The copper tube dia. 35 · wall 1.5 mm made a component of a cooling system with
freon R404a under 1.7 MPa as the cooling medium. The damaged length of the tube
was installed in an under-floor duct and directly covered with sand. The sand was covered
with a layer of tar board and poured with concrete. After one-year operation, leakages
appeared in form of longitudinal cracks (Fig. 1) concentrated within a strip at the tube
top.