The pressure vessels for low temperature operation must be as required by Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) as modified by this subpart.

The steels listed in UCS-6(b) of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) will be allowed only in Class III pressure vessels (see table 2 to § 54.01-5(b)).

The corrosion allowance must be as required in § 54.01-35.

(a) Postweld heat treatment is required for all carbon and low alloy steel Class I, I-L, and II-L vessels regardless of thickness. (Refer to table 2 to § 54.01-5 for applicable requirements.)

(b) Cargo tanks which are fabricated of carbon or low alloy steel as Class II pressure vessels, designed for pressures exceeding 100 pounds per square inch gage and used in the storage or transportation of liquefied compressed gases must be postweld heat treated regardless of thickness.

(a) Full radiography is required for all Class I and Class I-L vessels regardless of thickness. (Refer to table 2 to § 54.01-5 for applicable requirements.)

(b) Class II-L vessels must be spot radiographed. The exemption provided in UW-11(c) of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) does not apply. (Refer to table 2 to § 54.01-5 for applicable requirements.)

(c) Each butt-welded joint in a Class II or III pressure vessel cargo tank must be spot radiographed, in accordance with UW-52, regardless of diameter or thickness, and each weld intersection or crossing must be radiographed for a distance of at least 10 thicknesses from the intersection.

(a) Scope. (1) This section contains requirements for pressure vessels and nonpressure vessel type tanks and associated secondary barrier, as defined in §§ 38.05-4 and 154.7 of this chapter, and their parts constructed of carbon and alloy steels which are stressed at operating or hydrostatic test temperatures below 0 °F.

(2)(i) The service temperature is the minimum temperature of a product at which it may be contained, loaded and/or transported. However, the service temperature must in no case be taken higher than given by the following formula:

(ii) Only temperatures due to refrigerated service usually need to be considered in determining the service temperature, except pressure vessel type cargo tanks operating at ambient temperatures must meet paragraph (d) of this section. “Refrigerated service”, as used in this paragraph (a)(2)(ii), means a service in which the temperature is controlled by the process and not by atmospheric conditions.

(b) Specifications. Materials used in the construction of vessels to operate below 0 °F (but not below the designated minimum service temperature) must conform to a specification given in table UCS-23 in Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) and the following additional requirements:

(1)(i) For minimum service temperatures not lower than −67 °F, ferritic steels must be made with fine grain practice and must have an austenitic grain size of 5 or finer, and must be normalized. Consideration will be given to other heat treatments; refer to § 57.03-1(d) of this subchapter. Plate for pressure vessel applications must conform to the requirements of ASTM A20/A20M (incorporated by reference, see § 54.01-1). It may be produced by the open hearth, basic oxygen or electric furnace process and must conform to the requirements of table 1 to § 54.25-10(b)(1). (Other alloying elements may only be present in trace amounts.)

(ii) Mechanical properties must be within the following limits:

(A) Ultimate strength: 58,000 1-85,000 1psig.

(B) Yield strength: Minimum 35,000 psig. Maximum 80 percent of ultimate.

(C) Elongation minimum: 20 percent in 8 inches, or 24 percent in 2 inches, or 22 percent in 5.65 √A, where “A” is the test specimen cross sectional area.

(2) For minimum service temperature below −67 °F, but not below the designated minimum service temperature, ferritic steels must be normalized, low carbon, fully killed, fine grain, nickel alloy type, conforming to any one of the specifications in table 3 to § 54.25-10(b)(2). Consideration will be given to other heat treatments. Refer to § 57.03-1(d) of this subchapter for quenched and tempered steels. The ultimate and yield strengths must be as shown in the applicable specification and must be suitable to the design stress levels adopted. The service temperature must not be colder than the minimum specified in table 3 to § 54.25-10(b)(2) for each steel.

(3) The materials permitted under paragraphs (b)(1) and (2) of this section must be tested for toughness in accordance with and must satisfy the applicable requirements of subpart 54.05.

(4) Welded pressure vessels or nonpressure vessel type tanks and associated secondary barriers, as defined in § 38.05-4 of subchapter D of this chapter must meet the toughness requirements of subparts 57.03 and 57.06 of this subchapter with regard to weld procedure qualifications and production testing.

(5) The material manufacturer's identification marking required by the material specification must not be die-stamped on plate material less than one-fourth inch in thickness.

(c) Design. Pressure vessels must meet the requirements for Class I-L and II-L construction. (See table 2 to § 54.01-5 for applicable requirements). Except as permitted by § 54.05-30, the allowable stress values used in the design of low temperature pressure vessels may not exceed those given in table UCS-23 of Section VIII of the ASME BPVC for temperatures of 0 °F to 650 °F. For materials not listed in this table allowable stress values are determined in accordance with appendix P of Section VIII of the ASME BPVC.

(d) Impact tests. Weldments and all materials used in pressure vessel type cargo tanks operating at ambient temperatures and constructed of materials listed in table UCS-23 must pass Charpy impact tests in accordance with UG-84 at a temperature of −20 °F or colder, except as provided by paragraphs (d)(1), (2), and (3) of this section.

(1) Charpy impact tests are not required for any of the following ASTM materials if the thickness for each is 5/8 inch or less, unless otherwise indicated:

(i) A-182, normalized and tempered.

(ii) A-302, Grades C and D.

(iii) A-336, Grades F21 and F22 that are normalized and tempered.

(iv) A-387, Grades 21 and 22 that are normalized and tempered.

(v) A-516, Grades 55 and 60.

(vi) A-533, Grades B and C.

(vii) All other plates, structural shapes and bars, and other product forms, except for bolting, if produced to a fine grain practice and normalized.

(2) Charpy impact tests are not required for any of the following ASTM materials if the thickness for each is 1.25 inch or less:

(i) A-203.

(ii) A-508, Class 1.

(iii) A-516, normalized.

(iv) A-524.

(v) A-537.

(vi) A-612, normalized.

(vii) A-662, normalized.

(viii) A-724, normalized.

(3) Charpy impact tests are not required for any of the following bolt materials:

(i) A-193, Grades B5, B7, B7M, and B16.

(ii) A-307, Grade B

(iii) A-325, Type 1.

(iv) A-449.

(a) Toughness tests for the materials listed in UHA-51(a) in Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) for service temperatures below −425 °F, UHA-51(b)(1) through (5) for service temperatures below 0 °F, and UHA-51(c) for all service temperatures, must be performed in accordance with the requirements of subpart 54.05. These requirements are also applicable to nonpressure vessel type, low temperature tanks and associated secondary barriers, as defined in § 38.05-4 in subchapter D of this chapter. Such tests are required regardless of the vessel's design stress. Service temperature is defined in § 54.25-10(a)(2).

(b) Materials for pressure vessels with service temperatures below −320 °F must be of the stabilized or low carbon (less than 0.10 percent) austenitic stainless-steel type, produced according to the applicable specifications of table UHA-23 of Section VIII of the ASME BPVC. These materials and their weldments must be tested for toughness according to the requirements of subpart 54.05 except that the Charpy V-notch testing acceptance criteria will be in accordance with UHT-6(a)(4) and (5) of Section VIII of the ASME BPVC.

(c) Except as permitted by § 54.05-30, the allowable stress values used in the design of low temperature pressure vessels may not exceed those given in table UHA-23 of Section VIII of the ASME BPVC for temperatures of −20 °F to 100 °F.

(a) For service temperatures below 0 °F but not below the designated minimum service temperature, steel conforming to the specifications of table 1 to § 54.25-20(a) may be used in the fabrication of pressure vessels and nonpressure vessel tanks and associated secondary barriers, as defined in § 38.05-4 of subchapter D of this chapter. The ultimate and yield strengths must be as shown in the applicable specification and must be suitable for the design stress levels adopted. The service temperature must not be colder than −320 °F. Service temperature is defined in § 54.25-10(a)(2).

(b) The materials permitted under paragraph (a) of this section must be tested for toughness in accordance with the requirements of UHT-6 of Section VIII of the ASME BPVC (incorporated by reference; see § 54.01-1) except that tests must be conducted at the temperature specified in § 54.05-6 in lieu of that in UHT-5(c) of Section VIII of the ASME BPVC. Lateral expansion in a broken Charpy V-notch specimen is illustrated in figure 1 to § 54.25-20(b) and must be measured in accordance with the procedure outlined in ASTM A370 (incorporated by reference, see § 54.01-1).

(c) The qualification of welding procedures, welders and weld-production testing for the steels of table 1 to § 54.25-20(a) must conform to the requirements of part 57 of this subchapter and to those of subpart 54.05 except that the acceptance criteria for Charpy V-notch testing must be in accordance with UHT-6(a)(4) of Section VIII of the ASME BPVC.

(d) The values of absorbed energy in foot-pounds and of fracture appearance in percentage shear, which are recorded for information when complying with paragraphs (b) and (c) of this section must also be reported to the marine inspector or the Commandant, as applicable.

(e) Except as permitted by § 54.05-30, the allowable stress values may not exceed those given in table UHT-23 of Section VIII of the ASME BPVC for temperatures of 150 °F and below.

(a) The qualification of welding procedures, welders, and weld-production testing must conform to the requirements of part 57 of this subchapter. The requirements of § 57.03-1(d) of this subchapter apply to welded pressure vessels and non-pressure vessel type tanks of quenched and tempered steels other than 9-percent nickel.

(b) [Reserved]