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Subchapter 1. Unfired Pressure Vessel Safety Orders
Article 2. Design and Construction

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§455. Design and Construction of CNG and LNG Tanks.

(a) All CNG and LNG tanks for new installations over 15 psig shall be constructed, inspected, and stamped in compliance with the ASME Code (unless the design, material, and construction of the tank are accepted by the Division as equivalent to the ASME Code) and, except for "UM" vessels, registered with the National Board of Boiler and Pressure Vessel Inspectors. The stamping on all new tanks or on nameplates attached thereto shall include, in addition to the stamping required by the ASME Code or the National Board of Boiler and Pressure Vessel Inspectors, the following:

(1) CNG Tanks:

(A) The volumetric capacity in standard cubic feet of natural gas when filled to the limits provided by these regulations.

(B) The words "For CNG."

(C) The head and shell thicknesses.

(2) LNG Tanks:

(A) The net volumetric capacity in U.S. Gallons.

(B) The words "for LNG."

(C) The head and shell thicknesses.

(D) The minimum safety relief valve capacity in CFM air. (See 541(c) (1) and (2) ).

(b) Tanks of brazed construction are prohibited.

(c) The outer shell of a double wall cryogenic vessel shall be designed for the full range of pressure and/or vacuum to which it will be subjected, and provide for adequate structural support of the inner tank and insulation under all imposed loadings.

(d) Welding to the shell, head, or any other part of the container subject to internal pressure, shall be done in compliance with the ASME Code under which the tank was fabricated. Other welding is permitted only on saddle plates, lugs, or brackets attached to the container by the tank manufacturer.

(e) All LNG tanks for new installations for low temperature storage at 15 psig or less, shall, as a minimum, be designed, constructed, inspected, and certified in accordance with API "Standard, 620, Recommended Rules for Design and Construction of Large, Welded, Low-Pressure Storage Tanks" and the following additional requirements which will supersede where there is any conflict, or to the ASME Code.

Note: The references following in parentheses refer to specific paragraphs in API 620, 1978 Edition.

(1) The edges of the weld shall merge smoothly with the surface of the plate without a sharp angle. In making fillet welds, the weld metal shall be deposited in such a way that adequate penetration into the base metal at the root of the weld is secured. Although the provisions of 4.13 apply for horizontal butt joints, visible undercuts are not permitted for vertical butt joints. (4.13)

(2) The inspector shall have a valid certificate of competency issued by the Division. (5.02.1)

(3) The manufacturer shall have, and demonstrate, a quality control system to establish that all requirements including material, design, fabrication, examination (by manufacturer) and inspection (by the inspector) will be met. The written description of the quality control system shall, as a minimum, be in accordance with Appendix 10 of ASME Section VIII, Division 1. (5.02.3)

(4) Safety relief device and relieving capacities shall be in accordance with NFPA Pamphlet NFPA 59A and Appendix A, 1978 Edition.

(5) The manufacturer's report, or attachments, shall show for inner and outer tanks as a minimum:

(A) Manufacturer's name.

(B) Manufacturer's serial number for the tank.

(C) Nominal capacity.

(D) Design pressure for vapor space at the top.

(E) Design temperature.

(F) Maximum permissible specific gravity of liquid contents to be stored.

(G) Maximum level to which tank may be filled with liquid of that gravity, with full design pressure above the surfaces.

(H) Maximum level to which the tank may be filled with water for test or for purging purposes.

(I) Shell, head and other pressure boundary materials.

(J) Material thicknesses.

(K) Support and attachment materials.

(L) Nozzles, number and diameter.

(M) Year built. (5.27.2)

(6) The openings and/or connections between the tank and the pressure relief devices shall have an area at least equal to the combined areas of all the pressure relief inlets on that connection. The size of any discharge line shall be such that any pressure that may exist or develop will not reduce the relief capacity of the relieving devices below that required to properly protect the vessel. (N.3)

Where stop valves are used between the pressure relief devices and the tank, a written procedure shall be used to govern the use of the valves. Remote indicators shall be provided that will alert operating personnel when the stop valves are not in the fully open position or, alternately, reliable interlocks shall be provided to assure that minimum required relief capacity is always available. (N.8.)

(7) Design calculations shall be certified to be correct and complete by one or more currently registered professional engineers competent in the applicable field of design of LNG storage. The provisions of NFPA Pamphlet 59A, 1975, Section 4-1.3 shall be used for seismic loadings. For public utilities, the provisions of General Order 112(D) of the California Public Utilities Commission shall also be considered for all live loadings including Part III, Subpart B, Sections 193.115, 117 and 119, for seismic loadings, and shall be acceptable to the Commission.

(8) When butt joints are used in outer tanks, they shall be double welded and designed with a joint efficiency of 70% as a minimum in accordance with table UW-12 of ASME Section VIII, Division 1. (Q.6)

Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code; and Section 13241, Health and Safety Code.


1. Amendment filed 12-8-72 as procedural and organizational; effective upon filing (Register 72, No. 50).

2. Amendment filed 11-7-75; effective thirtieth day thereafter (Register 75, No. 45).

3. Amendment of subsection (a) filed 4-1-77; effective thirtieth day thereafter (Register 77, No. 14).

4. Repealer of subsection (e) filed 4-7-81 as an emergency; effective upon filing (Register 81, No. 15). A Certificate of Compliance must be transmitted to OAL within 120 days or emergency language will be repealed on 8-5-81.

5. Certificate of Compliance transmitted to OAL 7-7-81 and filed 8-6-81 (Register 81, No. 32).

6. Amendment of subsections (a) - (g), and renumbering of Section 459 to subsection (h) filed 1-5-88; operative 2-4-88 (Register 88, No. 4).

7. Amendment of section heading, section and Note filed 12-4-96; operative 1-3-97 (Register 96, No. 49).

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