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A105N Requirements Under NACE MR0175

A105N Requirements Under NACE MR0175

A105N Requirements Under NACE MR0175

Part of a project to expand a gas processing facility (H2S, CO2, and dehy) and there was a bit of a mix up where some small bore A105 fittings were installed where A105N fittings were specified. All of the fittings installed are compliant to NACE MR0175. It seems redundant to require A105N fittings being that NACE MR0175 requires some type of hot forming or heat treatment. With the fittings already being NACE MR0175 compliant, is there any benefit to them being normalized as well, or any risk if we don't cut them out and replace them with normalized fittings?

The fluid service is process drains and flare header connections at a TEG dehy, so the chances of coming in contact with sour services is very small, but can't say it's impossible.


RE: A105N Requirements Under NACE MR0175

Any risk? Yes. Unacceptable risk? To be decided by the end user. The stipulation of normalising is to provide a stable material baseline for material performance in H2S service, as opposed to the free for all of hot finishing. Does it impact performance in H2S environments? Evidence suggests that normalising helps. One thing that might swing it: what is the MDMT?

Steve Jones
Corrosion Management Consultant


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

RE: A105N Requirements Under NACE MR0175

Thanks for the response Steve.

The MDMT of the piping system is -20F.

In general, with the fittings already meeting the NACE requirements for hardness, S content, and Ni content, does the normalizing (or any heat treatment for that matter) just provide an additional level of performance against corrosion resistance?

Thanks again

RE: A105N Requirements Under NACE MR0175

Is -20F (-29C) derived by the process engineer from process calculations, or by the piping engineer looking at a table of materials that don't require Charpy testing at temperature down to -29C? Here are some recommendations from NACE Corrosion 2019, Paper 13361:

"Purchase specifications for the following steel grades ASTM A105, A234 Gr. WPB and A106 and in
general for all Curve B materials should be evaluated by designers, fabricators and end users based on
the lowest design temperatures and the toughness requirements before applying the impact test
exemptions allowed in the Code. The material toughness requirements should be reviewed on a case
by case basis and the following supplementary requirements should be considered in addition to the
requirements in ASME B31.3:
 A chemistry requirement of Mn:C ≥ 5,
 Flanges in the normalized condition,
 An ASTM grain size 7 or finer,
 Limits on boron and other micro alloy additions per the applicable ASTM standard, to be
included on the material test reports and
 Impact testing per ASME B31.3 per heat (if exempt from impact testing) at -29°C (-20°F).

It does look like that you have struck out on at least one, and part of another, issue. If the hardness results are trustworthy, there is a case for attempting a management of change process for the H2S service. However, someone might then dig into the temperature issue as well.

Steve Jones
Corrosion Management Consultant


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

RE: A105N Requirements Under NACE MR0175

PA Gasmasher,

Nace MR0175 provides exception to use ASTM A105 in place of A105N by para A2.1.3(a) provided hardness doesn’t exceed 187 Brinell Hardness. Check the MTRs to verify this.
Next, check the hardness for the weld joint. There are limits set by NACE MR0175.

Even though the exception is provided by NACE, many owners still wants A105N. The Owners specification shall govern in a project.

If you work for the Owner, initiate a MOC to cover the difference. If you work for the EPC, you have to raise a technical deviation notice to take Owners approval.


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