The three most significant results for the Thick Joint module analysis are the spring constant for the joint, the stresses in the joint, and the cycle life for the joint. These are discussed below.
Spring Constant
The software does not calculate the deflection of the joint. Instead it calculates the spring constant for the joint, which can be used in the Tubesheet module or elsewhere to determine the effect of the joint on the heat exchanger design.
Stresses
The software calculates the combined meridional bending and membrane stresses in the expansion joint and the attached cylinders. According to ASME, Section VIII, Division 1, Appendix 5, this stress should be limited to KS, where K is 1.5 for flat sections (the annular ring or cylinders) and 3.0 for curved areas of the inner and outer torus (or sharp corners). S is the basic allowable stress for the expansion joint material at operating temperature. Note, however, that this stress limit applies only to the stresses due to pressure - stresses due to deflection are limited by fatigue considerations rather than stress allowables. Thus the software only prints the allowable membrane plus bending stress for the case of shellside pressure.
Cycle Life
The cycle life of the joint is analyzed using the rules in the ASME Code, Section VIII, Division 1, Appendix CC. For Series 3xx stainless steels, nickel-chromium iron alloys, nickel-iron chromium alloys and nickel-copper alloys, the equation for cycle life is as follows:
N < [(2.2)/(( 14.2*Kg*Sn)/Eb - 0.03 )]^2.17
For carbon and low alloy steels, Series 4xx stainless steels, and high alloy steels, the equation for cycle life is:
N < [(2.0)/(( 15*Kg*Sn)/Eb - 0.011 )]^2.17
Where:
Kg = The fatigue strength reduction factor which accounts for the geometrical stress concentration factors due to local thickness variations, weld geometries, and other surface conditions. The range of Kg is 1.0 <= Kg <= 4.0 with its minimum value for smooth geometrical shapes and its maximum for 90 deg. welded corners and fillet welds. The program uses a Kg of 1.0 when the knuckle radius is greater than three times the expansion joint thickness.
Sn = The maximum combined meridional membrane and bending stress range in a flexible element due to the cyclic components of pressure and deflection.
Eb = The modulus of elasticity at design temperature. The software determines both the modulus of elasticity and the material type from the user-defined name of the external pressure chart.