95ksi (ish) nace compliant steel tube/casing at 9.5" dia. T95, vs 8630 vs 4130M - Elongation 3

[acrmnsm]

Dumb/brain fade question of the week.

All these steels are available at ~95ksi yield and below 22hrc to comply with Nace MR0175.

I'm just a bit confused as all the data I can find on T95 is that its elongation is limited to 0.5% (Source ISO/FDIS 11960:2010(E)) (and they give similar levels of elong for C110,L80,M65, H540, J55 etc

I HAVE A FEELING I JUST DO NOT UNDERSTAND HOW THE ELONGATION CALC IN 11960 WORKS, OR RELATES TO HOW I NORMALLY UNDERSTAND ELONG

For example for T95:
Ys = 95ksi(655MPa)
UTS = min 105ksi(724MPa)
Assume E = 205GPA
that gives approx elong at yield of 0.32%, easy and expected for steels
So if elongation is max of 0.5%, Then in 0.18% it hardens 10 ksi. This is a quite a lot of strain hardening compared to 8630 or 4130M, at 15-17% elongation.

I am confused. Please help a dummy become less dummy like..

 

[acrmnsm]

Sorry I should point out that ISO 11960:2010 is identical to API 5CT. It just depends on what side of the atlantic you are..

 

[OGMetEngr]

First, T95 will be above 22HRC. NACE MR0175 ISO15156 Annex A.2.2.3 and A.3.2 allows UNS G41xx0 (e.g. - 4130, 4140) to go higher than 22 HRC, up to 30/27/26HRC depending on H2S and pH levels. This is for "Downhole Casing, Tubing and Tubular Components". Also included are allowed strength ranges for these.

As for elongation, this is a minimum. I'm not aware of any applications that have an elongation maximum.

 

[redpicker]

I'm just a bit confused as all the data I can find on T95 is that its elongation is limited to 0.5% (Source ISO/FDIS 11960:2010(E)) (and they give similar levels of elong for C110,L80,M65, H540, J55 etc

You do not understand the requirement. There is no maximum elongation requirement for T95 (or any of the API casing grades). The requirement is that the yield strength of T95 is measured at 0.5% extension under load (EUL) (as opposed to measuring the yield at 0.2% offset). These are two different ways of measuring the yield strength. Historically, the EUL method is used for tubular goods.

The EUL method is older than the Offset method for measuring yield and goes back when load vs extension measuring equipment was expensive and considered unnecessary for simple yield strength determination. The old way to use this method would be to set a caliper at 1.005 times the gauge length (which is marked on the specimen). For example, for a 2.000" gauge length, you would set the calipers at 2.010". Then two technicians would perform the test; one watching the gauge marks on the specimen and telling the other when they lined up with the pre-set caliper. The other technician would watch the load indicator and record the load at the point the 1st technician announced that the gauge marks lined up with the caliper. As this method is not nearly as accurate or as well documented as using load-extension recording equipment and just reading the load where the extension was equal to 1.005 times the gauge length of the extensometer, the old method is no longer used.

Interestingly, a few years ago, API investigated eliminating the EUL method and just use the 0.2% offset method (like the rest of the world does). The workgroup reported that there would be small differences between the two methods which could result in product meeting spec (say, when measured with the 0.5% EUL method, but would not meet using the 0.2% offset. This made the manufacturers a bit uneasy. The manufacturers also mentioned that all of their labs were set-up and using the EUL method so there really was no reason to change they way the product had been qualified for close to 100 years.

rp

 

[acrmnsm]

Excellent, I do understand now, thank you. The documentation is not clear. I appreciate your help.