Road Valves for Portable Cryogenic Vessels

“Road Valves” were mentioned in the last article without defining them. A Road Valve consists of a 25psi or less relief device and an isolation valve installed as a bypass to the main safety relief on a portable cryogenic vessel. The purpose of this bypass system is to assure that pressure does not exceed 25psi while the vessel is transporting cryogenic liquid oxygen, nitrogen or argon over the road. The 25 psi mark is noted in the DOT exception found in 49CFR 173.320 and also outlined in specific exemptions established for a variety of cryogenic transports and portable vessels.

Compliance with the applicable exception or exemption typically requires that the vessel pressure be maintained at a level below 25.3 psi so most valves are set at 22-24psi for added assurance. It is the responsibility of the transporting driver to vent the vessel down below 25psi and open the road relief isolation valve prior to traveling with contents. Not all portable cryogenic vessels are fitted with road valves. For instance- Those built under DOT-4L or MC-338 specifications are typically able to travel at their full operating pressure.

The critical point here is that it is very important to understand the applicable guidelines and legalities for transporting cryogenic liquids with whatever vessel you are using. Ignorance of the law is no defense and fines related to DOT violations can be enormous. Most importantly- the guidelines were established not only for the safety of the operator, but also for those around them.

NOT PORTABLE- Skid Mounted Vertical Cryogenic Tanks.

What do you say when someone asks you to install a Road Valve on a vertical cryogenic bulk tank that is mounted on a fork pocket style palletized base and designed for stationary use only?

No.

There are tanks that are made to hold liquid for stationary applications only and are, in turn, not suitable for transporting cryogenic liquids. Many small vertical bulk tanks are now being fitted with fork pocket bases because it makes them so easy to move to a new installation site and set in place. In many applications the base also serves as the pad for the tank to support the legs. They also allow for pre-plumbing of final line manifolds and vaporizers. But- your typical 300 gallon or larger vertical cryogenic bulk tank is not made to be moved with liquid in it which is the common differentiator for “portable.”

True portable tanks are typically horizontal vessels that are built under DOT specs, exemption or exception and are designed to be moved full of liquid. Putting a base on a stationary tank does not make it all of the sudden qualified to be portable. And putting a Road Valve on a liquid oxygen, nitrogen or oxygen tank designed specifically for stationary use does not make it legal for transporting cryogenic liquids.

Granted- There are vertical vessels that are designed for transporting liquid including your typical DOT 4L cryogenic liquid cylinders and some of the micro-bulk vessels that are larger than the DOT 4L class. But- only certain specifically designed and classified vessels are for liquid transport. And the manufacturers of these vessels justifiably charge more for them so they provide very clear information on those vessels that are designed for transport.

There is significant risk associated with moving stationary-only vessels that are full of cryogenic liquids. Hazards include injury caused by tipping and turning over forklifts or other handling equipment. Inner vessel supports on stationary vessels are also not made to sustain movement of full vessels creating a lot of potential for damage to equipment and personnel. Stationary micro bulk vessels not designed for movement with liquid are regularly seen with broken neck tubes and other damage caused by someone improperly moving them full of liquid. These repairs are very expensive and not always even possible.

Let’s also not forget that improper transport of cryogenic liquids can result in very large fines. If you are not positive that your equipment is designed for liquid transport it is suggested that you ask a reliable source. There is nothing wrong with clarifying. And-You might just save someone from a serious injury.

4L DOT Cryogenic Liquid Cylinder Excessive Venting

The very best training sessions are those that get really conversational. Discussing case studies and reviewing alternative strategies are the root of “I learn as I teach.” One question asked this week was, “Do clients know to turn on their pressure builder isolation valves as soon as they receive their liquid cylinders?” The conclusion was that all too many users don’t know not to turn on the pressure builders on receipt.

A somewhat difficult issue applies when a system is set up with a primary and secondary bank of liquid cylinders tied into an automatic switch over control system. When the online bank of liquid oxygen, nitrogen or argon liquid cylinders runs low the system automatically switches over to the other bank. Since this could happen at almost any time the pressure builder(PB) valves have to remain open on the reserve bank.

If, though, it is known that the reserve bank will not go on line for several days then it is advisable to not turn on the PB valves right away. This is especially true if you have a Friday delivery to a facility that does not operate over the weekend. Just waiting until Monday to turn on the PB valve can add many days to the life of the liquid cylinders and greatly reduce product wasted to venting.

Boosting Brain Power-

Thanks to Traci Duez for providing a Linked In connection to the article "Six Ways to Boost Brain Power" http://www.scientificamerican.com/article.cfm?id=six-ways-to-boost-brainpower.

There is a lot of news coming out and related discussion regarding the ability to shape out thinking, moods, and attitudes. Any other neat links are welcomed.

PB Leaks & Excessive Product Loss

Yesterday was interesting.

Two of twelve 4LDOT cryogenic liquid cylinders tested at a client site had a combination of issues not commonly seen.

When liquid cylinders marked “bad” are returned trouble shooting is done to determine what (if anything) is “bad.” After initial visual inspection the next step is typically to put a little liquid nitrogen or oxygen into the vessel to build pressure and then leak check all up components on the vessel. This is necessary prep for NER or Simple NER testing.

Well, today while leak testing a dozen vessels, two were found to have leaks in the line between the Pressure Builder (PB) valve and the PB Regulator. This would normally not be noteworthy except for the fact that the PB isolation valve was closed on both vessels. Hence there was no way for pressure to hit this point in the line except for the fact that the PB isolation valve was obviously leaking by.

The net effect is excessive product loss that looks just like a vacuum problem.

See…. If the PB valve does not secure the PB vaporization line then liquid is allowed to leak into the line and vaporize. This liquid normally goes back into the top of the vessel creating excessive pressure. In the case of an external PB control line leaking this excess pressure leaks off. When doing an NER this would look like excessive vaporization requiring a trip to West Cryogenics for repair.

The trickiest thing about this particular issue is that neither of the leaks was apparent until the vessel was being filled with liquid. And the leaks were so small they’d have been hard to see during testing if the vessels were in a warm area.

Quality- Half Way to the Wall

Motorola presented a National Quality Day segment several years ago where they discussed “Half Way to the Wall.” It is a pretty neat concept that doesn’t seem to have become cliché, but possibly should.

Summarizing- Initial targets for quality are established by determining current baselines and then cutting the defect rate in half. If you are currently 50% good at something the idea is to move this up to 75%. A 75% you go for 87.5% good. There are several neat points to this system:

1) Fact-Based Decision Making is required. It is cliché to say you can’t make good decisions with bad information. The challenge in this age of TMI (too much information) is deciding what you really need to know and then gathering the information accurately;
2) Initial Gains are relatively much easier than later gains. It is as easy (or easier) to move from 80% to 90% than it is to move from 90% to 95%. The next step to 97.5% is even more challenging. Once defect rates become very low the challenge in keeping them good is not only not slipping back to old ways, but also not allowing new defects to creep in.
3) Marginal Utility (aka Law of Diminishing Returns) also comes into play at a point. The question “at what price success?” has value. The cost of training, test equipment, inspectors or other cures necessary to make small incremental gains just might not be worth it.

These concepts can be and are actively applied to liquid cylinder repairs by West Cryogenics and our clients. One of the most valuable tools used is the ability West has to monitor incoming vacuum levels on previously repaired liquid cylinders. Active use of this information allows for identification of potential issues so we can work together with clients to find root causes and affect solutions. A large percentage of cylinders returned with good vacuums can indicate operational or training issues at the client side. A rise from 2% to 8% “bad vacs” could indicate an issue at the supplier or user side.

One case found that a client’s cylinders were being exposed to excessive levels of cleaning chemicals resulting in high corrosion. Another found that liquid cylinders were too close to a welding or cutting procedure. Sparks from the procedure were melting tiny holes in vacuum rupture disks.

Large Tip Cutting Torch Oxygen Flow

Large tip cutting torches require high oxygen flow rates to operate properly. Flow rate requirements of +/- 1000 scfh are commonly encountered. It is also common for users to try and feed these large tip torches from a single liquid cylinder that has a vaporizing flow capacity of only +/- 300 scfh. The ineffectiveness of this has been discussed in previous articles, but never shown like this new video from Victor

http://www.jenobi.com/clientsites/thermadyne/video.htm

Hit the link and it should load right up. It provides a great explanation of the challenge of running large tip torches and the benefits of having proper liquid oxygen vaporization.

By the way- The side mount vaporizers shown are manufactured by West Cryogenics, Inc. and distributed by Eddie's Welding Supply and other gas and welding distributors.