Flanged and Flued Expansion Joints

File:PVE-4305, Last Updated: June 22 2010, By: LB
ASME VIII-1 mandatory Appendix 5 provides guidelines for the design of flanged and flued expansion joints, but does not provide methods of calculating the stresses, fatigue life or spring rate. ASME Appendix 26 (and EJMA) provides rules to calculate these values, but the configuration of a flanged and flued expansion joint does not match that used in appendix 26 or EJMA.

Here the rules of Appendix 26 are applied to an Appendix 5 flanged and flued expansion joint. The calculated results are compared to finite element analysis which shows that using the Appendix 26 calculation method is conservative.

Flanged and Flued Profile

Cross section of a flanged and flued expansion joint

 

Flanged and flued expansion joint

Flanged and flued expansion joint

The flanged and flued expansion joint has a straight crown and straight cuff neither of which are included in the ASME/EJMA stress and flexibility calculations. These straight sections affect the stresses, spring rate and cycle life. Here an expansion joint with the dimensions Db=24, t=1/4, w=3 and q=3 is examined by FEA with and without straight sections. The pressure used is 300 psi and the bellows is compressed by 1/2 inch.

Standard profile bellows

Profile of a bellows that can be analyzed by ASME/EJMA methods – no straight crown or cuffs are included. The section is swept 1° for analysis

 

Flanged and flued expansion joint

Stress results for the standard shape at 300 psi and 1/2″ compression. Maximum stress is 262,000 psi.

The initial stress results show a high stress of 260,000 psi which compares with an EJMA computed stress of 215,000 psi (see link below for the EJMA calculation results). The stress indicates that the bellows is operating above the yield point so the EJMA predicted spring rate will be too high. Comparing the accuracy of FEA vs EJMA methods is beyond the scope of this article.

The addition of the 1″ straight crown lowers the stress to 249,000 psi:

Addition of a straight crown

Addition of a 1″ long straight crown

 

Flanged and flued expansion joint

Stress results for the modified shape – same pressure and displacement. The stress has lowered to 250,000 psi.

The further addition of straight cuffs lowers the stress more:

Standard profile bellows

Straight cuffs have been added to the bellows

 

Flanged and flued expansion joint

Stresses have dropped to 175,000 psi

The bellows stress has now been lowered to 175,000 psi, less than the EJMA calculated 214,000 psi. The use of EJMA methods for this flanged and flued bellows is conservative and acceptable. The EJMA calculated spring rate will be too high and the theoretical cycle life too low both of which are conservative errors. See the link below for the EJMA calculations for this expansion joint.

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