Two types of vibration damage are prevalent in cross-flow regions of steam generators (Shin & Wambsganss, 1975).

• Tube-to-baffle impact.

• Tube-to-tube collision.

(Thorngren, 1970) deduced "damage numbers" for the two types of damage, based on the assumption that tube is supported by baffles and deflected by a uniformly distributed lift force. These damage numbers are given by following equations:

where

NBD < 1 for safe design. NcD < 1 for safe design.

CT = Maximum gap between tubes. d = Tube outer diameter.

dt = Tube inner diameter. /B1 = Tube-to-baffle-hole clearance factor.

E = Modulus of elasticity. gc = Gravitational constant.

Bt = Baffle thickness. p = Mass density of shell side fluid.

l = Length of tube between supports. V = Free stream velocity.

Sm = Maximum allowable fatigue stress [ASME Pressure Vessel code Sec. III].

Collision damage is usually predicted together with baffle damage, whereas the latter can be predicted without collision damage being indicated, i. e., baffle damage is important factor when appraising design (Erskine et al., 1973). (Burgreen et al., 1958) were the first to conduct an experiment to investigate vibration of tube for fluid flowing parallel to tube axis. (Quinn, 1962) and (Paidoussis, 1965) have developed analytical and empirical expressions respectively for peak amplitude. Paidoussis give the following expression:

A = a_4 U 1-6s1srQ-25 f dh_’I0’4 P2/3(5 x1Q-4 x Kp) d ~ai I + U2 I d ) I + 4p

Later on a number of expressions for peak and RMS amplitudes have been developed (Shin et al., 1975, Blevins, 1977).