1、Lessons Learned Entry: 1383Lesson Info:a71 Lesson Number: 1383a71 Lesson Date: 2003-10-14a71 Submitting Organization: MSFCa71 Submitted by: Louise SemmelSubject: Autoclave Purge Blower Failure Abstract: A mishap occurred in a large (18 X 20) autoclave resulting in damage to government property of ap
2、proximately $23K. The mishap was likely the result of a small amount of accumulated debris around a pneumatic valve, coupled with a minor error in pressure system logic, which failed to alert operators of the event prior to failure.Description of Driving Event: A mishap occurred in a large (18 X 20)
3、 autoclave at MSFC on August 13, 2002 resulting in damage to government property of approximately $23K. Two to four minutes into pressurizing the autoclave, operators noted that vessel pressure was not following the set-point value. Operators heard a loud noise outside the building and sent personne
4、l to investigate. Bystanders outside indicated the noise came from nearby construction. Approximately 5 minutes later, another loud noise was heard coming from the nitrogen pressure regulating assembly of the autoclave. Other than the noise, no system warning or error indicators were encountered. Th
5、e cycle was aborted and appropriate safety personnel were notified. A checkout of the facility revealed a failure of the purge blower. Equipment damage resulted from the mishap. Damaged components included the purge blower assembly, purge valve solenoid assembly (solenoid in green), purge valve (bel
6、ow the solenoid assembly) and the entire purge line from the blower to the autoclave pressure vessel. A piece of fan blade sheared from the shaft, ripped through the blower housing and hit the purge valve solenoid just before it came to rest on some nearby nitrogen supply piping. The investigation r
7、evealed the purge valve had remained open during pressurization of the autoclave allowing pressurizing gas (nitrogen) to back-flow into the purge blower and spin it in reverse until it Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-failed due to exc
8、essive load. Debris (probably caused by a mud wasp) had obstructed the vent sufficiently to prevent proper closure of the valve thus ultimately causing the blower failure. The Mishap Board recommended the following corrective actions be implemented prior to facility activation:1. Install screens ove
9、r all autoclave pneumatic outputs to prevent debris from clogging lines.2. Install a position indicator switch on the purge valve. Link this position indicator switch into the autoclaves programmable logic control (PLC) software so that the “all systems ready” interlock prevents operating the autocl
10、ave until the valve is properly closed. 3. Install a one-way “check” valve in the purge line to prevent back flow of nitrogen from the pressure vessel into the purge blower in the event of a purge valve failure. This valve shall be installed between the purge valve and the purge blower so it is outs
11、ide the autoclaves pressure boundary.Lesson(s) Learned: Pressure systems may operate safely for years until a specific set of conditions occur and a mishap results. Pneumatic systems should be installed in a way that takes maximum advantage of available logic controls. Check valves and additional ex
12、ternal controls should also be incorporated to minimize the potential for back flow into pressure vessels. Finally, even a relatively minor amount of accumulated debris due to age, shop conditions, or other environmental factors can result in mishap. Recommendation(s): 1. Screens have been installed
13、 over all autoclave pneumatic outputs to prevent debris from clogging lines.2. 3. Position indicator switches should be properly interlocked. In this case, the position indicator switch was not linked with the autoclaves programmable logic control (PLC) which would have allowed the valve to open onl
14、y if the purge valve were closed4. Use one-way “check” valves in purge lines to detect/prevent back flow into pressure vessels.Evidence of Recurrence Control Effectiveness: Recommended actions are incorporated and all systems are operating appropriately.Documents Related to Lesson: N/AProvided by IH
15、SNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Mission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Mishap ReportingMishap Report References: Autoclave Purge Blower FailureAdditional Info: Approval Info: a71 Approval Date: 2004-02-09a71 Approval Name: Lisa Boninea71 Approval Organization: MSFCa71 Approval Phone Number: 256-544-2544Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
