Original Date: 03/06/2006
Revision Date: / /
Best Practice : Corrosion Prevention
Raytheon Missile Systems’ Louisville facility, working with its vendors, implemented an innovative process for sealing bolt heads and insulating external connectors from the environment, preventing corrosion and water intrusion.
A corrosion control program has been in place at the Raytheon-Louisville facility since 1983. The Corrosion Control Program has its roots in a series of U.S. Navy (USN) Ordnance Alterations (ORDALTS) issued following an evaluation of the corrosion performance for the Phalanx Close-In Weapon System (CIWS). It was determined that corrosion problems on Phalanx were caused by galvanic corrosion between the aluminum components of Phalanx and stainless steel hardware. Water intrusion was also a contributing factor to the corrosion.
The ORDALTS prescribed the use of polysulfide sealants to isolate dissimilar metals and protect the hardware from the environment. The manual process was to seal with MIL-PRF-81733 polysulfide sealant, which was hand- applied, and top-coat the seal with AMS-S-8802 polysulfide sealant (Figure 2-1). The most common application was to seal bolt heads and connectors.
In 2005 Raytheon-Louisville worked with its material vendors to implement a better method for protecting hardware and connectors from the environment. The solutions were to use cold-shrink tubing on external connectors and poly caps for fastener heads. Poly caps are molded AMS-S-8802 polysulfide sealant filled with MIL-PRF-81733 polysulfide sealant, then frozen. Poly caps are supplied in the frozen state and thawed for use (Figure 2-2). Cold- shrink is expanded material that is constrained from collapsing. When the constraint is removed, the material collapses to its normal state and seals around the connector or cable. The mechanical seal is tight enough to insulate the connectors from the environment.
The implementation of poly caps has reduced touch labor for the hardware sealing operation by 75% and reduced the drying time necessary for polysulfide sealants by 50%. Hazardous material use and waste has also been reduced. Poly caps have increased safety due to a decrease in injuries associated with the application and removal process. Because it is a new method of applying the same material, this process did not require an engineering change. Cold- shrink has resulted in a 50% reduction in the time spent completing the connector sealing operation. The drying time of the polysulfide sealants and hazardous material has also been eliminated from this operation. Both processes have significantly increased the consistency and uniformity of the application of the material.
Figure 2-1. Hand-Applied Polysulfide
Figure 2-2. Poly Caps
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