API 570 T-MIN and MAWP with no pipe information

[Cristian N]

I am currently working as an API pipe inspector on a loading dock. A majority of the piping is overwater. That being said besides the design pressure and operating temperature, the customer has absolutely no previous history on the piping. Therefore, I will calculate the MAWP and T-Min per API 570 and 574 in order to provide recommendations.

However I am not sure what the Stress value or Y coefficient should be since there is no information on the pipes, by the way all piping is carbon steel.

 

[Cristian N]

Bump

 

[IFRs]

there are non destructive methods of positive metal identification that can tell you what the material is

 

[BenStewart]

Lacking any information a conservative and best endeavours approach could be followed, such as:

Select the lowest allowable stress from all carbon steel grades tabulated within the original design code;
Assume minimum NDT and select the appropriate weld quality/strength reduction factors;
Select a Y value consistent with carbon steel and the design temperature.

A first pass could be done on circumferential stress alone but there's also longitudinal stress that may be more onerous for MAWP and tmin - if you don't know what the piping loads are there is a routine in API 579 that you could follow, see the section on Supplemental Loads in Annex 2C.

 

[pdiculous963]

BenStewart's advice is exactly what is recommended by API 570 Sec. 7.5. Also, I agree that longitudinal stress will likely govern. At a minimum, span calculations should be performed considering weight of piping, product, and insulation (if present). Also, structural minimum thicknesses outlined in API 574 should be considered.