304L performance at High Temperature

[TrevorP]

We have had an emergency shutdown on our plant, and need to get in a new piece of pipework quickly to replace an economiser that will be sent for repair. The pipework is 12&quot; nb, and is for flue gases at low pressure <<1 bar, but high design temperature (810°C, 1490°F). I believe that the ideal pipework is 304H, but this is long delivery. Will 304L be OK in the short term (Say 2-3 months running)? What will be the failure mode, i.e. could the pipe potentially rupture catastrophically, or is it more likely to lead to a gradual leakage at the flanges?

 

[Metalguy]

Given what APPEARS to be low loads, if 304H survives for long periods of time, I see no reason why 304L would fail quickly. What was the failure mode of the old pipe?

You MIGHT have a small difference in strength, but corrosion-wise they should perform the same at those high temps.

 

[LSThill]

HI TrevorP (Chemical)

I disagree with Metalguy (Materials)304L @850F &quot;NO&quot;
alway check ASME SECTION II, MATERIAL &quot;PART D&quot;

RE: ASME SECTION II, MATERIAL &quot;PART D&quot; 304H @850F, SH=11,000 (OK); and 304L @850F &quot;NO&quot;

Leonard@thill.biz

http://www.thill.biz

 

[Metalguy]

Just because a material isn't &quot;approved&quot; by the code doesn't mean it won't work very well. He has an emergency condition, with very low apparent stresses.

At those very high temps. and conditions 304/304L does very well. We don't even know if he needs a code material or not.

 

[DLANDISSR]

TREVORP:
PER B31.3 (FOR PIPING) (ASME SEC II is for pressure vessels) 304L is OK up to 1500Deg F but the allowable stress drops off to 900PSI. 304H is also good for 1500Deg F and the stress drops off to 1400PSI.

304H is the best but 304L should perform satisfactorily, especially since the pressure is so low.

 

[kenvlach]

It doesn’t seem like a PV item so agree with Metalguy. Isthil, please note the T scale.
However, there are other SS alloys more suitable for high temperature.
Carpenter Stainless Steel. Selection. Alloy Data. Fabrication shows that the safe scaling temperature for 304 SS is 1600^oF (871^oC) whereas Types 446 and 7-Mo have a safe scaling temperature of 1900^oF (1038^oC).

 

[LSThill]

Hi TrevorP (Chemical)

I agree with DLANDISSR (Mechanical)& kenvlach (Materials), as the &quot;AI/engineer&quot; I would use 304H or better.

 

[TrevorP]

Thanks for the input - I appreciate it. No, this is definitely not a PV item.
In terms of corrosion, this is not really an issue - carbon steel would be acceptable, but am advised it will not take this kind of temperature. The rest of the existing pipework downstream of the economiser is 321 SS.
In terms of what caused the economiser to fail - that almost certainly was corrosion, but due to the chemical (High strength, high temperature caustic) on the other side of the economiser.