Low hydrogen electrodes are baked at high temperature by the manufacturer before packaging. Electrodes removed from a hermetically sealed container can be used immediately upon opening the container. My definition may differ from other people's definition because my experience has indicated some hermetically sealed containers are not impervious to the elements, i.e., humidity. A sealed tin free from all visual indications of damage is most likely hermetically sealed. Cardboard containers and plastic containers that are sealed with cellophane tape probably are not able to meet the low moisture requirements of many welding standards. Again, that is based on my experience and on-site tests that are far from scientific or closely controlled.
The storage conditions may vary from one manufacturer to another, but NAVSEA welding standards and AWS D1.1 are consistent with each other. Normal storage of low hydrogen electrodes should be in a vented electrode storage oven (electrical heating element) set at a temperature of no less than 250 degrees F. Notice that the temperature listed is a minimum, not a maximum, so those individuals that store the electrodes at a higher temperature are in good standing.
Once the electrodes have been exposed to the ambient environment for more time than that permitted by the welding standard, i.e. 4 hours for E7018, 2 hours for E8018, and 1 hour for E9018 per D1.1, etc., they must be rebaked at an elevated temperature to properly recondition them. The temperature may be as low as 500 degrees F or 600 degrees F, depending on the welding standard cited, to a maximum of 800 degrees F. The time of the rebake is typically one hour. This can only be done once.
I can't address the possibility of holding the electrodes at temperature (250 to 350 degrees F.) for too long a period. It doesn't sound reasonable when I consider comments from a well respected welding engineer that indicate holding electrodes at 250 degrees is actually too low a temperature to keep the electrodes completely moisture free.
Low hydrogen electrodes that do contain some moisture will have an aggressive penetrating arc that may appeal to some welders. The characteristic is the result of the diffusible hydrogen produced by the disassociation of the moisture in the welding arc. Likewise. the aggressive deep penetration of a cellulose electrode, i.e., the EXX10 and EXX11 electrodes, is the results of the hydrogen produced by the disassociation of the cellulose in the arc. In either case the diffusible hydrogen can produce undesirable tendencies of cracking under conditions of high carbon equivalency and high restraint and high cooling rates.
Best regards - Al
Well put and a welcome addition to the thread.
Griff
Cardboard containers and plastic containers that are sealed with cellophane tape aren't hermetically sealed. Are there manufacturers claiming otherwise?
Hg
Hg,
I do not believe the 'manufacturers' are claiming the containers are hermetically sealed. Many of the counter salesmen at local welding supplies do not know what is truly required to be 'sealed'. Most even have open 50 lb boxes that they sell by the pound out of. And as easily noted from other threads on this forum on this same topic, many welders/management run in and grab a few pounds thinking 'I just picked it up at the welding supply, it must be good'.
My impression is that some of the manufacturers don't package their low hydrogen in an attempt to keep costs down. They don't care if that means you have to bake the rod before you can use it. Not their problem. You are supposed to know proper storage and usage after you buy it from them.
Just my two tin pennies worth on the way your question was posed.
Have a Great Day, Brent
Al,
I think it would be well to note, since you cited times of atmospheric exposure, that low hydrogen rods with an 'R' or 'M' designator, such as Lincoln's Excalibur 7018, approximately double the exposure time previously cited. They are given a 9 hr. exposure limit.
I don't know all the nuts and bolts of 'WHY' but suffice it to say that the coating is different, the process of manufacturing is different, the testing, and the resultant ability to not draw moisture (hydrogen) as quickly as 'standard' 7018.
Most of my local suppliers get me the Lincoln Excalibur for the same price as the standard. Why would I even consider running the standard when I can pick up a few hours, which is occassionally very critical to a job where I don't have a rod oven handy. I also buy them in a 6 tin case of 10 lbs each. That way I don't have as much to lose if I end up over the time of exposure before I can get it to the rod oven. They are a very secure, easy to open tin. A pull ring sealed top that doesn't come open so easy that the seal is broken. Besides, I personally feel the Excalibur is a better running rod as well.
Have a Great Day, Brent
Excaliber is the rod of choice. Some like the Atom Arc, but the Lincoln lays sweeter. My opinion.
I didn't address the EXX18-R variety because the question cited E7018 specifically.
I usually recommend purchasing the 10 pound tins to my clients for the same reasons you listed and I am also an advocate of the Lincoln Excalibur and Atom Arc.
Most manufacturers make several different types of EXX18, each having a slightly different chemistry. I try to match the chemistry and manganese to the application, but that's another story and a different thread.
Best regards - Al
By weldktm
Date 06-20-2013 13:10
