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The Challenge

The Department of National Defence (DND) appointed Babcock Canada to conduct an Extended Docking Working Period (EDWP) for Her Majesty’s Canadian Submarine (HMCS) CORNER BROOK under the Victoria In Service Support Contract (VISSC). Visual inspections indicated significant and widespread corrosion on the crown of the pressure hull, where Babcock recorded pitting of up to approximately 30% of the parent material in depth. Standard methods to repair extensive areas of pressure hull corrosion conventionally rely on complete plate replacement which was not feasible within the EDWP program constraints. Using weld overlay was a valid option for repairing the corrosion; however, the available weld overlay repair procedure supplied by DND limited the pressure hull repair area to a maximum of 150mm2.

The Solution

As the corrosion on COR’s pressure hull covered an area greater than 150mm2, a new weld repair procedure was needed. Babcock worked with an Ontario based company to develop a new weld procedure that utilized an automated Gas Metal Arc Welding (GMAW) machine mounted to a rail. This allowed for consistent weld overlay over large areas. However, the procedure had to be certified before using the automated GMAW machine. Several weld coupons were created and underwent non-destructive / destructive testing. The non-destructively tests (NDT) performed included Visual Testing, Magnetic Particle Inspection, and Ultrasonic Testing & Radiography. The destructive tests performed included Charpy Tests, Tensile Tests, Cross-Weld Metal Tensile Tests, Side Bend Tests, Heat Affected Zone Charpy Tests, and a Plain Bulge Explosion Test. The weld procedure passed all criteria and deemed acceptable for use in the EDWP with DND approval of the revised weld overlay repair procedure.

Benefits to Customer

› Successful application of the weld repair to HMCS Corner Brook’s pressure hull for large-scale weld repairs up to 5m2 in size
› No pressure hull plate replacement to repair large areas of hull corrosion
› Expeditious repair of hull corrosion
› State-of-the-art and fully Canadian solution
› Developed a fully qualified automated GMAW welding procedure
› Developed agreed inspection test plan / NDT procedures for large-scale weld repairs