Welding stainless steel to mild steel

[picocg]

I want to replace a 4 inch threaded thru-deck corroded steel fitting (see attached photo) with a similar sized stainless steel NPT fitting used as an access for the emergency tiller arm on a 50ft motorized landing craft. Can a stainless steel pipe coupling be welded to a steel deck without short or long term consequences? If not what are my options? If so please specify the method.

Regards,

 

[metengr]

Why do you need to consider any stainless steel? I would use a carbon steel pipe coupling and fillet weld to the existing steel deck.

 

[picocg]

Thanks for the speedy reply metengr. The existing steel fitting has corroded (see attached photo) to the point where the plug is seized in place and can only be removed with brutal force and time. Not acceptable in an emergency. The vessel operates for two weeks of the year in the high arctic and remains beached outside for the rest. I'm considering a stainless steel or bronze plug in a stainless steel pipe coupling. In any event a maintenance free solution is required.

 

[metengr]

picocg;
Drill out the center of the plug and collapse it. Replace in-kind with carbon steel and apply a protective coating.

You can go with an austenitic stainless steel fitting, but this seems like more effort. If you decide to use a stainless steel fitting you need to fillet weld using an E309 stainless steel filler metal. Seems like more work than is necessary.

 

[picocg]

Thanks metengr. I neglected to add that this would be a minor modification to a complete vessel overhaul.

 

[Adalius]

If you have a choice in regards to consumables, see if you can get ahold of a Cronatron rep out by you (they were recently absorbed into Lawson products so you might need to look for a rep under that name). They have got some welding rod for stainless to mild that, in my opinion as a journeyman millwright and certified welder, outperforms E309 by leaps and bounds.

I'm in charge of purchasing rod for my company and we used Lincoln rod for, god, 30? years. Then the rep stopped by, I ran some passes of their various rods, he gave me some 10# samples of a couple I was interested in, and within a month all the foremen were asking for more of it. Their rods are a little on the pricey side but they're just amazing to run. The one thing you have to be careful of though is that if your weld calls for a AWS classified rod, some but not all of their alloys are classified. For instance, they have a rod that is a low hydrogen, 75,000# psi, similar composition to a 7018, but isn't classified so it can't be used for things like state certification tests.

 

[metengr]

Adalius;
I have been down this road many times. Stick with AWS classified weld rod and electrodes. Yea, I have heard of magic weld rod that a welder can use with no cleaning, in water, in mud, etc. I have heard it all.....

 

[Adalius]

Metengr:
I've been down this road many times myself, and welding with this rod for quite a few years without problem, but keep in mind Cronatron is a big outfit, not a fly by night manufacturer. I'm not claiming this is the 'magic rod' stuff, it's just really really good high quality rod. It's not that it can do things other rods can't, it just produces a really friggin nice weld and when it comes time to do break tests or acid etches on it, they're just flat out beautiful.

As I said, if you know you need AWS classified rod, use stuff that is classified, if you are in a position for shop welding or a repair that doesn't need a WPS, this stuff is the cats meow. And its not just sales pitch, I can say it having used it for years and having done VT, UT, MT, and destructive testing on them.

 

[picocg]

Thanks Adalius. Sounds like good stuff.Gonna Google it today. I'm pioneering a lot of new tech into this project so this may be another one to add to my list.