Plastic Air Tanks -- Important Safety Notice

Blog Date: 
Wednesday, January 30, 2013 - 15:17

Over the weekend, it was brought to our attention that a failure of the white polypropylene air tank, donated by Clippard (Clippard PN: AVT-PP-41, AndyMark PN: am-2007, FIRST Choice PN: fc13-100), had occurred. Since the incident, Clippard has been in direct contact with the team that experienced the failure and is working to determine the root cause of the failure.

Initial investigation suggests that the tank failed because it was subjected to twisting while pressurized. This caused the tank to experience stress and strain not consistent with its use case. We’d like to make sure all teams understand the hazards and risks associated with deformation of these tanks while pressurized and strongly advise against it. In other words, please depressurize your system before performing maintenance or adjustments.

In addition, suspicion surrounds the installation of the fittings in the tank. Clippard recommends using 2-4 layers of Teflon tape and tightening the ¼” NPT fitting to 10-12 inch pounds (do not to exceed 15 inch pounds).   If there is a leak detected, DO NOT continue threading in the fitting.  Remove the fitting and reapply the tape sealant. Over-torqueing NPT threads in plastic pressure tanks can introduce stress and cracks that could lead to failures. Do not measure installation based on distance or number of threads exposed as there is a large variance on NPT threading from a variety of manufacturers.

Although there is only one known occurrence, Clippard is offering to replace the units until further evaluation can be completed.  Clippard has alternate metal tanks and will ship at their cost.  Clippard will email all FRC teams who received tanks, either purchased from AndyMark or via FIRST Choice, with instructions on how to receive a replacement.   If you do not receive the email, contact Clippard via e-mail requesting an exchange, sales@clippard.com.

Small (16in3) metal tanks are still available in FIRST Choice. Also, there will be a limited number of large (32in3) metal tanks in the Spare Parts cases sent to events. Another option for veteran teams is to use last year’s tanks. 

While, of course, we all wish this incident hadn’t occurred, we very much appreciate Clippard’s quick and serious response to a safety concern. We also want to thank them for their long and continued dedication to FIRST, FRC teams, and the FIRST mission.

On behalf of FIRST and Clippard, we are very sorry for this issue. We ask that all FRC participants remember basic safety precautions (gloves when appropriate, safety glasses, tied-back hair) when working in your shop, so that you’re always better prepared for the unexpected.

I’ll blog again soon.

Frank

Comments

Team 4567 has two tanks from clippard that need to be replaced. Thank you!

Nick Isgro

As I noted above, Clippard will be sending you an email with details on tank replacement. If you don't receive that email by Friday, send an email to the address noted above to request your replacements.

Is there any data on the kind of impact forces these tanks can take? Like if a hang fails and your robot falls sideways from a few feet up on one will it explode?

FRC Team 4666 has two clippard tanks that need to be replaced

Please read the original blog carefully for information on obtaining replacements.

Will teams be allowed to continue to use these tanks at competition or will they be deemed to be an forbidden part? If forbidden will teams be allowed a grace weight allowance in the difference in weight between the plastic tanks and the metal tanks? FRC Team 2994

I won't be answering rules questions on this blog, but you may want to submit your question to our Q&A: https://frc-qa.usfirst.org/Questions.php

is there that great of a difference in weight that you would have to majorly change the robot?

i called a company who says they're the leading plastic tank supplier. They basically said they wouldn't sell me a tank if i was going to pressurize it and their supplier says the same to them...company i checked with was called http://www.plastic-mart.com . Sounded like decent advice to me.

We have some other plastic storage tanks that we used in previous years with no incidents to date. Can we continue using these?

I have a source in industry that recommends that plastic low pressure air tanks have a limited number of times fitting can be threaded into the tank before inducing failure.

Some industrial users of pressurized plastic tanks have told me that fittings should never be attached to plastic low pressure tanks using any tool except a properly calibrated torque wrench. This means it has been sent to a laboratory and tested within 6 months or a year depending on the type and laboratory. The tank threads have a limited number of times they can be used.

Also remember less experienced operators tend to over tighten fasteners.

Remember pipe threads are often tapered, and a small increase in depth can significantly increase stress.

With the discovery of the plastic tank issue, will a larger volume metal tank (steel) be allowed?

Team 3967 has 2 tanks that need to be replaced. Please tell how to do this?
Thank you

Please send an email to frcparts@usfirst.org (please remember, we're only replacing white tanks that say "Clippard" on the side - white tanks without the writing are not a concern). Your message will be filed and addressed after Championship. 

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