Worm Tracks

By Lawrence (*****)

Date 12-11-2016 02:02

Piping porosity is the only type of porosity that AWS D1.1 discusses in regard to acceptance criteria.

Porosity is not mentioned at all in the acceptance criteria for performance qualification.

Table 6.1 goes to some length to be clear that piping porosity is the only type of porosity that may be rejectable, and even those limitationsare liberal.

So to answer your question directly, No it is not correct to reject for the visual as you describe it.

If you wish to exceed the code, there is nothing wrong with that. So long as you present your critique to the Welders ahead of the testing.

By MalRD

Date 12-11-2016 17:31

Remember that there are two sections now 6 and 9 now that tubular has been separated, and yes 6.1 only notes piping porosity... Clause 9 contains Table 9.16 which is the tubular equivalent of 6.1

And yes i concur, piping porosity is all that is discussed regarding visual none macro inspection, they do mention porosity with size limitations for porosity other than just piping porosity in 9.22.1.1 e for macroetch test plates, but i digress.

But i guess the heart of my question would relate to whether "worm tracks" should be classified as porosity at all, and if so, given their shape, long and tubular would they fall into the category of piping porosity? Are they lines of holes on the surface denoting a possible void internally, no. But it does have the shape and form albeit on the surface of the weld, trapped between the slag and weld metal leaving the lower section of the void on the top of the weld face.

I can see how Lincoln call it a surface blemish rather than a discontinuity as at first sight it has no internal structure, and yes i know that exceeding the code is within any inspector or company/owners right I have seem many jobs that because of the cosmetic nature of the product note "No surface defects or any kind are allowable".

Yes all welders performing the test are informed prior to taking the test what is acceptable and not acceptable, I am in education so we are talking about the people testing are college students finishing off units we make sure they understand the requirements.

Lastly, I happen to agree with your assessment regarding rejecting for visual, my colleagues however do not and the last thing we want to have in a department is inspectors disagreeing regarding the code, so I adhere to the agreed criteria, but it doesn't mean i have to like it lol

By thirdeye (***)

Date 12-11-2016 17:31

I would agree with Lawrence's comments, especially the one about opting for a stricter company policy under certain circumstances.... in this case worm tracks. The examples I normally see not only have the track itself, but they generally have a pore at one end. A tip cleaner wire inserted into the pore can disclose a depth of 1/8" or more, so I look at that as a criteria for rejection as well. Even without the pore worm tracks telegraph a bad message to the end buyer and might imply that the shop lacks quality control and pride in their work. They really show up when painted, so all of my customers will opt to repair.

By welderbrent (*****)

Date 12-11-2016 18:37

MalRD,

I applaud your institutions desire to instill the highest possible quality in the students being taught there.

But, lets not cause misinformation in the application of the applicable code. This is where people have problems then in the REAL world. They get their signals crossed and tell others, 'you can't do that' or 'you can't leave that like that' when in truth there is nothing wrong with it.

Aesthetic or cosmetic, known also as Architecturally Exposed, members and applications are not that common compared to the standard interpretation of the structural codes.

So, to your specific query: No, that is not a porosity issue that needs to be dealt with under normal circumstances though the minute it is noted it can generally be handled fast and easy; turn down the volts or turn the wire feed speed up (an either/or situation) usually takes care of it though on occasion it is a cleanliness issue with paints, anti-spatter, or other contaminants being the cause.

When comparing A3.0, B1.10, B1.11, D1.1, WIT, and other references it is discovered that piping porosity is longer than its width and for a good example is from a lower surface extending to the weld face. This is real easy to envision with fillet welds as it extends from the root up to the weld face and is approximately perpendicular to the weld face or a 90° angle through the weld. That is not at all the result gotten with "worm tracks". Porosity, under all definitions, is cylindrical/spherical in shape not longitudinal on the surface of the weld.

Using thirdeye's example with the small porosity at the one end shows a small porosity hole with a worm track. If there were enough holes within the prescribed length of weld to add up to the rejectable total then you would have something. But, not as it stands.

It is an appearance discontinuity that may be used to fine tune one's welding parameters but is not rejectable per D1.1.

He Is In Control, Have a Great Day, Brent

By MalRD

Date 12-11-2016 22:21

Thank you Brent for the clarification, we believe it is an issue of wrong standoff distance and or moisture possibly in the wires flux, but probably the former as we control our wires and rods well and to code.

So going back to my original post, its more to the point that its "on" not "In" the weld, and yes if there were sufficient pores in the worm track it would disqualify it should they exceed permissible limits as per code.

Personally, i agree with everything that has been stated so far, I would also add as a caveat that the only time i would consider the worm tracks to be worthy of failing a weld coupon is if their depth on a shallow crowned reinforcement fell below the base materials surface line therefore thinning the section at the center of the weld, and then i would consider it under-fill, not porosity.

Now Porosity, as defined in Annex J is "Cavity-type discontinuities formed by gas entrapment during solidification", which is what worm tracks are... but again I agree porosity to me has always been holes in the weld face formed from inside the weld (mainly roots) and appearing on the surface, I will leave it as that solely because i am talking about visual inspection, but i am fully aware of the UT and RT tables that define other parameters and limits ( Table 6.2 etc.)

Thank you all for your great input, I just wish as i stated at my recent CWI re certification class that we had a hotline number to AWS to a help desk where they could answer questions like this that are not fully addressed in the code, after all it would give the committees a good direction to work towards when looking at what needs to be revised or covered in more detail in future editions :)

By welderbrent (*****)

Date 12-12-2016 00:28

Three points:
1) There is a "Hotline" of sorts. At least there used to be. It isn't listed like it used to be on the Services page with names and contact info for different staff personnel. There used to be one for someone who would answer questions but the answer was not to be considered as the final authority. You still needed to go through the committee to get a technical inquiry response for it to be final.

2) I tend to disagree with your statement that worm tracks are formed according to the definition of porosity. The texts of the various references all make it pretty clear that we are dealing with gas entrapped and/or attempting to escape THROUGH the weld metal. Those gasses which have succeeded in escaping the weld metal but are still trapped under already solidifying slag are the culprits for the gas tracks/worm tracks but as they are not through the weld they do not fit the definitions given. They do not run 'perpendicular' to the weld face. Different FCAW slags solidify at different rates. Some actually start hardening before the weld has solidified enough to trap gas so the gas is trapped between the weld pool and the slag which causes these pockets.

At least, that's my opinion.

3) Your consideration of CTWD is a good direction. Lawrence recently put some information together in a great post detailing how that distance was critical to proper moisture dispersal prior to actual weld metal deposit. Too much or too little work distance definitely contributes to discontinuities.

BTW, you do know that the seismic codes limit electrode atmospheric exposure for FCAW? A couple of days as I remember. D1.1 doesn't deal with it except to direct user to the manufacturer's recommended practice.

He Is In Control, Have a Great Day, Brent

By MalRD

Date 12-12-2016 03:02

1) Hmmm, I did hear that.... but then I could not find a number for it, so I assumed it had either been removed or for some reason it was for select people. However, without it being a definitive answer we might as well just ask the opinions of experienced CWI's in a forum such as this :)

2) What part didn't you agree with? It was a direct quote from the Annex in AWS D1.1 itself, or was it my defining worm tracks as porosity you didn't agree with? It is a cavity, made by a pocket of gas, which had escaped the weld metal... but yes it was trapped under the slag causing the metal to solidify around it. It technically could under that description be considered porosity, however I personally would not consider it to be as in most cases no holes are present, just a groove. Ive always considered porosity to be the holes in the weld, like the gas escaping from a thermal vent in a volcano leaves lava tubes, so worm holes fit the aws definition as they were formed by trapped gas, but its why I asked in my original question what you guys considered them to be, so thank you for your opinion ;)

3) We also use a 75/25 mix for dual shield that could also contribute as it is run off the manifold system at the college, so CO2 would also possibly fix the problem, but i think in our case its welder error as these guys are just learning, and other students can use it fine providing they use the recommended CTWD as defined in the manufacturers instructions. Point to note is that they do vary, as does the flux from manufacture to manufacturer, some are prone to absorbing moisture more, and yes there were a number of CWI's at the re-certification course i recently attended who work in Cali and were quite versed in the seizmic codes and i did hear of one guy in particular who had to build an oven to keep his wire in, I never did ask him how he dealt with the plastic of wooden spools lol, I suppose it has to be a consideration when selecting wire in the first place... Do i need to heat it in an oven so what type of spool does it come on ;)

Thank you all for your comments

By welderbrent (*****)

Date 12-12-2016 05:16

If you are using a 71T-1C you use CO2, If you are using a 71T-1M you use mixed gas, 75/25.

By Lawrence (*****)

Date 12-12-2016 12:42

Our conversation seems to have drifted down two paths (not a bad thing)

1. Is surface porosity allowable in a D1.1 inspection (if you care to define worm tracks as porosity)

2. What is the cause of worm tracks and how to make them go away.

The answer as related to #1 I think has been covered pretty well, but for added emphasis a reference to The Official Book of D1.1 Interpretations (second revision) tries to settle the matter fairly briefly.

By 803056

Date 12-12-2016 17:35

If one looks in AWS B1.11, the discontinuity we are discussing is call elongated porosity. As a matter of fact, the new edition of B1.11 includes the photograph Thirdeye was generous enough to contribute.

Best regards - Al

By 52757

Date 12-12-2016 21:24

Probably a silly question Al, but wouldn't the sharper edges of the "track" also possibly be a stress riser?

By 803056

Date 12-12-2016 22:04

It isn't the top edge that is an issue. The concern would be for any sharp notches at the bottom of the discontinuity (think "crack like") or if it represents a substantial loss of cross section.

If the elongated porosity is on the order of 1/32 inch deep by about 1/16 inch wide, it doesn't represent a substantial loss of cross section if the weld is larger than let's say 1/4 inch. That would represent a loss of cross section on the order of 0.0015 square inches or about 5% of the weld cross section for a 1/4 inch fillet weld.

The bottom of the elongated porosity is round, so it isn't a serious stress riser.

The elongated porosity might be classified as an ugly artifact, but it isn't an attribute to be evaluated if D1.1 is the governing code.

Al

By 803056

Date 12-13-2016 17:50

Nice catch, but I was responding to the question regarding "elongated porosity" versus the nonstandard term "chicken or worm tracks". Just to pull my britches up from my ankles a bit.

Al :wink:

By MalRD

Date 12-13-2016 05:38

I would add one more thing into the mix... remember that these are students who are doing certification plates, this isn't production welding (regarding the inspection I mean) It's clause 4 Qualification Part C which references the visual inspection criteria of 4.9.1, not 6.1.

By Lawrence (*****)

Date 12-13-2016 12:27

Agreed Mal, Performance quals have their own inspection criteria lined out as you say. I hinted at that in my initial response while in the very next line mentioning 6.1. So my fault for making the water muddy.

I will say this; When acceptable surface breaking porosity in a weld test assembly is accepted and further examination is done in the form of guided bends, that porosity will often be the point where rejectable defects propagate. Or in the case an assembly passes Visual and then is subjected to RT, a different set of criteria is then placed on internal porosity that may be linked to what breaks the surface.

In any case... D1.1 is very liberal in it's treatment of porosity.

By 803056

Date 12-13-2016 17:54

ASME Section IX doesn't address porosity at all. Nor does it address attributes like face reinforcement, root reinforcement, undercut, overlap, to name a few. As a matter of fact, there is no requirement in Section IX that prohibits the welder from welding a pipe such that a fart couldn't pass from one end to the other. All good!

Best regards - Al

By thirdeye (***)

Date 12-13-2016 19:13

When discussing porosity or undercut under Section IX, Authorized Inspection and National Board auditors often have a response along the lines of "...Section IX is a testing code, unlike Section VIII which is a production code".

Slightly off subject here but I believe the glossary in Section IX does list a definition for undercut, even though the code does not address it. And Section VIII, Div 1 does not explicitly address weld undercut. However, look at UW-35, it mentions a reduction in thickness due to welding and I recall that can not exceed 1/32" or 10% of the wall thickness, whichever is less, so this would imply internal or external undercut. Section VIII Div. 1 really gets some yardage with the term "rounded indications", as they can be slag, tungsten inclusions or porosity.

By 803056

Date 12-13-2016 20:43

Very true Thirdeye. That's why I ask the contractor what construction code they are welding to. I base my visual criteria on the construction and and I list the construction code on the performance test report.

Justification? Do I need to justify my actions. Section IX lists the minimum criteria. My clients and I opt to take a conservative approach to ensure the welder can meet production requirements.

Just my opinion.

Al

By MalRD

Date 12-13-2016 17:58

That it is Lawrence, that it is... and i agree, any underlying problems will expose themselves on inspection of the guided test coupons or on the test itself.