STRUCTURAL INTEGRITY ASSESSMENT OF SPHERICAL STORAGE TANKS

Abstract Two spherical storage tanks for ammonia (volume 1000 m 3 ) have been tested in 1998 and 1999 by Non-Destructive Techniques (NDT) in accordance with the Periodic Inspection Regulations. These storage tanks have been constructed in 1979 using microalloyed steel St.E460 according to DIN, with thickness of 30 mm. The large number of transverse cracks in weld metal and longitudinal cracks in heat-affected-zone and along fusion line of inner welded joints has been detected. In order to estimate the residual strength, from both storage tanks, plates 500x500 mm were cut for the chemical, metallurgical and mechanical investigations. These investigations encompassed detailed toughness testing, including standard Charpy specimens, tested on instrumented pendulum, and fracture mechanics testing on standard SENB specimens for fracture toughness evaluation. Using data obtained by Charpy and fracture mechanics testing, the structral integrity of cracked storage tanks has been assessed