316L vs. 316Ti, high temperatures (~600ºC), welded parts 2

[PDH95]

Hi,

I have read some information about the differences between 316L and 316Ti performances at high temperatures but I have some doubts yet. In our application, we have a kind of table made from a tube welded to a plate. That table is going to be at a high-temperature ambient (around 600 ºC) and normal air. Attending to the corrosion resistance, weldability and cost, what are the differences between 316L and 316Ti?

I have to say that we are from Europe, where the 316Ti is more common than in the USA.

Thanks.

 

[EdStainless]

600C is definitely in the creep range.
But either grade should have good stability at that temp. I wouldn't expect secondary phase formation in either of them.
Is this extended exposure of cyclic?
If cyclic then you have to think about the spalling of oxide and thermal expansion issues.

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[blacksmith37]

The 316, any grade ,is not a good choice for elevated temperatures. Moly oxide can cause accelerated metal loss in locations where there is not free gas flow. So places where the 316 rests against brickwork are affected. As I remember the moly oxide has a relatively high vapor pressure.

 

[PDH95]

Thank you for your answers!

EdStainless, it's a cyclic exposure. I don't know if there exists another alloy that avoids that spalling issue. I'm thinking on 309, 310, 321, ... but maybe with these alloys is difficult to find tube products, and the costs rise heavily.

blacksmith37, maybe the alloys that I mention above are better choices? In this case all the surfaces are exposed. In all the information that I found, I read that 316 (both L and Ti) is able to endure these temperatures reasonably well. For example, we have some thermocouples (from a reputed manufacturer) whose shealt is made from 316Ti, and the manufacturer places the service temperature limit up to 800ºC. I don't know, maybe it's inaccurate information.

 

[EdStainless]

309 or 310 would be much better options.
The other concern about cycling is the stresses from differential heating and cooling rates/
Don't try to build this too rigid, it need to be allowed to deform some.
The stresses have to go somewhere and if you restrict movement you will get thermal fatigue cracking.
I have never had issues with 316 and MoOx, but I have seen it in higher Mo grades.

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P.E. Metallurgy, consulting work welcomed

 

[XL83NL]

309 filler metal, as often used for DMW, is not recommended for high temperatures, I think roughly 350°C and upwards.
Since this is a welded construction, wouldn't that make 309 a MoC an unfavourable choice?

Huub
- You never get what you expect, you only get what you inspect.

 

[PDH95]

And considering that there is standard air, just heated, around the piece, something like a 304L can be a good choice? Well, maybe there is a little higher humidity than outside the furnace.

 

[EdStainless]

310 would be a more robust solution. The nice thing about 310 is that it has no residual delta ferrite in the welds and so it is much less likely to eventually form sigma phase embrittlement.
310 will also have more usable strength than other grades.
309 and 310 welds are commonly used on HT equipment up to temps nearing 1000C.

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P.E. Metallurgy, consulting work welcomed

 

[PDH95]

About 310 I found this statement "Exposure in temperature range 450-850ºC results in sensitization, hence reducing
subsequent wet corrosion resistance". What do you think about that? Maybe 310S can solve this problem, if it is true.