Author Topic: Remember the FCV poppet issue from STS-126?  (Read 3143 times)

Offline rdale

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Remember the FCV poppet issue from STS-126?
« on: 06/05/2010 12:46 PM »
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100020162_2010013890.pdf

     The presentation examines the background and objective of nondestructive crack detection, flow control valve assembly and poppet post flight evaluation, poppet properties. magnetic property characterization of lab data, NDE, eddy current inspection, simulation, eddy current criteria, poppet cycle testing and NDE criteria, and the use of ultrasonic surface wave for crack detection.

Offline DwightM

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Re: Remember the FCV poppet issue from STS-126?
« Reply #1 on: 06/05/2010 04:29 PM »
This is awesome.  I was an NDE tech for 10 years (5 in the USAF and 5 on the North Slope of Alaska) and EC was my favorite discipline , with UT as a close second.  The thorough attention to detail, and the cool tools they came up with, are impressive.  Thanks for posting this rdale.

Offline Chris Bergin

Re: Remember the FCV poppet issue from STS-126?
« Reply #2 on: 06/05/2010 06:19 PM »
I wrote about 30 articles on this:

http://www.nasaspaceflight.com/tag/fcv/

Offline DwightM

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Re: Remember the FCV poppet issue from STS-126?
« Reply #3 on: 06/05/2010 08:04 PM »
I wrote about 30 articles on this:

Yep, and they were some of my favorites, just never bothered commenting until now. 
All of the articles on this site (regardless of the author) do a great job of explaining complex & technical subjects in a very comprehendible way.
Maybe that last remark belongs in the 5 Year thread. :)
« Last Edit: 06/05/2010 08:05 PM by DwightM »

Offline iamlucky13

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Re: Remember the FCV poppet issue from STS-126?
« Reply #4 on: 06/10/2010 05:35 AM »
Do I remember it? Boy do I ever! The following mission, STS-119, seemed like the perfect mission to take a vacation to finally witness a launch in person. I had plenty of time being unemployed, things had settled into routine again post-Columbia, the LH2 cutoff sensor issue had been resolved, and it was scheduled for a time of year with typically very predictable weather in Florida.

And the FCV issue came up right after I bought my airline tickets. I still had a great trip to KSC. It was just quieter than I planned.

I appreciate the diligent followup, rdale. I remember it was quite a bit of work figuring the issue out and developing a justifiable launch criteria. A solid demonstration of the focus on safety.

I seem to remember some destructive testing, too. Didn't they at one point test a doubler plate by shooting pellets down a modified elbow with an air rifle or was that just an idea put forward?
« Last Edit: 06/10/2010 05:46 AM by iamlucky13 »

Offline AnalogMan

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Re: Remember the FCV poppet issue from STS-126?
« Reply #5 on: 07/05/2010 11:48 AM »
Here is another technical paper (for all you engineers) that gives a detailed analysis of the structural and acoustic modes of the Flow Control Valve.

Analysis of the STS–126 Flow Control Valve Structural-Acoustic Coupling Failure
NASA Technical Memo, May 2010

During the Space Transportation System mission STS–126, one of the main engine's flow control valves incurred an unexpected failure. A section of the valve broke off during liftoff. It is theorized that an acoustic mode of the flowing fuel, coupled with a structural mode of the valve, causing a high cycle fatigue failure. This report documents the analysis efforts conducted in an attempt to verify this theory. Hand calculations, computational fluid dynamics, and finite element methods are all implemented and analyses are performed using steady-state methods in addition to transient analysis methods. The conclusion of the analyses is that there is a critical acoustic mode that aligns with a structural mode of the valve.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100022153_2010024353.pdf

Offline iamlucky13

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Re: Remember the FCV poppet issue from STS-126?
« Reply #6 on: 07/07/2010 08:08 PM »
Hopefully I will have a chance to browse that paper in the next couple days, but the basic theory outlined wouldn't be a surprise.

Harmonics is an interesting topic. Challenging, but very interesting. It's particularly surprising when harmonic coupling shows up as potentially problematic in objects like valve poppets, which are often very solid looking due to their dimensions being driven by function more than stress.


Offline Seattle Dave

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Re: Remember the FCV poppet issue from STS-126?
« Reply #8 on: 08/02/2010 08:36 PM »

Offline rdale

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Re: Remember the FCV poppet issue from STS-126?
« Reply #9 on: 01/07/2011 11:07 PM »
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100042601_2010045113.pdf

The poppet failed during STS-126 due to fatigue cracking that most likely was initiated during MDC ground-testing. This failure ultimately led to the discovery that the cracking problem was a generic issue effecting numerous poppets throughout the Shuttle program's history. This presentation has focused on the laboratory analysis of the failed hardware, but this analysis was only one aspect of a comprehensive failure investigation. One critical aspect of the overall investigation was modeling of the fluid flow through this valve to determine the possible sources of cyclic loading. This work has led to the conclusion that the poppets are failing due to flow-induced vibration.

Offline rdale

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Re: Remember the FCV poppet issue from STS-126?
« Reply #10 on: 04/03/2011 06:32 PM »
[How many abbreviations can you fit into a presentation title :) ? ]

Space Shuttle Program (SSP) Orbiter Main Propulsion System (MPS) Gaseous Hydrogen (GH2) Flow Control Valve (FCV) Poppet Eddy Current (EC) Inspection Probability of Detection (POD) Study

The Director of the NASA Engineering and Safety Center (NESC),   
requested an independent assessment of the anomalous gaseous hydrogen (GH2) flow incident on the Space Shuttle Program (SSP) Orbiter Vehicle (OV)-105 during the Space Transportation System (STS)-126 mission. The main propulsion system (MPS) engine #2 GH2 flow control valve (FCV) LV-57 transition from low towards high flow position without being commanded. Post-flight examination revealed that the FCV LV-57 poppet had experienced a fatigue failure that liberated a section of the poppet flange. The NESC assessment provided a peer review of the computational fluid dynamics (CFD), stress analysis, and impact testing. A probability of detection (POD) study was requested by the SSP Orbiter Project for the eddy current (EC) nondestructive evaluation (NDE) techniques that were developed to inspect the flight FCV poppets. This report contains the findings and recommendations from the NESC assessment.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110007956_2011008813.pdf

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