Taken from the FRC Blog, 1/30/13: http://www.usfirst.org/roboticsprograms/frc/blog-plastic-air-tanks-important-safety-notice
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
An official email from Clippard was sent out about this as well (http://www.chiefdelphi.com/forums/showthread.php?threadid=112396).