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Investigate Alternate Sealant Materials for Countersunk Fasteners Head and Hole Cavities on Exterior of Submarines

Description:

TECHNOLOGY AREAS: Materials/Processes

ACQUISITION PROGRAM: PMS 392 IN-SERVICE STRATEGIC AND ATTACK SUBMARINES AND NEW CONSTRUCTION.

OBJECTIVE: To develop a sealant, equivalent to the existing PR-944F polysulfide material, to fill and fair-in the fastener head and cavities on submarine exterior hulls in order to level the surface and protect the fasteners from seawater.  The sealant must be significantly easier to remove than PR-944F without increasing installation and cure times.

DESCRIPTION: Countersunk fastener hole cavities (up to 5” diameter and up to 3” thick) on submarine exterior hulls are filled and faired with PR-944F polysulfide sealant to level the surface and protect fasteners from seawater.  In order to remove the fasteners the polysulfide sealant, PR-944F, must first be removed. The removal of this sealant is very labor intensive and requires hand tools.  For example, ship yards estimate that to remove the PR-944F polysulfide from submarine hulls takes 1251 man hours of labor to remove all PR-944F seam filler during a typical  major availability.

An equivalent, alternate sealant that is easier to remove is sought to reduce the time and labor currently required for maintenance, thus reducing costs to the navy.  The sealant must exhibit hydrolytic stability when immersed in seawater and exposed to pressure cycling; must be environmentally friendly; safe for workers to use; have no adverse impacts on fastener materials, epoxy paint, rubber, urethane, metallic and Glass Reinforced Plastic (GRP) substrates; and provide adequate adhesion to fastener materials, metallic/nonmetallic substrates, paint systems and hull coatings to remain affixed while at sea.  It must exclude water under pressure from the surfaces it adheres to and have minimal compression/set under pressure.  The application method must be feasible from a vertical, horizontal, or overhead location with minimal sags, runs, or drips without increasing installation and cure times beyond those currently existing for the PR-944F.  Installation, storage, shipping environments and requirements must be no more stringent than those currently required for PR-944F. Sealant packaging costs and shelf life shall be equivalent or superior to those for the current system.

PHASE I: Develop and define a concept to identify an environmentally friendly, safe sealant that is easier to remove than the current PR-944F.  Define concepts to show its capability to replace PR-944F on submarine hulls with equivalent capability to exclude water under pressure from the surfaces to which it is applied. Concepts must include test methodologies for measuring hydrolytic stability when immersed in seawater and exposed to pressure cycling with minimal compression/set. Conceptual materials must  have no adverse impacts on fastener materials, epoxy paint, rubber, urethane, metallic and Glass Reinforced Plastic (GRP) substrates, and provide adequate adhesion to fastener materials, metallic/nonmetallic substrates, paint systems and hull coatings to remain affixed in an at-sea environment.

PHASE II.  Demonstrate and validate the sealant identified from Phase I to replace PR-944F on representative submarine hull section or mock-up that incorporates the desired typical features of interest. This includes countersunk fastener hole cavities up to 5” diameter and up to 3” thick. Evaluate the sealant from Phase I to validate that it can be prepared and installed without increasing installation and cure times beyond those required by PR-944F. Verify installation environment requirements. The application method must be demonstrated to be feasible from a vertical, horizontal, or overhead location with minimal sags, runs, or drips. Ensure cured sealant does not shrink causing separation from edges or exposing substrate.

Removal methods shall be identified and employed to evaluate the ease of removal for the sealant. During removal of the selected material, it shall be demonstrated that there is no adverse impact on fastener materials, surrounding paint and hull coatings, as well as substrates.

The environmental requirements for material installation, storage and shipping will be determined and must be no more stringent than those currently required for PR-944F.  MSDS and material data sheets for the material shall be generated and supplied.  The required sealant kit packaging costs shall be determined and must be no more than the existing material costs.  Determine and evaluate any receipt inspection and quality assurance testing necessary for the sealant from Phase I including periodicity and test procedures.

PHASE III: Evaluate and validate the sealant to ensure that it meets the prescribed properties through testing a representative fabricated submarine hull section with fastener cavities.  A representative fabricated hull section should also be tested to evaluate the ease of removal of the sealant. The application method must be demonstrated to be feasible from a vertical, horizontal, or overhead location with minimal sags, runs, or drips, and the sealant must also be verified to be environmentally friendly and safe.  Evaluate the sealant from Phase II to validate that it can be installed without increasing installation and cure times beyond those required by PR-944F.  Verify installation environment requirements.

The environments and requirements for material installation, storage and shipping will be determined and must be no more stringent than those currently required for PR-944F Material Safety.  Data Sheets for the material shall be generated and supplied.  The required sealant kit packaging costs shall be determined and must be no more than the existing material costs.  The shelf life for the sealant from Phase II shall be determined and shall be no less than 1-year (preference for over 2 years).  Determine and evaluate any receipt inspection and quality assurance testing necessary for the sealant from Phase II including periodicity and test procedures.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Marine and architectural sealant.

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