Evaluation of Pressure Vessel LTA Per API 579
Evaluation of Pressure Vessel LTA Per API 579
(OP)
I recently performed a rerate of a 55 year old vessel. Based on inspection data there was some general thinning in the feed area, and everything else was in good order. The inspection report mentioned a goove adjacent to a nozzle that was described as “0.080 deep and about 1.5 inches long” There is a picture that show it to be what looks like a mechanical gouge. It is about 2.5 inches from a nozzle and completely covered by the nozzle reinforcing pad.
I evaluated the gouge using Section 5 of API 579 (Locally thin areas) and ignored the proximity limitations imposed by the API 579 evaluation. The evaluation indicated that the gouge would not limit the MAWP. However since there is a proximity limitation imposed by API 579, the evaluation methodology cannot be used. Section 9 of API 579 has similar proximity limitation. To complete the evaluation, I used the thickness at the bottom of the gouge as the available thickness for pressure and it resulted in a MAWP reduction.
QUESTIONS: 1. Is there some other methodology that can be used for evaluation of such a flaw (short of a FEA). Or can anyone direct me to some reference that might help me address another methodology (other than API 579) to evaluate this gouge.
2. Does the fact that the external nozzle reinforcing pad covers the internal flaw contribute any “safety factor” that might over-ride the potential combination of stress (the flaw and the nozzle welds) that is apparently the concern of the API 579 methodology.
I evaluated the gouge using Section 5 of API 579 (Locally thin areas) and ignored the proximity limitations imposed by the API 579 evaluation. The evaluation indicated that the gouge would not limit the MAWP. However since there is a proximity limitation imposed by API 579, the evaluation methodology cannot be used. Section 9 of API 579 has similar proximity limitation. To complete the evaluation, I used the thickness at the bottom of the gouge as the available thickness for pressure and it resulted in a MAWP reduction.
QUESTIONS: 1. Is there some other methodology that can be used for evaluation of such a flaw (short of a FEA). Or can anyone direct me to some reference that might help me address another methodology (other than API 579) to evaluate this gouge.
2. Does the fact that the external nozzle reinforcing pad covers the internal flaw contribute any “safety factor” that might over-ride the potential combination of stress (the flaw and the nozzle welds) that is apparently the concern of the API 579 methodology.





RE: Evaluation of Pressure Vessel LTA Per API 579
Your links do not work anymore.
Sometimes its possible to do all the right things and still get bad results
RE: Evaluation of Pressure Vessel LTA Per API 579
RE: Evaluation of Pressure Vessel LTA Per API 579
Exactly, such as the *actual* pipe stress applied to that nozzle [nozz loading]. However, what is the Min. Thickness in that area? If the bottom of the gouge is above Tmin [with a Corr Allowance}, buff out the gouge to a taper greater than 3:1 and document that spot. If there isn't enough metal left, preheat & weld. A small 'pick-up' weld repaie is cheaper than a proper evaluation of the flaw; stop talking/analyzing and fix it.
RE: Evaluation of Pressure Vessel LTA Per API 579
RE: Evaluation of Pressure Vessel LTA Per API 579