NACE TM0177 Method A or C?

[Sol71]

Hi,

What criteria should I use to choose between NACE TM0177 Method A and C?

The background for my question is the following: We are currently using 660 D bolts (Alloy A286/UNS S66286) on one of our subsea products, it is coated. NACE MR0175 have very conservative temperature value for the use of UNS S66286, max 65 deg C/ 149 deg F. We would like to do our own testing of the material according to NACE TM0177, on elevated temperatures. I know that FMC Technologies did this a few years back (Link) and later, a test on even further elevated temperatures (Up to 400 deg F) with a 5% NaCl Solution, 15 psia H2S. They used method C. I have some structural engineers her questioning why they haven’t used method A, since the material is going to be used for bolts. I know the principles of the two test methods, but I don’t have enough knowledge to determine which of the methods would be the best in our case or why FMC choose to use method C for their test.

Thank you.

 

[Dhurjati Sen]

Dear Sol71,

Quoting from TM0177

"Method A, the NACE Standard Tensile Test, provides for evaluating metals for EC resistance under uniaxial
tensile loading."

"Method C, the NACE Standard C-Ring Test,provides for evaluating the EC resistance of metals under conditions of circumferential loading (hoop stress)."

FMC must have thought that circumferential loading played an active part. If your structural guys think otherwise then you have to go for Method A.

Regards.

DHURJATI SEN

 

[Chumpes]

Hi
method A : tensile constant load (displacement increasing with time)
method C : bending constant displacement (load decreasing with time)

method A is certainly more conservative than method C, specimens/grades can fail method A and pass method C with exactely the same environment.

try to simulate the proper actual system : if the system is under constant load then method A is more adapted, if your system is under constant strain then method C is more adapted.

regards

 

[pradipgoswami]

Sol71,
Quotes from TM0177-2005:-
Method A, the NACE Standard Tensile Test, provides for evaluating metals for EC resistance under uniaxial tensile loading.It offers a simple unnotched test specimen with a well-defined stress state. EC susceptibility with Method A is usually determined by time-to-failure. Tensile test specimens loaded to a particular stress level give a failure/no-failure test result.

Method C,the NACE Standard C-Ring Test, provides for evaluating the EC resistance of metals under conditions of circumferential loading (hoop stress). It is particularly suitable for making transverse tests of tubing and bar. EC susceptibility with the C-ring test specimen is usually determined by time-to-cracking during the test. C-ring test specimens, when deflected to a particular outer fiber stress level, give a failure/no-failure result. When testing multiple C-ring test specimens at varying stress levels, an apparent threshold stress for EC can be obtained.

I've seen method C being adopted more for tubular sections. While method A is being universally popular for all shapes. For shapes like "Bolt" my understanding is Method A possibly would exhibit more reliable results.
Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299