Dear All,

I am doing analysis for the existing 6" catalyst line. during unloading the catalyst, the temperature can goes as high as 760 deg.C. Currently the line is doing well, but in the stress results show that it is failed under SUSTAINED LOAD all along the line. The highest percentage failed is 950%. I have checked the Hot Stress allowable which is so low, 15857 kPa for 760 deg.C, A312 TP316H. The expansion case is pass though.

How can I solve this problem? I have played around with the hanger load and restraint but it still failed. If there is no way in solving this, we may change the routing.

Any other suggestion to pass this sustained case?

Failures in sustained load can be resolved through adjusting support spans / pressure.

To get rid of nearly 10x overload, you will need to add a mighty lot of supports.

Are you confident that your input data is correct ? 950% overload on 15857 kPa suggests a calculated sustained stress around 150000 kPa. that seems very high for a system that would not normally see much pressure. You might check your densities, or perhaps, units used throughout.

I am guessing here on your piping code, but if it is B31.3 then the circumferential weld efficiency factor (Wc in Caesar II) is probably lowering your hot allowable extremely at all bends, tees, and reducers. You might need a stronger high-temperature material, thicker pipe walls, plus additional supports to solve this problem.

Hi all,

Thanks for the reply.

To add. the pressure is pretty low, 1.1 barG. Under normal operation which is 400 deg.C, the stresses are passed. But for the worst case scenario which is 760 deg.C, it failed. It runs horizontally about 6 meters with 4 constant spring hanger distributed along the line, then goes down about 30 meters with the small in this vertical arrangement.

The input is correct. And if you see B31.3 for A312 TP316H, indeed this allowable at 760 deg.C is correct 15857 kPa, at the bend or tee is about 9500 kPa. I tried to find suitable material, but seem like at 760 deg.C, the allowable all pretty low, and i believe the weight also not very much difference if we use the same routing just to pass about 900% failure in code.

You are at 1400F holy @#%$@#%@#% your material itself has little strength and the creep weld joint strength reduction factor greatly lowers that already low number.

The simple fact that you seem not to understand these simple things and what they mean speaks to the fact that you are practicing outside your area of expertise I advise you to get help with this work from something other than a mere web forum before your efforts result in a design that leads to failure and injury!

Consult with ur process dept and find out if the line will see 760 C for sure. In one of our FCC catalyst lines, process finally backed out saying this temp will never occur (ofcourse after a series of discussion amongst licensor, process and others concerned!!).

SAMAbdul,

This has been the root cause of more of my and others grief than one would think. And your comment is extremely well taken!

Le0nhart,

You can't blame it all on the temperature. You are overstressed at any temperature.

Do your support loads look reasonable for sustained weight?

I would double check the densities you used for contents weight, insulation weight and your material to make sure they are correct and consistant with your user units.

I've been known to accidentally plug-in density as lbs/ft3 when I should've input lbs/in3. When I do that I get results like yours....or worse.

Also check your C.A. and wall thickness for all elements to make sure there are no typos that are causing this.

Good luck,