ASME VIII-1 impact test requirements of UG-20 (f) and UCS-66 3

[mechengineer]

Material SA-516Gr70, non-normalized, thickness=22.2 mm, design MDMT is -29°C
1. As per UG-20(f) it is exempted from impact test.
2. As per UCS-66, obtained -5°C of MDMT from curve B, so impact test required or use SA-516Gr70 normalized.
In view above, there is conflict between UG-20(f) and UCS-66 in some cases. This will make people confusing, which one we shall follow, UG-20(f) or UCS-66? This may virtually make a contradiction between the client/user and manufacturer. The manufacturer prefers UG-20(f), but client may prefer UCS-66.

 

[SnTMan]

mechengineer, yes it can be confusing. But, if your design meets the limitations imposed by UG-20(f), and the client does not prohibit, then by all means use it. Otherwise you fall under UCS-66, which does contain provisions to reduce MDMT without impact test.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[mk3223]

IMO, sometimes it's not a clear line cut one from the other. So, the design is to follow the more stringent condition.

 

[SnTMan]

Well, not necessarily. The Code does permit UG-20(f) exemptions, subject to it's limitations.

Regards,

Mike


The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Jano6924]

To reinforce Mike’s comments see interpretation VIII-1-92-201:

Question: May pressure vessel materials be exempted from impact testing if all of the requirements of UG-20(f) in Section VIII, Division 1 are met, even though impact testing would be required under the provisions of Fig. UCS-66?
Reply: Yes.

Hope this helps.

 

[mechengineer]

Jano6924, Thanks.
The interpretation VIII-1-92-201 might give a great help to convince users. In fact, most of cases this may be only the way to convince clients, they would not be care what your explanation is at all if it is not mentioned in the Code.

 

[SnTMan]

Jano6924, good to know, thanks.

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[SJones]

UCS-66 is impact test exemption curves. It does not give MDMT. You probably wouldn't have to be worrying about which to apply if the MDMT has been set in accordance with its definition as opposed to someone simply looking at the lowest temperature they think that they can get away with and avoid impact testing.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[DK44]

The path of judgement for Impact test requirements as per code is

UG-20(f) > USC-66(a) > UCS-66(b) > UCS-68(c) > UG-84 > Matl. Specn.

At any stage from left to right of the path, if impact test is not required, we need not examine further to right.