How is explosion pressure determined for a reaction furnace that had a design pressure of 15 psig?

[Jaideepk]

I want to determine the maximum pressure a reaction furnace can take in case of an internal explosion. The material is SA516 70N, shell thickness is 0.625", CA is 0.125" and operating temperature is 675°F. Internal radius is 41" and E IS 0.85. I am not sure if I can use the regular circumferential and longitudinal stress formula to determine the pressure. I would appreciate your help.

 

[TGS4]

Unsurprisingly, this is a remarkably difficult question to ascertain an answer to. First, you have to define the duration and location of the explosion (really, what you're interested in is the pressure generated by the explosion and the time that this over-pressure event exists. In a cylinder, the pressure time-history can be quite complex, especially with reflected pressure waves. For a low-pressure vessel, the final failure may even be caused not by the over-pressure, but from the vacuum pressure generated immediately after the over-pressure.

Then, you're going to need to decide if you use minimum-specified properties for the steel or actual properties. Then, you're going to need to define "failure". Is it that something leaks? Is it that stresses exceed a certain value? What about local stresses? When I have done this, I use an elastic-plastic analysis (non-linear geometry and true-stress-true-strain curve), and also pay special attention to triaxiality (because that may be the initiation point for a failure). Of course, based on the duration of the explosion, you'll want to look into using strain-rate-dependant stress-strain curves - high strain rates typical of explosions can increase the strength of the material.

You'll also have to look into the temperature of the explosion and determine, based on the duration, whether that will raise the metal temperature.

So, not a simple task. You'll want to search the technical literature for "impulsively loaded vessels" for additional information. Good luck!

 

[Jaideepk]

Thank you TGS4. Where would you need to calculate this pressure, is there any benefit in calculating this value. The datasheet for the furnace, attached to a wasteheat boiler give an expsion pressure of 75psig at a stress of 0.9 of the hot yield. I could not figure out how this 75 psig was calculated. Would be knowing, by any chance.

Thanks

Jaideep

 

[TGS4]

My best guess is that the pressure/stress that you indicated is a uniform pressure and a hoop stress. It is somewhat interesting (and likely conservative), but certainly not related to anything that I would call "failure".