How to prepare a WPS compliance with NACE MR0175

Hardness testing

Understanding hardness and hardness testing can refer to CSWIP section 4.1.4 or ASTM A370, or applicable specification NACE MR0175 – 2 / NACE MR0103. So, in this topic, I would like to share information about object of hardness test, its importance and when we employ the hardness testing for welding procedure or production test.


Hardness test are applied to most material steels and commonly employed mechanical test as destructive test. Hardness test are important in piping, structural of industry and manufacturing. A higher of hardness values may be susceptible to cracking, either during fabrication or in-service and welding procedure qualification testing for certain steels and applications requires the test weld to be hardness surveyed to ensure no regions exceed the maximum specified hardness.

Test Methods

There are three widely used methods:
     Vickers - uses a square-based diamond pyramid indenter.
     Rockwell - uses a diamond cone indenter or steel ball.
     Brinell - uses a ball indenter.
The hardness value is given by the size of the indentation produced under a standard load, the smaller the indentation, the harder the metal.

Reference standards

ASTM A370:

Brinell hardness
ISO 6506-1 / ASTM E10 : Brinell hardness test

Vickers hardness
ISO 6507-1 / ASTM E384: Vickers hardness test

Rockwell C hardness
ISO 6508-1 / ASTM E18: Rockwell hardness test

Which materials are required to hardness survey?

Yes, commonly materials for use in H2S containing environments in oil and gas production may subject to hardness survey.

How to review the MTCs compliance with NACE MR0175?

Yes, this information should review in the MTC before ordering. This is supplementary requirement compliance with NACE MR0175 that shall be guaranteed the hardness testing in the MTC by the manufacturer.

Hardness values for carbon and low-alloy steels shall maximum 22 HRC with Ni < 1 %, are not free-machining steels and the following heat-treatment conditions of hot-rolled (carbon steels only); annealed; normalized; normalized and tempered; normalized, austenitized, quenched, and tempered; austenitized, quenched, and tempered.
The statement are commonly found at the footer denotes in the MTCs like ASTM A105N “N” = Normalized; or ASTM A234 grade WPB with “A” = Annealed.

In addition to: 

• Hardness value of ASTM A105 material shall not exceed 187 HBW.
• Hardness value of ASTM A234 material shall not exceed 197 HBW. (for grade WPB and WPC).
• Hardness value of corrosion-resistant alloys refer to NACE MR0175 – 3.

Hardness testing methods for welding procedure qualification

Welding procedure qualification shall normally be carried out using 2 method of the Vickers HV 10 or HV 5, or the Rockwell method. Below photos are the sample for reference, but you may ask your lab test to show it and evident during witnessing the test. There are different using methods as NACE MR0175 – 2 illustrations at fig. 2, 3, 4, 5, 6.

Figure 1 for butt welds (refer NACE MR0175-2 para.

Figure 2 for fillet welds (refer NACE MR0175-2 para.

Figure 3 for hardbanding - weld overlay (refer NACE MR0175-2 para.

Figure 4 for hard facing - weld overlay (refer NACE MR0175-2 para.

Hardness surveys for production

Product test shall normally be carried out using the Brinell method by portable hardness tester.
Location and position survey are detailed in the written procedure such as pipe O.D <= 100mm shall be at least 1 location, Pipe 100mm < O.D <= 250mm shall be at least 2 locations, and pipe O.D > 250mm shall be at least 3 locations. Each location subject to hardness survey shall be at least 5 points on Base Metal 1 + HAZ 1 + Weld Metal + HAZ 2 + Base Metal 2.

Note: Most project specifications are limited the hardness values for production after PWHT shall less than 200 HB.

Acceptance criteria accordance to NACE MR0175-2: 2015 Table A.1

Maximum acceptable hardness survey shall be max. 22 HRC or 250 HV. But these values depend on project specification and the applicable standard.
Please note that the hardness value should limit within 210 HV for HAZ area, and hardness value after PWHT should less than 200 HB.
Learn more project specifications or material requisitions.


If your project requires to comply with NACE MR0175, I recommend to focus at:

  • Hardness testing for material should note the grades with its heat treatment.
  • WPS qualification must employ macro test and hardness survey as figure in para.
  • There are two methods of hardness survey for welding procedure specifications are Vicker or Rockwell C.
  • Acceptance criteria for WPS (P1) shall be max. 275 HV, read more NACE MR0175 Annex A.
  • Hardness test after PWHT for WPS (P1) shall be max. 200 HB.
  • Nguyen Duy Bien

    Enjoy learning and researching, reading book. Knowledge welding inspection painting inspection.

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    Hi. Very useful knowledge. Thank you for sharing