scope:

Description of Driving Event:

White particulate residue from the ester-plasticized polyurethane 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 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 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 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.