Dewpoint, Realtive Humidity vs. Required NDE 2

[MotoGP]

Dear Welding Experts:

Please know that although I do not have an exhaustive source of reference materials handy, I have looked in AWS Welding Handbook and Welding Metallurgy, Lincoln Electric's Arc Welding Handbook, and a few other sources without any luck...I'll tell you all, I'm in dire need of some experienced replies pertaining to the subject matter.

When I was living on the Texas Gulf Coast, and assigned to offshore platform new construction, an experienced welder once told me that on the days that the humidity was high (virtually every day during the summer), that I could expect to see comparatively more "rejected" weldments (via VT and RT "uncovering" porosity) than I would expect on days when the relative humidity was less.

These words just "stuck with me", and now that I am assigned to oil tanker construction projects, part of my field engineering duties are to "assist" in the overall quality management that the yard takes on these projects.

I am working in Asia, and, you see, the yard that I am at sees fit to "call-out" in advance all the sites that will receive NDE. As such, the welders know well in advance where the RT's and UT's, etc. will be "shot". This has always had me wonder about many things, but, to keep it short (I guess way too late for that by now), on days when I can document "Texas Gulf Coast" relative humidity, and/or when welders are working at the Dewpoint temperature, should I, based on sound welding engineering principles, in fact "expect" that more welds will have the increased likelihood of weld porosity?

If so, how much "at random percentage" would you think that I would need to increase the amount of RT's and/or UT's?

Also, is there any way to remedy this situation? (if, in fact, a remedy is needed)

Or, instead of worrying about this, should I just have a beer and sit down and be quiet?

By the way, I'm speaking in generalities...that is, welding mild (sometimes high-tensile) carbon steel structure...Carbon Steel, SS and Cu-Ni pipe...some in the shop, some under-cover, some out-in-the-open...but NEVER in a climate-controlled environment.

Please accept my gratitude, in advance, for your words of insight.

Pete

 

[Metalguy]

*IF* you can make them use a little preheat AND keep the electrodes properly baked and dry right up until the minute they're used, you shouldn't have porosity problems regardless of the surrounding humidity.

 

[ledon]

I agree with Metalguy. So long as you control the moisture content in your filler metal and apply enough preheat to ensure a dry surface, you shouldn't have any issues.

 

[MotoGP]

Thanks, gents, for the information...I'll make a note of it.
Pete

 

[GRoberts]

Humidity is typically more of a concern from hydrogen absorption which would lead to cracking, than from porosity. Cracking is also a lot bigger problem if it occurs in that it could even happen after inspection if inspection takes place too soon after welding, and that a crack is much more detremental to the performance of the weldment than round porosity holes are. If there is enough moisture in the air to cause porosity from hydrogen, you could expect bigger problems than porosity I would expect. I did find a little data on the subject though.

From "Welding Steels Without Hydrogen Cracking" Second Edition by N Bailey et al, "Hydrogen potential figures should be used with caution when welding is carried out in hot, humid conditions. Such situations can lead to weld hydrogen levels somewhat higher than the standardised conditions under which most consumable manufacturers asses their products. It is likely that the absolute humidity, rather than the relative humidity (RH) is the controlling factor. Recent work with one type of electrode designed to give diffusible hydrogen contents below 3ml/100g, tipically gave 2ml/100g in test welded at ambient conditions of 20C & 40% RH. However, test welded under ambient conditions of 35C & 95%RH not only have diffusible hydrogen values of about 3.8-4.8ml/100g, but the electrode picked up sufficient moisture in a few hours exposure to these conditions roughly to double these levels, although exposure at 20C/40%RH and 26.6C/80%RH gave negligible increase in weld hydrogen contents after 9 hours exposure."

That said, it seems like exposure, which is tightly controlled by certain welding codes is much more important than humidity at the time of the weld. If welding conditions are marginal, humidity could push the welding conditions over the edge though. If moisture absorption is a concern, issueing small lots to welders or using portable ovens can help control the problem. As far as NDT, you can't inspect in quality, and an ounce of prevention is worth a pound of cure are some cliches that may apply in that if I was going to buy a structure welded in such humid ambient conditions, I would prefer to invest the money/time into keeping electrodes dry rather than extra inspection afterwards.