Using impulse hammers to identify debonded special hull treatment areas during VCS construction will save significant costs rather than correcting the problem after delivery. NDTnet photo
This Navy Metalworking Center (NMC) project investigated the use of impulse hammers to increase the accuracy of detecting debonded areas.
Special Hull Treatment (SHT) must be sufficiently adhered to the hull to permit longevity of the system and to ensure peak functional performance while in service. Debonding or delamination of the system can degrade both durability and performance. To ensure proper adhesion, quality inspections are completed after installation of the system. The current inspection process consists of manually tapping the SHT using a hammer to identify debonded areas, which is very subjective to the inspector performing the inspection.
Use of an impulse hammer mimics the current inspection method; however, the input force and response are measured electronically instead of using human senses. Prototype test equipment is being generated as part of this project. Additional evaluation and possible modifications need to be completed to transfer this technology into the construction process for VIRGINIA Class submarines (VCS).
Identifying and correcting a debonded SHT area during VCS construction is significantly less costly than correcting the problem after delivery of the ship. During construction, the processing equipment, staging, and environmental controls are already in place. While the labor to correct the problem in dry-dock is similar to that during construction, additional effort is required to set up the equipment and staging area and to establish the proper environment in a dry-dock situation. A cost avoidance of $348K per hull may be realized by repairing SHT debonds during construction as opposed to after delivery.
Detailed inspection procedures are being generated and used for training of inspection personnel, and construction references are being updated to identify the new inspection technique to be used during installation of the SHT system. Additional inspection systems must be procured by the shipbuilder to have sufficient testing capacity to support new construction. Implementation is planned for early 2013 at General Dynamics Electric Boat for SSN 786.
General Dynamics Electric Boat Corporation
Naval Sea Systems Command (NAVSEA)
Naval Surface Warfare Center, Carderock Division
PMS 450 Virginia Class Program Office
Portsmouth Naval Shipyard
Pearl Harbor Naval Shipyard
Puget Sound Naval Shipyard