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Subchapter 1. Unfired Pressure Vessel Safety Orders
Article 7. Compressed and Liquefied Natural Gas System

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§537. Piping Systems Valving and Labeling.

(a) General.

(1) All piping and tubing shall be tested after assembly and proved free from leaks at a pressure equal to the maximum working pressure of that portion of the system or its safety valve setting, whichever is greater, except for welded piping [see 536(a)(3)].

(2) Where excess-flow valves are used, the closing flow shall be less than the flow rating of the piping system between the excess-flow valve and the equipment downstream of the excess-flow valve.

(3) When two or more vessels, other than motor fuel tanks or cylinders, are manifolded together or when branches or restrictions are incorporated into the piping system, additional excess-flow valves or equivalent shall be installed where the flow rating of the piping is less than the closing flow rating of the excess-flow valves in the vessels. The additional excess-flow valves or equivalent shall be located as close to the point of branching or restriction as possible.

NOTE: A quick-closing manually operated valve may be considered equivalent to an excess-flow valve at the point of pipe size reduction or other restriction providing:

(1) It is equipped with a means for closing the valve manually from a point remote from the delivery connection.

(2) The loading and/or unloading line in which it is located is secured to a bulkhead complying with Section 532(a)(6).

(3) The quick-closing valve is in the pipeline on the tank side of the bulkhead.

(4) Bleed connections shall be provided in transfer systems to permit depressurizing the line before disconnecting. These bleed connections shall discharge at a safe place.

(5) Piping, compressors, pumps, valves, regulators, gaging and other vessel accessory equipment shall be protected against physical damage, including vehicular.

(b) Compressed Natural Gas.

(1) Except for safety relief valves and gaging connections all vessel connections, other than in motor fuel tanks or cylinders, larger than 1/4 inch pipe size shall have one of the following installed directly in each connection:

(A) A back-flow check valve to prevent flow from the tank.

(B) An excess-flow valve.

(2) A manually operated shut-off valve shall be installed as close to the vessel as practicable. Manually operated shut-off valves for DOT cylinders shall be provided in accordance with DOT regulations.

(3) Piping systems shall be protected against overpressure by safety relief devices. Relief devices installed to protect the piping system shall have sufficient capacity and shall be set to open at a pressure not exceeding 110 percent of the maximum allowable working pressure of the system or the pressure which produces a hoop stress of 75 percent of the specified minimum yield strength, whichever is lower.

(c) Liquefied Natural Gas.

(1) Except for safety relief valves and gaging connections all vessel connections, other than in motor fuel tanks, larger than 1/2-inch pipe size shall have one of the following installed directly in each connection (for the purpose of this Section tank connection location for double wall cryogenic vessels may be the point of penetration through the outer vessel or its jacketed extension):

(A) A back-flow check valve to prevent flow from the tank.

(B) A manually operated internal valve equipped with a means for closing the valve from a point remote from the delivery connection. The closing mechanism or its control shall be fitted with a fusible link having a melting point of 200 degrees Fahrenheit to 250 degrees Fahrenheit which will cause the valve to close automatically in case of fire.

(C) Either an internal valve which can be operated manually and will close on excess-flow conditions or one which is normally closed and is opened by pump discharge pressure. These valves shall be equipped with a means for closing from a point remote from the delivery connection and the closing mechanism shall be fitted with a fusible section as required in (B) above.

(D) An excess flow valve. In addition, there shall also be a quick closing automatic valve located as close to the tank as possible and which shall remain closed except during transfer. This valve shall be equipped with a means for closing automatically from a point remote from the delivery connection and shall be fitted with a fusible section having a melting point of 200 degrees Fahrenheit to 250 degrees Fahrenheit which will cause the valve to close in case of fire. Piping and valves shall be of austenitic stainless steel as listed in ANSI Code For Pressure Piping, B 31.3, 1966 Edition, Table 302.2.1A. Piping between the tank and the valve inlet shall be seamless and at least Schedule 40. All joints in the piping to and including the valve inlet shall be welded in accordance with 536(a)(3).

(2) (A) Systems installed in accordance with (A) or (B) above shall have a manually operated shut-off valve located as close to the tank as practicable. Systems installed in accordance with (D) above shall have a manually operated shut-off valve located between the quick-closing automatic valve and the vessel.

(B) Systems with tank connections installed in accordance with (C) above shall have a manually operated shut-off valve located in the loading and/or unloading pipelines between the tank and the pump, meter or bulkhead whichever is nearest the tank.

(3) Wherever liquid can be trapped between two or more valves, a safety relief valve shall be installed to prevent excessive hydrostatic pressure. This safety relief valve shall start to discharge at not less than 125 percent nor more than 150 percent of the safe working pressure of the piping system between the two shut-off valves.

(4) All LNG tank connections having manually operated shut-off valves shall be labeled to indicate whether they communicate with the vapor or liquid space. At least one of the following methods shall be employed in labeling these connections:

(A) Tags of metal or other suitable material labeled "Liquid" or "Vapor". These tags shall be fastened securely to the tank, to the primary manual valve or to the piping system at the valve. The legibility of these tags shall be maintained.

(B) Complete color painting of all visible parts of the piping or its insulation.

(C) Color bands not less than 4 inches wide at each tank connection or primary manual valve. These bands shall be readily visible on the insulation. Where identification is provided by complete color painting or by color bands, a color code shall be posted where visible from the transfer operation.

HISTORY:

1. Amendment of subsection (c)(4) filed 8-6-76; effective thirtieth day thereafter (Register 76, No. 32).

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