UHX design conditions 1

[McJe]

Dear all,

I've got a question about the different design conditions one should considder to calculate a heat exchanger with fixed tubesheets.

Sometimes the customer defines the design conditions theirself, but for quotation requests most of the times no conditions are predefined.

Depending on the choosen conditions, the results might differ a lot. The tubesheet thickness is strongly determined by these conditions.


Design conditions that sound logical to me are:
1) operating pressure on tube and shell side + mean metal temperatures.
2) start-up and shut down situations (some cases with pressure 0 or full vacuum if requested by customer). In these cases, the operating pressures and fluid temperatures are used.
3) Shell side / tube side failure: operating pressure + fluid temperatures

Do I need to include a design condition with:
4) the design pressures together with mean metal temperatures?
5) design pressures together with design temperatures?
6) operating pressures with design temperatures?

Am I missing important cases?

which cases do you take in account?

Best regards,
Jeroen.

 

[SnTMan]

McJe, Part UHX 13.4(a) explicitly lists design conditions to be considered, however others may be as well.

In my experience:
Use design pressures only, the difference between design and operating pressures will not usually have much effect on fixed tubesheet design.

Use mean metal temps only for the effects of differential thermal expansion. Design temperatures are rarely if ever used in evaluating fixed tubesheet design, see UHX 19.2.2

I would not normally consider any upset or start / shut down cases not specified by the customer, as it is difficult to determine which might be realistic and they can have a drastic effect on the design.

For a proposal I would consider, and so state, that only the normal operating case is considered unless the proposal explicitly requires other defined cases.

Regards,

Mike

 

[gr2vessels]

I would suggest to include other loads as well, typical for the fixed tubesheet, like the weight of the connected channel and/or return end cover, the external nozzle loads affecting the tubeside nozzles. Obviously, the design shall include the design pressure and temperature, not the operating conditions. However, the mean metal temperatures have to be used with the operating conditions, to avoid excessive over design.
Cheers,
gr2vessels