Glen Harm, Girard Equipment Inc, describes the characteristics of a pressure-relief vent.
DURING the Tank Truck Week Maintenance Track, panelists from the Truck Trailer Manufacturers Association discussed some of the latest developments related to pressure/vacuum relief vents and lean duplex tank repairs. Speakers also provided a regulatory update on wetlines, cargo tank construction under ASME Section XII, and Phase of the greenhouse gas emission rules.
The industry needs to put more effort into monitoring itself in terms of testing pressure relief devices (PRD), according to Glen Harm, engineering manager at Girard Equipment Inc.
“If we don’t do that, there’s going to be some catastrophic event where people die,” Harm said, “and then our government is going to get really involved and set a lot of different objectives we’re going to have to attain.”
He said the biggest reason to test the devices is safety, plain and simple.
“This is a safety device that’s put on a tank truck, and it relieves the pressure when pressure builds up,” he said. “That tank truck can turn into a huge bomb and go off if pressure is not relieved. So it’s really important to get the right pressure. If the pressure is too high, the tank can explode. If it’s too low, there are a lot of harmful gases that can be released out of the pressure relief device.”
He said they also need to be tested because the Code of Federal Regulations says it’s the thing to do, specifically in 49 CFR 180.407(c).
The Federal Motor Carrier Safety Administration (FMCSA) released a memo in October 2014 in which it stated that its investigations showed a “consistent pattern of non-compliance” regarding bench testing of PRDs—that cargo tank testing and repair facilities are “either failing to bench test PRDs or failing to test them appropriately by not determining the proper start-to-discharge and closing pressures.”
A registered inspector or design certifying engineer performs the test, as instructed in 49 CFR 171.8:
Registered Inspector means a person registered with the Department in accordance with subpart F of part 107 of this chapter who has the knowledge and ability to determine whether a cargo tank conforms to the applicable DOT specification. A Registered Inspector meets the knowledge and ability requirements of this section by meeting any one of the following requirements: (1) has an engineering degree and one year of work experience relating to the testing and inspection of cargo tanks; (2) has an associate degree in engineering and two years of work experience relating to the testing and inspection of cargo tanks; and (3) has a high school diploma (or General Equivalency Diploma) and three years of work experience relating to the testing and inspection of cargo tanks; or (4) has at least three years’ experience performing the duties of a Registered Inspector prior to September 1, 1991.
The person must be registered with the FMCSA, be familiar with DOT-specification cargo tanks and trained and experienced in use of the inspection and testing equipment needed, and have the training and experience required to meet the definition of “Registered Inspector.”
49 CFR 180.407 (d)(3) describes how the test should be done:
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 must open at no less than the required set pressure and no more than 110 percent of the required set pressure, and must reseat to a leak-tight condition at no less than 90 percent of the start-to-discharge pressure or the pressure prescribed for the applicable cargo tank specification.
Bench test apparatus: clean air supply; regulator to adjust air pressure; digital pressure gauge, NIST traceable; gate valve, to open and close air supply; and fixture to hold PRD.
To verify the PRD: venting capacity in square feet of PRD is equal or greater than the cargo tank; MAWP of PRD matches the cargo tank; set pressure of PRD matches the cargo tank; and connection size (3” or 4”) of the cargo tank matches the PRD.
49 CFR 180.417 (b)(2)(iii) describes the forms required:
Listing of all items tested or inspected, including information about pressure relief devices that are removed, inspected and tested or replaced, when applicable (type of device, set to discharge pressure, pressure at which device opened, pressure at which device re-seated, and a statement of disposition of the device [e.g., reinstalled, repaired, or replaced]).
Lean Duplex Repair
Peter Weis, chief engineer
Polar Tank Trailer
What is harder to weld: T316 or lean duplex material?
“A lot of people don’t have a lot of experience with it, so they would assume they would weld about the same,” Weis said. “That’s probably not a good answer. A lot of tanker companies are working with lean duplex now. A lot of these tanks eventually will need repair.”
Lean duplex has a microstructure that’s half ferrite and half austenite.
The pitting resistance equivalent is the same for T316 and LDX 2101 (lean duplex), but they are made differently. LDX 2101 has more chromium (21%, compared to 17%) and a lot less nickel (1.5%, compared to 11%). At the tail end, the tensile strength of LDX is 19% higher (94 to 75), “so you’re able to construct a tank with thinner material, so there are potential weight benefits. Depending on the markets for these different materials, if nickel is a high price, the LDX might suddenly become very attractive.”
• Appearance of the weld gives no indication of quality.
• Duplex doesn’t melt as readily as 300 series. Weld metal can lay on top.
• Requires better control of heat to preserve dual phase structure.
• Rapid cooling results in high ferrite—very small pipes, stud welds, spatter, welding too cool.
Specialized weld procedures are required:
• ASME T316 procedures do not qualify you for lean duplex. Written and qualified procedures are required by DOT regulations.
• ASME qualified welders—duplex to duplex, duplex to T316.
Regulatory & Legislative Update
John Freiler, engineering manager
Freiler gave an update on three issues:
• HM-213D Wetlines.
“PHMSA (the Pipeline and Hazardous Materials Safety Administration) had proposed a ban on them. Congress put a halt on the rule and demanded a GAO report. The GAO report issued in 2013 was very critical of the proposal. Despite this, PHMSA had kept the rule on its Significant Rulemaking Report as active. Until now. In the DOT’s October (2015) Significant Rulemaking Report, they report that based on the GAO’s findings, the rule will be withdrawn. So we should see that finally and formally removed. That doesn’t mean NTSB will stop going on about it. We may see it come back yet again. But the 213D version is finally done.”
• HM-241 ASME Section XII.
“According to reports issued to the ASME Section XII Code Development Committee, PHMSA’s rulemaking on this continues. The process was longer than some because of other priorities and personnel changes. Insiders at PHMSA have seen a new draft of the proposal and expect to see publication by the end of the year (2015). We expect that this will come out as a supplementary notice of proposed rulemaking to allow compliance with the 2015 ASME Section XII and NBIC codes as a voluntary alternative to using the CFR construction rules.”
• Environmental Protection Agency’s Phase 2 GHG rules.
“EPA and NHTSA have heavy-duty vehicles in their crosshairs. Phase 1 was aimed at tractors. Phase 2 is a 629-page shotgun aimed at tractors, trailers, vocational vehicles, heavy-duty pickup trucks, and vans. TTMA has expressed problems with EPA’s and NHTSA’s regulatory authority on trailers, and noted that the proposal has significant safety impacts and is overly broad and complex. We’ve criticized them a lot and hopefully they will take our comments to heart. For tank trailers, the proposal sticks mostly to requirements for low rolling resistance tires and Automatic Tire Inflation Systems. Fleets would be required to maintain and replace these systems or face a $3750 fine per device. One thing I’ve learned from watching the government all these years is that there’s a Phase 3 coming.” ♦
Find the NTTC Tank Truck Week archive with articles from 2014 to present