respective yield strengths. They were exposed in sea- 

 water at the surface, 2,500-, and 6,000-foot depths 

 for various periods of time to determine their sus- 

 ceptibilities to stress corrosion. Their data are given in 

 Table 50. A 3-inch-diameter circular, unrelieved weld 

 was made in the center of the 6 x 12-inch specimens 

 of some alloys to impose residual stresses in them. 

 Transverse, unrelieved butt welds were made in other 

 specimens for the purpose of simulating stresses 

 induced during construction or fabrication. These 

 residual stresses were multiaxial rather than uniaxial 

 as was the case with the specimens with calculated 

 stresses. In addition, values of these residual stresses 

 were indeterminable. These specimens were exposed 

 in seawater under the same conditions as those above. 

 Their data are given in Table 51. 



Alloy AIS1 630,H925 with a transverse butt weld 

 did not fail by stress corrosion when stressed to 75% 

 of its yield strength either at the surface or at depth. 

 However, it did fail due to the unrelieved stresses 

 imposed by the circular weld after 403 days of 

 exposure at the 6,000-foot depth. The crack pro- 

 pagated across the weld bead. 



Specimens of transverse, butt-welded AISI 

 631,TH1050 failed when stressed to 50% of its yield 

 strength and exposed both at the surface and at 

 depth. Specimens with circular welds also failed when 

 exposed at the surface and at depth. At the surface 

 the cracks extended radially from a point inside the 

 circle to the circular weld bead. At depth the crack 

 extended across and around the outside edge of the 

 weld bead. 



Specimens of transverse, butt-welded AISI 

 631,RH1050 failed when stressed to 75% of its yield 

 strength and exposed at the 2,500-foot depth. Speci- 

 mens with circular weld beads also failed when 

 exposed at depth. The cracks originated at the out- 

 side edge of the weld beads and propagated circum- 

 ferentially in both directions either at the edge of the 

 weld bead or in the heat-affected zone. 



Specimens of alloy AISI 632,RH100 with a trans- 

 verse butt weld did not fail by stress corrosion when 

 stressed to 75% of its yield strength and exposed 

 either at the surface or at depth. However, a specimen 

 with a circular weld failed during 402 days of expo- 

 sure at the 2,500-foot depth. The origin of the crack 

 was on the outside edge of the weld bead, and it 

 propagated circumferentially in both directions in the 

 heat-affected zone. 



Alloys AISI 634, CRT; AISI 635; ASTM 

 XM16,H950 and H1050; AL362.H950 and H1050; 

 and alloy 18Cr-14Mn-0.5N were not susceptible to 

 stress corrosion under the conditions of these tests. 



Alloy PH14-8Mo,SRH950 with a transverse butt 

 weld failed by stress corrosion cracking when stressed 

 to 50% of its yield strength and exposed at depth. 



Specimens of 15-7 AMV in the A, RH1150, and 

 RH950 tempers failed by stress corrosion cracking 

 when stressed at 35, 50, and 75% of their respective 

 yield strengths and exposed at depth. Alloy 

 15-7 AMV, RH1 150 failed when exposed at depth due 

 to the stresses imposed by it being squeezed between 

 insulators such that it was slightly bowed. Alloys of 

 15-7AMV,RH1150 and RH950 failed by stress cor- 

 rosion when exposed at depth; the cracks originated 

 at unreamed, drilled holes in the specimens. 



5.4.6. Mechanical Properties 



The effects of exposure on the mechanical 

 properties of the precipitating-hardening stainless 

 steels are given in Table 52. Generally, the mechanical 

 properties of the precipitation-hardening stainless 

 steels were adversely affected by exposure in seawater 

 both at the surface and at depth. 



5.5. MISCELLANEOUS STAINLESS STEELS 



Included in this category are the case and 

 specialty stainless steels which could not be included 

 in the other classifications. Their higher nickel con- 

 tents and the addition of molybdenum are to increase 

 the range of protection of their passive films and to 

 increase their r< istance to pitting corrosion. Because 

 these passive films are so much more resistant to 

 destruction, any corrosion '-• localized in the form of 

 crevice and pitting. 



The chemical compositions of the miscellaneous 

 stainless steels are given in Table 53, their corrosion 

 rates and types of corrosion in Table 54, their stress 

 corrosion behavior in Table 55, and the effect of 

 exposure on their mechanical properties in Table 56. 



These alloys were considerably more resistant to 

 corrosion than the other alloys. There were two cases 

 of crevice corrosion at depth of alloy 20Cb, with the 

 deepest attack being 102 mils. There were also two 



134 



