FHWA Official Contributes Answers To Frequently Asked Tank Questions

The Federal Highway Administration (FHWA) receives many questions from managers in the tank truck industry. William Quade, FHWA official, provided answers to frequently asked cargo tank queries during the National Tank Truck Carrier Cargo Maintenance Seminar October 19-21, 1998, in Chicago, Illinois.

Question: Is it legal to downgrade an MC312 cargo tank to the MC306 specification?

Answer: No. After August 31, 1995, a cargo tank may not be certified to an MC300-series specification to which it was not originally constructed.

Question: Can an MC306 cargo tank that was taken out of specification service be returned to MC306 service after August 31, 1995?

Answer: Yes, under certain conditions. See the FHWA flowchart on re-certifying cargo tanks. The flowchart can be obtained by contacting the local FHWA office.

Question: Can an MC307/312 multispecification cargo tank in MC307 service prior to August 31, 1995, be changed to MC312 service after August 31, 1995?

Answer: Yes. Since the tank originally was constructed to both specifications, it can continue to be operated under either specification.

Question: If a specification plate is being replaced by an owner or registered inspector, what date should be used for the cargo tank certification date?

Answer: Use the original specification certification date.

Question: What should be done about a specification plate that is missing required information?

Answer: A complete specification plate should be obtained from the cargo tank manufacturer. If the manufacturer is no longer in business, all required information should be marked on the specification plate by the registered inspector and cargo tank owner.

Question: What should the owner of an ASME stamped cargo tank do if the Ul-A form is missing? The U1-A form is required by ASME for every tank that is manufactured and attests to basic construction, such as material used and its thickness.

Answer: The U1-A form should be obtained from the original manufacturer or the National Board of Boiler and Pressure Vessel Inspectors. If the original manufacturer is no longer in business and the form is not on file with the National Board, the owner and registered inspector may copy the information from DOT specification plates and ASME Code Plates and certify compliance with the specifications.

Question: When determining compliance with the dimensional requirements for rear-mounted hardware protection, where are measurements from the protection device to the tank and piping taken?

Answer: If, when moved horizontally, the rear-end protection device could contact the tank or piping, the measurement would be taken from the surface of the rear-end protection device closest to the front of the vehicle. If, when moved horizontally, the rear-end protection device would not contact the tank or piping, the measurement would be taken from the surface of the rear-mounted protection device farthest from the front of the vehicle.

Question: What is adequate anchoring of a cargo tank to its chassis or the vehicle it is loaded upon?

Answer: Anchoring must be constructed in a method that eliminates any motion between the tank and the frame/vehicle. The motion must not occur when the cargo tank motor vehicle is subjected to the loads required in 178.345-3(b) and (c).

Question: What should be done if manufacturing defects, such as vents above the overturn protection device, are discovered during the external visual inspection?

Answer: All defects discovered during an inspection or test are required to be noted on the inspection form and corrected prior to placing the cargo tank back into service. FHWA should be notified of defects occurring during manufacturing or modifications of cargo tanks.

Question: What marking is required on a cargo tank after thickness testing is conducted due to discovery of an abrasion or corrosion during an internal or external visual inspection?

Answer: Thickness testing of small areas where defects are discovered is part of the internal and external visual inspection. This taking of limited thickness readings during the internal visual or external visual inspection is not considered to be a thickness test and would require no marking on the cargo tank. The presence of corroded or abraded areas and thickness readings taken must, however, be noted on the inspection report.

Question: Must the inspection/test facility check to make sure the cargo tank owner has a Certificate of Compliance as part of inspections or tests?

Answer: No. During inspections and tests, the registered inspector is certifying that the cargo tank has successfully passed that inspection or test, not that the tank meets all requirements of the regulations.

Question: Should the test pressure marked on the specification plate on MC306 or DOT406 tanks be used for the 180.407(g) pressure test?

Answer: Not necessarily. The correct test pressure for the pressure test should be determined from the chart in 180.407(g)(1)(iv).

Question: Does extending the height of a cargo tank overturn protection device to accommodate the additional height of a pressure-relief valve meeting the DOT400 series leakage requirements meet the definition of a modification?

Answer: Yes. A change in the design and construction of an overturn protection device, such as raising the height, would affect the lading retention capability of the cargo tank as the modified overturn protection devices.

Question: Does transferring a rear-end protection device from one chassis to another during a cargo tank remounting meet the definition of a modification?

Answer: No. If there is no change in the design or the method of attachment to the chassis, this would not constitute a change in the design and construction of the device, and therefore not be a modification.

Question: Is there a required marking on the specification plate for an existing cargo tank mounted on a new cargo tank motor vehicle?

Answer: No. The original specification plate for a cargo tank motor vehicle should not be altered. If the mounting includes a design modification, 180.413(d) requires that a supplemental certificate of compliance be issued and a supplemental specification plate be attached to the vehicle. If the mounting does not change the original design and construction of the cargo tank motor vehicle, no documentation is required on the specification plate or the certificate of compliance. However, we recommend that a supplemental certificate of compliance be completed as a record of the mounting.

Question: After August 31, 1998, can an MC300 series vent be installed on an MC307 cargo tank?

Answer: No. After August 31, 1998, any new pressure-relief device installed on a specification cargo tank must meet the dynamic pressure surge standards in 178.345-10(b)(3). All other features of the device may meet the MC307 standards or the new DOT407 standards.

Question: Can an MC307 vent be installed on an MC312 cargo tank?

Answer: No. The MC312 cargo tank specifications required a pressure-relief device meeting the ASME Code or a rupture disc. After August 31, 1998, any new pressure-relief device installed on a specification cargo tank must meet the dynamic pressure surge standards in 178.345-10(b)(3). Section l80.405(c)(2) allows for MC312 pressure-relief devices to be replaced with devices meeting the DOT412 specifications. Therefore, a pressure-relief device on an MC312 cargo tank must be replaced with either a pressure-relief device that meets the ASME Code and 178.345-10(b)(3), or a pressure relief-device meeting all requirements of 178.345-10 and 178.345-11.

Question: After August 31, 1998, is it permissible to repair an MC300 series pressure-relief valve that fails a bench test?

Answer: Yes. It is permissible to repair a pressure-relief vent that is currently installed on a cargo tank if the repaired valve will successfully pass a bench test. However, replacement vents installed after August 31, 1998, must meet the leak tightness standards in 178.345-10(b)(3).

Question: After August 31, 1998, if a frangible or fusible vent needs replacement, must it be replaced with a pressure-relief vent meeting the DOT400 series requirements?

Answer: No. A frangible or fusible vent needing replacement can be replaced with another frangible or fusible vent.

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