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ASME B31.3 Allowable Stress for ASTM B366 UNS N06625 Class 1

ASME B31.3 Allowable Stress for ASTM B366 UNS N06625 Class 1

ASME B31.3 Allowable Stress for ASTM B366 UNS N06625 Class 1

(OP)
Hi,
I'm currently raising new / revalidating existing Particular Material Appraisals (PMAs) for ASTM materials for use under the Pressure Equipment Directive (PED).
For these, I have to specify the Tensile / Yield values and the (basis of) the Allowable Stress values.

ASME B31.3 Table A1 covers UNS N06625 Grade 1 in pipe (ASTM B444) & forgings(ASTM B564), but not fittings (ASTM B366).
In the past, where I have needed values for materials not listed in ASME B31.3 Table A1, I have always based them on ASME B31.3 Section 323.3.2(d) plus the Tensile / Yield values within the ASME BPV Code.
However, in this instance the ASME BPV Code lists UNS N06625 Grade 1 in pipe (SB444) & forgings(SB564), but not fittings.
SB366 UNS N06625 fittings are listed, but this obviously covers both Grade 1 & Grade 2 fittings.
On this basis, the pipe & forgings would be based on Tensile / Yield values of 120 / 60 ksi but the fittings would be based on Tensile / Yield values of 110 / 50 ksi.

ASTM B366 Section 7.1.2.4 (for UNS N06625 Grade 1) specifies that the mechanical properties for the finished fitting shall comform to the minimum UNS N06625 Grade 1 mechanical properties for the starting product, which in this case is pipe.
On this basis I intend using the ASME B31.3 Table A1 values for ASTM B444 UNS N06625 Grade 1.

Is this the correct approach?

The other issue is that the PED limits the allowable stress to 2/3 Yield Strength at temperature whereas B31.3 uses 9/10 Yield Strength at temperature, but that's a different problem........

Thanks, Paul J.

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