Steel grades AISI 1526 vs API 5L-X42 2

[enginerding]

We have a condition where we specified API 5L-X42 pipe for a billboard column and the client would like to increase the height. We asked for mill specs of the pipe to verify strengths and the client could not produce any. So we had the pipe tested. The test showed acceptable tensile and yield strengths, but the elongation in 2" was only 12.5%.

We then asked for a chemical analysis of the steel, and the testing company gave us the chemical composition and noted that it meets AISI Grade 1526. I don't know anything about this steel grade.

The client understands that we cannot increase the height without some reinforcement, and we intend to design this reinforcement if possible.

Can anyone explain what issues I will have working with the AISI 1526 instead of the API 5L pipe? Any suggestions on addressing these issues?

 

[salmon2]

API X42 PSL1 allows .28 and .26 % C for seamless and welded pipes, which means your 1526 chemistry could well within API 5L. Of course you have to check other elements like S and P.

The elongation is a problem because X42 requires 22%. Something is not right given such low e. And your chemistry could be not 1526, instead, a HSLA grade possibly.

 

[metengr]

The 1526 steel is a plain carbon steel grade with Mn above 1.0% by mass, in comparison to the plain carbon steel 10XX grades, where the Mn is 1% or less.

There could be several reasons for the reported low elongation values for this steel grade; the first being tensile coupon size and orientation or this tube material could have been supplied in a cold worked condition. Second, do you have reduction of area values reported for the tensile test coupons? By the way what do you claim as acceptable tensile and yield strength values? What specification did you compare to determine acceptable values???

 

[enginerding]

I don't know the size of the coupons cut from the steel, but the cross section of the sample tested is .4980" x 0.3770". Fy = 55.4 ksi, Fu = 66.3 ksi, Elongation in 2" = 12.5%. We compared the strengths to that required for API 5L-X42 pipe and also the API 5L-X46 we were hoping to have it re-graded to so it could handle the height increase.

We don't have reduction of area numbers reported for these tests.

We did have a couple more mechanical tests on this same piece of pipe. They used bigger cross sections - about 0.75" x 0.4". Both tested better, but still not at the API 5L specs. The yields were around 59 ksi and the ultimate around 71 ksi. The elongations in 2" were 18.1% and 19.3% for the additional two tests.

Is this what you are looking for?

 

[salmon2]

The way you do with two additional tensile tests is not to ASTM E8 to me, while your first test is right - using 0.5'' wide specimen. I guess your pipe wall thickness is ~0.377'' then for 0.75'' width of specimen, the min e for X42 will be 24% instead of 22%, in my first reply, for 0.5'' width of specimen, if what you are doing is acceptable. You are changing the ratio between cross section and gauge length. The ratio has to be same to compare elongations and this is why reduction of area is a better gauge for ductility.

As metengr suspected your strength numbers look like a cold worked pipe. Are your tensile tests in transverse direction or longitudinal? Are they done at room temperature? They should be in longitudinal direction and at room temperature. Are they seamless or welded? What is heat treatment? Where is tensile couple being taken? Without original MTR, it is tough.

 

[metengr]

Thanks. How was the existing pipe material identified? Since you have tensile testing of actual coupons, I would have a full chemistry performed to ensure proper typing of material (if this had not been already done above). If a portable alloy analyzer was used, there could a misidentification of the material. A lab analysis will confirm if this is 1526 or some other alloy, and these results can determine weldability.

This material if it is 1526 would fall under ASTM A 529. Looks like it would be a Grade 55 - 50 Ksi minimum YS based on the second set of coupons. Minimum elongation by specification is 20% for this grade.

 

[enginerding]

We are still trying to identify the existing pipe. It should have been API 5L-X42 because that is what we specified and that is what the client ordered. They are now looking into the pipe supplier's other jobs to make sure these have been supplied correctly. The supplier cannot provide mill data on this particular pipe.

The 1526 grade was determined by a lab analysis. If you would like, I could list all the chemical information they gave us.

Our client will cut coupons longitudinally from the pipe when they have them tested. I assume they are tested that way as well. The pipes are usually welded with a vertical seam, but I did not see this one.

I do not know why they used different width samples for the additional tests. Actually, I had not even noticed that until you asked what sized samples were taken.

 

[metengr]

enginerding;
After thinking about this, you need to reject the pipe material because it does not meet your original specification requirement and, most important , you have no traceability for this material. I am not a believer of trying to establish new pedigree papers on unknown material because of issues related to past fabrication. For example; this material could have been seam welded despite not being able to visually observe a weld because welded pipe can be turned to size. Second, other than limited mechanical property testing, you have possible notch toughness concerns if this billboard is installed in a cold weather climate. In certain applications you can disposition material to work using rigorous engineering analysis. However, when it comes to rigging, lifting or structural applications where you have risk of personnel injury or damage to property, there is too much risk to take on.