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Chromate Sealant Alternatives
 


Current Usage
A wide variety of chromated organic sealants is used to seal equipment against water ingress in applications such as electronics and interior and exterior panels in vehicles and aircraft. Chromates are incorporated into some sealants to inhibit corrosion of underlying metals.
 
Typical Applications
Specifications
  • Joint sealing
  • Aircraft interior and outer mold line panels
  • Polysulfide sealants for aircraft access panels, windshields
  • Vehicle access panels
  • Electronic equipment
  • Non-setting sealants
  • Aircraft bays, wheel wells, fuel tanks, radomes
  • Wet-install fasteners
  • Army and Marine Corps tactical shelters
MIL-PRF-81733D
QPL-81733
MIL-S-8802
 
ESOH Issues
Sealants may contain Cr6+, solvents such as toluene.
Cr6+ (CrVI, hexavalent chromium) is a known carcinogen that is strongly regulated under:
·         EPA Clean Air Act regulations
·         OSHA Occupational Exposure to Hexavalent Chromium (Cr6+ Permissible Exposure Limit is currently 5 μgm-3)
·         European regulations (RoHS and REACH)
·         DoD Policy Memorandum on Minimizing the Use of Hexavalent Chromium
Toluene is a VOC (volatile organic compound) and a HAP (hazardous air pollutant).
Exposure
Personnel may be exposed at the OEM level, during depot overhaul and repaint, and during operational level removal of access panels for inspection and repair.
·         The primary exposure issue involves applying the sealant since the Cr6+ and HAP concentrations are highest when the material is new.
·         Removing chromated sealant is an additional potential Cr6+ exposure source. 
·         Because sealants are usually well hidden, they do not present a significant source of exposure to users during service, but operational and depot maintainers will be exposed when removing panels, windshields, fasteners, etc. that may be sealed with chromated sealants.
Alternatives, Applications, Status
Primary alternatives are chrome-free, low-HAP versions, of which there are many on the market. Alternatives are commercially available and some have been authorized and implemented, especially in vehicles and commercial aircraft. Chromated sealants are not used in any Boeing commercial aircraft.
 
Common Cr6+ Alternatives
Examples of Alternatives, Authorizations, Implementations
Specifications
Faying and fillet sealants (edges and overlaps)
Non-Cr sealants, C-17
 
Tape sealants
Teflon tapes, C-17
 
Chrome-free wet-install sealant
Polythioether sealant. Pre-coated fasteners in validation
AMS 3277
 
For detailed technical and performance information, validations, authorizations and implementations see Surface Engineering Database. Search for Chromate Sealant Alternatives or High VOC Material Alternatives.