REG NASA-LLIS-0990-2000 Lessons Learned Degradation of Pur-Ester Polyurethane Tubing due to Aging.pdf

1、Lessons Learned Entry: 0990Lesson Info:a71 Lesson Number: 0990a71 Lesson Date: 2000-11-24a71 Submitting Organization: GSFCa71 Submitted by: Suong LeSubject: Degradation of Pur-Ester Polyurethane Tubing due to Aging Description of Driving Event: White particulate residue from the ester-plasticized po

2、lyurethane purge line was flushed from the tubing wall and contaminated the NOAA N SBUV/2 (Solar Backscatter Ultraviolet Radiometer) Flight Model (FM) 8 while the instrument was under purge. A sudden burst of high pressure and excessive flow through the purge line had possibly resulted in rupturing

3、an in-line membrane filter causing the white platelet particles to pass through the inlet filter of the instrument. At the time, no flow meter was placed in the purge line. Although the MIL-HDBK-695, Rubber Products: Recommended Shelf Life, stipulates a shelf life of three (3) to five (5) years for

4、polyester urethane products, this purge tubing had been in service for the past fifteen (15) years up to the time of the incident. Some polyester urethanes have poor resistance to humidity (MIL-HDBK-695). Urethanes also are not resistant to ultraviolet radiation. Both conditions existed during clean

5、 room storage of the SBUV/2 instrument. The material was visibly degraded as it became less flexible and opaque with residue buildup on the inside and outside of the tubing walls. Lesson(s) Learned: The ester polyurethane is unsuitable for purging when used beyond its recommended shelf life. More cr

6、itical, however, is the potential contamination problem due to the transfer of ester plasticizer to the instrument while under purge. The ruptured filter resulted in transferring particles from the degraded purge line to the contamination-sensitive SBUV/2 instrument. Subsequent cleaning, realignment

7、 of optics, and numerous levels of testing were needed to restore the instrument to specifications. This incident had a significant impact to instrument schedule and, therefore, cost. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s):

8、 1. Replace the Pur-ester polyurethane tubing with Teflon tubing, which is inert, resistant to moisture, clean, plasticizers-free, and has a shelf life of up to twenty (20) years.2. 3. Install a more rugged 0.01 micron stainless membrane filter that can filter out smaller particles and withstand hig

9、her burst pressure.4. Install an in-line flow meter to control flow rate and to meet the instruments flow specifications.5. Inspect the purge line routinely to ensure proper operation of filters, meters, gauges, and the source of purge gas.Evidence of Recurrence Control Effectiveness: N/ADocuments R

10、elated to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Ground Equipmenta71 Parts Materials & Processesa71 Test Articlea71 Test Facilitya71 Test & VerificationAdditional Info: Approval Info: a71 Approval Date: 2001-10-15a71 Approval Name: Jay Liebowitza71 Approval Organization: GSFCa71 Approval Phone Number: 301-286-4467Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-