Porosity

Date 06-02-2010 06:51

May be you can try to use RT...if that equipment is very dangerous.
or you can use a subsurface Magnetic Examination.

regards

By js55

Date 06-02-2010 12:06

Shane,
'Normal' is essentially perpendicular to the weld surface.
This piping porosity thing has always been a problem. Somehow I suspect the terminological loophole has a history.
I do believe it should say just porosity or maybe segregate the two if piping porosity is of some specific concern.
However, I also believe the code guys know exactly what they intend, and that they intend 'piping' porosity as defined, although almost everyone I know of interprets it as just plain porosity.
An argument I would have is that technically speaking there is no criteria for porosity as we commonly know it in AWS D1.1 and that a weld reject for porosity has no code basis, though I do it all the time.

By jwright650 (*****)

Date 06-02-2010 12:11 Edited 06-02-2010 12:23

"'Normal' is essentially perpendicular to the weld surface. "-quote

Jeff, shouldn't that read.... " parallel to the weld surface"...?<----forget I said this, read below.

EDIT:
OK....I think the term is a bit mis-leading...after looking at the definitions again, I agree with Jeff....C-Table 6.1 Item 8(page 483 in 2008) describes the situation and also references Annex K.

After looking at Annex K,..... Piping porosity is different than elongated piping porosity.

Piping porosity is PERPENDICULAR to the weld surface,
.....while Elongated piping porosity is PARALLEL to the weld surface.

Clear as mud?

By 803056

Date 06-02-2010 13:10

Porosity is any gas filled void. Spherical porosity is fairly innocuous to the strength of a weld. However, piping porosity is a different story. It has length that is perpendicular to the face of the weld and reduces the cross sectional area of the weld. The amount of piping porosity that breaks the surface of the weld is a fraction of the porosity that is subsurface.

Spherical porosity typically occurs at the start of a weld because there is insufficient shielding of the molten weld puddle. Likewise, the crater can have porosity if insufficient shielding is provided (thick of GMAW without post gas flow or GTAW when the welder pulls the torch away before the weld crater has cooled).

Piping porosity is often associated with surface contamination or moisture between two members. The porosity forms at the liquid solid interface where the solubility of the dissolved gas is suddenly reduced. The interface is "mushy" and the gas bubble leaves an elongated void as it works its way to the surface of the weld bead.

While I am no fan of porosity of any kind, the code committee apparently is of the mind that spherical porosity is not a major concern for structural applications. As mentioned already, the visual acceptance criterion only addresses piping porosity and not spherical or elongated porosity. I usually include criteria for elongated and spherical porosity in the project specification and as a drawing note when given an opportunity before the job is put out to bid. If I am tasked with developing the welding procedures for the project, I take exception to the visual criteria of D1.1 and include criteria for spherical and elongated porosity in the WPS.

Here is a twist for you. AWS D1.1 states the contractor is responsible to develop WPSs for the work, but the engineers I work with typically have me develop the WPSs for the project. The engineer for the project I am currently working on, a retrofit entailing considerable field welding and some shop welding, has had me develop WPSs for each type of weld joint as the work has progressed. This is being done to ensure the contractor does exactly what the engineer wants them to do. Even when the work entails simple fillet welds, my WPS has to include the actual joint with the individual members shown. The WPS is provided as part of the drawing package, an extension of the drawings. We have used this process for several recent projects and it works very nicely. The contractor is happy to receive the direction and the engineer is confident the welds are done the way he expects them to be done. Oversight is provided to ensure the WPS is followed. The engineer's position is that it is a waste of time and money going through several revisions of the contractor's WPS until they provide stumble upon one that satisfies his concerns.

Best regards - Al

By jwright650 (*****)

Date 06-02-2010 13:28 Edited 06-02-2010 13:31

Al,
Take a look at Annex K.....it only mentions piping porosity(two kinds)
1. Piping porosity.
2. Elongated piping porosity.

It give definitions for both...never mentions spherical porosity at all....which baffles me.

edit: BTW, AWS A3.0:2010 is of no help here.....

By Shane Feder (****)

Date 06-02-2010 13:57

Guys,
Thanks for the response but I am no closer to an answer.
The commentary (at home so cannot quote section) of AWS D1.1 states that surface breaking "piping porosity" is considered detrimental to a welds strength but other types of surface breaking porosity are considered less detrimental.
I am sorry but that is a load of hogwash !
1 Does less detrimental mean it is acceptable or not ?
2 There is no mention (please correct me if I am wrong) in AWS D1.1 Table 6.1 of cluster porosity or elongated porosity (AWS terminology) so does that mean they are acceptable or not ?
3 If the body of the "void" is below the surface how can you possibly tell with VT whether its length is longer than its width and therefore it is piping porosity or the length is less than the width and it is classed as "other" which apparently is acceptable.

My issue is I am in Thailand looking after a subcontractor and the client has appointed an over enthusiastic Thai third party inspector.
He is making an issue over isolated gas pores and while I agree that GPs do not look aesthetically pleasing I cannot hammer the sub contractor if a singular pore is deemed acceptable to the code.
I have no problem with the subcontractor touching up the welding at our modularisation yard but he is refusing to release from the workshop a 30 - 40 ton module that has 3 or 4 gas pores in hundreds of metres of welding.

Any help greatly appreciated,
Regards,
Shane

By js55

Date 06-02-2010 14:43

Shane,
MY course of action at this time would be to contact the client and explain to him the problem with his own inspector and that there is no basis for rejection. If the inspector is going to insist upon rejection then perhaps additional costs should be involved. Costs ususally gets the clients attention.

By 803056

Date 06-02-2010 13:57 Edited 06-02-2010 14:02

Hello John;

Annex K only includes definition pertinent to AWS D1.1. Spherical or rounded porosity is not an issue, so it would not be included in Annex K.

You can look at AWS B1.10 Guide for the Nondestructive Examination of Welds under the heading of Porosity. They differentiate between spherical porosity and elongated porosity (both surface and piping). However, the level of detail is scant. After all, B1.10 is a guide.

AWS B1.11 is a guide for visual examination. There is a new revision due shortly (in AWS terms, which is similar to talking about geological time). Again, the level of detail may be wanting. I chair the subcommittee that will be revising B1.11 for the next release due in 2015. I will keep this discussion in mind so the subject can be included in the next release. I took over the committee after the major changes had already been made, so there were limitations to what additional materials could be added or revised for the 2010 release. I hope to break new ground with the 2015 release.

Back to Shane's question, porosity that isn't included in the definition of piping porosity is acceptable, i.e., there is no basis of rejecting it utilizing the criteria provided by AWS D1.1. B1.11 can be used to arbitrate the nature of the porosity if there is a question of being piping porosity or an other type of porosity.

Best regards - Al

By jwright650 (*****)

Date 06-02-2010 14:13

LOL...now I am really confused......LOL...no surprise there.

quote by Al..."Annex K only includes definition pertinent to AWS D1.1. Spherical or rounded porosity is not an issue, so it would not be included in Annex K."...end quote

Unless I missed something, Shane is working to AWS D1.1 and as Shane (and I) mentioned earlier...AWS A3.0 is of no help either.

The words...."spherical" or "cluster"...describing porosity are never mentioned in either AWS D1.1:2008 Annex K or AWS A3.0:2010.

"piping" is the only description for porosity that I saw and it describes that in two ways: parallel and perpendicular to weld surface

By 803056

Date 06-02-2010 14:29

If the porosity is elongated, i.e., located on the surface and parallel to the axis of the weld, it is acceptable per D1.1.

If the porosity is elongated and the axis of the porosity is perpendicular to the weld face, it is rejected per D1.1.

Porosity that is neither elongated or classified as piping is a "non-issue" per D1.1 and cannot be rejected based on the criteria provided by D1.1 if visual examination is the only method specified.

A corollary to this situation is undercut when working with ASME Section VIII. There are no criteria for undercut in Section VIII, as a matter of fact; the word undercut does not exist in Section VIII. You cannot reject a weld because of undercut. You can say the weld is rejected because of material thinning, but not because of undercut.

Acceptance or rejection is based on the criteria provided by the applicable welding standard. Remember the AWS CWI review; the inspector does not formulate inspection criteria. The inspector simply verifies the work complies or does not comply with the criteria provided to him.

Best regards - Al

By Joey

Date 06-02-2010 14:57 Edited 06-02-2010 16:00

"A corollary to this situation is undercut when working with ASME Section VIII. There are no criteria for undercut in Section VIII, as a matter of fact; the word undercut does not exist in Section VIII."

Are you sure :) ?

Best Regards
Joey

here are the clues that can be found in Section VIII ;

1. Weld Quality – If a defect exists at the toe of a weld that can be characterized as a crack-like flaw, i.e.
undercut, and this defect exceeds the value permitted by Part 7, then a reduction in fatigue life shall
calculated by substituting the value of I1 mss in Equation (5.76) with the value given by Equation (5.76). In
this equation, a is the depth of the crack-like flaw at the weld toe. Equation (5.76) is valid only
when a t ≤ 0.1.

2. (the word undercut does not exist?) it states.... r = the radius of the undercut

By 803056

Date 06-02-2010 16:57

Hello Joey;

You are going to have to provide more than a hint. What clause are you quoting from?

Al

By Joey

Date 06-03-2010 05:31

Al

I’ve no argument except to say that the word undercut is indeed can be found in ASME VIII. I do remember that I read it somewhere in ASME VIII but my codes at home are old edition and might give you the wrong clauses.

Now that I’m in the office and have checked the 2007 ed in the company library, I’m pleased to provide you the following clauses.

Div 1 ---- 2-12 (a) (1)

Div 2 ---- 5.5.5.3 (b) ; Fig 6.2 and Table 7.6 (6)

Div 3 ---- E-200

:) Joey

By 803056

Date 06-03-2010 20:52

OK, I'm looking at the Division 1, Section VIII w/ 2003 addenda. All the clauses have prefix letters, i.e., UG, UW, etc.

Granted, it is a bit dated. Has the numbering system changed?

Best regards - Al

By Shane Feder (****)

Date 06-02-2010 14:46

John / Al / Jeff,
Thank you for your responses but I am still lost.
AWS D1.1 Table 6.1 (8) states you cannot have any visible "piping porosity" ........ in certain CJP welds.
If you have a tiny pinhole at the surface of a CJP weld how can you possibly tell the size/shape of the void connected to that "pinhole" that is subsurface without RT or UT ?
Is it piping porosity (unacceptable) or spherical porosity (apparently acceptable) ?

Now I know why I drink so much. LOL !!
Regards,
Shane

By mroach

Date 06-02-2010 15:48

Shane, That statement only applies to 8 (A) & (C) depending on the type of connection. Take a look at the general notes regarding the shaded areas. You are right, there is no way of knowing the diameter or length of what is subsurface by visual inspection alone. Even with MT or PT testing the evaluation must comply with the visual acceptance criteria of table 6.1. Distance, size and frequency seem to be the only concern. Depending on the type of connection the porosity may not even be an issue. It might not look good but by code it may be perfectly acceptable. MR

By js55

Date 06-02-2010 19:40 Edited 06-02-2010 19:42

My best arguments I canmuster are (assuming what I believe is your position, in that you dispute the rejectability) that sometimes there is an angular appearance to the porosity that could indicate the piping type. This happens frequently with the SAW flux moisture/nitrogen/flux burden generated porosity.
Another approach would be that if the TPI is arguing its rejectability it is then incumbant upon HIM to prove his case. If you can't see it, he can't either.
If only visible inspection is required and you can't determine that its piping porosity then it isn't piping porosity. You are not required to enhance the examination to determine the nature of the porosity.

By 803056

Date 06-02-2010 20:42 Edited 06-02-2010 21:17

There is nothing stopping you from inserting a small diameter wire in to the hole to determine if there is "depth" to the porosity. The analogy I would offer is it is no different than using a fillet gage to measure the size of a fillet weld.

If it has depth that is a multiple of the diameter, it is piping porosity and has to be evaluated. If it is shallow, it is spherical until it is determined by exploration to be something different.

If the TPI wants to explore the condition it is at his expense if it turns out to be anything other than piping porosity. The contractor pays the cost of the repair if it turns out to be piping porosity.

There may be a few questions asked before he makes such a call again when the TPI’s employer receives a bill for unnecessary repairs.

There are times when I have requested the contractor to do some grinding to allow me to better assess certain conditions. An example would be when I notice the contractor isn’t using extension tabs (run-off tabs) at the ends of the groove welds. A quick touch of the grinder usually reveals incomplete fusion at the ends of the groove. If I am wrong and the welds look good I am allowed to eat a few crow feathers. If I am correct, the contractor gets the opportunity to repair all the groove welds.

Al

By js55

Date 06-02-2010 21:03

I had forgotten the wire method. That would work well.
Been doing this long Al?

By 803056

Date 06-02-2010 21:16

I've been poking things into holes for as long as I can remember!

Al ;)

By Shane Feder (****)

Date 06-03-2010 00:01

Thanks guys,
Al - great idea and I will give it a try today.
Oxy / acetylene tip cleaners should work perfectly.
Cheers,
Shane

By 803056

Date 06-03-2010 03:27

Perfect!

Al

By kipman

Date 06-03-2010 21:36

Take my advice and don't use tip cleaners. I used to use that method and once found some piping porosity that was rejectable. Of course you can imagine there was alot of "no way" and "prove it". So I whipped out the tip cleaner and jammed it in there, and of course the welder was convinced that with that tip cleaner I had reamed out the porosity until it was >1/32 inch in diameter. I only use smooth wire now.
Mankenberg

By js55

Date 06-04-2010 11:21

Hopefully wth more than a tip cleaner. :)

By CWI555

Date 06-03-2010 16:41

Lets see if I can get this pdf attached.

Attachment: AWSPorosity.pdf (359k)

By mroach

Date 06-03-2010 17:54

Thanks CW1555, This helps a lot. If I have this right it is by the definition of what "piping porosity" is that opens the door for the inspector to further evaluate a suspect indication by what ever means that is available. Even though the code nowhere specifies "verify by inserting a small diameter wire to determine length" if the inspector determines that the length exceeds the diameter in some cases even a single indication may be rejectable. MR

By CWI555

Date 06-03-2010 20:23 Edited 06-14-2010 22:52

No, not by whatever means is available. Whatever means implies grinding etc. A better phrasing would be reasonable means. There is no prohibition to using a wire to verify the nature of a porosity. Do keep in mind that the opening size criteria should be meet first before you bother sticking in a wire.

Regards,
Gerald

By Superflux (****)

Date 06-10-2010 00:25 Edited 06-10-2010 00:28

For the 1/32" porosity gage, I've always use .035 GMAW wire. Yes, It Is .004 oversized so some .034, .033 and even a couple of .032 holes may have slipped by me, but the price is right. Cut the end diagonally for a needle sharp point.