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Up Topic Welding Industry / Inspection & Qualification / Repair of Discontinuities
- - By cwi_level_II Date 07-19-2012 17:50 Edited 07-19-2012 17:52
I'm a CWI working at a company for less than 3 months.  They use primarily SAW, which I have pretty limited experience with.  A question has come up about repair procedures.  I have had it drilled in my head over the years that repairing of weld discontinuities should ALWAYS be done with a low-hydrogen process.  The company has always used SAW to repair SAW welds.  I'm trying to convince my boss that since we do NOT keep our flux in an oven and occasionally have problems with porosity due to moisture contamination of the flux (a seperate issue that I'm working on changing) that SAW is not the ideal process to be making repairs with, and that spray transfer GMAW, is better suited to repairing sections of welds that have failed UT, or have surface discontinuites. However since they have done things this way for 40+ years he doesn't see the need to change unless I can provide some research or documentation proving that I am right.  D1.1 clause 5.26 is actually a little sketchy on this as it does not specifically require a low-hydrogen process to redeposit new weld metal into a repair. We are making a wide range from 1/4" to 3" v-groove butt welds (B-L2a-S/B-U2-S).  Anyone have any ideas?
Parent - By RonG (****) Date 07-19-2012 18:13
Why do you feel SAW should not be used? If the defect is removed why would you have a problem going back with I dentical Flux & Wire? If you use anything else it would need to be qualified also.
Parent - - By welderbrent (*****) Date 07-19-2012 18:31
I'm not sure why you were taught that low-hydrogen was the ONLY way to repair discontinuities.  When we weld with FCAW, innershield or dual-shield, and get a bad spot we clean it out and repair it with the same.  Also with GMAW (spray transfer). 

SAW will go back over itself and the repair area just fine.  Now, your flux is a separate issue.  If you are getting the discontinuities because of the moisture in the flux I would think they would be anxious to remedy the situation.  But there is no reason to switch to another process for the repairs other than convenience.  Such as: I worked in a forming plant and after the product came off the line there was no way it was going back through the stationary forming unit with welding to do a repair.  So as it moved down the line we would air arc out the bad spots and used wire to weld it back in. 

But, it sounds like your product can go back through the system, or, your system is portable.  At any rate, the SAW will do the job cleaner and faster than any of the others for any re-work that is required.

Sorry.  Just my two tin pennies worth.

Have a Great Day,  Brent
Parent - By jwright650 (*****) Date 07-23-2012 20:06

>Now, your flux is a separate issue.  If you are getting the discontinuities because of the moisture in the flux I would think they would be anxious to remedy the situation.


Brent is spot on here....as a fabricator, repairs are something that you want to eliminate as much as possible. The cost of placing non-quality welds is an expense that you don't have to have, and is a very correctable issue.

I do not understand the boss wanting the production to be using flux that is not dry and free of moisture. They are just asking for problems when trying to place quality welds, when they don't bother to keep the flux dry.
Parent - - By G.S.Crisi (****) Date 07-24-2012 18:16
Just to make a clarification about the technical welding language used.
Discontinuities do not need to be repaired. Defects do.
The difference between discontinuities and defects is that discontinuities are tollerated by the applicable standards while defects are not.
Giovanni S. Crisi
Sao Paulo - Brazil
Parent - By jwright650 (*****) Date 07-24-2012 18:32
Excellent point Giovanni! :cool:
Parent - - By welderbrent (*****) Date 07-24-2012 19:32
Anything that causes a weld to not be a perfect weld is considered a 'discontinuity'.  Then it also depends a little on various codes especially when you get away from AWS D1 codes and look at API 1104 or ASME codes.  See A3.0 Terms and Defs and D1.1 Clause 4, 5, & 6 several references.

Discontinuities then fall into two classes, Acceptable or Rejectable.  Rejectable discontinuities are also termed 'defects' and/or 'flaws' (see AWS A 3.0).   Ref D1.1, 6.26.8 "discontinuity shall be accepted or rejected on the basis of ..."

You also run into the various trades and different locations in the world where 'non-standard' terminology gets used.  And many of us fall into that trap, using non-standard terminology such as 'ground' instead of 'work lead/connection'. 

According to D1.1, 6.6.5; 5.15.1.2; and others, discontinuities are repaired when they fall into certain conditions for size, extent, type, etc.  In other cases the code states 'the weld' with discontinuities exceeding given perameters is to be repaired.  Usually by removal and re-welding.

Thus, discontinuities are not always tolerated.  It depends upon the code and the evaluation.  They may be rejectable and require repair procedures.

Have a Great Day,  Brent
Parent - By qcrobert (***) Date 07-24-2012 21:43
Thank you, Brent, that will go into my "library"...  :cool:

QCRobert
Parent - - By CWI555 (*****) Date 07-25-2012 11:55
"Thus, discontinuities are not always tolerated.  It depends upon the code and the evaluation.  They may be rejectable and require repair procedures."

Discontinuities are always tolerated.
Discontinuities that meet the definition of a 'flaw' may or may not be rejectable.
A defect, or reject, are flaws that exceed established size/type values of which if let go, could be detrimental to the service of the component in question.

You cannot have a weld without a discontinuity. A discontinuity is a variance in the normal physical structure. The act of putting in a weld adds that variance.
Parent - - By welderbrent (*****) Date 07-25-2012 15:12
Gerald,

I don't want to get into a war on symantics with this, and I appreciate your comments. 

Personally, I find it more within the bounds of the AWS provided definitions of "discontinuity", "defect", and "flaw" to say that a discontinuity is NOT always tolerated.  BECAUSE, as you stated indirectly, all welds have discontinuities to various degrees.  Discontinuity and flaw go together according to A3.0 in that a flaw is an undesirable discontinuity.  It does not say it is a defect or rejectable.  A defect is a rejectable discontinuity.  Now, you have to go to A3.0 and D1.1 references mentioned above to make that association and it obviously only applies to D1.1 application.  Other codes and their sponsoring organizations may define them diffferently. 

So, when a discontinuity is beyond the perameters of the Acceptance criteria of whichever code, in this case D1.1, Table 6.1, it becomes a Rejectable Defect/Discontinuity.  If it is within the Acceptable tolerances of the code then it is an Acceptable Flaw/Discontinuity.

How can a Discontinuity be ALWAYS tolerated if they MUST be repaired when they pass the Acceptable tolerances of the applicable code?  Now, maybe the emphasis here should be more on the word "tolerated"?  That may not have been the correct way to express the application of all the other words.  I used it because the Professor had used it without thinking about it.  So, they would ALWAYS be tolerated, but they still must be repaired when they are not acceptable.  I can go along with that.  Every word becomes important in how we use it.

Thank you for your input.

Have a Great Day,  Brent
Parent - - By CWI555 (*****) Date 07-25-2012 15:58 Edited 07-25-2012 16:09
How can a Discontinuity be ALWAYS tolerated if they MUST be repaired when they pass the Acceptable tolerances of the applicable code?

If they pass the acceptance criteria, they are acceptable and therefore do not go into the realm of reject/defect. 
No offense, but I am having a hard time grasping why one would repair an acceptable weld to begin with?

My take on the subject crosses various codes. In order of increasing severity;

Discontinuity; Break in normal physical structure
Indication; Discontinuity of a size detectable to the examination medium, but below the recordable threshhold.
Flaw; Indication that exceeds the minimum recordable size, but stays under the minimum rejectable size.
Reject/Defect; A flaw that exceeds the maximum size deemed acceptable by the governing code/engineering specification.

Regards,
Gerald
Parent - - By jwright650 (*****) Date 07-25-2012 16:38
I'm not taking a particular side in this discussion, however I was taught early in my inspection career VVVV this VVVV:

>Discontinuity; Break in normal physical structure
>Indication; Discontinuity of a size detectable to the examination medium, but below the recordable threshhold.
>Flaw; Indication that exceeds the minimum recordable size, but stays under the minimum rejectable size.
>Reject/Defect; A flaw that exceeds the maximum size deemed acceptable by the governing code/engineering specification.

Parent - - By Lawrence (*****) Date 07-25-2012 18:07
Interesting thread..

Would you guys please hurry up and come to an agreement so that I can give my fall semester students the proper language

Heh
Parent - By TAC (*) Date 07-25-2012 21:47 Edited 07-25-2012 22:17
That's right Lawrence, we must teach them to properly deposit these discontinuities. :lol:
Parent - By welderbrent (*****) Date 07-25-2012 21:26 Edited 07-25-2012 21:29
Gerald,

Boy this time I really used the wrong word.  When I said "pass" I meant they exceeded or 'went past' the criteria that put them into the 'rejectable' area of the table.  I did not mean that by 'passing' they were acceptable.  So, I agree with you, you (nor I, nor any one else) would want to repair an acceptable discontinuity.

I haven't finished reading Al's addition here, but I just put this newest word misunderstanding together and thought I should clarify my last post. 

And as to your definitions/explanations at the bottom of your post, I agree.

Come on Lawrence, we all know you don't need Gerald and I to reach an agreement in order for you to be able to teach.

Have a Great Day, Brent

Edit: Great addition and examples Al.  Thanks.
Parent - - By G.S.Crisi (****) Date 07-27-2012 15:37
Brent,
You say that "Rejectable discontinuities are also termed defects ....". This is exactly what I said in my first posting, so we agree.
Giovanni S. Crisi
Parent - By welderbrent (*****) Date 07-27-2012 16:54
Mostly you are right Professor.  It is just that 'Defects' are also 'Discontinuities'.  I felt the point you made needed a little more clarification.  I wasn't totally DISAGREEING with you, just clarifying the terminology.

Have a Great Day,  Brent
- - By 803056 (*****) Date 07-25-2012 18:24 Edited 07-26-2012 00:20
While the following may not be a technical correct differentiation between a discontinuity and a defect, it should suffice for our purposes.

A discontinuity is an interruption in the normal structure of a material.

A defect is a discontinuity that by nature of its size, location, or frequency causes it to be unacceptable, i.e., it does not comply with the applicable acceptance criteria.

A discontinuity can occur at the atomic level, i.e., a vacancy, a slip dislocation, grain boundaries, etc. or on a microscopic scale, such as a segregation, in-homogeneity, small liquation crack, micro fissure, a small hydrogen crack, etc. or it can be on the macroscopic scale such as undercut, overlap, porosity, incomplete fusion, etc.

Once the discontinuity no longer meets the appropriate acceptance criteria, it is classified as a defect which may result in the part or component being scrapped or repaired. The decision to scrap or repair is usually left to the manufacturer's discretion.

An indication results from the change caused by the discontinuity when it interacts with the probing medium (energy) of a NDT method. Examples of indications include: a visual indication of a crack is a black line caused by light entering the crevasse and not being reflected toward the inspector. A magnetic particle indication is the accumulation of magnetic particles attracted to the site where there is flux leakage due to a crack or other discontinuity. An indication is the stain that appears as liquid penetrant seeps out of an open discontinuity.

Best regards – Al
Parent - - By Lawrence (*****) Date 07-26-2012 00:15
Atomic discontinuities!!!!!!!!!!!!!!!!

Give us more Al

MORE!
Parent - - By 803056 (*****) Date 07-26-2012 00:28
You like that huh?

Just think of the strengthening mechanism of an alloy system. The interstitial and substitution solid solutions distort the lattice thereby strengthen the base metal. Precipitation hardened alloy systems utilize the clumping of the alloying constituents within the lattice to distort the lattice to strengthen it. The pile-up of precipitates reduce slip to resist creep and plastic deformation.

We depend on discontinuities. They are not always a bad thing.

Al
Parent - - By ssbn727 (*****) Date 07-26-2012 07:39
True that!

Another important factor is determining the amount of the precipitates being piled up as well as where they are piling up...
Because we don't want too many interstitial compounds/alloys piling up and more empty spaces forming in the metal lattice...
So we have to know what these interstices are made of in order to determine the size of the "holes" which are determined by the size of the interstices small atoms which are usually made up of: hydrogen, carbon, nitrogen and boron.

So an interstitial compound or alloy is a compound that is formed when an atom of sufficiently small radius sits in an interstitial "hole" in a metal lattice.

And that is a very tired attempt to describe some "atomic" discontinuities... I'm going to sleep already!!! Insomnia stinks!!!

Respectfully,
Henry
Parent - - By 803056 (*****) Date 07-26-2012 21:03
Those pesky little atoms!

Al :grin:
Parent - - By ssbn727 (*****) Date 07-26-2012 22:10
Hi Al!

That was a really good write up in inspection trends!!!
They sure are pesky little "Hagg" phases indeed!:razz::yell::fat::twisted::confused::lol::wink::cool:

An interstitial element is an impurity found in "pure" metals. The quantity of these elements affect the physical properties of the metal.
They can be introduced during the manufacturing process.

The most common interstitial elements are Hydrogen, Carbon, Nitrogen, and Oxygen (I forgot to include Oxygen in the previous post).
These elements are small enough to fit between normal crystalline lattice locations.
In contrast, elements that replace locations within the crystalline structure are called substitutional elements.

An example of the effects of interstitial elements can be found in Grade 1 through 4 titanium. Although the grades 1 through 4 are
considered commercially pure, they have varying tensile strengths as well as other different properties.
These differences are caused by the amount of interstitial elements present in the titanium.

respectfully,
Henry
Parent - - By 803056 (*****) Date 07-26-2012 23:55
Don't stop now. You're just getting to the good stuff!

Thanks Henry. It always good to hear someone is reading the stuff I write.

How are you feeling these days?  I hope all is good.

Best regards - Al
Parent - - By ssbn727 (*****) Date 07-27-2012 03:54
I'm still on O2 24/7, still weak, still cantankerous towards mostly people I don't know...
My Kidney function is way better as are my blood counts and the funny thing about this episode is that the liver was totally unaffected...

I'm still in very acute pain and the drugs are only masking the pain until they wear off and that always happens 15 minutes before my next dose.
I'm starting to get around better as I no longer need to use the walker and that alone is tremendous progress in my book!

Pretty soon I'll be able to write more frequently as my home care folks finish re-arranging my office area so I can sit there in comfort.

I've got to get in touch with our mutual friend to let him know that I haven't forgotten about the work I owe him.
I just don't have the stamina yet to sit and type long enough before my back starts going bonkers!
Anywho, thanks for asking and please keep giving us the good stuff you write about as well as the bad.

Respectfully,
Henry
Parent - By welderbrent (*****) Date 07-27-2012 04:03
Well, I'm glad Al asked and thank you for the update Henry.  Good to know.

You are still on my prayer list though.

Have a Great Day,  Brent
Parent - By jwright650 (*****) Date 07-27-2012 14:14
Henry,

Good to see you back and hopefully you'll be with us on a more frequent basis. Get well soon brother.
Parent - By G.S.Crisi (****) Date 07-27-2012 15:48
Welcome back, Henry!!
We're all happy to see you in this Forum again!! May I ask you exactly what sickness have you had?
Giovanni S. Crisi
- By 803056 (*****) Date 07-27-2012 19:50
Hello Henry;

It is good to hear from you, and better yet that you are doing much better.

Best regards - Al
Up Topic Welding Industry / Inspection & Qualification / Repair of Discontinuities

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