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(continued) which it may be contained, loaded and/or transported. However, the service temperature shall in no case be taken higher than given by the following formula:
ts=tw-0.25(tw-tB)
where:
ts=Service temperature.
tw=Boiling temperature of gas at normal working pressure of container but not higher than +32 °F.
tB=Boiling temperature of gas at atmospheric pressure.
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, 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) shall conform to a specification given in Table UCS–23 in the ASME Code and the following additional requirements:
Note: For high alloy steels refer to §54.25–15. For heat treated steels refer to §54.25–20.
(1)(i) For minimum service temperatures not lower than -67 °F., ferritic steels shall be made with fine grain practice and shall have an austenitic grain size of 5 or finer, and shall be normalized. Consideration will be given to other heat treatments. Refer to §57.03–1(d) of this subchapter. Plate for pressure vessel applications shall conform to the requirements of ASTM A 20 (incorporated by reference, see §54.01–1). It may be produced by the open hearth, basic oxygen or electric furnace process and shall conform to the requirements of Table 54.25–10(b)(1). (Other alloying elements may only be present in trace amounts.)
(ii) Mechanical properties shall be within the following limits:
Ultimate _58,000 \1\-85,000 \1\ p.s.i.
strength
Yield strength _Minimum 35,000 p.s.i.
_Maximum 80 percent of ultimate.
Elongation _20 percent in 8 inches, or
minimum
_24 percent in 2 inches, or
_22 percent in 5.65 [radic]A,
where ``A'' is the test specimen
cross sectional area.
Table 54.25-10(b)(1)
------------------------------------------------------------------------
Manganese
Minimum service \1\ temperature °F Max. C \1\ range \1\
percent percent
------------------------------------------------------------------------
-30........................................... 0.20 0.70-1.35
-50........................................... .16 1.15-1.50
-67........................................... .12 1.30-1.60
------------------------------------------------------------------------
\1\ At service temperatures intermediate between those specified,
intermediate amounts of carbon and manganese will be allowed (in
proportion to the actual service temperature variation from that
listed), provided all other chemical and mechanical properties
specified for steels in this temperature range are satisfied.
Range
percent
Si.......................................................... 0.10-0.50
Maximum
S........................................................... 0.035
P........................................................... 0.035
Ni.......................................................... 0.80
Cr.......................................................... 0.25
Mo.......................................................... 0.08
Cu.......................................................... 0.035
Nb.......................................................... 0.05
V........................................................... 0.08
(2) For minimum service temperature below -67 °F., but not below the designated minimum service temperature, ferritic steels shall be normalized, low carbon, fully killed, fine grain, nickel alloy type, conforming to any one of the specifications in Table 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 shall be as shown in the applicable specification and shall be suitable to the design stress levels adopted. The service temperature shall not be colder than the minimum specified in Table 54.25–10(b)(2) for each steel.
Table 54.25-10(b)(2)
------------------------------------------------------------------------
Steel Minimum service temperature
------------------------------------------------------------------------
A-203, 2\1/4\ percent, Ni, normalized.... -80 °F. for Grade A.
-75 °F. for Grade B.
A-203, 3\1/2\ percent, Ni, normalized.... -130 °F. for Grade D.
-110 °F. for Grade E.
5 percent Ni, normalized................. Dependent on chemical and
physical properties.
------------------------------------------------------------------------
(3) The materials permitted under paragraphs (b) (1) and (2) of this section shall be tested for toughness in accordance with and shall 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 (Tank Vessels) of this chapter shall 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 shall 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 54.01–5(b) 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 the ASME Code 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 Code.
(d) 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), (d)(2), and (d)(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 1/4 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.
[CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGFR 69–127, 35 FR 9977, June 17, 1970; CGD 73–133R, 39 FR 9178, Mar. 8, 1974; CGD 74–289, 44 FR 26007, May 3, 1979; CGD 77–069, 52 FR 31626, Aug. 21, 1987; CGD 85–061, 54 FR 50964, Dec. 11, 1989; USCG–1999–5151, 64 FR 67178, Dec. 1, 1999; USCG–2000–7790, 65 FR 58460, Sept. 29, 2000]
§ 54.25-15 Low temperature operation—high alloy steels (modifies UHA–23(b) and UHA–51).
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(a) Toughness tests for the materials listed in UHA–51(a) of the ASME Code 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, shall 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 (Tank Vessels) 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. shall 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 the ASME Code. These materials and their weldments shall 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 the ASME Code.”
(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 the ASME Code for temperatures of -20 °F. to 100 °F.
[CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 73–133R, 39 FR 9178, Mar. 8, 1974; CGD 73–254, 40 FR 40164, Sept. 2, 1975]
§ 54.25-20 Low temperature operation—ferritic steels with properties enhanced by heat treatment (modifies UHT–5(c), UHT–6, UHT–23, and UHT–82).
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(a) For service temperatures below 0 °F. but not below the designated minimum service temperature, steel conforming to the specifications of Table 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 (Tank Vessels) of this chapter. The ultimate and yield strengths shall be as shown in the applicable specification and shall be suitable for the design stress levels adopted. The service temperature shall not be colder than -320 °F. Service temperature is defined in §54.25–10(a) (2).
Table 54.25-20(a)
------------------------------------------------------------------------
Minimum
service
Steel temperature,
°F.
------------------------------------------------------------------------
A-333, 9 percent Ni, grade 8.............................. -320
A-334, 9 percent Ni, grade 8.............................. -320
A-353, 9 percent Ni, double normalized and tempered....... -320
A-522, 9 percent Ni, NNT, Q and T, forging................ -320
A-553, 9 percent Ni, quenched and tempered................ -320
------------------------------------------------------------------------
(b) The materials permitted under paragraph (a) of this section shall be tested for toughness in accordance with the requirements of UHT–6 of the ASME Code except that tests shall be conducted at the temperature specified in §54.05–6 in lieu of that in UHT–5(c) of the ASME Code. Lateral expansion in a broken Charpy V-notch specimen is illustrated in Figure 54.25–20(b) and shall be measured in accordance with the procedure outlined in ASTM A 370 (incorporated by reference, see §54.01–1).
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(c) The qualification of welding procedures and welders and weld production testing for the steels of Table 54.25–20(a) shall conform to the requirements of part 57 of this subchapter and subpart 54.05 except that the Charpy V-notch testing acceptance criteria shall be in accordance with UHT–6(a) (4) and (5) of the ASME Code.
(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 shall 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 the ASME Code for temperatures of 150 °F. and below.
[CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by CGD 73–133R, 39 FR 9179, Mar. 8, 1974; USCG–2000–7790, 65 FR 58460, Sept. 29, 2000]
§ 54.25-25 Welding of quenched and tempered steels (modifies UHT–82).
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(a) The welding requirements in UHT–82 of the ASME Code shall be modified to require that the qualification of welding procedures and welders and weld production testing shall conform to the requirements of part 57 of this subchapter. The requirements are §57.03–1(d) of this subchapter are applicable to welded pressure vessels and nonpressure vessel type tanks of quenched and tempered steels other than 9 percent nickel.
(b) [Reserved]
Subpart 54.30—Mechanical Stress Relief
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§ 54.30-1 Scope.
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(a) Certain pressure vessels may be mechanically stress relieved in accordance with the requirements in this subpart.
(b) [Reserved]
§ 54.30-3 Introduction.
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(a) Large conventional pressure vessels used to transport liquefied petroleum and natural gases, at “low temperatures” may often be difficult to thermally stress relieve. Where no other problem, such as corrosion exists, mechanical stress relief will be permitted for Class II-L pressure vessels.
(b) Mechanical stress relief serves to cause small flaws, particularly in the weld zone, to yield plastically at the flaw tip resulting in a local relief of stress and a blunting of the crack tip. To achieve the maximum benefit from mechanical stress relief, it is necessary that the stresses so imposed be more severe than those expected in normal service life. At the same time, it is necessary that the stresses which are imposed are not so high as to result in appreciable deformation or general yielding.
(c) The weld joint efficiencies as listed in Table UW–12 of the ASME Code shall apply except that a minimum of spot radiography will be required. UW–12(c) of the ASME Code which permits omitting all radiography does not apply. Spot examination shall follow UW–52 of the ASME Code and in addition these vessels will be required to have radiographic examination of intersecting circumferential and longitudinal joints for a distance of at least 20 times the plate thickness from the junction. See §54.25–8 on spot radiography.
(d) Severe cold forming will not be permitted unless thermal stress relief is used. For example, parts of the vessels which are individually cold formed, such as heads, must be thermally stress relieved, where the extreme fiber strain measured at the surface exceeds 5 percent as determined by:
Percent strain=(65t/Rf)[1–(Rf/Ro)]
where:
t=Plate thickness.
Rf=Final radius.
Ro=Original radius (equals infinity for flat plate).
[CGFR 68–82, 33 FR 18828, Dec. 18, 1968, as amended by USCG–2000–7790, 65 FR 58460, Sept. 29, 2000]
§ 54.30-5 Limitations and requirements.
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(a) Class II-L pressure vessels which require stress relief (see Table 54.01–5(b)) may be mechanically stress relieved provided:
(1) The steels from which they are fabricated do not specifically require thermal stress relief in UCS–56 of the ASME Code and have a ratio of yield to ultimate tensile strength not greater than 0.8. For example: A–537 steels could be mechanically stress relieved.
(2) Pressure difference across the shell is not greater than 100 pounds per square inch, thickness of shell is not greater than 1 inch, and the design temperature is not greater than 115 °F.
(3) It will carry liquids of specific gravity no greater than 1.05.
(4) Design details are sufficient to eliminate stress concentrators: Mechanical stress relief is not acceptable in designs involving the following types of welded connections shown in UW–16.1 of the ASME Code:
(i) Types l, m, n, and p because of nonintegral reinforcement. Type o will be acceptable provided the plate, nozzle, and reinforcement assembly are furnace stress relieved and the reinforcement is at least 6 inches or 10t, whichever is larger, from the plate head.
(ii) Types d, e, and f because expansion and contraction stresses are concentrated at the junction points.
(5) That no slip-on flanges in sizes greater than 2 inches are used.
(6) The categories A and B joints are type one as described in Table UW–12 of the ASME Code and all categories C and D joints are full penetration welds. See UW–3 of the ASME Code for definition of categories.
(b) When a pressure vessel is to be mechanically stress relieved in accordance with §54.30–10(a)(1), its maximum allowable working pressure will be 40 percent of the value which would otherwise be determined. However, an increase of this 40 percent factor may be permitted if the stress relief is carried out at a pressure higher than that required by §54.30–10(a)(1) and an experimental strain analysis is carried out during stress relief. This evaluation should provide information as to the strains at the saddles, welded seams and nozzles as well as the body of the vessel. The hydrostatic pressure applied during stress relief should be such that, except in the case of welds, the stresses in the vessel shall closely approach but not exceed 90 percent of the yield stress of the material at the test temperature. The proposed experimental program should be submitted to the Commandant for approval prior to its use. Photo-elastic coating, strain gaging, or a brittle coating technique is suggested for the experimental analysis.
§ 54.30-10 Method of performing mechanical stress relief.
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(a) The mechanical stress relief shall be carried out in accordance with the following stipulations using water as the pressurizing medium:
(1) At a hydrostatic pressure (measured at the tank top) of 1 1/2 times the design pressure. (See UA–60(e) of the ASME Code.)
(2) At a temperature of 70 °F. or the service temperature plus 50 °F., whichever is higher. Where the ambient temperature is below 70 °F., and use of water at that temperature is not practical, the minimum temperature for mechanical stress relief may be below 70 °F. but shall not be less than 50 °F. above service temperature.
(3) The stress relief shall be at the required temperature and pressure and held for a period not less than 2 hours per inch of metal thickness, but in no case less than 2 hours.
(b) It is considered preferable that mechanical stress relief be accomplished with the tanks in place on their saddles or supporting structure in the barge or ship in which they will be utilized. In any case, it is considered mandatory that the tank be supported only by its regular saddles or supporting structure, without any auxiliary or temporary supports.
§ 54.30-15 Requirement for analysis and computation.
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(a) A stress analysis shall be performed to determine if the tank may be exposed to excessive loadings during the mechanical stress relief process. This analysis should include consideration of the local stresses in way of saddles or other supporting structure and additional bending stresses due to the weight of the pressurizing liquid particularly in areas of high stress concentration. While it is necessary that the general stress level during the process be in excess of the normal working level, the calculated maximum stress during test shall not exceed 90 percent of the yield strength of the material at test temperature. The supporting structure shall be analyzed to verify its adequacy.
(b) In all cases where the tanks are mechanically stress relieved in place in the ship or barge and the tanks are designed to carry cargoes with a specific gravity less than 1.05, the ship or barge shall be shown to have adequate stability and buoyancy, as well as strength to carry the excess weight of the tank during the stress relief procedure.