Jacketed vessel bulging on inside

[kwisatz_haderach]

We have a jacket heated agitated thin film dryer in our plant . 6 months ago it bulged on the inside. We fabricated a new vessel and after running for 6 months, it again got damaged by bulging on the inside on 6 locations like a flower. What might be the reason for this? This vessel is empty on the inside with blades scraping the inside of the shell and outside it is jacketed and heated by 2 bar steam through spiral baffles. Please tell me your thoughts about possible reasons behind this? Is the thickness sufficient. Please tell me how to calculate the thickness for external pressure. I got stuck on the unsupported length since it is stiffened by spiral baffles.

 

[r6155]

Any drawing?, any photo?
Regards

 

[LittleInch]

"Scraping"??

Are you missing wall thickness?

Have you checked/ measured?

Thermal miss match or Thermal cycling??

I would ignore the effect of the spiral baffles in your calculations. How "spiral" are they?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

We need images.
How is condensate handled?
Slugs of water in the system could cause some real issues.

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P.E. Metallurgy, consulting work welcomed

 

[kwisatz_haderach]

Please find the attached drawing.

 

[kwisatz_haderach]

EdStainless, condensate is passed from bottom of the jacket through two 1" condensate lines to a 2" line to ball float trap. According to the operator, it run smoothly for hours before it got damaged.

 

[r6155]

Need complete details of spiral baffles and jacket.

Regards

 

[XL83NL]

More details are needed.

But Ill give it a shot (Im not an expert by any means in this stuff). It appears you have inward buckling - external pressure issue?
Is the shell sufficiently strong for the coincidental case of 2 bar(g) on the jacket, and perhaps a low pressure (or even vacuum) on the shell - thus higher dP over the shell. Together with the heavy agitator on top, providing a compressive load on the shell? The shell is only 5 mm, which seems very small...

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

 

[EdStainless]

On your drawing show us where these bulges happen.
Have they been in similar locations both times?
What has been changed?
If they tell you nothing that just means that they didn't record it or measure it.
Something has changed either in the hardware or the process.
I am with XL83, I don't believe that the vessel is designed for 2bar external + vacuum internal.
Perhaps there used to be a system to prevent internal pressure drop?

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P.E. Metallurgy, consulting work welcomed

 

[LittleInch]

It looks to me like it just isn't able to handle internal vacuum.

There may be some reduction in wall thickness as well.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jt1234]

Interesting. I also have jacketed vessel (with half pipe and internal agitator). As other people said, check your calculation for external pressure due to the jacket design pressure. Most likely this was missed. In addition, internal force by the agitator due to the liquid viscosity and the rotating speed can deform the shell in an uneven way as blades sweeping around. Imagine by yourself how the force push and pull by eddy current that the shell will deform if not rigid enough. Unfortunately code does not talk about shell deformation, and I do not know how you can calculate the sweeping force without CFD analysis. In addition, SS is much soft than CS, and 5 mm is just too thin in my opinion.
In all, not rigid enough.
5 mm may be good for pressure, but many not be good for dynamic loading as stated above. Double down on the thickness or add external stiffeners to make shell rigid to resist sweeping force. Check external design pressure.

 

[LittleInch]

The jacket doesn't look spiral to me....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Compositepro]

The picture clearly shows that the inner wall buckled inward and plastically deformed around the the scrapers. Too much differential pressure across the inner wall. The spiral baffles certainly were not acting as stiffeners. The baffles were either not welded to the inner wall or the weld failed.

 

[kwisatz_haderach]

Edstainless, two times the bulge happened at the bottom jacket where the condensate drains, also i forgot to mention there is a blower that sucks the volatile gases out through the inside of shell. The bottom cone portion is open to atmosphere and i don't think it got clogged.

 

[kwisatz_haderach]

Little Inch, is it possible this could happen due to water hammer?

 

[kwisatz_haderach]

jt1234,how do you calculate the allowable external pressure for a vessel that has spiral baffles as this. What length do you take as unsupported length? I calculated without considering the spiral baffles and it got me around 1 bar. But the vessel worked well more than 3 months before suddenly failing like this.

 

[kwisatz_haderach]

Little Inche, jacket isn't spiral, it's just a CS cylindrical shell outside the SS shell, but to allow the steam to pass in a spiral manner throughout the periphery of the shell there are this flat strips of metal stitch welded in a spiral manner around the shell.

 

[LittleInch]

The baffles will add a little bit of strength but not much so it looks like you're operating very close to collapse pressure so any small change life e.g. a excess of condensate or small blockage in your system or flexing of the shell as the baffles go round and the shell will suddenly collapse.

Your shell is simply too thin.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[XL83NL]

What’s the metal temperature of the shell and jacket, approximately? They have different CTEs which also can be a real cause of additional stress

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

 

[r6155]

The complete drawing/sketch with dimensional information has not yet been sent to us, therefore I cannot provide any responsible feedback.

Regards