Pressurizing DOT Cans and Drums

Moving liquids out of DOT drums and cans from 5 gallon to 55 gallon drums by pressurizing the container is a technique often used in research. It avoids the cost?of purchasing and installing a pump and eliminates seal and rotating equipment problems. It produces a reliable steady flow that can easily be achieved with a regulator and some gas piping.

It also, sadly, has some safety issues not always fully and correctly evaluated.

?The International Fire Code (IFC) in 5703.6.3 requires all piping systems must be tested to at least 5 psig. This is above the DOT leak test requirements in 49 CFR 178.6XX of 4 psig for packing group I and 3 psig for packing group II and III containers. IFC 5705.2.2 limits the pressure used to pressurize anything to below the containers maximum allowable working pressure (MAWP)?by a pressure relief device in addition to a regulator. So technically one is violating the fire code since you need to test the system to above the container’s MAWP.

The container’s robustness is also highly suspect. DOT containers are not individually tested. Rather a representative sample is tested. This is, of course, completely at odds with the ASME code which requires all vessels to be individually tested before use. Furthermore, DOT codes do not have any allowance for fatigue and use a different safety factor than ASME codes. This results in a much less robust vessel, typically one rated for only ~60% of the ASME basis.

Finally, DOT tests are for integrity of the container during transportation. A container that bulges or deforms but stays leak tight will be passed. Tests I conducted with standard DOT containers, repeating the leak and hydro test required in 49 CFR 178.604 and 603?(on admittedly only 3-4 samples) showed most deformed badly at pressures above 3 psig. Leakage almost always occurred above 5 psig.

Providing a relief device to limit the pressurizing gas to 3 psig or less is challenging. As discussed in my article, Performance Analysis of Small Size Pilot Plant and Laboratory Relief Valves (Process Safety Progress, Sept 2003), small (<1/2”), relief valves operating below 10 psig showed a strong tendency after time to relief at well over the 10% limit suggested by the code, often as high as 50%.?This was true of all manufacturers tested in both the tests reported in the article and in two rounds of follow up tests afterwards.?While a 3 psig relief valve that does not open until 4.5 psig is normally not an issue for a robust vessel, this over pressure is often enough to cause a container to bulge and occasionally leak. Using a bubbler or similar hydrostatic head device is a good solution by fabricating one to product 2-3 psi often results in a very large column or a very heavy liquid. Many commercial fills have non-trivial heath and toxicity issues which complicate the issue.

There is also some issue with potential liability as I have found that asking a DOT container supplier to confirm that their product is designed to be pressurized to any pressure usually results in an awkward silence if not an outright disavowal. Hence, if an accident occurred, the potential for legal problems is probably much higher.

Finally, any external fire is likely to cause the DOT container to fail rapidly and allow the contents to feed the conflagration. While this is true for storage areas and addressed in the local fire code requirements, the potential and the resultant effects on a small pilot plant or laboratory operation are often overlooked. This can result in a more serious hazard arising, albeit it at a much lower probability, than the hazard analysis and risk assessment for the operation addressed.

My advice is to consider the numerous drum pumps and small pumps available to transfer the liquid and use them instead.

For more information on this and many other pilot plant and laboratory safety issues you may want to consider the course Pilot Plant and Laboratory Safety given by Engineered Career Solutions July 13-15, 2022. More information on this course, formerly given by AIChE and the University of Wisconsin, can be found at https://ecstechtraining.com/pilot-plant-lab-safety