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Up Topic Welding Industry / Technical Discussions / No preheat or PWHT for low hydrogen
- - By newinsp (**) Date 08-17-2013 22:56
The new textbook here has a story about a welder in Antarctica.  The story is also on this AWS web page: http://www.aws.org/w/a/wj/2001/08/0010/

"Because of the lack of humidity, preheating the steel was not needed," he said. Postweld heat treatment was also unnecessary for the same reason. "The metal did react differently at first contact with the heat, which took a little getting used to. It seemed the metal was shocked at first contact with the heat. It was hard to get a nice vertical flow, but once the metal warmed up it went smoothly. My first vertical pass there was a mess."

Wonder what Code he was welding to?
Parent - - By Superflux (****) Date 08-18-2013 00:08
There is a small town in northern Wyoming of which several people have and (still) do work down there (must say something about the winters up here!). In fact two of my friends met in McMurdo and eventually married. He is a maintenance supervisor "on the Ice" and they both have remarkable stories to tell. I've often thought of doing a stint there, but definitely not now as funding is being cut and it is not as good of conditions as it once was. Now if I could sign up for say a 30 or 60 day in and out, that would be cool and doable, but alas, they only accept 6 month contracts.
Parent - By newinsp (**) Date 08-18-2013 13:22
That would certainly be an interesting one time adventure. 

It still bothers me how they weld without preheat.
Parent - - By Tyrone (***) Date 08-19-2013 11:44
Interesting article newinsp.
I hope someone did their homework on the no pre/post heat call.

Tyrone
Parent - By Superflux (****) Date 08-19-2013 13:46
My friend is en route to the ice and I'll try to follow up on this when he gets settled in. This has piqued my curiosity.
Parent - - By js55 (*****) Date 08-19-2013 14:06
I don't buy it in either case.
Preheat isn't all about humidity. It is also about hardenability, which would be greatly accelerated under those cold conditions.
Now if you are talking all austenitics then the transformation isssue is negated.
And PWHT has nothing to do with humidity.
There may be metallurgical reasons for no prehaeat or PWHT but it isn't humidity.
Parent - By jwright650 (*****) Date 08-19-2013 14:24

>Preheat isn't all about humidity. It is also about hardenability


Right.....slowing the cooling rate of the weld and haz is what pre-heat is all about...whether you are wanting to give the hydrogen time to escape or lessen the likelyhood of quenching the weld and hardening.
Parent - - By welderbrent (*****) Date 08-19-2013 14:45
Guys, Guys, Guys...

All is well.  Haven't you seen the new 'Cold Fusion' electrodes?  :roll: 

They work almost as well as the 'Brown's Gas' available through all non reputable suppliers.

Have a Great Day,  Brent
Parent - - By 99205 (***) Date 08-21-2013 00:39
LMAO, "Brown Gas".
Parent - - By welderbrent (*****) Date 08-21-2013 03:41
It has been a while, I think I can still find my copy of the report.  Have you ever read it?  It would make a great comedy skit. 

Have a Great Day,  Brent
Parent - By 99205 (***) Date 08-21-2013 16:02
No, I haven't read it. I'd like to see it.
Parent - By Len Andersen (***) Date 08-21-2013 19:46
Fellow AWS'ers,
    There are steels that might "fit" what they are talking but in no way is it a generalization. Need the money as a CWI and machine froze with minus 5o. Put the scaffolds on the ice and go with preheat and get to zero with a tent. Hope I am helpful.
           Sincerely
Len Andersen weld@spemail.org
               914-536-7101 / 914-237-7689 (H)
POB 1529 / NYC 10116-1529 ( $1160 per year Caller Box GPO NYC / Most Secure Service At Largest Post Office )
- - By 803056 (*****) Date 08-19-2013 16:57
I have heard this before on projects near the poles where the temperatures are very low, i.e. subzero.

The rational I heard was the need for preheat when welding low carbon steels is a nonissue because the primary concern is with diffusible hydrogen. Diffusible hydrogen is atomic hydrogen which is free to move (by diffusion) within the atomic lattice. The very low temperatures reduce the atomic spacing so that the hydrogen is largely immobile, i.e. it does not diffuse and collect interstitially between the iron atoms. Without diffusion and "clumping" together, the danger of hydrogen cracking is minimal. Together with the low hydrogen content, even with rapid cooling, the quantity of Martensite formed is minimal.

That discussion assumes that hydrogen molecule (diatomic hydrogen) is the sole force acting on the surrounding structure causing the crack to initiate.

There is another theory that postulates hydrogen cracking is the result of diffusible hydrogen (monatomic) combining chemically with excess carbon that is prevalent in Martensitic microstructures (supersaturated solution of carbon). Still, key to hydrogen cracking is the need for hydrogen that is free to diffuse from one location to another. It is hypothesized that due to the very low temperatures, the hydrogen is largely confined within the atomic lattice so diffusion isn't possible and the possibility of hydrogen cracking is largely eliminated.

Just food for thought.

Best regards - Al
Parent - By jwright650 (*****) Date 08-19-2013 17:16
Al, Given what you said, do you see the D1 committee revising the code regarding prohibiting welding below the min temp shown in D1.1 clause 5.12.2(0°F)?
Parent - By welderbrent (*****) Date 08-19-2013 17:34
You do serve up some interesting 'food' there Al.

Now, how about procedures?  I would presume that they would have to do PQR's and establish their own unique welding procedures and prove their ability to perform? 

Also, what type of temperatures are we talking about to get to this point where 'theoretically' (I failed theory by the way, too much of a realist) the hydrogen is not an issue? 

Looking through Annex 'I' of D1.1 I find some interesting info about measuring of the HAZ for hardness to determine potential for cracking but it also revolves around hydrogen I believe.  It definitely still involves pre-heat.  So, how does this relate to the HAZ with the obviously very quick cooling rate which would still cause 'hardness' would it not?

Have a Great Day,  Brent
- - By 803056 (*****) Date 08-19-2013 17:48 Edited 08-20-2013 14:24
Hey, I just threw the information out there. You can decide if it makes sense to you.

No one said they were required to meet D1.1. I doubt there is a building code that has been adopted by the few penguins populating the Polar Regions.

As for the susceptible temperature range for hydrogen assisted cracking, it is stated to be between -50 degrees F and 450 degrees F. At temperatures lower than -50 it is essentially immobilized and at temperatures greater than 450 it is free to effuse to the environment without causing problems. That is the principle of a hydrogen bake-out; heat the weldment to a specified temperature and hold it at that temperature to allow the hydrogen to effuse.

Best regards - Al
Parent - - By welderbrent (*****) Date 08-19-2013 19:28
"No one said they were required to meet D1.1."

Absolutely true.  Jumped to a fleeting thought without fully analyzing the situation.  Sometimes curiousity creeps in before brain can take over.  Still worth pondering.  Do you have a 'theory' on that aspect if there were a D1.1 application? 

Thank you for the temps.  Definitely on the cold side.

Have a Great Day,  Brent
Parent - - By jwright650 (*****) Date 08-19-2013 19:38
My point with mentioning D1.1 even though the article didn't mention that the welding had to be done to a particular code.

...was....

that since hydrogen and hardness doesn't seem to even matter at temps below zero, why does D1.1 even mention it as a concern for the welder who is placing the welds or the material, because it prohibits welding when temps are zero and below, even states that an enclosure may be erected to help the atmospheric conditions, yet it also states that by using this structure doesn't not alter the fact that the preheat requirements are still in effect.
Parent - - By 803056 (*****) Date 08-20-2013 15:03 Edited 08-20-2013 15:06
Temperature is just one determining factor in hydrogen assisted cracking. The temperature range at which delayed hydrogen cracking is associated with is above -50 degrees and below 450 degrees F. That isn't to say if can't happen at temperatures above or below the temperature I listed. Even those values are open to interpretation as evidenced by Linnert using -150 degrees F as being the lower threshold.

I guess one could use the bell curve distribution to define the critical temperature range for hydrogen assisted cracking. Are you satisfied with a 95% assurance cracking will not occur? Would you be more comfortable with a 99% assurance cracking will not occur? 

Life is a statistic. How safe do you have to feel before you make that leap from the diving board? The older you are, the more broken bones you've suffered, and the more experienced you are, the more conservative you may be and you may well look for that 99.9% assurance your head won't be smashed when you hit the bottom of the pool.

One’s tolerance for failure is influenced by experience. Young people are usually bolder than older people. Older people, having experienced failure, tend to be more conservative in their approach to solving problems. In the case of hydrogen assisted cracking, I would favor the conservative approach, There is no guarantee hydrogen cracking isn't an issue even when all the factors are considered. The chance of success improves if one considers the following:

1)  Welding process: select a low hydrogen process, i.e., bare filler metal versus covered electrodes.
2)  Covered electrodes; select a mineral covered electrode, i.e., low hydrogen, versus organic coverings such as E6010.
3)  Storage conditions of the low hydrogen electrode. The Polar Regions are a very cold environment that have very low humidity in comparison to the Tropical Regions.
4)  The carbon equivalency of the base metal is low if welding low carbon steels.
5)  Surface cleanliness, i.e., freedom of organic compounds and sulfur bearing compounds.
6)  The use or absence of preheat and the resulting microstructure.

Let’s take a closer look at welding in the Polar Regions.
a) The base metal will most likely be a low carbon steel with a very low carbon equivalency. Good
b) The electrode will most likely be a covered electrode since the SMAW process is the least complicated and a good choice for remote situations. Good
c) The electrode can be a low hydrogen type that is stored in factory sealed tins to ensure optimum storage conditions. Good
d) Ambient temperature and moisture content; very, very low. Little chance the electrode will absorb moisture when there is none to absorb. Good
e) Surface cleanliness: there is no reason not to have clean, paint free surfaces. Good
f) Cooling rate: fast cooling without preheat (bad), but the low carbon equivalency means the amount of Martensite present is rather low. Good

I believe it is possible to weld without preheat in cases where due consideration is given and both the designers and welders understand the influence of the factors involved. If the base metal has a high carbon equivalency, if the electrodes are not low hydrogen, or if there are organics present in the area to be welded, my level of confidence would be reduced very quickly. 

Best regard - Al
Parent - By welderbrent (*****) Date 08-20-2013 15:49
Understandable. 

It's not that we have to be 100% comfortable with the process, just enough that we believe all due dilignece has been taken so that the odds are in our favor.  That, in many ways, is what our entire job is about...increasing the odds.  There is nothing perfect no matter how many engineers and then inspectors were involved in the project.  It is a very rare thing that you will find a piece that is 100% perfect when finished.

Have a Great Day,  Brent
Parent - - By MMyers (**) Date 08-20-2013 17:35
"Temperature is just one determining factor in hydrogen assisted cracking."

I like the mnemonic device I was taught by a welder turned technician who worked at EB:

Hydrogen cracking is caused by ****T

Stress
Hydrogen
Miiiiiiiicrostructure (emphasize the I)
Time
Temperature

But to agree, if we push any one variable out of the "danger zone", the chances of hydrogen cracking are decreased.  Belts and suspenders are encouraged though, so we as professionals tend to control as much as possible to ensure success.  Generally this is done by controlling microstructure through preheat controls, controlling hydrogen through cleanliness and consumable controls, and providing a post weld bake out which controls temperature for sufficient time to allow hydrogen to effuse out of the weld metal.  Most of the "stress" factor is left to the designer of the weldment, though careful weld sequencing can sometimes assist here. 

Of the story, the hydrogen part is pretty believable to me.  What concerns me is the lack of preheat and resultant microstructure in the weld metal and HAZ.  Obviously that too is a multi-tiered reaction and one likely considered by the designers, but it's glossed over in the article and would be cool to learn about.  The metallurgical and mechanical behavior of the material at those service temperatures would be an interesting topic.  I wonder if they're using common structural steels or have had to turn to less common materials suitable for those fabrication techniques and service conditions.
Parent - - By 803056 (*****) Date 08-20-2013 21:01
Mike, did you put some time in at EB in Groton or a different location?

Al
Parent - - By ssbn727 (*****) Date 08-22-2013 05:21
Ohhhh Geeez!!!!! The land with plenty of HY-80. 100, 120 and 140 back in it's hey days!!! I almost forgot about all the HTS & CRS being used all over the place and the "Cupro" - Nickel & Nickel Copper, Inconel, many different grades of Stainless steels we welded all day and all night back when Reagan said to the Soviets "Tear Down This wall!!!" and labeled The Soviet Union - "The Evil Empire" as we came so close to Nuclear Armageddon way back in 1983! Only to find ourselves worrying about someone sneaking in a suitcase bomb these days!!:eek::eek::eek::roll::roll::roll: It never ends until it finally does one day...:sad::sad::sad:

Another one who worked in Rotten Groton, CT...:roll::razz::grin::wink::cool::cool::cool:

What a gig! That was my home for five years!:eek::eek::eek::roll::roll::yell::yell::yell:

It's a totally different place these days and I'm not talking for the better either.:sad::sad::sad:

Respectfully,
Henry
Parent - By js55 (*****) Date 08-22-2013 14:12
Henry,
Been to the museum in Groton. Walked through the Nautilus.
Its a small museum but quite cool.
Parent - - By MMyers (**) Date 08-22-2013 14:20
Never been employed there, but I have done work for them on a couple different projects. I've climbed the hill a time or two.
Parent - - By 803056 (*****) Date 08-22-2013 15:42
I never welded on the subs, but I've done several welding and inspection projects on their site. Heart Attack Hill is a fitting name.

Al
Parent - - By ssbn727 (*****) Date 08-23-2013 18:48 Edited 08-24-2013 10:42
Hi Al, Jeff and Mike!

That museum is pretty cool indeed! All of the exhibits like the Polaris A-3 missile in sections, and the interactive TV displays showing movies of the different era's of submarine warfare including some film from WWI... This is the only Submarine Museum in the US exclusively managed by the United States Navy...  Here's the link if anyone's interested:

http://www.ussnautilus.org/

Also, here's a link with a list of submarine museums located all over these United States of America, and included in the list are a couple of Russian Foxtrot subs and even a WWII German U-Boat

http://www.submarinemuseums.org/

There's a huge museum near Seattle way around Allen's neck of the woods... The Naval Undersea Museum is an official naval museum located at Keyport, Washington, USA.
The museum is one of the 12 Navy museums that are operated by the Naval History & Heritage Command.
The museum sits next to a branch of the Naval Undersea Warfare Center. Here's the link:

http://www.history.navy.mil/museums/keyport/index1.htm

Respectfully,
Henry
Parent - By 803056 (*****) Date 08-23-2013 18:57
Some of the museums are tough to get into with all the security concerns, especially if they are on a base, which many of them are.

Best regards - Al
Parent - By ctacker (****) Date 08-24-2013 04:49 Edited 08-24-2013 04:54
I was just at the undersea naval museum a couple weeks ago at Keyport. It is not on base, and the best part is it's free to the public.
Attachment: P1020705-1.jpg (0B)
Parent - - By MMyers (**) Date 08-19-2013 19:37
"As for the susceptible temperature range for hydrogen assisted cracking, it is stated to be between -50 degrees F and 450 degrees F"

Do you by chance have a source for that?  I am hoping to find a plot that relates effusion time/rate to temperature and hoping a document with the sort of information you mention would have such a plot.
Parent - - By 803056 (*****) Date 08-19-2013 19:58
I got the -50 to 450 degrees F from my course notes taken during my metallurgy courses back in my school days. I also found some information in Linnert's Welding Metallurgy Volume 2. Linnert used the temperature of -150 degrees F as being the lower threshold temperature.

Al
Parent - - By MMyers (**) Date 08-19-2013 20:01
Thank you, Sir.  I'll give Linnert's book a look.  I'll need to really sit down and read it, but this Bohler document looks promising:
http://www.boehler-welding.com/france/files/BW_Sonderdruck_Wasserstoff_ENG_08-2012.pdf
Parent - By 803056 (*****) Date 08-19-2013 21:11
I'll have to give this one a read as well. Thanks - Al
- By Dualie (***) Date 08-21-2013 06:58
on the same token as a fabricator and erector you try and keep tabs on things and have a good idea whats going on in the shop at all time.   But there comes a time when you cant keep tabs on everything and your people get lazy or rushed.    Things get missed, you try to keep 3 levels of safety's in place that things don't but they always do.

Currently I'm involved in one of the most complicated custom homes i have ever seen,  theres hundreds of goofy connection plates and tabs for steel to wood connections all over the place with old ball engineering that calls for mostly 1/4" fillets but some get 3/8" fillets.     Some of them get missed by 3 levels of checking including my in house QC.   IF it wasn't for the TPI catching this and brining it to my attention it would have just gotten passed down the line and ended up as a report and an NCR.  basically getting no where but into pockets.  

I'm not saying you need to baby sit but give the benefit of the doubt and give them the fighting chance of fixing it right the first time.
Up Topic Welding Industry / Technical Discussions / No preheat or PWHT for low hydrogen

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