Impact test temperature for sub-size impact test specimen

[sw007]

I am reviewing a welding procedure which is applied to a vessel with a Minimum Design Metal Temperature (MDMT) of -50 deg F. The PQR test coupon thickness is 0.375 inch (9.525 mm). The impact test specimens are sub-sized impact test specimens: 10 mm x 5 mm x 55 mm. The PQR shows that the impact test temperature of the sub-sized specimens is -50 Deg F.

ASME VIII Div.1 UG-84 (c)(5)(b): Where the largest possible test specimen has a width along the notch of less than 80% of the material nominal thickness, the test, for Table UCS-23 materials having specified minimum tensile strength of less than 95,000 psi , shall be conducted at a temperature lower than the MDMT by an amount equal to the difference (referring to Table UG-84.2) between the temperature reduction corresponding to the actual material thickness and the temperature reduction corresponding to the Charpy specimen width actually tested.

Does the PQR impact test temperature meet UG-84 requirement? Based on my understanding, PQR impact test temperature of -50 deg F is not correct because of the sub-size specimen. The correct impact temperature should be (-50 - 20) = -70 Deg F.

Please advise, thanks.

 

[metengr]

Does the PQR impact test temperature meet UG-84 requirement?

Yes.

Based on my understanding, PQR impact test temperature of -50 deg F is not correct because of the sub-size specimen. The correct impact temperature should be (-50 - 20) = -70 Deg F.

No. You need to review UG-84 (h) regarding impact tests of weld procedure qualification. In short, this section refers you back to UG-84 (c) 4. You can read on for guidance. In essence the ratio of full thickness to subsize is used to correct for the CVN value.

 

[sw007]

metengr:

Thanks for your information.

But I still not understand why UG-84(c)(5)(b) is not applied. Looks like this is the impact temperature requirement for both production and PQR impact tests.