Hello folks,

Im new to this forum but so far have found it a great source of information but now im hoping that you can help me.

I am doing a bit of investigation into the testing the hardness of bolts etc.

I am wonder does anyone know what standard covers the re-testing of a material if the first time it is tested they do not meet the desired hardness specification.

At this moment we have the following statement but I need to find if it is linked to a recognised standard or is it an instruction which we have decided is acceptable.

“In the event hardness testing returns a result outside the specification the following actions are permitted.

The area may be retested by making 2 additional strikes next to the first strike. If the average of the three readings meets the material specification the area is acceptable. For components on accordance with NACE MR0175 / ISO 15156n no individual reading may be greater than 2 Rockwell C hardness scale Units above the acceptable maximum value.

If the average of the three readings is still not acceptable the area may be ground. Grinding to prepare additional hardness testing shall be done in the same location as the original readings and may only be performed one time”

Has anyone heard this statement before and know where it comes from or alternatively does anyone know of a possible standard relating to hardness retesting?

Many Thanks

Welcome to The Cove! :bigwave:
It could be my own squeamishness, but I would think this is not a retest that the original operator should perform.

An inspection process should be designed in a way that brings confidence in its results. If the inspection process is questionable enough to retest in a second or third place, I would work on the process.

If, however the material fails hardness in one place, why would it be deemed acceptable in inspection so long as it passes hardness test in a second or third spot? If further tests seem warranted, they could be performed in a material review for a kind of MRB process, but this is more than I would expect to see done to bolts unless they are really expensive.

Hello:

According to ASTM some tests have precedence in the results (ASTM A325). When we delivered two years ago a huge lot of bolts to our client, and the hardness test of the bolts failed.

We did destructive tests (Ultimate Tension Resistance Test) and this test according to the standard takes precedence over the hardness test so the lot was accepted after the rejection that was made.

Hope I could help in something!

Regards

After further investigation I have found that paragraph 1 i.e. takeing the average of 3 result comes straight out of NACE MR0175, but I am still looking for a standard which says that grinding of the test piece is acceptable. ASTM E 18 says work hardening should be avoided but surely grinding will work harden the surface.

thanks palpeurdedieu for you input but it is an internal document which states this and I have been asked to find out where this comes from.