Rehab Compared to New- Questions

Thanks to all of you who are sending in great questions including these today:

Q: Do rehabilitated liquid cylinder vacuums last as long as the vacuums on new cylinders? I have some rehabilitated cylinders that have been in service 3-5 years, and have a bad vacuum. I know there are a lot of variables, mostly cylinder handling.

A: You are right. There are a lot of variables. It is actually possible for a rehab vacuum to be better than new depending on the quality of the original vessel manufacturing and first vacuum pull. Heating, time and vacuum pump strength make huge differences in performance. Generally, though, rehabs are done on older vessels so they will be less pristine after rehab than when brand new. They might also have experienced damage, corrosion and introduction of moisture into the annulus. All these factors can affect long-term performance and reinforce the importance of both manufacturing and service quality and process integrity.

Q: I also noticed that, after rehab, there are some welded patches on the cylinders. Do these patched areas cause some new leaks just because a patch cannot be as good as solid material?

A: If the welds are done properly they should not be a new source of leaks (with “properly” being the key word). Leaks are more frequently the results of damage, corrosion or bad metal integrity.

Flow vs. Pressure- Boiled Frog Syndrome

Customer Y calls in January to ask about problems with his cutting torch work. “I just don’t understand. In August, everything seemed to be working fine. Now we are extra busy and my guys just can’t seem to cut like we were. We’ve turned the pressure builders all the way up, but that just doesn’t seem to help.”

Visiting, we find that several things have changed since August. He is, in fact, a great deal busier and now has 3 to 5 torches running off a liquid cylinder where he previously had 1 or 2. They’ve moved up to larger bore cutting tips and it is colder outside. All have combined to reduce the flow of vaporized oxygen gas that he is able to get to each torch.

This is a common and often misdiagnosed problem- especially where changes have occurred gradually or where users have switched sources from high pressure oxygen cylinders to cryogenic liquid oxygen. In many cases, the attempted solution is to increase pressure by going to high pressure liquid cylinders or cranking up the pressure builder on what they have. This sometimes makes the problem even worse by overflowing available ambient vaporization.

If the real issue is inadequate flow of gaseous molecules then the solution is often as simple as adding additional vaporization downstream. Very high use applications such as feeding multiple oxygen lances or large cutting tips might require you to link multiple liquid cylinders or go to a larger tank.

- Photo provided courtesy of Oxylance, Inc.

A Really Smart Fireman

Answering the phone I hear, “Hello, sir. This is ___ of the ___ Fire Department in __, California. I am responding to a call at ___ University Chemistry Department and hope you can help.”
“Of course, what’s up?”
“Well, sir. I am outside a lab that has a liquid nitrogen cylinder that has been venting off very hard for a good while and I’m trying to get a few answers before going in. I understand that liquid cylinders are supposed to vent, but we want to be sure there is no danger of an explosion.”

a) How’d he get my phone number?
b) Is there a potential danger?
c) How will we know?

a) He had a scope and was able to see the “K” tag that we and all other DOT-4L authorized repair centers are required to put on liquid cylinders that we repair. It also has our phone number.
b) Since he could see the “K” tag I asked if he could also see the data plate. He answered yes and reported the liquid cylinder was a 4L-200 rated vessel. And, he could even see the pressure gauge which was reading about 220psi.
c) We’ll talk more about DOT 4L ratings later, but for now suffice it to say that the cylinder was not likely to be an explosion hazard at that moment. So- all is OK? Not necessarily.

And just as I was about to tell him so he said “Oh, and don’t worry, sir. I’m very aware of the potential asphyxiation hazard in the room and have a breathing air pack on and an oxygen monitor. Thank you for your help” and hung up.

More like Thank You for Yours! I wish I had his name or even had the time to note the Department or University. He was smart , appropriately cautious and personified Falstaff’s statement in Henry IV:

"The better part of valour is discretion, in the which better part I have saved my life."

Used Equipment Scarcity

Purchasing used or reconditioned equipment is one way of helping cash flow for startups and boosting the profits of established operations. Like any tactic, it is great if it works. During the past several years, though, it has gotten harder to find good used cryogenic tanks at any price. Here are just a few of the reasons:

- Rising steel prices and other costs have driven new equipment prices up considerably. This makes it easier for companies to justify rehabbing equipment and continuing to use it. Even if owners have no immediate needs they find it hard to sell off equipment when the cost of repurchasing a similar tank later is so high.

-Industry “Majors” regularly fed used equipment into the market until they realized that the equipment they were selling off was costing them business. Simply put- smaller independents were buying used cryogenic tanks and coming right back to take away clients by offering lower rental rates on cheaply purchased equipment. Many large companies now take the position that the opportunity cost of selling used tanks that end up in the hands of competitors far outweighs the sale price.

-Strong demand has made it easier to place liquid oxygen, nitrogen or argon equipment pulled from one site with another client in short order. In fact, suppliers have typically found that equipment moved to a new client generates higher rentals than at the old clients so upgrades are encouraged.

-Risk calculations also come into play for sellers who have to weigh short term savings against long-term exposure.

There are few clues on what will occur during 2009 related to used cryogenic equipment markets. For now there is nothing that indicates either an increase in availability or lowering of prices.

Customer Vacuum Question- Part 2

Q: “What is the difference between the vacuum pulled on the liquid cylinder annular space and the vacuum pulled on a high pressure gas cylinder at filling?”

A: The difference is the level of vacuum needed to meet your intended purpose. The vacuum needed to insulate cryogenic liquids and inhibit energy transfer to keep them in a liquid state is a lot harder to achieve than the vacuum needed to remove impurities and contaminant gases for refilling a gas cylinder. Vacuum for cryogenics or cylinder filling is usually expressed as inches or microns of atmosphere. The smaller the value is the better the vacuum. Since microns are a lot smaller than inches (1 micron = 0.00003937 inches) it is easy to see that a 5 micron vacuum is much better than a 5 inch vacuum.

As mentioned in Part 1, vacuums for super-insulated cryogenic vessels are typically pulled down well below 10 microns. This is only 1/100 of a millimeter of atmosphere. Conversely, Ric Boyd of Cryovations (good people) notes that the vacuum level needed to pull impurities for a gas cylinder refill is typically only about 27 inches although there are specialty gas fills that require 50-100 micron vacuum levels.

Customer Vacuum Question- Part 1

A client called yesterday with a couple of good questions. Here is the first:

“Do you pull vacuums on liquid cylinders when you rehab them and if so to what level?”

Yes. Cryogenic liquid oxygen, argon and nitrogen have very low boiling points. Nitrogen for instance boils (converts to gas) at
-195.8 °C or -320.44 °F. Keeping argon, nitrogen and argon cold enough to maintain them in a liquid state requires specialized vacuum insulated containers. Cryogenic liquid cylinders are double walled vessels with a super-insulation wrapped inner container that holds the liquid and is inserted into a slightly larger outer vessel. The annular space (annulus) between the two vessels is used to insulate the liquid. After both vessels are sealed leak tight a vacuum is pulled on the annulus to remove virtually all atmospheric molecules and impede the transfer of energy.

To be an effective insulator this vacuum has to be pulled to very low levels. Leaks will result in a loss of vacuum and the need for rehab. West Cryogenics performs a helium mass-spec leak investigation at rehab to check for molecular level leaks. Then the vacuum is pulled to < 10 microns. The vacuum pull is done in two phases (hot and room temperature) to assure all moisture and other stray molecules are removed. A final inspection is performed after refinishing and other testing to verify that the vacuum has not risen due to latent moisture or a leak that needs to be found and repaired. If final inspection shows a weakening of the vacuum then the liquid cylinder goes back to mass-spec and vacuum restoration.

Dangers of an Improperly Decommissioned Liquid Cylinder

Disasters are rarely caused by a single action or event. More often than not they result from a series of small failures that culminate in a whopping show stopper. You might have already seen the attached presentation. If not- Hit the link below and take a moment to see just how wrong things can go when people “rig” equipment, disable safety devices and use it in ways not intended.

www.cdc.gov/eLCOSH/docs/d0500/d000585/d000585.ppt

Cryogenic News Introduction

Thank you for sharing a moment or more of your time to check out this blog. It is my wish that you will find some of the information shared to be helpful, interesting, enlightening or even occasionally inspiring.

Cryonews is focused on items of interest to cryogenic industry suppliers, users, and students taking into account the wide diversity of people and applications in the field. Liquid Oxygen, Argon, and Nitrogen have an incredible number of uses in areas from Medical Oxygen in Hospitals, Research and Homecare to Manufacturing, Construction, Welding Jobs, Demolition, Food and Beverage Production, Harvesting, Special Effects and more. In turn, new posts will intentionally traverse a pretty wide open course going wherever the light shines that moment. And there will be frequent posts with no seeming relevance delivered guilt-free.

This blog is intended as a source for industry news, tips, and insights. Questions, ideas, and links that might be considered worthy of note will be valuable and appreciated. Inevitably, we’ll find that others are wondering or interested in the same things. I'll endeavour to provide responses that are accurate and avoid “the sin of being booooring.”