Internal Loads on Pressure Vessel

[GravyBagel]

I work with several large pressure vessels. In operation, the vessel lids are removed and heavy tooling/materials are placed into the vessels (similar to a composite autoclave). I am not a pressure vessel engineer, but I am very concerned that the stresses applied by the tooling are not being accounted for in the design of these vessels. The drawings include a pressure and temperature rating as well as a hydrostatic test, but none of the documentation makes any reference to point loading or solid loads within the vessels. The vessels are delivered without internal components to support this tooling. Support rings are dropped into the vessel to support the tooling, but not attached, lest they be considered 'altering the vessel'.

For those with more experience, I was hoping you could provide insight on whether these concerns are valid or not and if so, how might I broach this topic with corporate leadership? (Ideally with some code references for credibility)

Thank you!

 

[JStephen]

The problem you have is that you don't need to bother calculating stresses for a negligible load, but then the only way to confirm if it is negligible is to calculate the stresses anyway.
You have stresses at the point of contact or increased loading at the supports.
In the case of the supports, one thing to check is if the vessels were designed for a full-of-liquid condition, but only operate as partially full or full of steam/gas/vapor instead. In which case, actual operating loads may be lower than design loads.
The higher the design pressure, the less likely the weight of the internals will affect the design, but there's no way to confirm a particular case without running up some numbers one way or another.

 

[GravyBagel]

Hmm, I suspect I wasn't very clear. We are placing steel tooling that is roughly the full water weight that the vessel will hold. That load is sitting on a ring resting against the head of the vessel. As the load ring is not perfectly matched to the vessel, there are also stress concentrations resulting from fit mismatch, so we're probably talking about most of that load sitting in 3 to 4 places.

I don't believe these negligible loads, but I may be off base here compared to typical loads experienced by pressure vessels. The vessel is designed for a full-of-liquid condition, but operating in a partially-full-of-steel-and-other-stuff condition (roughly equal weight, very different distribution. I worry that this changes the loading condition significantly.
These particular vessels are designed for vacuum and 50 psi, running at 300°C. The use band heaters though, so I strongly suspect that 300°C inside the vessel (air temp) means something much higher at the surface of the vessel. This is another battle I am fighting regarding the safety of this equipment, but not inherently related to this. Just noting that these vessels are not running under simple conditions. We have seen some of them slowly collapse over time under the load due to vacuum, not a sudden collapse, but a gradual failure.

My current concern is coming from a major scale up that has occurred, where a larger vessel was ordered. I think we are going to get ourselves in trouble or worse and get someone hurt. I'm trying to make sure that I'm not being a windbag though and coming from a place of reason.

 

[SnTMan]

...but none of the documentation makes any reference to point loading or solid loads within the vessels.

You can take it to the bank that fabricators do not design for loadings that they are not aware of.

Regards

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TGS4]

Likely a valid concern. What's the Code of Construction for these vessels (need that for an appropriate Code reference)?

 

[GravyBagel]

Likely a valid concern. What's the Code of Construction for these vessels (need that for an appropriate Code reference)?

ASME Boiler and Pressure Vessel Code (2004 Edition), with the exception of Sections III and XI.

 

[TGS4]

Is it Section VIII, Division 1, or Division 2? Or something else? Section I (unlikely)?

 

[GravyBagel]

Section VIII Div 1, 2004 Edition A 05 Addenda is listed on the drawing.

 

[TGS4]

UG-22 subparagraphs (b), (c), and (d).

 

[GravyBagel]

My man! Thank you.

 

[RVAmeche]

Isn't your concern that the designer wasn't aware of these toolings and loads? Ie not captured in UG-22?

 

[GravyBagel]

So a little update on this. We had previously spec'ed and built smaller vessels without considering loading of internals. This was done for decades with no issue, so I'm not going to try to rock that boat. The latest vessel is much larger, which is where my concern comes in. That being said, I was able to get the drawings and specifications and there was allowance added into these for internal loading and the design and specification is much better than previous iterations of these vessels. My concerns are largely subsided.

Thank you all for your help on this one.