49 C.F.R. § 180.407 – Requirements for test and inspection of specification cargo tanks.

(a) General.
1. (1) A cargo tank constructed in accordance with a DOT specification for which a test or inspection specified in this section has become due, may not be filled and offered for transportation or transported until the test or inspection has been successfully completed. This paragraph does not apply to any cargo tank filled prior to the test or inspection due date.
2. (2) Except during a pressure test, a cargo tank may not be subjected to a pressure greater than its design pressure or MAWP.
3. (3) A person witnessing or performing a test or inspection specified in this section must meet the minimum qualifications prescribed in § 180.409.
4. (4) Each cargo tank must be evaluated in accordance with the acceptable results of tests and inspections prescribed in § 180.411.
5. (5) Each cargo tank which has successfully passed a test or inspection specified in this section must be marked in accordance with § 180.415.
6. (6) A cargo tank which fails a prescribed test or inspection must:
  1. (i) Be repaired and retested in accordance with § 180.413; or
  2. (ii) Be removed from hazardous materials service and the specification plate removed, obliterated or covered in a secure manner.
7. (7) The use of video cameras or fiber optic equipment is authorized for any test or inspection, or portion thereof, provided all the required areas and elements can be viewed and evaluated in accordance with this subpart.
(b) Conditions requiring test and inspection of cargo tanks. Without regard to any other test or inspection requirements, a specification cargo tank must be tested and inspected in accordance with this section prior to further use if:
1. (1) The cargo tank shows evidence of dents, cuts, gouges, corroded or abraded areas, leakage, or any other condition that might render it unsafe for hazardous materials service. At a minimum, any area of a cargo tank showing evidence of dents, cuts, digs, gouges, or corroded or abraded areas must be thickness tested in accordance with the procedures set forth in paragraphs (i)(2), (i)(3), (i)(5), (i)(6), (i)(9), and (i)(10) of this section and evaluated in accordance with the criteria prescribed in § 180.411. Any signs of leakage must be repaired in accordance with § 180.413. The suitability of any repair affecting the structural integrity of the cargo tank must be determined either by the testing required in the applicable manufacturing specification or in paragraph (g)(1)(iv) of this section.
2. (2) The cargo tank has sustained damage to an extent that may adversely affect its lading retention capability. A damaged cargo tank must be pressure tested in accordance with the procedures set forth in paragraph (g) of this section.
3. (3) The cargo tank has been out of hazardous materials transportation service for a period of one year or more. Each cargo tank that has been out of hazardous materials transportation service for a period of one year or more must be pressure tested in accordance with § 180.407(g) prior to further use.
4. (4) [Reserved]
5. (5) The Department so requires based on the existence of probable cause that the cargo tank is in an unsafe operating condition.

(c) Periodic test and inspection. Each specification cargo tank must be tested and inspected as specified in the following table by an inspector meeting the qualifications in § 180.409. The retest date shall be determined from the specified interval identified in the following table from the most recent inspection or the CTMV certification date.

Compliance Dates—Inspections and Test Under § 180.407(c)
Test or inspection(cargo tank specification, configuration, and service)	Date by which first testmust be completed(see Note 1)	Intervalperiodafter first test
External Visual Inspection:
All cargo tanks designed to be loaded by vacuum with full opening rear heads	September 1, 1991	6 months.
All other cargo tanks	September 1, 1991	1 year.
Internal Visual Inspection:
All insulated cargo tanks, except MC 330, MC 331, MC 338 (see Note 4)	September 1, 1991	1 year.
All cargo tanks transporting lading corrosive to the tank	September 1, 1991	1 year.
MC 331 cargo tanks less than 3,500 gallons water capacity in dedicated propane service constructed of nonquenched and tempered NQT SA-612 steel (see Note 5)		10 years.
All other cargo tanks, except MC 338	September 1, 1995	5 years.
Lining Inspection:
All lined cargo tanks transporting lading corrosive to the tank	September 1, 1991	1 year.
Leakage Test:
MC 330 and MC 331 cargo tanks in chlorine service	September 1, 1991	2 years.
All other cargo tanks except MC 338	September 1, 1991	1 year.
Pressure Test:
(Hydrostatic or pneumatic) (See Notes 2 and 3)
All cargo tanks which are insulated with no manhole or insulated and lined, except MC 338	September 1, 1991	1 year.
All cargo tanks designed to be loaded by vacuum with full opening rear heads	September 1, 1992	2 years.
MC 330 and MC 331 cargo tanks in chlorine service	September 1, 1992	2 years.
MC 331 cargo tanks less than 3,500 gallons water capacity in dedicated propane service constructed of nonquenched and tempered NQT SA-612 steel (See Note 5)		10 years.
All other cargo tanks	September 1, 1995	5 years.
Thickness Test:
All unlined cargo tanks transporting material corrosive to the tank, except MC 338	September 1, 1992	2 years.
Note 1: If a cargo tank is subject to an applicable inspection or test requirement under the regulations in effect on December 30, 1990, and the due date (as specified by a requirement in effect on December 30, 1990) for completing the required inspection or test occurs before the compliance date listed in table I, the earlier date applies.
Note 2: Pressure testing is not required for MC 330 or MC 331 cargo tanks in dedicated sodium metal service.
Note 3: Pressure testing is not required for uninsulated lined cargo tanks, with a design pressure MAWP 15 psig or less, which receive an external visual inspection and lining inspection at least once each year.
Note 4: Insulated cargo tanks equipped with manholes or inspection openings may perform either an internal visual inspection in conjunction with the external visual inspection or a hydrostatic or pneumatic pressure-test of the cargo tank.
Note 5: A 10-year inspection interval period also applies to cargo tanks constructed of NQT SA-202 or NQT SA-455 steel provided the materials have full-size equivalent (FSE) Charpy vee notch (CVN) energy test data that demonstrated 75% shear-area ductility at 32 °F with an average of 3 or more samples >15 ft-lb FSE with no sample <10 ft-lb FSE.

(d) External visual inspection and testing. The following applies to the external visual inspection and testing of cargo tanks:
1. (1) Where insulation precludes a complete external visual inspection as required by paragraphs (d)(2) through (d)(6) of this section, the cargo tank also must be given an internal visual inspection in accordance with paragraph (e) of this section. If external visual inspection is precluded because any part of the cargo tank wall is externally lined, coated, or designed to prevent an external visual inspection, those areas of the cargo tank must be internally inspected. If internal visual inspection is precluded because the cargo tank is lined, coated, or designed so as to prevent access for internal inspection, the tank must be hydrostatically or pneumatically tested in accordance with paragraph (g)(1)(iv) of this section. Those items able to be externally inspected must be externally inspected and noted in the inspection report.
2. (2) The external visual inspection and testing must include as a minimum the following:
  1. (i) The tank shell and heads must be inspected for corroded or abraded areas, dents, distortions, defects in welds and any other conditions, including leakage, that might render the tank unsafe for transportation service;
  2. (ii) The piping, valves, and gaskets must be carefully inspected for corroded areas, defects in welds, and other conditions, including leakage, that might render the tank unsafe for transportation service;
  3. (iii) All devices for tightening manhole covers must be operative and there must be no evidence of leakage at manhole covers or gaskets;
  4. (iv) All emergency devices and valves including self-closing stop valves, excess flow valves and remote closure devices must be free from corrosion, distortion, erosion and any external damage that will prevent safe operation. Remote closure devices and self-closing stop valves must be functioned to demonstrate proper operation;
  5. (v) Missing bolts, nuts and fusible links or elements must be replaced, and loose bolts and nuts must be tightened;
  6. (vi) All markings on the cargo tank required by parts 172, 178 and 180 of this subchapter must be legible;
  7. (vii) [Reserved]
  8. (viii) All major appurtenances and structural attachments on the cargo tank including, but not limited to, suspension system attachments, connecting structures, and those elements of the upper coupler (fifth wheel) assembly that can be inspected without dismantling the upper coupler (fifth wheel) assembly must be inspected for any corrosion or damage which might prevent safe operation;
  9. (ix) For cargo tanks transporting lading corrosive to the tank, areas covered by the upper coupler (fifth wheel) assembly must be inspected at least once in each two year period for corroded and abraded areas, dents, distortions, defects in welds, and any other condition that might render the tank unsafe for transportation service. The upper coupler (fifth wheel) assembly must be removed from the cargo tank for this inspection.
3. (3) All reclosing pressure relief valves must be externally inspected for any corrosion or damage which might prevent safe operation. All reclosing pressure relief valves on cargo tanks carrying lading corrosive to the valve must be removed from the cargo tank for inspection and testing. Each reclosing pressure relief valve required to be removed and tested must be tested according to the requirements set forth in paragraph (j) of this section.
4. (4) Ring stiffeners or other appurtenances, installed on cargo tanks constructed of mild steel or high-strength, low-alloy steel, that create air cavities adjacent to the tank shell that do not allow for external visual inspection must be thickness tested in accordance with paragraphs (i)(2) and (i)(3) of this section, at least once every 2 years. At least four symmetrically distributed readings must be taken to establish an average thickness for the ring stiffener or appurtenance. If any thickness reading is less than the average thickness by more than 10%, thickness testing in accordance with paragraphs (i)(2) and (i)(3) of this section must be conducted from the inside of the cargo tank on the area of the tank wall covered by the appurtenance or ring stiffener.
5. (5) Corroded or abraded areas of the cargo tank wall must be thickness tested in accordance with the procedures set forth in paragraphs (i)(2), (i)(3), (i)(5), (i)(6), (i)(9), and (i)(10) of this section.
6. (6) The gaskets on any full opening rear head must be:
  1. (i) Visually inspected for cracks or splits caused by weather or wear; and
  2. (ii) Replaced if cuts or cracks which are likely to cause leakage, or are of a depth one-half inch or more, are found.
7. (7) The inspector must record the results of the external visual examination as specified in § 180.417(b).
(e) Internal visual inspection.
1. (1) When the cargo tank is not equipped with a manhole or inspection opening, or the cargo tank design precludes an internal inspection, the tank shall be hydrostatically or pneumatically tested in accordance with 180.407(c) and (g).
2. (2) The internal visual inspection must include as a minimum the following:
  1. (i) The tank shell and heads must be inspected for corroded and abraded areas, dents, distortions, defects in welds, and any other condition that might render the tank unsafe for transportation service.
  2. (ii) Tank liners must be inspected as specified in § 180.407(f).
3. (3) Corroded or abraded areas of the cargo tank wall must be thickness tested in accordance with paragraphs (i)(2), (i)(3), (i)(5), (i)(6), (i)(9), and (i)(10) of this section.
4. (4) The inspector must record the results of the internal visual inspection as specified in § 180.417(b).
(f) Lining inspection. The integrity of the lining on all lined cargo tanks, when lining is required by this subchapter, must be verified at least once each year as follows:
1. (1) Rubber (elastomeric) lining must be tested for holes as follows:
  1. (i) Equipment must consist of:
    1. (A) A high frequency spark tester capable of producing sufficient voltage to ensure proper calibration;
    2. (B) A probe with an “L” shaped 2.4 mm (0.09 inch) diameter wire with up to a 30.5 cm (12-inch) bottom leg (end bent to a 12.7 mm (0.5 inch) radius), or equally sensitive probe; and
    3. (C) A steel calibration coupon 30.5 cm × 30.5 cm (12 inches × 12 inches) covered with the same material and thickness as that to be tested. The material on the coupon shall have a test hole to the metal substrate made by puncturing the material with a 22 gauge hypodermic needle or comparable piercing tool.
  2. (ii) The probe must be passed over the surface of the calibration coupon in a constant uninterrupted manner until the hole is found. The hole is detected by the white or light blue spark formed. (A sound lining causes a dark blue or purple spark.) The voltage must be adjusted to the lowest setting that will produce a minimum 12.7 mm (0.5 inch) spark measured from the top of the lining to the probe. To assure that the setting on the probe has not changed, the spark tester must be calibrated periodically using the test calibration coupon, and the same power source, probe, and cable length.
  3. (iii) After calibration, the probe must be passed over the lining in an uninterrupted stroke.
  4. (iv) Holes that are found must be repaired using equipment and procedures prescribed by the lining manufacturer or lining installer.
2. (2) Linings made of other than rubber (elastomeric material) must be tested using equipment and procedures prescribed by the lining manufacturer or lining installer.
3. (3) Degraded or defective areas of the cargo tank liner must be removed and the cargo tank wall below the defect must be inspected. Corroded areas of the tank wall must be thickness tested in accordance with paragraphs (i)(2), (i)(3), (i)(5) and (i)(6) of this section.
4. (4) The inspector must record the results of the lining inspection as specified in § 180.417(b).

(g) Pressure test. All components of the cargo tank wall, as defined in § 178.320(a) of this subchapter, must be pressure tested as prescribed by this paragraph.

(1) Test Procedure—(i) As part of the pressure test, the inspector must perform an external and internal visual inspection, except that on an MC 338 cargo tank, or a cargo tank not equipped with a manhole or inspection opening, an internal inspection is not required.
(ii) All self-closing pressure relief valves, including emergency relief vents and normal vents, must be removed from the cargo tank for inspection and testing according to the requirements in paragraph (j) of this section.
(iii) Except for cargo tanks carrying lading corrosive to the tank, areas covered by the upper coupler (fifth wheel) assembly must be inspected for corroded and abraded areas, dents, distortions, defects in welds, and any other condition that might render the tank unsafe for transportation service. The upper coupler (fifth wheel) assembly must be removed from the cargo tank for this inspection.

(iv) Each cargo tank must be tested hydrostatically or pneumatically to the internal pressure specified in the following table. At no time during the pressure test may a cargo tank be subject to pressures that exceed those identified in the following table:

Table 1 to Paragraph (g)(1)(iv)
Specification	Test pressure
MC 300, 301, 302, 303, 305, 306	The test pressure on the name plate or specification plate, 20.7 kPa (3 psig) or design pressure, whichever is greater.
MC 304, 307	The test pressure on the name plate or specification plate, 275.8 kPa (40 psig) or 1.5 times the design pressure, whichever is greater.
MC 310, 311, 312	The test pressure on the name plate or specification plate, 20.7 kPa (3 psig) or 1.5 times the design pressure, whichever is greater.
MC 330, 331	The test pressure on the name plate or specification plate, 1.5 times either the MAWP or the re-rated pressure, whichever is applicable.
MC 338	The test pressure on the name plate or specification plate, 1.25 times either the MAWP or the re-rated pressure, whichever is applicable.
DOT 406	The test pressure on the name plate or specification plate, 34.5 kPa (5 psig) or 1.5 times the MAWP, whichever is greater.
DOT 407	The test pressure on the name plate or specification plate, 275.8 kPa (40 psig) or 1.5 times the MAWP, whichever is greater.
DOT 412	The test pressure on the name plate or specification plate, or 1.5 times the MAWP, whichever is greater.

(v) [Reserved]
(vi) Each cargo tank of a multi-tank cargo tank motor vehicle must be tested with the adjacent cargo tanks empty and at atmospheric pressure.
(vii) All closures except pressure relief devices must be in place during the test. All prescribed loading and unloading venting devices rated at less than test pressure may be removed during the test. If retained, the devices must be rendered inoperative by clamps, plugs, or other equally effective restraining devices. Restraining devices may not prevent detection of leaks or damage the venting devices and must be removed immediately after the test is completed.
(viii) Hydrostatic test method. Each cargo tank, including its domes, must be filled with water or other liquid having similar viscosity, at a temperature not exceeding 100 °F. The cargo tank must then be pressurized to not less than the pressure specified in paragraph (g)(1)(iv) of this section. The cargo tank, including its closures, must hold the prescribed test pressure for at least 10 minutes during which time it shall be inspected for leakage, bulging or any other defect.
(ix) Pneumatic test method. Pneumatic testing may involve higher risk than hydrostatic testing. Therefore, suitable safeguards must be provided to protect personnel and facilities should failure occur during the test. The cargo tank must be pressurized with air or an inert gas. The pneumatic test pressure in the cargo tank must be reached by gradually increasing the pressure to one-half of the test pressure. Thereafter, the pressure must be increased in steps of approximately one-tenth of the test pressure until the required test pressure has been reached. The test pressure must be held for at least 5 minutes. The pressure must then be reduced to the MAWP, which must be maintained during the time the entire cargo tank surface is inspected. During the inspection, a suitable method must be used for detecting the existence of leaks. This method must consist either of coating the entire surface of all joints under pressure with a solution of soap and water, or using other equally sensitive methods.
(2) When testing an insulated cargo tank, the insulation and jacketing need not be removed unless it is otherwise impossible to reach test pressure and maintain a condition of pressure equilibrium after test pressure is reached, or the vacuum integrity cannot be maintained in the insulation space. If an MC 338 cargo tank used for the transportation of a flammable gas or oxygen, refrigerated liquid is opened for any reason, the cleanliness must be verified prior to closure using the procedures contained in § 178.338-15 of this subchapter.
(3) Each MC 330 and MC 331 cargo tank constructed of quenched and tempered steel in accordance with Part UHT in Section VIII of the ASME Code (IBR, see § 171.7 of this subchapter), or constructed of other than quenched and tempered steel but without postweld heat treatment, used for the transportation of anhydrous ammonia or any other hazardous materials that may cause corrosion stress cracking, must be internally inspected by the wet fluorescent magnetic particle method immediately prior to and in conjunction with the performance of the pressure test prescribed in this section. Each MC 330 and MC 331 cargo tank constructed of quenched and tempered steel in accordance with Part UHT in Section VIII of the ASME Code and used for the transportation of liquefied petroleum gas must be internally inspected by the wet fluorescent magnetic particle method immediately prior to and in conjunction with the performance of the pressure test prescribed in this section. The wet fluorescent magnetic particle inspection must be in accordance with Section V of the ASME Code and CGA Technical Bulletin TB-2 (IBR, see § 171.7 of this subchapter). This paragraph does not apply to cargo tanks that do not have manholes. (See § 180.417(c) for reporting requirements.)
(4) All pressure bearing portions of a cargo tank heating system employing a medium such as, but not limited to, steam or hot water for heating the lading must be hydrostatically pressure tested at least once every 5 years. The test pressure must be at least the maximum system design operating pressure and must be maintained for five minutes. A heating system employing flues for heating the lading must be tested to ensure against lading leakage into the flues or into the atmosphere.
(5) Exceptions.
1. (i) Pressure testing is not required for MC 330 and MC 331 cargo tanks in dedicated sodium metal service.
2. (ii) Pressure testing is not required for uninsulated lined cargo tanks, with a design pressure or MAWP of 15 psig or less, which receive an external visual inspection and a lining inspection at least once each year.
(6) Acceptance criteria. A cargo tank that leaks, fails to retain test pressure or pneumatic inspection pressure, shows distortion, excessive permanent expansion, or other evidence of weakness that might render the cargo tank unsafe for transportation service, may not be returned to service, except as follows: A cargo tank with a heating system which does not hold pressure may remain in service as an unheated cargo tank if:
1. (i) The heating system remains in place and is structurally sound and no lading may leak into the heating system, and
2. (ii) The specification plate heating system information is changed to indicate that the cargo tank has no working heating system.
(7) The inspector must record the results of the pressure test as specified in § 180.417(b).

(h) Leakage test. The following requirements apply to cargo tanks requiring a leakage test:
1. (1) Each cargo tank must be tested for leaks in accordance with paragraph (c) of this section. The leakage test must include testing product piping with all valves and accessories in place and operative, except that any venting devices set to discharge at less than the leakage test pressure must be removed or rendered inoperative during the test. All internal or external self-closing stop valves must be tested for leak tightness. Each cargo tank of a multi-cargo tank motor vehicle must be tested with adjacent cargo tanks empty and at atmospheric pressure. Test pressure must be maintained for at least 5 minutes. Cargo tanks in liquefied compressed gas service must be externally inspected for leaks during the leakage test. Suitable safeguards must be provided to protect personnel should a failure occur. Cargo tanks may be leakage tested with hazardous materials contained in the cargo tank during the test. Leakage test pressure must be no less than 80% of MAWP marked on the specification plate except as follows:
(i) A cargo tank with an MAWP of 690 kPa (100 psig) or more may be leakage tested at its maximum normal operating pressure provided it is in dedicated service or services; or
(ii) An MC 330 or MC 331 cargo tank in dedicated liquified petroleum gas service may be leakage tested at not less than 414 kPa (60 psig).
(iii) An operator of a specification MC 330 or MC 331 cargo tank, and a nonspecification cargo tank authorized under § 173.315(k) of this subchapter, equipped with a meter may check leak tightness of the internal self-closing stop valve by conducting a meter creep test. (See appendix B to this part.)
(iv) An MC 330 or MC 331 cargo tank in dedicated service for anhydrous ammonia may be leakage tested at not less than 414 kPa (60 psig).
(v) A non-specification cargo tank required by § 173.8(d) of this subchapter to be leakage tested, must be leakage tested at not less than 16.6 kPa (2.4 psig), or as specified in paragraph (h)(2) of this section.
(2) Cargo tanks used to transport petroleum distillate fuels that are equipped with vapor collection equipment may be leak tested in accordance with the Environmental Protection Agency's “Method 27—Determination of Vapor Tightness of Gasoline Delivery Tank Using Pressure-Vacuum Test,” as set forth in Appendix A to 40 CFR part 60. Test methods and procedures and maximum allowable pressure and vacuum changes are in 40 CFR 63.425(e). The hydrostatic test alternative, using liquid in Environmental Protection Agency's “Method 27—Determination of Vapor Tightness of Gasoline Delivery Tank Using Pressure-Vacuum Test,” may not be used to satisfy the leak testing requirements of this paragraph. The test must be conducted using air.
(3) A cargo tank that fails to retain leakage test pressure may not be returned to service as a specification cargo tank, except under conditions specified in § 180.411(d).
(4) After July 1, 2000, Registered Inspectors of specification MC 330 and MC 331 cargo tanks, and nonspecification cargo tanks authorized under § 173.315(k) of this subchapter must visually inspect the delivery hose assembly and piping system while the assembly is under leakage test pressure utilizing the rejection criteria listed in § 180.416(g). Delivery hose assemblies not permanently attached to the cargo tank motor vehicle may be inspected separately from the cargo tank motor vehicle. In addition to a written record of the inspection prepared in accordance with § 180.417(b), the Registered Inspector conducting the test must note the hose identification number, the date of the test, and the condition of the hose assembly and piping system tested.

(5) The inspector must record the results of the leakage test as specified in § 180.417(b).

(i) Thickness testing.
(1) The shell and head thickness of all unlined cargo tanks used for the transportation of materials corrosive to the tank must be measured at least once every 2 years, except that cargo tanks measuring less than the sum of the minimum prescribed thickness, plus one-fifth of the original corrosion allowance, must be tested annually.
(2) Measurements must be made using a device capable of accurately measuring thickness to within ±0.002 of an inch.
(3) Any person performing thickness testing must be trained in the proper use of the thickness testing device used in accordance with the manufacturer's instruction.
(4) Thickness testing must be performed in the following areas of the cargo tank wall, as a minimum:
1. (i) Areas of the tank shell and heads and shell and head area around any piping that retains lading;
2. (ii) Areas of high shell stress such as the bottom center of the tank;
3. (iii) Areas near openings;
4. (iv) Areas around weld joints;
5. (v) Areas around shell reinforcements;
6. (vi) Areas around appurtenance attachments;
7. (vii) Areas near upper coupler (fifth wheel) assembly attachments;
8. (viii) Areas near suspension system attachments and connecting structures;
9. (ix) Known thin areas in the tank shell and nominal liquid level lines; and
10. (x) Connecting structures joining multiple cargo tanks of carbon steel in a self-supporting cargo tank motor vehicle.

(5) Minimum thicknesses for MC 300, MC 301, MC 302, MC 303, MC 304, MC 305, MC 306, MC 307, MC 310, MC 311, and MC 312 cargo tanks are determined based on the definition of minimum thickness found in § 178.320(a) of this subchapter. The following Tables I and II identify the “In-Service Minimum Thickness” values to be used to determine the minimum thickness for the referenced cargo tanks. The column headed “Minimum Manufactured Thickness” indicates the minimum values required for new construction of DOT 400 series cargo tanks, found in Tables I and II of §§ 178.346-2, 178.347-2, and 178.348-2 of this subchapter. In-Service Minimum Thicknesses for MC 300, MC 301, MC 302, MC 303, MC 304, MC 305, MC 306, MC 307, MC 310, MC 311, and MC 312 cargo tanks are based on 90 percent of the manufactured thickness specified in the DOT specification, rounded to three places.

Table I—In-Service Minimum Thickness for MC 300, MC 303, MC 304, MC 306, MC 307, MC 310, MC 311, and MC 312 Specification Cargo Tanks Constructed of Steel and Steel Alloys
Minimum manufactured thickness (US gauge or inches)	Nominal decimal equivalent for (inches)	In-service minimum thickness reference (inches)
19	0.0418	0.038
18	0.0478	0.043
17	0.0538	0.048
16	0.0598	0.054
15	0.0673	0.061
14	0.0747	0.067
13	0.0897	0.081
12	0.1046	0.094
11	0.1196	0.108
10	0.1345	0.121
9	0.1495	0.135
8	0.1644	0.148
7	0.1793	0.161
3/16	0.1875	0.169
1/4	0.2500	0.225
5/16	0.3125	0.281
3/8	0.3750	0.338

Table II—In-Service Minimum Thickness for MC 301, MC 302, MC 304, MC 305, MC 306, MC 307, MC 311, and MC 312 Specification Cargo Tanks Constructed of Aluminum and Aluminum Alloys
Minimum manufactured thickness	In-service minimum thickness (inches)
0.078	0.070
0.087	0.078
0.096	0.086
0.109	0.098
0.130	0.117
0.141	0.127
0.151	0.136
0.172	0.155
0.173	0.156
0.194	0.175
0.216	0.194
0.237	0.213
0.270	0.243
0.360	0.324
0.450	0.405
0.540	0.486

(6) An owner of a cargo tank that no longer conforms to the minimum thickness prescribed for the design as manufactured may use the cargo tank to transport authorized materials at reduced maximum weight of lading or reduced maximum working pressure, or combinations thereof, provided the following conditions are met:
1. (i) A Design Certifying Engineer must certify that the cargo tank design and thickness are appropriate for the reduced loading conditions by issuance of a revised manufacturer's certificate, and
2. (ii) The cargo tank motor vehicle's nameplate must reflect the revised service limits.
(7) An owner of a cargo tank that no longer conforms with the minimum thickness prescribed for the specification may not return the cargo tank to hazardous materials service. The tank's specification plate must be removed, obliterated or covered in a secure manner.
(8) The inspector must record the results of the thickness test as specified in § 180.417(b).
(9) For MC 331 cargo tanks constructed before October 1, 2003, minimum thickness shall be determined by the thickness indicated on the U1A form minus any corrosion allowance. For MC 331 cargo tanks constructed after October 1, 2003, the minimum thickness will be the value indicated on the specification plate. If no corrosion allowance is indicated on the U1A form then the thickness of the tank shall be the thickness of the material of construction indicated on the UIA form with no corrosion allowance.
(10) For 400-series cargo tanks, minimum thickness is calculated according to tables in each applicable section of this subchapter for that specification: § 178.346-2 for DOT 406 cargo tanks, § 178.347-2 for DOT 407 cargo tanks, and § 178.348-2 for DOT 412 cargo tanks.
(j) Pressure vent bench test. When required by this section, pressure relief valves must be tested for proper function as follows:
1. (1) Each self-closing pressure relief valve must open and reseat to a leaktight condition at the pressures prescribed for the applicable cargo tank specification or at the following pressures:
  1. (i) For MC 306 cargo tanks:
    1. (A) With MC 306 reclosing pressure relief valves, it must open at not less than 3 psi and not more than 4.4 psi and must reseat to a leak tight-condition at no less than 2.7 psi.
    2. (B) With reclosing pressure relief valves modified as provided in § 180.405(c) to conform with DOT 406 specifications, according to the pressures set forth for a DOT 406 cargo tank in § 178.346-3 of this subchapter.
  2. (ii) For MC 307 cargo tanks:
    1. (A) With MC 307 reclosing pressure relief valves, it must open at not less than the cargo tank MAWP and not more than 110% of the cargo tank MAWP and must reseat to a leak tight-condition at no less than 90% of the cargo tank MAWP.
    2. (B) With reclosing pressure relief valves modified as provided in § 180.405(c) to conform with DOT 407 specifications, according to the pressures set forth for a DOT 407 cargo tank in § 178.347-4 of this subchapter.
  3. (iii) For MC 312 cargo tanks:
    1. (A) With MC 312 reclosing pressure relief valves, it must open at not less than the cargo tank MAWP and not more than 110% of the cargo tank MAWP and must reseat to a leak tight-condition at no less than 90% of the cargo tank MAWP.
    2. (B) With reclosing pressure relief valves modified as provided in § 180.405(c) to conform with DOT 412 specifications, according to the pressures set forth for a DOT 412 cargo tank in § 178.348-4 of this subchapter.
  4. (iv) For MC 330 or MC 331 cargo tanks, it must open at not less than the required set pressure and not more than 110% of the required set pressure and must reseat to a leak-tight condition at no less than 90% of the required set pressure.
  5. (v) For DOT 400-series cargo tanks, according to the pressures set forth for the applicable cargo tank specification in §§ 178.346-3, 178.347-4, and 178.348-4, respectively, of this subchapter.
  6. (vi) For cargo tanks not specified in this paragraph, it must open at not less than the required set pressure and not more than 110% of the required set pressure and must reseat to a leak-tight condition at no less than 90% of the required set pressure or the pressure prescribed for the applicable cargo tank specification.
2. (2) Normal vents (1 psig vents) must be tested according to the testing criteria established by the valve manufacturer.
3. (3) Self-closing pressure relief devices not tested or failing the tests in paragraph (j)(1) of this section must be repaired or replaced.
  Editorial Note:For Federal Register citations affecting § 180.407, see the List of CFR Sections Affected, which appears in the Finding Aids section of the printed volume and at www.govinfo.gov.

[Amdt. 180-2, 54 FR 25032, June 12, 1989]