D1.2(2003) Tensile readings.

Date 01-31-2008 21:39

You hit the nail on the head and it bent over, is it a good nail? And you my friend have "bent nails" to deal with.

The thickness is the width and the width is the thickness, someone typed the number in the wrong column.

The tensiles are less than the required 24 ksi, so the tests fail per D1.2 and Section IX. The engineer can't "over-ride" the code requirements if the project specifications, contract, purchase order, or building code requires compliance to the codes mentioned.

You have more than a little "tweeking" to do, you need to requalify the procedures if the job requires qualified WPSs.

Best regards - Al

By GRoberts (***)

Date 02-01-2008 01:13

Are you sure they reported it right? The tensile load was not .1977 lb. It could have been .1977 kips (1 kip = 1000lb). If you don't have the original lab reports, see if the lab you used (if you know) still has them. They may be able to shed some light on it.

By 803056

Date 02-01-2008 02:36

He didn't list the units, but if you use the values of load listed in terms of kips, the UTS is "correct" as you suggest.

Al

By Mikeqc1 (****)

Date 02-01-2008 15:11

Could you explain this to me in more detail, what is meant by tensile load and what does that refer to in the test and why would that change the reported result? Please forgive the Rookie question but its something I need to know.

By 803056

Date 02-01-2008 16:15

The individual that completed the PQR form simply interchanged the thickness and the width of the test pieces when they recorded the data. Many people would consider the thickness of the pipe wall to be the thickness of the test specimen and the width of the specimen would be the measurement taken parallel to the axis of the weld. It really doesn't make a difference in the outcome because the terms are multiplied together to yield the cross sectional area.

The maximum load is listed presumably in terms of kips which is not the typical units of measure for the maximum load. The typical units for load are in terms of pounds unless the magnitude is very high. It is simply a matter of significant numbers. The answer can not be in terms that have more significant numbers than the least "accurate" measurement used in the calculations. The UTS is usually reported to the nearest 100 psi increment, not to the nearest 1 psi increment unless the answer is very small. For instance, 15 100 PSI (15.1 ksi) is preferred to 15 117 psi (15.117 ksi).

As an example: when you divide the maximum load (2100 pounds) by a cross sectional area (0.509), the mathamatical answer of 4125.7367 psi does not utilize the concept of significant numbers or the fact that the load was reported to the nearest 100 pound increment. The acceptable way of reporting the answer is 4.1 ksi or 4 100 psi.

Here is a couple of examples of significant numbers:

Area: 0.225 inches multiplied by 0.446 inches. There are three significant numbers used in the initial measurements. The area is width X thickness = 0.100 square inches (using significant numbers). The mathamatical answer is 0.10035 which indicates measurements are more "accurate" than they actually are. I believe this concept was developed when the engineers and scientists depended on their slide rulers to perform their calculations.

Ultimate Tensile Strength

Maximum load - 4125 pounds
Size of the specimen 0.225 X 0.446 inches

UTS calculated with significant numbers and scientific notation: 4.13 X 10^3 / (2.25 X 10^-2 X 4.46 X 10^-2) = 0.411X 10^5 = 41.1 ksi = 41 100 psi
UTS calculated on a calculator without regard to significant numbers: 4125/(0.225 X 0.446) = 41 106.127 psi

This is the best answer I can provide. I might be incorrect, but it's the best I can do.

Best regards - Al

By Kix

Date 02-02-2008 13:11

I'm sorry I put a decimal in front of the tensile load.(not supposed to be there) Ya know I don't have the sheet right in front of me, but I'm pretty sure the units are PSI. Wouldn't after welding 6061-T6 it not be as strong as the original base metal or is the 24,000psi a hand me down for 6061-T6 in the as welded condition? The parts in production get no heat treat or ageing. I looked for notes to see if there was a reading for the as welded condition, but 6061-T6 didn't have one. These pulls were done from a welded 6061-T6 pipe coupon with 4643 filler. All the data I have from this testing facility is very sketchy. We sent them 2 pipe coupons apparently of different sizes and wall thicknesses and they sent back 2 reports with the same wall thickness and identical mechanical test #'s. Funny thing is the customer has already reviewed these documents and ok'd everything. I don't know if they knew what they were looking at, but I have a goll darn situation on my hands now.

Thanks guys for the posts!

By 803056

Date 02-02-2008 14:30

Some of the heat treatable aluminum alloys loss considerable strength and ductility when they are welded. Even if they are solution heat treated after welding, they do not regain their original properties.

6061-T6 aluminum is just one of those that are degraded when they are welded. The minimum allowable tensile strength, if AWS D1.2, B2.1, or ASME Section IX are the governing documents, is 24 ksi. The failure is typically in the HAZ adjacent to the toe of the weld.

The laboratory most likely machined the samples to produce a rectangular cross section. They are suppose to retain some of the root pass if they follow the requirements of the welding standards mentioned above. As a point of information, some welding standards require the bend samples to be machined to 1/8 inch thick if the test piece is thicker than 1/8 inch. The machining requirements of both the tensile test and bend test samples have to be monitored to verify it is done properly.

It would not surprise me that your customer approved them. They may not have the expertise in-house to do a proper review. They depend on the supplier to be cognizant of the requirements and they review the paperwork to see that it is in place. They then look at the certifying statements at the bottom of each document, i.e., the PQR, WPS, and WPTR, if the certifying statement reads that the tests were prepared, welded, and tested in conformance with the applicable welding standard, their assumption is that they meet all the requirements including the required NDT (if any) and the mechanical properties.

In my humble opinion, the people that placed their signatures on the present welding documents have been fraudulent. Any welders qualified to the current WPS are not properly qualified or certified. If this work is for a federal, state, or local government, or if the work is covered by a building code or OSHA, or included in the Federal Register (shipboard pressure piping and pressure vessels) then there could be criminal legal repercussions if something fails in service.

Lawyers just love to follow the paper trail when something goes crunch or boom in the middle of the night. They bring in their technical experts to review calculations, test reports, welding documents, QC reports etc. to see who was responsible or who didn't do their job properly.

Trust me, you don't want to be the subject of a deposition or on the witness stand trying to explain why you didn't follow the requirements of the purchase order or contract specification if someone is injured or killed as a result of a product failure. Even if you did everything correctly, if is not a comfortable situation to be in.

If I were in your position, I would not hesitate to bring this matter to the attention of "upper management" and recommend that the procedures be requalified as well as the welders to make sure everything is on the "up and up" under your watch. You can't do much about what was done in the past, but you can influence the present and future. As for the laboratory that did the original testing, I would think twice about using them in the future.

A word of caution: It has been my experience that many laboratories do not use the correct bending mandrels when bending anything other than 3/8 inch thick carbon steel samples. For the purposes of internal audits and to provide an additional comfort level for my customers, I always include the dimensions of the test samples and the bend radius (or diameter) of the mandrel used in my reports. You might consider using AWS B2.1 Specification for Welding Procedure and Performance Qualification and AWS B4.0 Standard Methods for Mechanical Testing of Welds as the basis of your welding program and laboratory testing if you are not working to any specific welding standard. Make sure the lab doing the work has in-house copies of the reference documents, i.e., include a reference to AWS B2.1 and AWS B4.0 in your purchase order. In some cases the problem with the testing performed by laboratories is not entirely their fault. For instance, if they are simply asked to "bend test these samples" and they are most familiar with API requirements, which uses the same bend mandrel on all thicknesses of materials, you can expect they will not meet your expectations when testing to something other than API. The misunderstand can easily be that the testing regiment is not clearly stated in the purchase order or work order. Make sure you order the proper tests and reference the proper welding standards when you subcontract the laboratory work. If you don't understand the requirements, don't expect the laboratory to. If you need to hire a consultant to set up your in-house program, do so. It will be a worthwhile investment for your company and your easy of mind.

I commend you for doing your homework and discovering the problem.

Best regards - Al

By Kix

Date 02-04-2008 13:36

I'm not using the same lab that was used in the past. Your right about some labs not using proper bend radiuses because I caught the lab that I'm using right now bending A514 T1 at a 1.5" bend radius. I talked to them about it and they are watching things a bit closer now. The bend straps still passed thank goodness so I bought it off. I think what sucks is that this old lab is in the clear because all they say they are supposed to do is send a test report back to my company and it is up to us to fill out a PQR off of the report. They did this, but at the time we did not have anyone that really knew what they were looking at when filling out our PQR's. My new lab gives me a new WPS(just with the new referencing PQR'S) and a PQR in Arcworks format so I don't have to type up anything except for the fillet weld PQR's I plan to do in house. Speaking of that is it legal for me to cut up and etch my own fillet weld coupons and write a PQR on them since I'm a CWI? Do you think it would be a good idea just to let the lab do the fillet weld coupons as well?

By 803056

Date 02-05-2008 12:59

Don't forget that you are still responsible to review and accept the WPS generated by a third party. Are you that comfortable they are doing it right?

You are a CWI, I would think that you should be writing the WPSs in a format your welders can use. Most "canned" WPSs are not written for the welder, they are written just to meet the code. Those are two entirely different objectives. All too often the people writing the computer programs are computer geeks with little to no actual fabrication or welding experience.

What information are you providing to the laboratory? I find it difficult to imagine they have all the information required to complete a PQR that is factual.

Best regards - Al

By Kix

Date 02-05-2008 13:46

I'm sorry for the confusion Al. What I meant was I send a written WPS by me with how the coupon was welded with the test coupons to the lab in Arcworks format. The one thing the WPS does not have on it is a referencing PQR's because the coupon has not passed the test yet. Once the tests have been done and they passed, a CWI from the lab types up a PQR with results and the other information that is needed (just enough to meet code like you said). He sometimes retypes the WPS for me not changing anything, but only adding the referencing PQR #'s.(I usually do this, but he is a pretty good guy and does it if he has the time) Most of the time I will rewrite the PQR's adding more detail to some area's like qualification ranges and making them a bit more user friendly etc etc. I've noticed that he usually fills out as little as possible.