Impact test B31.3 for CS

[jpstress]

Hi,

There is method in ASME B31.3 for MDMT reduction by using Figure Fig 323.2.2b base on stress ratio. However, if applying this method, the Code requires the material shall be isolated from any impact loads.

My question: if the line is outlet of PSV or has two phase flow, shall it be forced to impact test even Fig 323.2.2b says OK for MDMT reduction??

 

[SJones]

A couple of points:

1. Technically, it isn't actually 'reducing' DMT, it's a provision for the setting of a DMT below the allowable minimum temperature value for the material;

2. The answer to your question is: it is up to the owner/designer to ensure that it is acceptable to deploy the measures stipulated in the standard accounting for all feasible scenarios.

Thus, it becomes a case of assessing what failure modes may occur, whether they are tolerable as is, or whether impact testing can serve to provide a suitable barrier to an unacceptable top event resulting from the failure mode.

One possible failure mode to consider could be cracking from thermal shock in a constrained piping system, for example.

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.

 

[georgeverghese]

We typically do not use this rule in brownfield applications since it is almost impossible to confirm any other hidden mechanical stresses ( displacement or thermally induced) on the piping or connected devices. I have not seen a single case where this rule has been used in brownfield applications. Engineers often talk about following this route, but that is about as far as it goes.