The M119 Towed Howitzer was designed and built in the UK. The 105mm gun was subsequently purchased for use as a “lightweight” weapon for the U. S. Army. A corrosion assessment of the howitzer was performed tier the howitzer was delivered to the Army for evaluation. The results of the assessment revealed that the howitzer was not designed for corrosion resistance.
BACKGROUND
The M119 Light Howitzer was a “non-developmental item” procured horn the United Kingdom (UK). Anon-developmental item is a component or system that is already in service and is immediately adaptable for Army use. This means the system does not have to undergo the normal environmental testing regime used to qualify new systems coming out of R & D. The M119 howitzer was intended to replace the heavier M102 and M101A1 towed howitzers currently in the Army inventory. The M119 howitzer can be air-lifted by helicopter to enhance its mobility to be used anywhere in the world. Otherwise, its normal prime mover is the High Mobility Multipurpose Wheeled Vehicle (HMMWV). Older howitzers usually required larger vehicles for their towed mobility. The U. S. Army Armament, Munitions and Chemical Command has a Corrosion Prevention and Control (CPC) Policy No. 702-7 which directs CPC be an integral part of the life cycle for all mission material. The policy includes a CPC review of the design along with maintenance and operational procedures.
APPROACH
A dual approach was used to perform the corrosion assessment. The first approach was to contract with a firm that had some corrosion assessment experience. This firm was tasked to review the design of the system which included on-site surveys of the howitzer. In addition the operation and maintenance manuals were reviewed for corrosion adequacy. The contractor was directed to identify the corrosion problems and supply recommended solutions to the problem.
The second approach was an in-house effort to review the drawings and assess the adequacy of the protective finishes on the component parts. These component parts makeup the major assemblies that may be painted or given some other final finish.
RESULTS
The contractor determined that low carbon steel was the material of choice for the design. In some cases, the parts were only treated with a rust preventive oil. In most cases, the finish of choice was manganese phosphate plus oil. Some parts, basically fasteners, were coated with cadmium. There were a number of dissimilar metal (galvanic) couples. Copper-alloy bushings in contact with aluminum were the worst case. In other areas, the copper alloy bushings were in contact with phosphate coated and oiled steel parts. Since the oil is water displacing, it can also be displaced by water leaving a copper-steel galvanic couple which results in corrosion of the phosphate coated steel. A unique aspect of the lightweight howitzer is the tubular stainless steel trails. The stainless steel material is 15-5 PH which denotes that the material can be precipitation hardened (heat treated) to achieve a high strength and thus reduce the weight of the trails.
