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# B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

## B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

(OP)
Im doing some calcs for a thermowell at high pressure and temperature. Material is UNS N06600 at 550 °C design. Using para 304.1.3, I run into the issue that I cant determine Pa2 since (b) requires me to calculate 90% of yield for N06600 acc. ASME II-D table Y-1. Table Y-1 ends at 500 °C for N06600 (or at 525 °C for certain ASTM specs). I believe some time ago this question was asked here as well, but I cant remember the outcome. Any ideas?

### RE: B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

You can use the yield vs temp curve in API 579-1/ASME FFS-1. At that temp, are you into creep? If so, you should be using isochronous curves.

### RE: B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

(OP)
Thanks. Acc II-D, time dependent properties start at 480-510 °C for UNS N06600 (notes T11-T12). The calcualtions Im doing are performed more often, for other materials as well, quite often beyond 550 °C. II-D doesnt list yield strengths for any material beyond 550 °C, so the quesiton is broader. Where in API 579-1 do I need to look, F.7.4?

### RE: B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

2E.2. Make sure to be using the 2016 Edition.

Depending on the length of time at that temperature, the tangent modulus for creep can be much much less than the short-term elastic modulus. Even if the design temperature is in the creep regime, double-check the operating temperature. If it's not in creep, then your usual method should be fine.

### RE: B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

(OP)
Thanks. The operating temperature is non-creep indeed.

Another issue I quite often have with ASME VIII-1 for thermowell calcs, is that the L/D is far greater than 50. More in the range of 500. UG-28 doesnt specify any caution for such extreme values of L/D; would there be any?

### RE: B31.3 para 304.1.3 - external pressure in creep regime (II-D Table Y-1)

(OP)
Anyone who can offer advice on the L/D>>50 issue? Is any caution requires re the use of the rules in VIII-1 when L/D is approx. 500?

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