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Up Topic Welding Industry / General Welding Discussion / Arc Marks
- - By PipeIt (**) Date 02-13-2009 19:47 Edited 02-14-2009 12:23
Its my understanding that arc marks fracture the metal and de-rate the structural significance of the piping by destroying the metallurgical structure or something like that.

I was somewhat uneducated on what arc marks do/cause until I started reading posts on this site. I've always known you can bust a test because of them.

My question is what about when you weld a pad eye or a d-ring on a piece of pipe, should that technically be a no no?
Parent - By Lawrence (*****) Date 02-13-2009 20:06
The short answer is that attachments to pipes also require engineering controls and approved procedures.
Parent - - By johnnyh (***) Date 02-13-2009 20:09
Technically yes.
Parent - - By scrappywelds (***) Date 02-14-2009 00:48
IN MY OPINION AND FROM WHAT I HAVE SEEN, ARC MARKS ARE MADE OUT TO BE ALOT MORE THAN THEY ARE. MY REASON FOR SAYING THAT IS I HAVE SEEN .150 WALL TUBES RUNNING PRESSURE OF 2500 PSI WITH 50 YEAR OLD ARC MARKS.  BUT OFCOURSE I COULD BE HORRIBLELY WRONG.  IN THE POWER BOILER BUISNESS YOU TRY NOT TO MAKE AN ARC MARK, BUT SOMETIMES IT HAPPENS DRRESS IT DOWN AND GO ON.
Parent - - By DaveBoyer (*****) Date 02-14-2009 01:45
It is a bigger NO NO in some materials than others.
Parent - By Superflux (****) Date 02-14-2009 02:54 Edited 02-14-2009 03:03
Weld and welding related defects/discontinuities leading to failures... It is usually not one but a series of often unrelated problems that cause catastrophies.
Missmatching components, improper filler materials (who was it that suggests using S/S to avoid porosity???), I've seen stuff globbed together and placed in severe service environments that held for years. And also the complete opposite scenario holds true. Science and engineering have established materials, processes, designs and techniques that provide repeatable results for us to build sound structures and dependable machines.

      "BUT OFCOURSE I COULD BE HORRIBLELY WRONG"

I doubt the last words from your surgeon you want to hear B4 going under anesthesia is...
"They told us never to do it this way in med school, but in your case I dont care, I feel like bending the rules today. Besides, I've heard of cases in Borneo that survived...Read it somewhere on the internet!".
Parent - - By pipewelder_1999 (****) Date 02-14-2009 05:29
Not to take away from the need to make good quality tube welds but because of the ratio of the wall thickness to diameter a 1" .150 wall tube would be affected less by an arc strike than a 42" Pipe with a .500" wall. A 24" pipe with a similar wall thickness to diameter ratio would have a 2.88" wall thickness.

A boiler tube failure would probably release a significantly less amount of energy than cross country pipeline.

I am not familar with cross country pipeline and have no idea what the operating pressures and temperatures are or even what the common sizes are but I think the possibility of an arc strike causing a failure is probably much higher in pipelines.

I don't have any evidence to support this and maybe the pressures are so low that its the same .
Parent - By pipewelder_1999 (****) Date 02-15-2009 20:44
Speaking with someone familar with the industry he indicated a 16" line with .281 wall could have 1000 PSI. For a 1" .125 wall tube to have a similar level of stress, it would have to have 6800 PSI of pressure in it to have an equivent unit stress.

One thing I am not considering is the allowable stress and at certain temperature. At boiler operating temperatures, the allowable unit stress would be lower than for a something operating up to 600 ish.

It seems that pipelines are running closer to the edge as far as unit stress levels go but I may be wrong
Parent - - By hogan (****) Date 02-16-2009 16:38
scrappywelds,
I have worked with boilers many times in the past. With recovery boiler specifically, I have seen arc strikes that have caused catastrophic failures. No offense and nothing personal, but welders and inspectors have different experiences. I'm sure you have seen 50 year old arc strikes that had no influence on the integrity on the unit, I have as well. As an inspector we are called out when there is a failure. So the things you feel are old wives tales really do happen, maybe you have just not been involved. I have seen super heater loops that split at arc strikes, resulting in unbelievable damage. Tube walls that have blown out due to arc strike.
Parent - - By pipewelder_1999 (****) Date 02-16-2009 18:17
I recently read an interesting book by one of the boiler water chemistry people on boiler tube failures. One of the interesting things I noted was the LACK of failures directly related to welds. I believe the figure was 2%.

For a superheater loop to split, it was more than likely thinned or corroded or somehow operating outside of its allowed parameters.

I worked with a company for a few years that had "emergency Outage" contaracts at a peper milla nd municipal power plant. The only weld related failure I ever noticed was a corner wall tobe window weld t hat leaked and a superheater outlet pipe spoolt that cracked do to incorrect material being welded in.

I'm not saying they don't occur. My experience is somewhat limited however during a 2 or 3 year peiod I was pretty busy in the boiler industry. Sootblower Lances, Fireside corrosion/erosion at smelt spouts, low water conditions etc. Though some may have ben adjacent to a weld, the primary cause was something else.

I have never seen a waterall or superheater or econ or reheat fail due to a weld. That could also be a result of the types of plants I worked in and how maint and repair was done before. I have cut out sume existing tubes with jammed up square groove butt welds that were still kickin in 900 PSI garbage burners.
Parent - - By hogan (****) Date 02-16-2009 19:30
Don't get me wrong, this is not a common occurrence. But it has happened. An unintentional strike when replacing a 6 pack, or in combination with issues inherent in the rolling of tubes(at drum), an unattended stinger makes contact while everyone is focused stabbing tubes in a drum.
On a side note I was involved with one emergency outage due to poor stabbing techniques. These guys had used a pipe wrench for leverage when installing tubes into the mud drum. The teeth of the wrench had indented the inside and outside of the tube at the bend. The outage was due to one location leaking. Upon inspection it was found that approximately 25 of the 200 tubes had this issue. Most in the center rows. This turned out to be a very expensive repair. This boiler was down (unscheduled) for almost a week.
Parent - By pipewelder_1999 (****) Date 02-16-2009 21:25
I have seen tube handling marks ouside the drum but still in the roll open up a little during expanding. An arc strike at this location could probably cause some interesting things. Of course that would be unlikely.
Parent - - By Joe Davidson (**) Date 02-14-2009 05:18 Edited 02-14-2009 06:02
An arc strike cools rapidly creating a high hardness HAZ, this is a brittle area that can cause cracks. If you could see it you would see it looks like a tooth with roots(cracks) running down. I have been told that even if you grind them off they will open up on a bend test. So even for D-rings it could cause the pipe to fail prematurely. I am not an expert, but this is what I have always been told.  Hope it helps. Joe
Parent - - By darren (***) Date 02-14-2009 05:55
there was a good thread on it and i cant remember who but someone posted some bent coupons with only arc strikes on the and they all bust.
Parent - - By PipeIt (**) Date 02-14-2009 12:22
Great feedback and input, this is a great sight with a wealth of knowledge.
Parent - - By 803056 (*****) Date 02-14-2009 22:33
I believe our good friend John Wright was the fellow that told us of the experiment he uses to show the deleterious effects of an arc strike.

Drag the electrode across a piece of 3/8 x 1 1/2 carbon steel bar and subject the area with arc strikes to a bend test.

Most of us are used to using a bend fixture to ASME and AWS requirements. Those that are using a bending fixture to API 1104 requirements may not see the same results. The bend diameter for API is more generous than either ASME or AWS. I believe API 1104 is 1 3/4 inch radius where as AWS/ASME is 3/4 inch radius. A very important difference if you have ever considered using a welder qualified to API on an AWS or ASME project. You might want to check my figures, they're based on my fragile memory and that ain't saying much!

Happy Valentine's Day!

Best regards - Al
Parent - - By darren (***) Date 02-16-2009 07:18
also someone mentioned that they attended a engineers conference and that the result of the conference was that there has never been a catastrophic failure of something or other  (cant remember this part), but the protocol was to continue to treat arc strikes like a critical deficiency.

bend them to code determine if they pass then bend em till they stretch and malform for your own knowledge is the way i like to treat my own coupons.... or my competitors....cause its welders competitive nature that makes us better and why a lot of us enjoy the job.
darren
Parent - - By mpitt (*) Date 02-19-2009 16:48
On the AISC websites Engineering FAQ's they say that "In Statically loaded structures arc strikes need not be removed, unless such removal is required in the contract documents" but for "Cyclically loaded structures arc strikes may result in stress concentrations that would be detrimental to the serviceablility of such structures and should be ground smooth and visually inspected for cracks."

D1.1  states "Cracks or blemishes cause by arc strikes shall be ground to a smooth contour and checked to ensure soundness."

If the  job specs say all welding to be done per AWS D1.1,since D1.1 is mentioned in the job specs, all arc strikes have to be removed and inspected. It does not state if it is to be done visually or some other NDE method.

API 1104  A.5.3 gives accepttable limits for unrepired arc burns. It also states "Arc burns that contain cracks visible to the eye or on conventional radiographs are not covered by this appendix and shall be repaired or removed."
Parent - By hogan (****) Date 02-19-2009 18:49
Typically a structure will not be built to AWS. It will be built to AISC which states all welding will be to AWS.
Parent - By darren (***) Date 02-20-2009 10:07
thank you mpitt
that is a very comprehensive post
darren
Parent - By jwright650 (*****) Date 02-20-2009 14:16
(I would quote paragraph 5.29 from D1.1, but mpitt already has done that)
"D1.1  states "Cracks or blemishes cause by arc strikes shall be ground to a smooth contour and checked to ensure soundness."-quote

AWS D1.1:2008 paragraph C-5.29 Arc strikes result in heating and very rapid cooling. When located outside of the intended weld area, they may  result in hardening or localized cracking, and may serve as potential sites for initiating fracture.

I think these bend tests prove this out...now as an inspector, is it up to me to now prove that this material is sound and safe for use in the structure as is with these arc strikes / drag marks?....I don't think so, therefore when I see it, it gets addressed. I don't want or need the added responsibility of proving that the material is OK "as is" or not.
Parent - - By jwright650 (*****) Date 02-16-2009 12:33
Since others have mentioned my pictures, I'll post them again.
I had a welder lay 5 pieces of 2" wide, 3/8" thick, flat flatbar side by side and then had him drag a E7018 quickly across 4 of these pieces. Then I had him grind lightly on these pieces until he could no longer see his arc strikes. Once he was satisfied that he had fixed his arc strikes, then I bent all 5 of them in my coupon bender for A36 material(including the one without arc strikes).

A36 flat bar with arc strikes, ground out to the welder's saticfaction and then bent in a coupon bender.


close up


I still have these pieces to use as discussion points with my new welders who are in training.
Parent - - By 3.2 Inspector (***) Date 02-16-2009 16:51
HEY!
You took that picture on my birthday :)
Dont know why I mention that.........LOL

3.2

Great Pictures btw.
Parent - - By hogan (****) Date 02-16-2009 17:44
So your almost 3 years old?
Parent - By js55 (*****) Date 02-16-2009 18:29
Could somebody point out the location of the rejection criteria for arc strikes under ASME B31.1, B31.3, and ASME Section I?

thank you
Parent - By mountainman (***) Date 02-16-2009 18:30
that's funny. i don't care who ya are!
Parent - By Lawrence (*****) Date 02-16-2009 18:48
Seems pretty obvious to me

He's  3.2

>snort<

Parent - - By 3.2 Inspector (***) Date 02-17-2009 06:21
Yes, thought thats was clear when reading my posts.

3.2
Parent - - By scrappywelds (***) Date 02-18-2009 04:55
don't get me wrong, arc strikes are bad. I try not to make them, but it does happen. the best thing you can do is try not to make them, and if you do document the arc strike, see what the inspector want to do or the client, and go on with whatever is wanted or needed. control what you can control and don't sweat the small stuff.   Yes I DID recomend 309L for carbon steel porosity when all else fails.
Parent - By jrw159 (*****) Date 02-18-2009 16:43
Scrappywelds,
  You make a very good statement, "the best thing you can do is try not to make them, and if you do document the arc strike, see what the inspector want to do or the client, and go on with whatever is wanted or needed."

This is very upfront and really is the way to approach it. :-)

jrw159
Parent - - By Kix (****) Date 02-18-2009 16:58
Who prepped those coupons?  I no it wouldn't of made any difference in this outcome, but I'm a perfectionist. ;-)
Parent - - By jwright650 (*****) Date 02-18-2009 17:34
Those were not coupons, they were regular ole A36 flat bar with an arc strike across them. I had the welder take care of the arc strike for a reason. I wanted him to be satisfied that I didn't do something fishy, so I had him ground them out. Then I bent them.
Parent - - By DaveBoyer (*****) Date 02-19-2009 04:30
As a matter of interest, have You tested how deep You have to grind to get below the affected material?
Parent - - By jwright650 (*****) Date 02-19-2009 13:27
Not really....that would be a good idea to see just how deep the arc strikes have an effect on the parent material....this may be dependant on the arc strike and the amount of time the electrode was in accidental contact though.
Parent - - By pipewelder_1999 (****) Date 02-19-2009 13:32
John,

Have you tried it with an actual bead. Maybe one small and fast but acceptable. Or maybe just a spot tack. Good quality but very short duration.
Parent - By jwright650 (*****) Date 02-19-2009 14:29
Hi Gerald, no I haven't tried anything else.....just what you see there.
Parent - - By Kix (****) Date 02-19-2009 13:38
Man that's a good visual to show students and what can happen with arc stikes.  So dId you just pretty much take a rod and drag it across a plate real fast to make a bunch of arc stikes or how did you do it?
Parent - - By jwright650 (*****) Date 02-19-2009 14:28
I laid the 4 pieces of flat bar on a welder's table, I explained that this was an experiement that I wanted to try and asked him to quickly drag an E7018 across to simulate an arc strike. He made one quick swipe with the rod. Then I asked him if that happened, how would he repair it, he said he would grind it out. So I asked him to show me...he grabbed the grinder and proceeded to grind out where he saw the arc strikes. I then asked him if he thought it would be OK now, and he agreed that he thought it should be OK now. So I took those pieces and turned the ground side away from the plunger so the material would stretch across the arc strikes and bent them. I asked him to watch me perform the bending, so he would know that I didn't do anything to them to make them tear.
Parent - - By Kix (****) Date 02-19-2009 18:53
Very cool!!  I learned something today.  I knew they were bad and that they affected the surface, but I would of never thought that they would have opened up like they did.
Parent - - By scrappywelds (***) Date 02-19-2009 23:09
I need to make a clarification of my difination of a arc mark. Mine is an arc mark is an accidental firing of the elctrode, arcing only long enough to produce the arc. Not to bee confused with an arc drag  where the welder intentional fires off outside the intended area to be welded and continues to maintain an arc to get to the intended weld area what we call " peter tracks ". There is in my book a big difference.
Parent - By Lawrence (*****) Date 02-19-2009 23:16
"an arc mark is an accidental firing of the elctrode, arcing only long enough to produce the arc."

The example Scrappy provided above is enough to be a problem.

Untempered martensite (the result of rapid cooling from a small arc strike on cold metal) is what can cause the failure (or at least the defect).

Surface temper etching is the best way to detect removal, but I don't think the codes want to demand it for various reasons....   You will find specific requirements for surface temper etching on HSS when they have been welded, ground or machined.

You could take an example piece like John provided and make a single arc on it and it would also make a brittle fracture on the spot of the arc under bend conditions.
Up Topic Welding Industry / General Welding Discussion / Arc Marks

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