Girard says that PHMSA's 2009 rewrite effort has created confusion, so stick with the original requirement for pressure relief vents
Feb 1, 2011 12:00 PM, By Rick Weber
CARRIERS should focus on the original verbiage in the Pipeline and Hazardous Materials Safety Administration's (PHMSA) legislation dealing with re-qualifying pressure relief devices (180.407), rather than the rewritten version of 2009, according to Dave Girard, vice-president of Girard Equipment Inc.
Girard addressed proper methods for vent testing under 49 CFR Part 180 during National Tank Truck Carriers' 2010 Cargo Tank Maintenance Seminar in Louisville, Kentucky. Girard's presentation was part of the Cargo Tank 101 portion of the program.
The original regulation, written in 1990, contained this wording regarding external visual inspection and vent testing in 180.407(d)(3):
“All re-closing relief valves must be externally inspected for any corrosion or damage which might prevent safe operation. All re-closing pressure relief valves on cargo tanks carrying lading corrosive to the valve must be removed from the cargo tank for inspection and testing. Each re-closing pressure relief valve required to be removed and tested must open at the required set pressure and reseat to a leak tight condition at 90% of the set to discharge pressure or the pressure prescribed for the applicable cargo tank specification.”
The 2009 version had changes in verbiage, as indicated in italics:
“All re-closing 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 open at no less than the required set pressure and no more than 110% of the required set pressure, and must reseat to a leak- tight condition at no less than 90% of the start to discharge pressure or the pressure prescribed for the applicable cargo tank specification.”
“Somewhere, my eighth-grade English teacher is rolling in her grave,” Girard said. “I don't know why they did this. The Federal Register indicated that there were some comments submitted by a propane tank dealer that take issue with the original verbiage. When we saw this change, we didn't' think they really were calling for anything different, so we really kind of missed it.
“Stick with the original requirement. This requirement has been in place since 1990, and has proven to be an excellent guide to proper re-qualification of pressure relief devices. If the original requirement is followed and your vents meet these standards, you will be able to properly re-qualify your valves per 180.407 (d)(3).
“We believe that the requirements are essentially unchanged and that PHMSA made the verbiage more complicated than it needed to be. A typical DOT 407 Tank with 25 psi MAWP will have the vent set to discharge at 120% to 132% of MAWP, or 30-33 psi.”
He said that 178.345.10, the code requirement that cargo tank builders must use when producing tanks, specifies a range of settings between 120% and 132% of MAWP.
The code reads:
“Each cargo tank must be equipped to relieve pressure and vacuum conditions in conformance with this section and the applicable individual specification. The pressure and vacuum relief system must be designed to operate and have sufficient capacity to prevent cargo tank rupture or collapse due to over-pressurization or vacuum resulting from loading or unloading, or from heating and cooling of lading.”
Said Girard, “We get a lot of calls at Girard Equipment about this issue. We think PHMSA has made a mess of this thing. I think it's strange that they would allow valves to be reset at that pressure. The settings for these valves when the tanks are built is a range. It opens at 120% to 132%. It's not a static number. It could be as high as 33 psi. We've told people to stick to the original requirement.”
Girard also talked about test stands, saying that they need to be clean, because debris and dirt can impair the ability to get an accurate reading.
“We see a lot of test stands that are dirty,” he said. “You have a flat surface, and somebody throws a wrench on it and somebody throws a tire iron on it. It might be difficult to get good readings.”
Girard went over the reporting and record-retention requirements listed in 180.417(b)(2)(iii):
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)).
He finished with the code regarding vacuum relief devices in 178.347.4:
(1) The vacuum relief system must limit the vacuum to less than 80% of the design vacuum capability of the tank.
(2) If pressure loading or unloading devices are provided, the pressure relief system must have adequate vapor and liquid capacity to limit tank pressure to the cargo tank test pressure at the maximum loading or unloading rate. The maximum loading and unloading rates must be included on the metal specification plate.
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