[KoenigCNC]

I convert a lot of old Stainless Steel Kegs to Boilers and brewing Pots. In the past using surplus decommissioned kegs I weld Legs on them, A drain on the bottom and various side ports as needed for the insertion of the heating element and temp probe. etc. Generally they weld up just fine. I got one the other day for a customer who had been using his brew kettle as a Propane fired brew pot.

He placed the keg over propane fired burner and brewed with. He has been doing this for a while. He wanted me to put legs on it and a bottom drain. Welded up OK but the fitting got a tilted a little so I screwed in a small pipe and straightened the bung and a circle in the bottom of the keg cracked. I have done this many times with no problem after welding to straighten up a fitting. Tried to fill the crack and blew a hole in it.

My question is. Could the fact that the keg had been used for brew kettle over a propane fired burner for some time cause it to become brittle? I already ate the mistake and gave him a new never used on a burner conversion so this is more of a information finding question. I have done hundreds of these and never had a bottom just crack out. Thought this is the first one that was used over a burner.

[exnailpounder]

I do my share of keg welding too. I only had one incident involving cracking when I brazed a nipple on instead of welding it. It was too much heat for too long and the keg cracked around the fitting. I tried to weld a new fitting in the old hole and it would not weld, just blew holes and cracked and split. I am guessing that heating a keg over a burner does brittle it some especially over time. The hot/cold cycle of the thin metal work hardens it. Thats my best guess. I have a keg of my own that I use as a boiler over propane so I guess I wont be welding anything on the bottom of it. By the way, I had to cut out an area around the brazed fitting and weld in a patch to install a new nipple. I will never braze on a keg again.

[KoenigCNC]

Thanks for the reply. I had the same problem trying to fix it.

[Rick_H]

I agree with direct heat it will make the stainless brittle, I'm not sure what grade stainless those kegs are made from. I just fixed an old crab pot for a guy I work with ran into a similar issue.

[exnailpounder]

I agree with direct heat it will make the stainless brittle, I'm not sure what grade stainless those kegs are made from. I just fixed an old crab pot for a guy I work with ran into a similar issue.

I have read that kegs are 304. I use 308l on them and it welds up nice. 304 is tough but I really do think the cycling brittles them over time. They are meant for pressure, not heat.

[Poland308]

I've seen a lot of SS gas fired burner plates and heat exchangers that get spider webbed with stress cracks from the close proximity with the flame. It's the nature of the beast. I'm not sure if it's from the heat cool cycle or more of a metallurgical change from the flame contact. I know that some companies that use 304 for process are trying to get away from it if they have other options. Stress cracks start to show up in the HAZ of a weld only a few years after install if the pipe sees a large temp swing during normal operation.