Hardness relating to failure?

[bsum]

I was wondering if anybody had information that would help relate a hardness test (Brinell, Vickers, Rockwell, Scleroscope, etc.) to strength failure. I am particularly after yield strength or tensile strength in heavy pipes. Any links or information would be greatly appreciated! Thank you.

 

[metengr]

bsum;
Can you please re-phrase your question? Hardness testing is more typically used as a quality control check to assure either material repaired or new pipe material received is acceptable for use in service.

 

[bsum]

Well I have a project and to sum it up...... there are a few "bad" pipes in the whole lot and we want to be able to get a rough estimate of the yield and tensile strength from a hardness test. It is not viable to run other tests because it would take so long but we need to know what pipes are bad because they will shear. So we need a quick test that can be run on all of the pipes.

Thanks metengr!

 

[stanweld]

Both Brinell and Vickers can be used to provide an estimate of tensile strength but not yield strength.

 

[bsum]

Stan-
For heavy duty, large diameter pieps, what would you recommend? Why not Rockwell? And which tests would be possible to do in a field rather than office?

 

[stanweld]

Tellebrineller, Pin Brineller, MIC 10/MIC 20 (essentially HV10)or equivalent. Rockwell does not convert truly to Brinell or Vickers; thus, accuracy of tensile strength comparison is further impaired.

 

[metengr]

there are a few "bad" pipes in the whole lot and we want to be able to get a rough estimate of the yield and tensile strength from a hardness test.

Not taking anything away from hardness testing, you had better review or obtain a check of the chemical composition of the "bad" or I would prefer "rejectable" pipe material. Hardness provides one bit of information. When it comes to material disposition, you can hire an organization to perform a PMI (Positive Material Identification), this is a nondestructive test that can be done quickly to type material. You need both chemical composition and hardness to do a proper evaluation.

 

[unclesyd]

Aside for the sage advice given above can you give a little more information as to why you know they are bad?

Is it a material difference or just a hardness difference in the same material?

To say something will shear off is very bad as you would normally expect leak before break.

 

[davefitz]

unclesyd;
Yield and UTS are relevant for low temp piping, but for high temp piping (P91, P92) the finding of adequate yield and UTS is not sufficient to confirm acceptable pipe characteristics, as those pipes are designed based on creep properties. In addition to chem composition,UTS and yield , confirmation of correct crystal structure is required.

 

[stanweld]

Second unclesyd request. Provide more info on nature of the problem; material type/grade, material processing requirements, suspected mix, etc.

 

[redpicker]

Ok, I am going to assume you are referring to drill pipe because, in with drill pipe, V-150 designates a 150,000 mininum yield strength material. Generally, the manufacturers will use a modified 4130 (higher Cr and Mo) quenched and tempered tube for this. The minimum hardness expected would be around 34 HRC (321 HBW). The upper limit would be around 44 HRC (415 HBW). The expected hardness range is somewhat wide because Drill Pipe is not generally qualified thorugh hardness testing.

As far as hardenss testing method, you pretty much confined to portable methods. Brinell would be the most accurate, followed by portable Rockwell. At the bottom would be re-bound testers (Equi-Tip type). With Brinell, however, you have to grind a flat on the pipe to perform the test. As the pipe is inspected for wall thickness, this test alone can scrap the joint. With the portable Rockwell, you can generally get a good enough surface by sanding the surface to bright metal, but you can run into surface decarburization that would result in a low reading. The rebound testers also require a prepared surface. They also can be very operator-dependent, so the results are not as accurate.

So, you might not be able to do what you are wanting to do with a hardness test. That is, the methods to be used might not be accurate enough to detect the differences you are looking for.

Maybe you can go about this another way. This grade is a very specialized grade and there are only 2 or 3 manufacturers that produce it. Without knowing why you feel some of the joints are bad, it is kind of difficult, but if it is because of mixed lots, maybe a wall thickness inspection will help seperate the lots. This material is generally traceable, so if you got the traceability numbers from the joints in question, maybe the manufacturer could help.

rp