SMAW Welder Qual.-RT vs Bend Tests 7

[Metalguy]

Anyone have good data on welder qual. pass/fail results for RT vs. bend testing? Materials are P1 and P3 steel, ~0.5" to 1" thick. Typical weld indications are slag, not porosity/cracks, etc.

We presently use only bend tests, but have too much slag in production welds. Will making the welders qualify with RT help? Electrodes are 7018, 8018 and 9018, baked well.

 

[metengr]

Metalguy;
Why would you attempt to settle for less quality in production welds? I have used RT or bend testing with the same results. I typicaly require RT for contractor welders to qualify against during boiler outages because we use RT for field welds to assure welder quality, if the Code does NOT require it.

The bend test is a more rigourous test, and I use it for our company welder qualification. If you have slag entrapment problems, this is related to technique that must be corrected with your welders.

 

[Metalguy]

Thanks, Metengr

I also thought the bend test was more rigorous, but a *very* knowledgeable welding engineer/welder whose opinion I greatly respect just told me that the RT is more rigorous-checks the entire weld/HAZ volume, and a welder can get lucky and have the surface/near surfaces of the bend specimen OK but still have slag below.

I wonder if anyone has actually done side-by-side comparison testing.

 

[metengr]

Metalguy;
We did not find any difference in comparing test methods. In other words, we evaluated coupons that did not pass RT and were not able to pass subsequwnt bend tests some time ago and found equal results. As far as which method is more sensitive, all tests either nondestructive (like RT) or destructive (bend tests) have limitations as to detectability of flaws.

 

[unclesyd]

You may have the electrodes cooked too much. The flux on an electrode is design to flake off and if baked or overheated this property is demised. Check you temperatures to those recommended by the specific electrode manufacturer.
After the removal from the oven or can it very important to keep the rods in the proper condition normally by the use of a portable rod box. I’ve seen all sorts of problems with welding that the proper care of the rods would improve. I’ve seen another old trend that has made a come back lately, that is I can float the slag out.
Is the porosity gas or slag or both?
Does it have any general shape?

meteng, Metalguy
For years every welder (SMAW) that welded on our site was tested both by RT and Bend Testing. We had two areas that we also required side bends. My boss did a study such as stated comparing the two testing methods. If my windmill is still working it worked out in our case that about 80% that failed the RT also failed the Bend Test. This would be tempered somewhat as if the RT was really bad there was no Bend Test. When we quit doing the RT internally it was deemed that the Bend Test would suffice for the welder testing. Objection! We found that this produced a lot more defective welds in areas requiring 100% RT.

 

[pipewelder1999]

I have taken and given quite a few weld tests for both piping jobs and boiler outages. The bend test usually taken are from heavy wall coupons and are side bent. I have seen welders with 100% RT rates on prior outages at different plants sometimes fail these bend tests.

Pass/Fail Rates on qualification coupons may not be a good indicator of welder ability during production. It may show the ability to meet the requirements of an applicable code but it is not as valuable as observations made during testing and during subsequent production welding.

Slag trapping may be the result of many factors. In addition to those previously mentioned there is also bead placement, groove angle, rod angle, size of puddle and I'm sure there are others. Before looking to modifying your welder qualification testing method maybe consider making some other observations.

Are the production welds prepped and fitup consistantly ? Do any of the welds have compound bevels ? Are welders using larger electrodes for production than used in qualification testing ? Are the welds difficult to get to?

If you can't thinkof any other contributing factors I am at a loss.

Have a nice day






Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com

 

[GRoberts]

I certainly don't have any data, but I have worked at places doing bend tests and RE, and it seems like it is harder to pass RE than bend tests. If you can put in a good root and cap, you can pass bend tests, but for RE, every pass has to be good. Also, with RE, you can gain enough experience to make a good guess as to why the welder failed, and subsequently help them improve their work. It is harder to do with bends.

 

[Metalguy]

Thanks for all the good replies! The electrodes are carefully baked, so I'm ruling that out. We DID have a big slag problem with one weld when the prod. manager (and COO of the company) decided to use 5 mm electrodes instead of the usual 4 mm. The ASME code somehow allows a welder to qual. with 4 and then use 5 on the job-that should be fixed! We don't use 5 mm anymore, at least not on *my* job in this shop.

The job weld preps. for SMAW are usually just back-ground with a hand grinder following SAW, which is about 80% of the weld.

My feeling is that we should make the welders pass BOTH RT and bend tests--this is nuke pressure-vessel work. Most of the welds done so far with SMAW have "annoying" amounts of small slag-like inclusions, but easily pass the code requirements.

 

[sayee1]

Guided bend tests as described in QW 141.2 are tests to determine the degree of soundness and ductility of groove weld tests. As per QW 142, Radiographic examination can be only substituted for mechanical testing for groove weld performance qualification as permitted in QW 305. Remember that QW 305/QW304 permits RT as a SUBSTITUTE for bend tests except for GMAW-SC mode. Also most welder/operator straps are qualified on >10 mm thickness straps, typically more than 13mm straps to qualify for all thicknesses. If that is the case, you would be using SB tests. A SB test is through the cross section of weld, so as per section IX you are testing two cross sections of the weld for a WPQT and if there is a slag in the cross section or just below (either on the surface which is in the bend radius and along the OD of the SB or slightly below the surface) it is bound to open up during the bending.

However by doing RT, you are examining a length of the weld to examine for consistent and defect free welds where the rejection criteria is as specified in Sec IX. Again, with RT, you are not checking the ductility of the weld, but only degree of soundness. So funny as it may seem, most client specifications for Oil and Gas offshore platforms and associated piping restrict the indiscriminate substitution of RT for Bend tests. As a welding engineer, my ppersonal preference would be
1. RT/UT+SB (Some vendors/contractors use the NDE as a screening for selecting areas without defects for the SB which is wrong)
2. SB
3. RT

Finally, the procedure qualification program is designed to protect you against the defects like the ones you described. Give me one good reason why it is related to the welder and not the supervisor or the prod mgr who forced the decision on the welder to use a 5 mm. I am sure the welder would have resented the idea, I presume that it is not 5G position welding you are talking about or surely the welder would have outrightly refused. However if you really want to use such a modification of the process, you need to give additional training to the welder especially with safeguards like the groove angle to be used in that case. Provide the experienced welder with the right tools and "listen to him" and you should be able to avoid most defects.

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!

 

[Metalguy]

Sayeeprasadr,
Agree with what you have written. Unfortunately the welders here, AND the welding supervisor, are almost never consulted--they are simply TOLD what to do. BUT, it turns out that I didn't have the latest info. Seems the welding qual.tests have been changed from SB's to RT now, except for cladding. I'm going to see if we can get them UT'd as well.

ALL of the 5 mm welding was done in the flat position, but they are not going to used anymore-especially now that I know what they did. Fortunately most of the welders are real good, but upper management always tries to push them to go faster. I think I am slowly winning THAT battle.

 

[stanweld]

The low (H4, H8) diffusible hydrogen electrodes have been formulated with limited arc stabilizing elements. Excessive heating/baking of the these electrodes can lead to numerous flaws, including porosity, slag, lack of fusion. These electrodes are not really meant for prolonged storage but are to be used within a short period after opening of its sealed packaging. Even when properly stored a shorter arc lenghth must be maintained by the welder. This may be a contributor to your problems, assuming that your welders are properly deslagging after each pass.

 

[JoeTank]

Metalguy,

You state... "The ASME code somehow allows a welder to qual. with 4 and then use 5 on the job-that should be fixed!"

The ASME Code does not allow the welder to qualify with 4mm rods and then allow them to use 5mm rods in production. The writer of the WPS must allow that to occur.

There are many instances where the use of larger rods in production is appropriate. And of course there are situations when it's not. That's not a Code issue. ASME IX provide only the basic stuff. To allow use of larger rods for production is an issue to be addressed be the writer of the WPS.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[stanweld]

Qualification of welders is done to assure that the welder is capable of producing sound welds. When the manufacturer/contractor uses the easiest methods permitted by Codes to qualify its welders, it often does so to its own detriment. Qualification testing is the employers screening tool to prevent poor workmanship and expensive rework.

Codes specifically permit the manufacturer/contractor to make the qualification test more stringent and to be representative of the work to be performed in the field. It is important that all steps in making the qualification weld be witnessed by a competent test instructor/supervisor. If at any time during the test, the instructor/supervisor determines that the welder is incapable of consistently making sound welds in the field or shop, the test can and should be terminated.

In a very recent audit of our welding operations on a major project, I witnessed a welder unable to properly stack his weld beads on a heavy wall pipe qualification coupon and visually examined a completed, unsatisfactory cap on his small diameter test coupon and would have terminated the test there and then. He was permitted by the test instructor to complete welding the coupons and make the bend test,which failed. The test instructor was properly instructed to tighten his requirements. It is not prudent to hire "warm bodies" making expensive rework especially when considering that the reject rate was hovering near 15%.