Can you take credit for a localised MDMT < Vessel MDMT? 2

[robsalv]

Basically, when reviewing an existing vessel's MDMT / MAT, every part of the vessel construction is reviewed and the warmest determined MDMT sets the vessels MDMT.

That is the level 1 view. This suggests that some parts of the vessel are suitable at lower temperatures. Hold that thought.


Here is a scenario:

- Largeish tower with an inlet nozzle 1/3 the way down. There's a credible contingency where a cool stream (not a shock chill situation) could enter the tower at a few degrees below the tower's listed MDMT. The stream is a small percentage of total tower volume so warms up to general tower temperature quickly. Alarms and procedures are in place to control inlet temperature and avoid breaching MDMT.

Now I haven't done the detailed MDMT review on the tower yet, but I'm confident that the local MDMT around the inlet nozzle can be shown to be below the global MDMT, especially if one applies a level 2 analysis locally.

The fluid only enters while the plant is operational and no contingency can be thought off that the whole tower will be cooled to the inlet fluid temperature.

Sooo, is it outside the codes to set a localised MDMT lower than the global MDMT?


...I was going to put this in the code forum, but this is a practical scenario in managing pressure equipment.


I'd appreciate your time and thoughts. Thanks in advance.

Cheers

Rob

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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[gr2vessels]

Rob,
Does UCS-160 apply to your column? It might.
cheers,
gr2vessels

 

[SJones]

ASME VIII Div 1, UG-20, (d).

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[robsalv]

Hmmmm, gr2vessel, I see why you are an MVP.

I think you have potentially provided a pathway to an answer. Even though I'm in Australia, the vessel is a circa 1960 ASME Vessel. Our local pressure vessel code doesn't have a similar clause that I can see... but a case may exist based on ASME VIII.

Alternatively, I've had a suggestion to fit an engineered teflon liner / refractory lining which projects into the vessel and therefore the cool fluid enters directly into the warmer mass of the tower fluid without contacting any metal...



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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."

 

[robsalv]

Didn't see your reply there SJones.

Hmmmm, rerate the tower locally with a new design temperature zone?????

Another option to consider!

Cheers

Rob



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"Life! No one get's out of it alive."
"The trick is to grow up without growing old..."