MAWP of Expansion Joint on Fixed Tube sheet Type Exchangers.

[DK44]

When designing Fixed Tube sheet Exchangers having Shell Expansion Joint, as per ASME Sec VIII Div 1 by PV Elite, it is observed that MAWP on Shell Side and Tube side due to Expansion joint effect (especially its annular flat portion)is much lower than Design pressure. PV Elite appear to give a mild warning not firm like if lower by other components.
1. Why PV Elite does not give firm warning.
2. Does code require to calculate MAWP for Expansion joints also.
3. Meeting this condition appears difficult due to thinness of the Expansion joint / Bellows.
4. Is it necessary to comply with MAWP to be always higher than Design pressure even with Expansion joint effect.

 

[SnTMan]

DK44, 1. No idea. Suggest you contact Hexagon / Integraph / Coade.
2. No, see definitions, MAWP
3. Yes, expansion joints are troublesome, but are routinely designed successfully.
4. No, but MAWP must be at least equal to design pressure.

Regards,

Mike


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

 

[DK44]

Thank you SnTMan.
Regarding 2, do you mean that by Code, it is not necessary to calculate MAWP for Expansion joints / Bellows on Shell. Is it not an essential pressure part? I am not clear on this.

 

[SnTMan]

It is not required to calculate for any component or chamber of a vessel, nor for the vessel as whole an MAWP that exceeds the design pressure for that component, chamber or vessel.

Quoting from the definition: "The design pressure may be used in all cases in which calculations are not made to determine the value of the maximum allowable working pressure."

Regards,

Mike


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

 

[DK44]

Thank you SnTMan.
When client advises Hydro test Pressure to base on MAWP and some times even MAP, is it exempted by code to exclude MAWP / MAP calculations for Expansion joints / Bellows. But under Hydro test pressure based on MAWP / MAP of all other Pressure parts, the Expansion joint / Bellows being subjected to same Test Pressure may be over-stressed.
How to deal this situation.

 

[SnTMan]

DK44, the test pressures shall be based on the MAWP of each chamber of the vessel The MAWP of the chamber is based on the lowest MAWP of all the components making up the chamber. As previously noted this MAWP may be set to the design pressure.

Component stresses at hydro are obviously higher that the allowables used for design. This is usual and expected. Note that Code places no actual limit on stresses at hydro, although it is fairly common for client specs to limit them to 90% of yield at the test temperature.

As to the expansion joint itself you should note that the larger portion of the design stresses are due to differential thermal expansion between the shell and the tubes. You should also note this source of stress is absent during hydro as the shell and tube sides are presumably at the same temperature.

Hydrotest pressures should not present a problem for a proper design. If in doubt, calculations can be performed for hydro pressures to confirm.

Regards,

Mike

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

 

[DK44]

Thank you SnTMan once again.
1. If MAWP is greater than Design pressure, it can be set to (Limited to) Design Pressure if agreed by the Client. However, if the MAWP is lower than design pressure it cannot be set so. The question is if MAWP for the expansion joint / Bellows is calculated,found least and less than Design pressure, what to do.
2. Does Expansion Joint / Bellows suppliers provide MAWP for the component?

 

[SnTMan]

DK44, 1. Redesign the joint. Each component of the vessel must meet the design conditions.
2. In my experience: a) Flanged & flued joint, the vessel designer is responsible for the design, MAWP will rarely if ever be set higher than design pressure. The joint supplier merely fabricates the joint.
b) Bellows joint: The joint supplier is responsible for design and fabrication, but to design conditions supplied by the buyer. MAWP will rarely if ever be set higher than design pressure.

Regards,

Mike

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

 

[DK44]

SnTMan,
Nay the Bellows suppliers are responsible for design, manufacture, testing and supply of the Bellows.
Do they guarantee the MAWP ≥ Given Design Pressure

 

[SnTMan]

In my experience they guarantee only to the design conditions supplied by the buyer.

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

 

[DK44]

SnTMan.
1. Guaranteeing given Design conditions is a must and OK.
2. But Calculations is their responsibility which include MAWP / MAP when required.
3. The question is when required, can MAWP and MAP be calculated for EJ / EB, if so by what method.
4. Do the suppliers of the component provide such calculations.

 

[SnTMan]

DK44 I cannot offer anything further. You really need to ask these questions of your proposed vendor(s).

Regards,

Mike

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