Wash. Rev. Code § 70.79.290
If, upon inspection, a boiler or pressure vessel is found to comply with the rules and regulations of the board, and upon the appropriate fee payment made directly to the chief inspector, as required by RCW 70.79.160 or 70.79.330, the chief inspector shall issue to the owner or user of such a boiler or pressure vessel an inspection certificate bearing the date of inspection and specifying the maximum pressure under which the boiler or pressure vessel may be operated. Such inspection certificate shall be valid for not more than fourteen months from its date in the case of power boilers and twenty-six months in the case of low pressure heating boilers, and for not more than two months longer than the authorized inspection period in the case of pressure vessels. Certificates shall be posted under glass in the room containing the boiler or pressure vessel inspected. If the boiler or pressure vessel is not located within a building, the certificate shall be posted in a location convenient to the boiler or pressure vessel inspected or, in the case of a portable boiler or pressure vessel, the certificate shall be kept in a protective container to be fastened to the boiler or pressure vessel or in a tool box accompanying the boiler or pressure vessel.
RCW 70.79.290