In the May 2021 AWS journal page 22 is an article titled Welding Preheat for tube and pipe.
Under the heading, Why welds are preheated, first bullet it reads : To prevent hydrogen cracking in the weld metal or heat effected zone.
I'm good with that, but what followed has me asking the question.
It reads..." This is accomplished by driving off moisture prior to the start of welding,". Well I'll be darned, doesn't that sound like it actually sounds, like it holds some magic surface moisture?
Admittedly, I'm calling BS to the statement. But...I'm wondering if it's worth explaining that it doesn't.
There would be a great difference between "driving OFF moisture" compared to 'driving OUT moisture'.
But, it is a bit conflicting and hard to explain to many who have no understanding. (Not intended to mean you in any way)
Have a Great Day, Brent
I think the intent is to remove dew or condensation (water) from the surface of the material. Water which has hydrogen as part of it's make up.
Same goes for applying coatings; if the surface temperature is within 5° of the dewpoint the coating authorities have written code to prohibit the application of coatings until the dewpoint and the surface temperatures are farther apart because they want to prevent applying a coating over moisture.
I did a double take on that as well. The English language can confound many of us, so I, like John, gave the author the benefit of doubt and "assumed" he intended to say "evaporate any surface moisture".
I could be wrong, but I'm hoping the author wasn't implying the base metal was a sponge that absorbed moisture.
I guess this is an example of where the writer has to choose the words carefully lest those of us that are mere mortals don't misconstrue what was intended.
Al
Plasma56,
I understand your post, but when I read the article I took it to mean to remove dew or condensation prior to welding in an effort to prevent hydrogen cracking. No matter how it's worded, "driving off or driving out" moisture, my experience has been that you will still need to explain in greater detail what that means to welding students, project management or project engineers. Because some, not all, but some will think that carbon steel material is like a sponge and is saturated with moisture.
I think part of where that myth comes from is when you first apply the torch to get some heat into the material, moisture appears on the surface and the assumption is that it comes from the material rather than being a byproduct of the combustion process of the torch.
While I assumed it was a poor choice of words in explanation, it was a published poor choice. But in an effort to stop the spread of miss information, as moot as it maybe, your responses may be the best of clarifying correction to end the myth.
Thank you for your replies.
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