slim_boy_fat
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Do these carry a gas supply? 
- Thread starter 123hotchef
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123hotchef
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Do these carry a gas supply?
not carry no the big bit at the top is where combustion takes place the gas and air is mixed and ignited by a glow plug
Brad93
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The reason I think it may not be repairable is from looking at the level of corrosion and particularly the white oxidation/precipitation the part may well be completely depleted of Cr, Mo, and Ti.
The grade is 316 titanium stabilised.
What happens is to get the strength and creep properties at elevated temperature, they don’t use 316L which is low carbon, they use standard 316 and then add in titanium which is a grain refiner and when heated into the detrimental (I think it’s the gamma) phase the titanium mops up the carbides that would otherwise form with the chromium or molybdenum and render the part and expensive lump of mild steel.
The problem to me is you say the oven can do 500 degreees. 316Ti can withstand continuous temperatures of up to 400 degrees.
Past that it’s life expectancy is limited.
Given what we have discussed about steam, salts and chlorides from food being cooked, and the elevated temperatures (stresses) this all points to stress corrosion cracking.
Possibly accelerated further by the oven cleaner which is most probably strongly acidic or alkaline.
Unfortunately people think stainless steel is the answer to all corrosion problems but it does have limitations.
If you was going to make that part again and believed the oven was going to be in service for a number of years I would be inclined to replicate the heat exchanger from Inconel 625 (UNS N06625) sheet.
You can see from the pictures that the areas the fan has been cooling have stood up to the thermal cycles much better. The areas where the combustion takes place and away from the cooling action of the fan show the most corrosion.
Inconel 625 can withstand temperatures of 649 degrees Celsius before starting to grow carbides.
What I’m worried about is that we will not be able to get a sound weld in material that deteriorated.
Like you say we could cut sections out and patch but it looks like getting a small quantity of 316Ti could be an issue.
The grade is 316 titanium stabilised.
What happens is to get the strength and creep properties at elevated temperature, they don’t use 316L which is low carbon, they use standard 316 and then add in titanium which is a grain refiner and when heated into the detrimental (I think it’s the gamma) phase the titanium mops up the carbides that would otherwise form with the chromium or molybdenum and render the part and expensive lump of mild steel.
The problem to me is you say the oven can do 500 degreees. 316Ti can withstand continuous temperatures of up to 400 degrees.
Past that it’s life expectancy is limited.
Given what we have discussed about steam, salts and chlorides from food being cooked, and the elevated temperatures (stresses) this all points to stress corrosion cracking.
Possibly accelerated further by the oven cleaner which is most probably strongly acidic or alkaline.
Unfortunately people think stainless steel is the answer to all corrosion problems but it does have limitations.
If you was going to make that part again and believed the oven was going to be in service for a number of years I would be inclined to replicate the heat exchanger from Inconel 625 (UNS N06625) sheet.
You can see from the pictures that the areas the fan has been cooling have stood up to the thermal cycles much better. The areas where the combustion takes place and away from the cooling action of the fan show the most corrosion.
Inconel 625 can withstand temperatures of 649 degrees Celsius before starting to grow carbides.
What I’m worried about is that we will not be able to get a sound weld in material that deteriorated.
Like you say we could cut sections out and patch but it looks like getting a small quantity of 316Ti could be an issue.
123hotchef
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The oven temp can be set to a max of 250 deg C so I was just guessing at the temp of the combustion part of the heat exchanger being 500 deg C
You seem to know your stuff Brad I value the experts opinions just glad I asked on here before trying to mig it!
