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
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
"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.
Mike, did you put some time in at EB in Groton or a different location?
Al
Henry,
Been to the museum in Groton. Walked through the Nautilus.
Its a small museum but quite cool.
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.
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
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.htmRespectfully,
Henry
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
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.