B31 CC 181

[Hipressure]

B31 CC 181

I am trying to understand this case; is it one of alternative acceptance criteria or is it alternative technique?

We are trying to employ PAUT on 31.3 piping using the given acceptance criteria for UT in 31.3. However this code case was brought up in discussions and it was determined that if PAUT was to be used, this CC (including acceptance criteria) had to be followed in its entirety.

Greatly appreciate any and all comments and/or interpretations on this CC.

Regards

 

[ndeguy]

Its definitely about both!

The preeamble states that the Committee is of the opinion that alternative acceptance criteria can be applied in lieu 0f 344.6.2. of B31.3. This is a switch from acceptance criteria based on comparison with the amplitude from known reflectors to the measured defect height (versus its length and material thickness).

Plus (d) of the Code Case calls for use of a device employing "automatic computer-based data acquisition".

Interesting if unusual point about using phased array with the standard acceptance criteria. Without doing the math comparison for various material thicknesses it is generally accepted that the alternative acceptance criteria, which are based on materials and stress data rather than traditional "workmanship" values, are more lenient, especially in the case of low defect height versus material thickness ratios, e.g. inter-run cold lap. Exceptions to this can be in cases of several separate defects where interaction rules are invoked - think of automatic MIG pipe-welding systems such as Phoenix or Serimer where the sequential fire-up positions are not staggered and a small length of LOF (10 mm say) is in each successive vertical position. These are interactive and such fire-up defects in 3 or 4 successive runs would give an unacceptable interactive defect height.

Which welding process(es) will you be utilising? If all manual (TIG root/SMAW fill and cap) I dont know why you could not set your PAUT sensitivity using the standard ASME calibration block assessing defect length for reference-curve breaking indications.

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[Hipressure]

All welding processes will be manual, no GMAW. We intend on using a calibration blocks developed from the same material, diameter and thickness as the weld.