee]

qclarry,
I have had many an argument over this and IMHO the only true reflection is length of total weld versus length of defects.
If you look at the "per butt" system - hypothetically a 5o mm long defect in a 50 nb joint is considered equivalent to a 5 mm defect in a 600 nb joint.
They are both considered defective joints but the amount of "clean" weld is significantly greater in the large bore pipe but the welder receives no recognition of this.
Tracking weld repair rate by butt can be effective on a pipeline where all joints are the same diameter and same thickness but for projects with numerous diameters and thicknesses it can give a totally untrue reflection of welding quality.
Cheers,
DD

 

[DVWE]

Another common way performance is tracked in this industry is number of RT shots taken vs number of RT shots failed. In a simple example, a 36" pipe may take 10 RT shots in 1 weld. If one shot fails, that would be a 10% failure rate. Realistically, a good welder has one failed RT shot in about 50, or 2%.

This is the most common way shop performance is tracked in the piping industry. Most shops count total RT shots vs total RT shots rejected to calculate their shop RT reject rate as a whole. I am unsure how it is done in a structural environment.

 

[weldstan]

It really depends on your use of the figures. When impressing customers, the inch per lineal inch is impressive. From a repair cost standpoint, the repaired butt welds versus number of butt welds made may be more important to the employer of the welders when used to reduce the number of repairs (additional training, welder termination, etc.).

 

[Duwe6]

I was taught that the "magic number" , by the X-ray butt weld, is 6%. If your reject rate gets up to 6%, it is time to scrutinize the entire welding program. This includes welder quals, criteria for downgrading welders from 'X-ray butt' to 'socket & fillet only', filler procurement [purchased 'cheap' stuff vs. premium product, drafty/breezy conditions at site of welding, possible 'overcalls' when the RT's [X-rays] are 'read'.