Weldment hardness survey. 1

[VeryPicky]

Hello.
I have been requested by my client to perform the hardness survey of carbon steel piping weldments intended for sour oil service.
The test shall comprise of parent metal, weld metal and HAZ measurements.
My old trusty, portable telebrineller is not acceptable to my client due to the indentation size that is not ideal for HAZ measurement.
My options seem to be: microdur and equitip. Unfortunately I don't have enough experience with those methods. My understanding is that equitip is not suitable for metal thicknesses below 2".
Any tips regarding those two methods?
Can you recommend any other method to give indentation small enough to test HAZ and still receive reliable results?

 

[Carburize]

I would send a sample of weld to a local lab and ask them to carry out the hardness survey using a Rockwell machine. Rockwell C is the definitive hardness scale in NACE MR 01 75 so using that scale cuts out any debates about the validity of conversions etc.

 

[GRoberts]

For hardness testing of the HAZ, Rockwell A or C is commonly used, but it is proven to be too large and indentation to accurately reflect HAZ hardness. The preferred practice is HV10 or less (HV5 or HV1 are common). This will give a more accurate reading of the HAZ hardness. I don't have any experience with the equitip, but the microdur indentation size is comparable to or smaller than the HV10 (from the view of my uncalibrated eyeball). Logically, since it is a hand operated instrument, it could not give to large of an indentation due to the force available. The results on the microdur can be operator dependant, and good calibration with the proper test specimens is necessary. But overall, it seems to be at least as accurate as other portable hardness testing methods, if not more so.

 

[VeryPicky]

Thank you guys for answering my question.
Unfortunately the pipe is in the field and I can not take it to the lab. It must be a portable method and giving small indentation. I am afraid Rockwell test is out of the question.
My question was triggered by some discussions I had with NDE companies, who were claiming the Microdur was giving them very erratic readings.

 

[grampi1]

There is no field hardness technique that can be used for acceptance. Field hardness is a gross QC tool only.

Microdur is the best field tool. For microdur, do a good job grinding a flat, macroetch to determine location of fusion line. Try to run the microdur vertical if possible. Make sure the operator is highly qualified on Microdur. Use the MIC10 version if at all possible as it has a self check for getting the angle of contact correct. Then take at least 5 readings per location and average, do not use single values. If some welds are harder than others, this will come out. But it would be folly to claim the weld is hard or soft vs spec requirements, without cutting a sampe out and doing a correct cross section using HV10 or 5. Rockwell is a waste of time for welds.

 

[ijzer]

We have good experiences with the Microdur and some bad experiences with the Eqotip.
But what is wrong with the old fashened Poldy hammer?

 

[Metalguy]

I'm not familiar with the Microdur machine, but have used an Equotip many times with excellent results. Unfortunately it is pretty expensive, but very light and portable. It depends on testing a rigid surface, and a heavy cal. block/backup support is included.

Properly used, it gives very accurate results--nearly as good as a good lab. Rockwell tester.

 

[Carburize]

This is a bit of drift on this thread but in response to GROBERTS the issue you raise is one which has caused problems for years.
The original data on which NACE MR 01 75 was established was based on hardness tests using Rockwell C and attempts to use conversions from HV do not work. The microstructures of HAZs have small harder areas when tested using HV which are not detected by the larger impression of the Rockwell C. These harder areas were almost certainly present in the original samples on which the NACE document was based but were never measured.
It is for this reason that for sour service conditions when NACE MR 01 75 is referenced Rockwell C is the definitive test - although HV gives a more meaningful survey in terms of hardness variations it only confuses the issue when it comes to establishing compliance with the NACE document.
Sorry - I know this doesn't help the original poster but its been one of my soapbox issues for twenty years.