Informal Pressure Testing Correspondence with NASA

On Mon, Feb 10, 2003 at 02:19:42PM -0600, ECORD, GLENN M. (JSC-ES4) (NASA) wrote:

Dear Mr. Bliss,

Pressure systems to be flown aboard NASA aircraft are now evaluated for acceptability and safe flight by Engineering at JSC. One reason for the change is that experimental systems may not always comply with specific codes and standards, but can still be designed and operated as safe systems. Although we have only limited personnel for this purpose, myself and Ms. Beatrice Santos part of our time, it is our intent to work with experimenters like yourself to achieve safe pressurized systems. These systems are now regarded as Category B systems and are accepted based on good design and test practice and Engineering evaluation.

We request a schematic and manufacturer/pressure rating information on the components, etc. that you will use for your system. A brief explanation of how the system is put together, how it is intended to work, safeguards, and what you intend to do with the system on the ground and during flight would be very helpful. As for your pressure vessels and proof testing the answer depends on a number of things.

Depending on the "pedigree" of your vessels it may be that no specific proof testing on your vessels is necessary. For example, if these are new DOT rated vessels they should have been proof tested by the supplier and you should have, or can get, verification of this. The same is the case for certain pressure vessel suppliers such as Wylie and Hoke, etc. who supply laboratory rated vessels, already proof tested. On the other hand if these are vessels from some previous application, unknown pedigree, or are newly designed vessels that have not been pressure certified then a proof test may be necessary. The point I want to make is that we need to know more about your system and its parts to be able to assist or recommend. With a little more information we can tell you whether your vessels need to be proof tested or not.

It is important to us to begin our familiarity with a pressurized system as early as possible and your cooperation is appreciated. I can be reached at 281 483-8924 and Beatrice Santos can be reached at 281 244-5555. Please feel free to call, or e-mail information and ask any other questions you might have. The best help to us at this time would be a working understanding of structural, physical, and operational aspects of your pressure system and the pressure vessel pedigree.

Best Regards,

Glenn M. Ecord
Integration Technical Manager
Fracture Control & Pressure Vessels
NASA/JSC ES4 Houston, TX 77058
281 483-8924
glenn.m.ecord@nasa.gov

Thanks for your reponse. To confirm, PSG now intends to have *all* pressure systems flown for KC135 experiments classified as category B, no matter what? We don't have formal documentation of our system yet -- let me give you a quick informal rundown just so we have a basis of discussion.

Our experiment is a free-floater that uses cold gas propulsion for manuevering. There are two independant pressure systems, each a mirror image of the other. They consist of a DOT Exempt tank (air, 4500psi; structurally mounted to the experiment) with an attached regulator with 1000psi output and low-side and high-side gauges and reliefs via a commercial quick-disconnect (appropriately rated -- 12MPa, I think). The QD on the tank is connected to a matching QD on a piece of ASTM A312 304SS Schedule 40 pipe (I don't have the figures handy, but we do have calculations showing maximum allowable pressure per ANSI B31.3 of better than 1800psi). That piece of pipe terminates in another commercial QD, (rated 1000 psi MAWP) which connects to a commercial QD attached (via a 1/4" pipe Schedule 80 nipple and a 1/4-to-1/8 reducing coupling) to a commercial aluminum 8-port 1/8 NPT manifold (rated to 1500psi).

The manifold is structurally mounted to the frame of the experiment. Six 1000 psi QD's are connected to the manifold, two of them via short extensions ("street nipples") that we manufactured (Designed to better than 2000psi). (The other two portsare plugged). Each of those QDs connects to a mating QD on a piece of ASTM A312 pipe which is routed to a commercial solenoid valve (1500psi MAWP). The valve is attached via a brass close nipple (calculated to 1800+psi per ANSI B31.3) to a thruster, which is a 1.7" long piece of 3/4" OD 304SS with a 1/8NPT27 port, at 7/32" bore leading to a #60 orifice, with a 1/2NC13 external thread. The thruster is passed throuh an aluminum mounting bracket and a 1/2NC13 nut applied to mount it. As a slight complication, we have alternative (replacement) regulators with 200 psi output which we may have to change to at the last minute -- obviously we intend to certify at the higher pressure.

All commercial components are based on their manufacturer's recommendations for pressure limits. All fabricated components conform in design and manufacturing to ANSI B31.3 with one significant exception -- many of the bends necessary do not conform to the 8% maximum flattening limit specified in 332.2.1. We have done no testing aside from leak testing at MAWP (with CO2). Obviously the system has experienced no failures at MAWP during these leak tests. :) I know from prior contact with PSG that the tank is exempt from hydro within the time limit specified for its DOT exemption (good through next year; I don't have the specific dates here but have them in the lab).

I don't know what the testing requirements are for the remainder of the pressure system. I'm particularly unclear on the requirements for testing of the regulator itself.

Thanks for your time.

David Bliss
University of Washington