A composite vessel comprising: a composite wall forming an internal chamber for containing a fluid, the composite wall having at least one through-wall penetration (14a-14d) and an exposed end grain at the through-wall penetration (14a-14d); and a composite vessel fitting (112, 212, 312, 412) secured to the composite wall at the through-wall penetration (14a-14d), the fitting comprising a sealing surface arrangement that seals against opposite inner and outer surfaces of the composite vessel and protects the end grain from exposure to internal fluid and external environment by preventing migration of environment materials from the outer surface to the inner surface while preventing leakage of the vessel contents; wherein the fitting (112, 212, 312, 412) is non-destructively removable from the composite vessel; and characterised in that the sealing surface arrangement includes: a first sealing surface (140; 240; 340; 440) that interfaces with the outer surface of the composite vessel and fluidly seals against the outer surface; a second sealing surface (142; 242; 342; 442) that interfaces with the inner surface of the composite vessel and fluidly seals against the inner surface; and a third sealing surface (144; 244; 344; 444) that interfaces and seals against a through-wall part of the fitting, wherein the through-wall part extends through the penetration (14a-14d) of the composite vessel. a composite wall forming an internal chamber for containing a fluid, the composite wall having at least one through-wall penetration (14a-14d) and an exposed end grain at the through-wall penetration (14a-14d); and a composite vessel fitting (112, 212, 312, 412) secured to the composite wall at the through-wall penetration (14a-14d), the fitting comprising a sealing surface arrangement that seals against opposite inner and outer surfaces of the composite vessel and protects the end grain from exposure to internal fluid and external environment by preventing migration of environment materials from the outer surface to the inner surface while preventing leakage of the vessel contents; wherein the fitting (112, 212, 312, 412) is non-destructively removable from the composite vessel; and characterised in that the sealing surface arrangement includes: a first sealing surface (140; 240; 340; 440) that interfaces with the outer surface of the composite vessel and fluidly seals against the outer surface; a second sealing surface (142; 242; 342; 442) that interfaces with the inner surface of the composite vessel and fluidly seals against the inner surface; and a third sealing surface (144; 244; 344; 444) that interfaces and seals against a through-wall part of the fitting, wherein the through-wall part extends through the penetration (14a-14d) of the composite vessel. a first sealing surface (140; 240; 340; 440) that interfaces with the outer surface of the composite vessel and fluidly seals against the outer surface; a second sealing surface (142; 242; 342; 442) that interfaces with the inner surface of the composite vessel and fluidly seals against the inner surface; and a third sealing surface (144; 244; 344; 444) that interfaces and seals against a through-wall part of the fitting, wherein the through-wall part extends through the penetration (14a-14d) of the composite vessel.