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

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§536. Piping Standards.

(a) General.

(1) All pipe, tubing, fittings and other piping components between the tank and the first shutoff valve shall be designed for the full range of pressures, temperatures and loadings to which they may be subjected with a factor of safety of at least 8 based on the minimum specified tensile strength at room temperature. All other pipe, tubing, fittings and other piping components shall be suitable for the full range of pressures, temperatures and loadings to which they may be subjected with a factor of safety of at least 4. In no case may underground piping be less than Schedule 80 for piping systems having a working pressure exceeding 100 psi. Any material used, including gaskets and packing, shall be compatible with natural gas and its service conditions.

(2) All piping and tubing shall be run as directly as practical with adequate provisions for expansion, contraction, jarring, vibration and settling. Exterior piping may be either buried or installed aboveground and shall be well supported and protected against mechanical damage.

Underground piping shall be buried not less than 18 inches below the surface of the ground unless otherwise protected. All underground piping shall be protected from corrosion by coating in compliance with Section 533(b) or equivalent. Zinc coatings (galvanizing shall not be considered adequate protection for piping below ground.

(3) All welded piping shall be fabricated and tested in accordance with the ANSI Code for Pressure Piping, Petroleum Refinery Piping, B31.3, 1966 Edition or equivalent.

(4) All valves shall be suitable for the full range of pressure and temperature to which they may be subjected. The manufacturer shall stamp or otherwise permanently mark the valve body to indicate the service ratings. Other piping components such as strainers, snubbers and expansion joints shall also be permanently marked by the manufacturer to indicate the service ratings. All materials such as valve seats, packing, gaskets, diaphragms, etc. shall be resistant to the action of natural gas under the conditions to which they are subjected.

(5) Use of the following is prohibited:

(A) Valves, cocks, fittings and other piping components of cast iron or semisteel other than ASTM Specifications A-536-67, Grade 60-40-18; A-395-68; A-47-68, Grade 35018 and A-445-66 unless they have pressure-temperature ratings at least equal to 1 1/2 times the design service conditions. In no case shall valves of cast iron or semisteel other than the 3 ASTM specifications listed above be used for primary stop valves.

(B) Street ells and screwed service tees.

(C) Valves of a design that will allow the valve stem to be removed without removal of complete valve bonnet or disassembly of the valve body.

(D) Plastic pipe, tubing, hose and fittings, without written permission from the Division.

(E) Valves with valve stem packing glands which cannot be repacked under pressure, unless there is another stop valve of acceptable type between them and the vessel. This does not apply to service valves.

(F) Aluminum tubing for exterior locations and threaded aluminum connections and adapters that are required to be connected or disconnected as part of the filling or transferring operation for those connections and adapters that are specifically designed with special threads suitable for this service.

(G) Pipe nipples in lieu of couplings or flanges in tank connections.

(H) Copper alloy with copper content exceeding 70 percent.

(b) Compressed Natural Gas. Hose shall not be used in lieu of manifolds, piping or tubing between dispensing tanks and cylinders and the connection for the loading and/or unloading hose connections, except that a section of metallic hose not to exceed 24 inches in length may be used in each pipeline to provide flexibility where necessary. Each section shall be so installed that it will be protected against mechanical damage and be readily visible for inspection. The manufacturer's identification shall be retained in each section.

(c) Liquefied Natural Gas.

(1) Flanged joints or threaded joints which have not been seal welded on liquid lines between the tank and the first shutoff valve are prohibited.


(2) All LNG piping over 2-inch pipe size shall be welded flanged or silver brazed with a material having a melting point exceeding 1,000 degrees Fahrenheit. Compression type couplings and threaded joints shall not be used except that seal welded threaded joints may be used.

(3) Piping 2-inch or smaller may be threaded, welded or flanged except as prohibited in 536(c)(1).

(4) Threaded nipples and pipe shall be at least Schedule 80.

(5) Plugs shall be solid or else they shall be bull plugs of at least Schedule 80 seamless pipe.

(6) For service temperatures of minus 20 degrees Fahrenheit or above, threaded piping and tubing with compression type couplings may be used except as prohibited in 536(c)(2).

(7) Pipe supports for piping having a service temperature below minus 20 degrees Fahrenheit shall be designed to minimize heat transfer so that support steel embrittlement

and piping restraints caused by ice formation will be prevented.

(8) Bellows type expansion joints in low temperature service shall be provided with external insulation that will prevent ice from forming on the bellows.


1. Amendment of subsections (a)(1) and (a)(5)(F) filed 3-29-74; effective thirtieth day thereafter (Register 74, No. 13).

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