NACE MR0175 compliant Hardness Testing 1

[bryansonnier]

NACE MR0175 calls out specific hardness testing requirements for certain materials. In order to test for hardness, you can't just thump the piece of steel and listen, like testing a watermelon (although technically speaking there are tools that do just that). Is there an approved standard or standards for testing hardness? If so, what are the pros and cons of them?

Basically we have to test small runs of parts probably 50 a year or less. A large benchtop rockwell tester seems too expensive but can i rely on the much cheaper Leeb testers to in the very unlikely event there is a failure we could say "we tested the hardness" and not get laughed out of court. We are trying to determine which one to purchase. If the benchtop is the only way to go, i don't think our product would be competitive and we may as well not be in the market, but I want to create a safe product as well so i'm hoping for a little guidance.

EDIT:
So i've looked at some of the ASTM standards and there is a standard for portable rockwell testers (ASTM E110) and also for leeb testers (ASTM A965). The leeb testers are much more economical but is there any thing anywhere that states you should use this and not that when it comes to NACE (specifically MR0175) or is it just up to the discretion of the customer requirements. If just the customer then there may be an issue because as far as most of our customers are concerned if you hit it with a hammer and it goes ping and not bong its hard enough. I'm being sarcastic here but not by much.

 

[jmec87]

If hardness measurements on parent metal are specified, sufficient hardness tests shall be made to establish the actual hardness of the steel being examined. Individual HRC readings exceeding the value permitted by this document may be considered acceptable if the average of several readings taken within close proximity does not exceed the value permitted by this document and no individual reading is greater than 2 HRC above the specified value. Equivalent requirements shall apply to other methods of hardness measurement when specified in this document or referenced in a manufacturing specification.
NOTE The number and location of hardness tests on parent metal are not specified in the ANSI/NACE MR0175/ISO 15156 series.
For ferritic steels, EFC Publication 16[38] shows graphs for the conversion of hardness readings, from Vickers (HV) to Rockwell (HRC) and from Vickers (HV) to Brinell (HBW), derived from the tables of ASTM E140 and ISO 18265. Other conversion tables also exist. Users may establish correlations for individual materials.

Is there an applicable product standard (i.e. API 6A, API 6D) that your parts must meet? If so, this standard usually specifies the allowable hardness testing methods. API 6A requires hardness testing in accordance with ISO 6506, ISO 6508, ASTM E10, ASTM E18, or ASTM E110.

If not, then I think it is a gray area. Rockwell and Brinell testing (either bench top or portable King Brinell-style testers) are commonly used and seem to have acceptable accuracy. If you use Brinell testing, then convert per ASTM E140.

I don't have experience with Leeb but I am aware that some people have significant concerns about its accuracy and repeatability. That is why it is not an acceptable method for API 6A products.

 

[bryansonnier]

Thank you for the API reference, i didn't think to check there for some silly reason.