Purpose:
Virtually every military gas turbine engine (GTE) system in service depends on electrolytic hard chrome (EHC) plating in the engine overhaul process. Navy, Air Force and Army aircraft depots generally use EHC in GTE maintenance to rebuild worn or corroded parts following machining to restore dimensional tolerance or to replace worn or damaged chrome that had been previously applied. Hard chrome plating utilizes chromium in the hexavalent state (hex-Cr) which is a known carcinogen. As a result, the Environmental Protection Agency has issued fairly stringent air emission standards for hex-Cr, and the Occupational Safety and Health Administration has established a permissible exposure limit (PEL) for hex-Cr in the workplace at a level of 0.1 mg/m3, with an expectation that the PEL will be substantially reduced in the near future, thus greatly increasing the cost of chrome plating to the Department of Defense (DoD). Because of increased operational requirements on GTEs, there are additional concerns that are related to the in-service performance of EHC. High-velocity oxygen-fuel (HVOF) thermal spray coatings are being validated by the Hard Chrome Alternatives Team (HCAT) and the Joint Group on Pollution Prevention under a separate ESTCP program as a replacement for EHC for line of sight applications on aircraft components such as landing gear and hydraulic actuators. The current project will parallel that effort with the objective of validating HVOF coatings as a cost-effective, superior performance replacement for EHC plating on different types of components used in gas turbine engines.
Description:
The HCAT is working with the DoD Propulsion Environmental Working Group to develop and execute Joint Test Protocols (JTP) to qualify HVOF and advanced plasma spray coatings as a replacement for EHC. Partnerships are being established between original equipment manufacturers and the military. These include General Electric Aircraft Engines with the Naval Aviation Depots in Jacksonville, Cherry Point, and North Island for the TF34, T58 and LM2500 engines; Pratt & Whitney with Oklahoma City Air Logistics Center (ALC) for the F100 and TF33 engines; and Rolls-Royce Allison with San Antonio ALC for the T56 engine. The JTPs will include extensive material testing, such as fatigue, wear, and corrosion testing, and selected component and engine testing to verify the performance of the thermal spray coatings in comparison to EHC coatings. In addition, producibility testing and assessments will be conducted which will include stripping, grinding, and assembly/disassembly operations. Joint Test Reports will be issued on the results of the testing, and cost/benefit analyses comparing thermal spray to EHC will be prepared. At the conclusion of the project, new repair procedures will be documented for the depots.
Benefits:
Successful demonstration and validation of the thermal spray coatings for the repair of gas turbine engines and their insertion into DoD depots will result in a significant reduction in toxic waste disposal and a safer working environment. Use of the thermal spray coatings will also result in a reduced turnaround time for repair and increased performance, leading to a reduction in life-cycle costs. (Anticipated Project Completion - 2005)
Contacts:
Mr. Bruce Sartwell
Naval Research Laboratory
Code 6176
4555 Overlook Avenue, SW
Washington, DC 20375
Phone: (202) 767-0722
Fax: (202) 767-3321
E-mail: sartwell@nrl.navy.mil
Mr. Frank Ivancic
Chairman, DoD Propulsion Environmental Working Group
Air Force Aeronautical Systems Center (ASC/LPJ)
2145 Monahan Way (Building 28)
Wright-Patterson AFB, OH 45433
Telephone: (937) 255-0444 ext. 3185
Fax: (937) 656-7118
E-mail: frank.ivancic@wpafb.af.mil
