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MAWP Under Corroded Condition Per API-660

MAWP Under Corroded Condition Per API-660

MAWP Under Corroded Condition Per API-660

(OP)
Hi All,

API-660 Section 6.1.1 c states the following about the MAWP to be reported in the drawings and the nameplate submitted by the HX manufacturer "The maximum allowable working pressure (MAWP) in the corroded condition and at the design temperature for the shell side and tube side". We have specified a Shell and Tube HX to be designed as per TEMA standards and in the proposal we stated this statement. My questions are:

1. Is this statement is good enough per TEMA design also?
2. Per ASME Section VIII DIV I Mandatory Appendix 3 as stated below, the MAWP id the lowest of the MAWPS determined for all the components and is not inclusive of the corrosion allowance. The question then arises why API-660 is asking for MAWP under corroded condition when MAWP is already determined without taking corrosion into consideration?. Am I interpreting the code correctly?

"maximum allowable working pressure: the maximum gage pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident temperature for that pressure. This pressure is the least of the values for the internal or external pressure to be determined by the rules of this Division for any of the pressure boundary parts, including the static head thereon, using nominal thicknesses exclusive of allowances for corrosion and considering the effects of any combination of loadings listed in UG-22 that are likely to occur (see UG-98) at the designated coincident temperature [see UG-20(a)]. It is the basis for the pressure setting of the pressure-relieving devices protecting the vessel. The design pressure may be used in all cases in which calculations are not made to determine the value of the maximum allowable working pressure."

Your expert replies would be very helpful while I will also do my own reading.

Thanks and Regards,
Pavan Kumar

RE: MAWP Under Corroded Condition Per API-660

That seems redundant to me.

The only reason I can think of why API-660 Section 6.1.1 c is written like that is in case the user mixes up the definition of MAWP and MWP.

MWP DOES include corrosion allowance.

I'm interested in hearing what others have to say as well.

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