Accepting/Rejecting material substitutions in boiler

[coolniks37]

Hi can anyone help me with this topic?
When we envisage boiler materials, material procurement will come back offering a substitute material.
For example, SA515GR70 instead of SA516Gr70. SA240TP304 against SA240TP310S etc etc

My question is
1) What are the critical factors to look for while accepting/rejecting such cases?
2) Mostly both these materials have Min Tensile strength, Yield Strength, Max allowable temp range etc are same.
3) So is it only required to see, the stress values at design temperature ?
4) What about material composition? Carbon, Cr, Ni contents etc too vary. How to evaluate a situation like this?

 

[JStephen]

If you don't know why the materials being used were selected in the first place, then there's no rational way to evaluate the substitution.
In some cases, it is simply a matter of using material with equal yield strength, allowable stress, toughness, corrosion resistance, etc.
In some cases, especially with the stainless steels and other alloys, the designer may have been trying to solve very specific corrosion or welding issues, where they know that using X material welded in Y procedure is resistant to a particular product in a particular service, etc.

 

[pradipgoswami]

Hi Coollinks,

One has to see if the proposed original vs suggested substitution materials meet requirements of ASME Sec-II, Part-D, with respect to allowable stress , and also the service environments. You may read clause PG-5(5.1....5.5) for further clarifications.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[metengr]

First off, for an existing boiler you should be working under the NBIC requirements for repairs or replacement of boiler components. There are rules for material substitutions under the NBIC otherwise material substitutions can result in alterations of a boiler, in lieu of repairs.