longitudinal tensile stress in tube portion 102 is quite low away from plug 104 as one travels along tube portion 102 towards plug 104 the longitudinal tensile stress begins to increase indicating how weld joint 106 constrains the expansion of tube 102 when hydraulic fluid is applied inside cylinder 100 the longitudinal tensile stress reaches a maximum in the vicinity of weld joint 106 it rapidly falls off as we traverse path u201c p u201d into plug 104 in a similar fashion the hoop stress indicated by curve 302 is at a maximum in tube 102 and drops to near zero in weld joint 106 thus the longitudinal tensile stress in cylinder 100 reaches a maximum at weld joint 106 this high longitudinal tensile stress produces weld joint failure its effects are amplified by the fact that it is applied right at the root of a u201c crack u201d u2014 the joint between the tube and the plug where the weld is formed this region while not formed by cracking but by welding is a stress concentrator due to its very small radius of curvature right where the weld is formed fig3 b illustrates the changes in cylinder stress provided by the use of o ring 124 as in the.