mallable iron plumbing fittings

[julianf]

Im inexperienced with TIG (so there's the disclaimer out the way!)

I welded a malleable iron fitting today. This sort of thing -

It was just a black iron fitting, not galvanized or anything. I was welding it into the base of an old oil tank (mild steel sheet).

Whilst i was welding the fitting, i dwelt for too long, and it looked like when you get expanded polystyrene close to a flame. I thought id burnt through the fitting, but the inner wall was fine.

I filled the mess with filler wire anyhow, and it tested leak free at the end.

Again, im a novice - im curious as to why this metal behaved like this, and how to avoid it better next time? (the sheet that i was welding it into just melted normally)

 

[Tigman]

maleable fittings are not good for welding , they are similar to cast iron , I have never tried it myself , it may be prone to cracking if under stress !

 

[AndyStobbs]

They don't weld well with any process in my experience. Get a porous weld.

 

[julianf]

Ok, thank you.

In this case, its not a stress part - its simply so i can put a drain valve on the bottom of a tank - no large forces.

In hindsight, i may have done better soft soldering in a tank fitting, but its done now.

 

[doubleboost]

It is better to "braze" them
It is even better to use steel fittings

 

[Welderpaul]

Easy way round, done it loads of times on tanks..weld a threaded socket on first (They are 'proper' steel), then screw the elbow into it (With a nipple if you don't have a male-ended elbow)

 

[Shox Dr]

If you use a steel or SS rod it will more than likely crack. I've successfully braised them using SIF No8.

 

[marfyboy]

I had one of those thrown at me as an apprentice after I had gone to the merchants for our welder. so learnt pretty quickly steel for welding and steam and malleable for pipefitting

 

[julianf]

Ive had some people tell me to grind out the part and do it again, but im not even sure how i would do that (its right in the corner, and i wouldnt be able to get a grinder in there)

The part is currently leak free. Ive worked out that it will have 4-500g of force on the square inch that is in question, but I dont know if it being welded into the corner (centre of fitting about 1.5" from either side) is a good thing or not, with regard to flex from the rest of the volume of the tank.


If i really thought it was going to fail, of course id have to find a way to get it out. What do you think?

 

[AndyStobbs]

If you've made any kind of decent job of welding it on, it wont fall off with 500g sitting on it.