Repair of LOX & LN2 tanks affected by SCC

Field erected storage tanks for storing liquid oxygen and liquid nitrogen are high tech storage devices. A typical tank is a double walled tank, the inner tank is made of stainless steel and the outer tank wall is made of carbon steel.The inter space between the inner tank and the outer tank is evacuated and filled with low thermal conductivity perlite powder.The inner tank and the outer tank is held in place by stainless steel wedges. One end of the Stainless steel wedge is welded to the out side of the inner stainless steel tank and the other end is welded to the inside of the carbon steel tank.The tanks were erected close to the sea shore. The atmosphere is humid and salt laden. When the tanks were ready we asked the steel plant authorities to provide raw water for hydraulic testing. Steel plant authorities could not provide the water required and asked us to postpone hydraulic testing. After one year steel plant authorities asked us to carry out hydraulic testing. When we went inside the stainless steel tank we were surprised to find a number of cracks on the surface. Examination of the cracks closely led us to conclude that the cracks are stress corrosion cracks. We will explain how we came to this conclusion later.