REG NASA-LLIS-1798-2007 Lessons Learned - Braycote Grease retains tribological properties for 17 years in controlled storage.pdf

1、Lessons Learned Entry: 1798Lesson Info:a71 Lesson Number: 1798a71 Lesson Date: 2007-08-06a71 Submitting Organization: HQa71 Submitted by: Gena Hendersona71 POC Name: Paul MunafoSubject: Braycote Grease retains tribological properties for 17 years in controlled storage Abstract: This is a lessons lea

2、rned from NASA Engineering Safety Center (NESC) Technical Bulletin on Braycote Grease. Please also view attached document. A scheduled inspection of the Rudder/Speed Brake actuators on Space Shuttle orbiter OV-103 revealed fretting corrosion, micropitting, wear and discoloration of the lubricant Bra

3、ycote 601. A decision was made to replace the actuators with the existing spares, a single ship set which had been in controlled storage for the past 17 years. Data did not exist on the lubricity of Braycote 601 grease after extended storage. Based on testing data, there is no significant difference

4、 in lubricity due to separated or degraded grease and no evidence that the grease will degrade at steady state in ambient temperatures.Description of Driving Event: A scheduled inspection of the Rudder/Speed Brake actuators on Space Shuttle orbiter OV-103 revealed fretting corrosion, micropitting, w

5、ear and discoloration of the lubricant Braycote 601. A decision was made to replace the actuators with the existing spares, a single ship set which had been in controlled storage for the past 17 years. Data did not exist on the lubricity of Braycote 601 grease after extended storage. Testing and ana

6、lysis were undertaken to investigate two key issues: a71 Issue 1: Oil separation of grease into its component oil and thickener is known to occur in storage. Its effect on lubricity is not known. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Issue

7、1 Results: Lubricity testing was performed on aged grease, and grease that exhibited oil separation obtained from several sources, including grease that had been removed from the OV- 103 actuators. Three test protocols were used: (1) Falex Block on Ring; (2) Spiral Orbit Tribometer (SOT); and (3) We

8、deven Associates Machine (WAM) testing. In all cases, no detrimental effect on lubricity was observed due to storage and/or grease that experienced oil separation.a71 Issue 2: Chemical reactions involving the grease and the gear/housing material, 9310 steel, could lead to formation of Lewis acids, r

9、esulting in corrosion, pitting, and cracking. The degree to which the chemical reactions were occurring in the actuators was unknown. Issue 2 Results: Investigations into potential chemical reactions of the grease with the actuator steel were addressed in three ways: (1) an extensive literature revi

10、ew; (2) WAM testing to duplicate the conditions observed in the used actuators; and (3) Thermodynamic analysis, using Thermal Gravimetric Analysis (TGA), to bound the amount of degradation/mass loss that might occur during 17 years of controlled storage. The literature review revealed that absent tr

11、ibological action, i.e., no stress on the lubricant, no significant mass loss should occur below 190C. The WAM testing was successful in duplicating the fretting corrosion and micropitting effects observed on OV-103 by high frequency low amplitude wear testing, thus reinforcing the results reported

12、in the literature for similar material/lubricant combinations. The TGA testing and thermodynamic analysis predicted no significant corrosive effects from static, controlled storage for 17 years. Based on testing data, there is no significant difference in lubricity due to separated or degraded greas

13、e and no evidence that the grease will degrade at steady state in ambient.Lesson(s) Learned: Programs should periodically review hardware components to ensure that they are operating within qualification and certification limits. When hardware exceeds these limits, testing or analysis should be perf

14、ormed to properly envelop the actual operational environment. Based on testing data, there is no significant difference in lubricity due to separated or degraded grease and no evidence that the grease will degrade at steady state in ambient temperatures.Recommendation(s): Tribological action, heat,

15、or other forces are required to effect the performance of Braycote grease. Evidence of Recurrence Control Effectiveness: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/ADocuments Related to Lesson: Click here to download document. Mission Director

16、ate(s): N/AAdditional Key Phrase(s): a71 Integration and Testinga71 Safety and Mission Assurance.a71 Safety and Mission Assurance.Maintenancea71 Additional Categories.a71 Additional Categories.Flight Equipmenta71 Additional Categories.Ground Equipmenta71 Additional Categories.Packaging, Handling, St

17、oragea71 Additional Categories.SpacecraftAdditional Info: a71 Project: Space Flight and Ground SystemsApproval Info: a71 Approval Date: 2007-09-07a71 Approval Name: ghendersona71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-