Impact Testing Requirements Per Section VIII UCS66 1

[chayes]

I am reviewing weld procedres from a vendor fabricating a vessel for me from A516 Gr. 70 c/s. The wall thickness of the vessel is 1 1/4". The procedure that has been submitted does not include impact testing. My question is:

My MDMT is 0°C. It appears to me that impact testing is required per UCS-66 at that temperature. I don't comply with all rules of UG-20(f) (nominal thickness>1"), so that does not allow me to take exclusion to the requirement. Am I missing an exclusion for the impact testing, or is it really required?

Also, it would appear to me that the plate used would need to be normalized.

This is not my area of expertise, so I appreciate any assistance and advice that anyone is kind enough to share.

 

[TomBarsh]

The primary rules for MDMT rating and impact test exemption for this material (carbon steel) are located in UCS-66. The rules of UG-20(f) provide some additional exemptions to those in UCS-66. Sometimes the exemptions of UG-20(f) will govern the impact test exemption, other times the rules of UCS-66 may be used to justify a colder impact test exemption temperature and rated MDMT. See the flow chart in Figure UCS-66.2.

The MDMT rating/impact test exemption is based on the "basic rating" taken from Fig UCS-66 for the nominal thickness. For 1.25" curve B material this is 43° F. If there is excess thickness over that required for pressure and other loads then this temperature can be further reduced by Fig UCS-66.1.

Depending on the thickness required for pressure it seems reasonable to exempt this material to the 0° C.

 

[chayes]

I was hoping that this was the case. Thank you for the good info!

 

[codeeng]

In addition to TomBarsh's comments you can also refer to UCS-68(c) where a further 30F reduction in MDMT impact test exemption can be claimed where PWHT is performed but not required by Code.

 

[JoeTank]

If the material is normalized and fine grain practice, the SA516-70 material drops down to Group D. In that case it can be used at a lower MDMT that the Group B materials. You may wish to look at that and determine if impact testing is exempted for this material.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com