Abstract: A composite vessel and fitting for a through-wall penetration having an exposed end grain. The fitting includes a sealing surface arrangement that seals against the composite vessel and prevents leakage of the vessel contents while protecting the end grain from exposure to internal fluid and/or external environment. The fitting includes an outer part, an inner part, and a through-wall part extending between the inner and outer parts across the penetration. An outer seal arrangement includes an outer seal having a first sealing surface that seals against the outer surface of the composite vessel to restrict environmental contaminants migrating to the end grain. An inner seal arrangement includes at least one inner seal having second and third sealing surfaces. The second sealing surface seals against the inner surface of the composite vessel and the third sealing surface seals a leak path or interface between the inner part and through-wall part to restrict internal fluid migrating to the end grain.