NACE MR 0175 Requirements

[Angsi]

Code: ASME Div 1
Vessel: A516 Gr 70 + 3mm SS316L clad

Re clause 5.2.1 under section titled Fabrication. It says
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Overlays applied to carbon and low ally steel or to martensitic stainless steels by thermal processes such as welding, silver brazing, or spray metallizing systems are satisfactory for use in sour environments, provided the ****substrate does not exceed the lower critical temperature during application****. In those cases in which the lower critical temepratures are exceeded, the componenet must be heat treated or thermally stress relieved in accordance with procedures that have been shown to return the base metal to 22 HRC maximum.
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Can someone please tell me what "substrate does not exceed the lower critical temperature during application*" means? Does the lower critical temperature get exceeded every time production welds are made on the vessel and thus PWHT of the vessel becomes inevitable?

Thanks.

 

[SJones]

It may be better to look at clause A.13 of ISO 15156-3 (sorry but I can't give the clause number of the NACE document as I use only ISO) that deals with corrosion resistant claddings, linings, and overlays. My approach is to ensure the soundness of the overlay and not worry about the substrate also having to meet the ISO 15156 requirements.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[Angsi]

One more question. Using normal ASME welding procedures on lets say A516 Gr. 70 material, can a 22 HRC be easily achieved without any PWHT?

Thanks.

 

[SJones]

Impossible to predict - depends on specific material, weld process, welding procedure specification, filler metal, etc etc.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[ravera]

If I recall correctly, HRC 22 is close to a Brinell hardness of 241 which has an equivalent tensile strength of appx 118,000-120,000 PSI. A516 Plate will never achieve these values under normal heat treat conditions.

 

[adrianviorel]

I think SJones is right about the fact that substrate is not to be considered for corrosion resistance. In fact, in normal conditions, substrate will never get into contact the operating fluid. Else, why using the overlay?
On the other hand, in my opinion, HRC<22 is more a statistical observation, that could be justified by taking into account that a certain granulation leads to a corresponding hardness, and, in the mean time, assures a better corrosion resistance-due to the fact carbures are put into solid solution, and they are not precipitating at granule limit. I must warn you that these are memories since 15 years. I could be wrong; therefore, please check "Materials" manuals.