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Up Topic Welding Industry / Technical Discussions / MAG with Dissimilar metals
- - By MRWeldSoCal (***) Date 11-26-2013 18:44
So we have had this discussion many a times.  Here is a photo of these SS 17-4 pins we are welding to an A633 plate.  We are using a 309L-17 5/32 Excalibur electrodes.  Now I understand the permeability of the different materials creates an indication along the weld edge when it is between the steel and the stainless, but why when next to the stainless of the weld and the pin itself?  Now a level 3 rejected these welds, while the engineer approved them. He swore they were cracks.  

          Most of you know my post lately have been dealing with the expansion and contraction of circular welds on three dissimilar platforms.  We had finally come to a working rhythm.  The part itself is kept between 200-250 degrees at all times, before welding it’s at 250 and when sitting it is in an oven at 350.  Once the last weld is made they are wrapped in a thick welding blanket and let to cool for 24-48 hours.  Took long enough but we got it all finally.  THEN THIS REJECTION. ATTACHED PHOTOS

Irritates me because we have welded about 180 of these pins and these would be the first to get rejected.

A question I have based on the permeability of these metals is why does each layer of weld (309) have an indication at each toe edge? 

If they at least are similar metals why the indication between them?

Also are 17-4 SS and 309 SS dissimilar enough to show an indication based on the permeability?

Can anyone give me an atomic answer to why this happens????

Thanks for any input

Jordan
Attachment: SSPINSINDI.JPG (225k)
Attachment: SSPINSINDI2.JPG (244k)
Parent - - By fschweighardt (***) Date 11-26-2013 20:53 Edited 11-26-2013 20:59
17-4 is martensetic, 309 is austenitic, and the 633 should be ferritic
should be some dilution zone, but those indications are pretty defined.  Have you tried dye penetrant to see if they are really cracks that are open to the surface?

I would get some PT and some UT in there to see what you can see.  I happen to think that the mag testing is horribly misapplied to this part
Parent - - By 803056 (*****) Date 11-26-2013 21:27 Edited 11-26-2013 21:37
I second the suggestion that PT be substituted for MT.

It has already been established that one can expect a magnetic particle indication to form between dissimilar metals or even ferromagnetic metals that have differences in heat treatment or chemistry that can cause a change in permeability. That being the case, why continue to use a NDE method that produces suspect indications?

There are Level III and there are self /employer proclaimed Level III.

Years ago I had a client tell me they had four Level III. During the tour of their facilities their Level IIIs showed me how they were testing aluminum struts on their bench wet mag machine. I asked them and the resident government inspector if they found many cracks. They were very happy to tell me they hadn't found any cracks in the aluminum struts since they started to use the MT method. I can safely say I didn't put  lot of faith in their test reports.

We have already discussed the differences between a Level III qualified and certified by the employer to SNT-TC-1A and one that has been tested and certified by ASNT and the ACCP program. Why continue to use Level III that may or may not have the technical expertise to do the job properly?

The suggestion to use the penetrant test method side steps all the possible problems introduced by MT.

Frankly, I would not be overly surprised to discover cracks along the toe of the weld with the combination noted. However, I would expect to see the crack along the toe of the weld against the 17-4 stainless.

Best regards - Al
Parent - - By 46.00 (****) Date 11-26-2013 22:55
I am of the same opinion as  fschweighardt. I feel the use of MT is terribly out of place in this case and I would request PT of this piece of equipment to confirm . I don't know where you are finding your level 3's but I would be asking some very strong questions that would put a cast of doubt on your original MT reports!
Parent - - By CWI555 (*****) Date 11-27-2013 01:06
"I don't know where you are finding your level 3's"
Parent - - By ctacker (****) Date 11-27-2013 04:46
Careful now, I just got my level 2 UT and MT from that box.
Parent - By 803056 (*****) Date 11-27-2013 12:10
Be afraid, be very afraid.

Congratulations! Now, all you have to do is remember everything they taught you in class!

Best regards - Al
Parent - - By MRWeldSoCal (***) Date 12-06-2013 13:55
Al-

So there is some light at the end of the tunnel.  I may be a CWI at one of Orange Countys biggest NDT labs.  They are looking for a fresh CWI to train and in their facitilty they have some of the most powerful X-rays in couthern california, They train in house for all NDT methods except for UT I believe.  Takes my daily commute from 56 miles to 6 miles. Also I will get to do field work, mostly for the military and aerospace.  Pretty excited about taking such a big step.  Pretty mcuh all D17.1 there, so I have to get used to the decimals when measuring, not the bullet holes allowed in D1.1

Is there a list or outline for what the test content is like for the ASNT testing for the different levels?  Why doesnt someone take the time to teach the science portion of whats happening during MT for instance?  I couldnt believe that there has been so much confusion by so many different NDT organizations about this one detail.  Good thing I have you guys and this forum to get a better understanding.  Hope all is well out in New England!

Jordan
Parent - By 803056 (*****) Date 12-06-2013 14:56
ASNT publishes a list of subjects to be covered by the various NDT methods.

The information includes the fundamentals and science behind each test method. However, as I have said, when specifying or referencing a qualification/certification schema, the Owner has to make a choice. There are three ASNT schemas for certifying NDT personnel. The oldest and least stringent is SNT-TC-1A; it allows the contractor/employer to modify the recommendations for training, qualifying work experience, and examinations. The next is CP-189: it is a standard that specifies the minimum requirements for training, experience, and examinations. It is an employer based program, but the Level III that administers the program has to be certified through ASNT and must abide by a code of ethics similar to the code of ethics the CWI has to agree to. Then there is the ACCP central certification program through ASNT. ASNT administers the Level II and Level III examinations. The examinations are very tough and cover all aspects of the test method.

You get what you pay for. You can get a family pet by picking up a stray on the side of the road. It might be the smartest, healthiest pet you ever hope for. However, there is always the chance it is disease riddled, flea infested bag of problems. The cost: 2 gallons of gasoline and the time it takes to drive slowly along the highway for an hour or two. You could go the pet store and pay a small sum and the pet comes with a 2 hour warrantee. It might be in better health, it may have been bathed before you picked it up, but it may have been inbred, but the cost was reasonable. Then, if you have a small fortune, you can buy the critter from a breeder that  will provide a certification stating the animal's pedigree. In the end, you usually get what you ask for if you are willing to pay the price.

Steel, automobiles, or NDT credentials are no better than what you specify and are willing to pay for.  

I will bet you a week's wages that none of the technicians you encountered would or had passed the ASNT's ACCP examinations. There is a very high probability they did not receive the training or the hours of experience specified by CP-189. And going a few steps further, I'll bet your previous employer never reviewed the NDT contractor's written practice, their NDT procedures, or the qualifications and certifications of the technicians. More than likely, they went with the contractor that offered their services for the lowest price and where looking for the lab to rubber stamp the work. You get what you pay for and what you demand by doing your homework.

Just remember that you want to take a different route. Do more than the minimum required by your employer and don't be afraid to purchase textbooks on the subjects/test methods you want to learn.

Good luck in your new position.

Al
Parent - - By ssbn727 (*****) Date 11-27-2013 00:05
A633
is a normalized HSLA plate steel for applications where improved notch toughness is
desired. Available in four grades with different chemical compositions, the minimum yield point
ranges from 42 to 60 ksi depending on grade and thickness.

fschweighardt does make an important point about the A633 possibly being a ferritic steel but, the real question here is which specific grade are we talking about here Jordan???

Is it the grade with small amounts of Cr, NI, and Cu with a very slight higher amount of Mn (D), or the grade with less C(A), or is it the grade a tiny amount of Vanadium, or the grade with a tiny amount of Moly (C), or the grade that has no niobium but has a very small amount of N (E)? There are some variations in the composition with respect to the exact % amounts of the micro-alloying elements depending on thickness and mill form for one grade, and one grade has the option of including some of the elements or not that distinguishes that grade from the other ones... So, which grade is it? A,C,D or E???

Here's a .pdf from ASM that covers A633 as well as the other four out of six grades of HSLA Steels, including: Weathering Steels, MicroAlloyed Ferrite - Pearlite Steels, As Rolled Pearlitic Steels, Acicular Ferrite (Low Carbon Bainite) Steels, Dual Phase Steels and Inclusion - Shape Controlled Steels...

http://www.asminternational.org/content/ASM/StoreFiles/06117_Chapter%203B.pdf#page=3&zoom=110.00000000000001,26,536

So this may or may not be important enough but then again, it just may be. :lol::wink::cool:

Respectfully,
Henry
Parent - By 803056 (*****) Date 11-27-2013 12:11
You are a good resource to have around Henry.

Best regards - Al
Parent - - By MRWeldSoCal (***) Date 12-06-2013 13:24
Our WPS states C & D, but I believe it is C that we are using
Parent - By ssbn727 (*****) Date 12-07-2013 11:43
Hmmm, Makes sense picking the one with the Moly in it because that's the one they should be using with that app although D is acceptable also.
Parent - - By MMyers (**) Date 11-27-2013 14:53
Do you have the luxury of cutting a weld (even a test weld in the same materials/restraint conditions) and preparing it metallographically to demonstrate that the structures between the three regions are different?  I'm thinking the testing goes something like this:
Weld test on protoypic material/heat treat/restraint.  A scrapped part would be the best option if you have one laying around. 
MT and have everyone agree there are indications
Section weld in 4 quadrants minimum, 8 if you have enough weld
Send the samples to a lab and have them polish and micro etch them.  They'll enjoy the challenge of micro etching the different materials.  You might want to send along a section of the base metals so they can focus on micro etching the weld only on your welded samples.
Examine weld soundness and demonstrate that the indications are indeed just indications and not rejectable defects
Examine weld microstructure to demonstrate that what everyone knows is true, that the materials have different microstructure
Use this work as the foundation of a short memo to the engineer/HMFIC to change the inspection method.
Parent - - By MRWeldSoCal (***) Date 12-06-2013 13:27
No we dont have that luxury, The pic intself is trace coded to a specific part and machined specific. We also take serious precaution to not arc strike them on accident by sleeving the pins before welding.  If there is a bad weld or something wrong we put them into a CNC and route out the welds.  But yea you are right, that would make it easy to spot.

Jordan
Up Topic Welding Industry / Technical Discussions / MAG with Dissimilar metals

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