3M, PPG (through its PRC-DeSoto brand), and H.B. Fuller (through its Royal Adhesives and Sealants line) each offer their own polysulfide fuel tank sealant families, and platform bonding specifications, OEM approvals, and existing shop qualifications often determine which supplier's product is actually specified on a given program rather than one brand being universally preferred. It's common for an MRO shop to stock more than one brand to match whatever the original build called out.

Across PPG and similar polysulfide sealant lines, Class A generally denotes a brushable liquid used on fasteners, Class B a thicker thixotropic paste for fillet and injection seals, and Class C a thinner grade suited to faying-surface sealing. An S or M designation sometimes indicates a sprayable or fast-curing variant. The exact class definitions can vary slightly by manufacturer, so the specific product's datasheet should be checked rather than assuming the letter alone tells the full story.

Polysulfides combine strong resistance to jet fuel and aviation gasoline with the flexibility to withstand vibration and joint movement over the life of the aircraft, a combination that's harder to achieve with other common sealant chemistries. That's why they remain the default choice for integral fuel tank and fuselage sealing despite newer sealant chemistries being available for other applications.

AC-730 was engineered specifically for fuselage applications where dissimilar metals meet, adding a corrosion-inhibitive package on top of the base fuel resistance. If the joint doesn't involve dissimilar-metal contact and general fuel tank sealing is the only requirement, a standard grade like AC-350 may be the more straightforward choice, but the actual joint configuration should drive the decision.

Not by default. Chromate-free formulations like AC-730 are designed to deliver corrosion inhibition through alternative additive packages, aimed at helping programs meet chromate reduction initiatives without giving up the corrosion protection function. Performance should still be confirmed against the specific joint's requirements rather than assumed from the chromate-free label alone.

Qualification varies by product, class, and grade. Current certification status and any customer- or platform-specific specification approvals should be confirmed for the exact grade in question before specifying it on a program. Contact the technical team for documentation.

Yes. The Krayden technical team works directly with engineers and MRO teams on sealant selection, datasheets, and application support for new production and repair work.