DETERMINATION OF OPTIMUM AMBIENT TEMPERATURE RE- TORQUE DWELL PERIOD FOR PTFE BASED GASKETS 2006 ASME Pressure Vessels and Piping Conference James E.B. Frew Jerry Waterland Virginia Sealing Products, Inc. Hopewell, VA USA
Railroad Tank Cars- Primary Focus Of Study >500,000 PTFE Gasketed Connections In Service In U.S Assortment of standard & non-standard flanges Unique Operational Issues: Vibration, Harmonic Frequencies, Impact
PTFE Based Gasket Materials 1) Required depending upon the commodity 2) Known initial creep relaxation behavior 3) Post assembly, 24 hour re-torque dwell period specified
24 Hour Re-Torque: Delays Car Repair Completion Reduces Repair Shop Throughput Increases Repair Costs, Impacts Car Availability Huge Economic & Availability Impact For Shorter Re-Torque Dwell
Potential Consequences If Post Assembly Re-Torque Is Not Performed: Loose Bolts (Ft-Pound Definition) NARs (Non-Accidental Releases) Fines/Penalties
Re-Torque Testing 2" x 300# Welding Neck/Blind Raised Face Flanges - 120 Ft.-lbs. 0.00600 0.00500 eptfe W/Corr. Insert 2 hr Re-Torque eptfe W/Corr. Insert 24 hr Re-Torque Bolt Elongation (in.) 0.00400 0.00300 0.00200 0.00100 Residual Bolt Elongation After 24 Hours: 2 Hour Re-Torque = 0.0028 24 Hour Re-Torque = 0.0038 0.00000 0 500 1,000 1,500 2,000 2,500 3,000 3,500 Time (min.) Study conducted to determine: 1) Specific re-torque requirements and characteristics of various PTFE based gasket materials used within Railcar Fleets 2) Potential identification of a suitable shorter re-torque dwell period This study focused on a 2-hour re-torque dwell period Analysis: Comparison Of Residual Bolt Load After 2 Hour and 24 Hour Re-Torque Dwell Periods
PTFE Based Materials Evaluated Virgin, skived In This Study White, glass filled, skived Blue, glass filled, skived HS-10 Process Barium Sulphate filled HS-10 Process micro-cellular cellular 1 st generation expanded st generation expanded 2 nd generation expanded 1 st generation expanded, with corrugated insert
Text Fixture Used For Study NPS 2 x 300 WN/Blind Flanges Strain-Gauged Bolts Assembly Torque = 120 ft-lb (lubricated) 15.8 ksi gasket assembly stress Fixture Selected To Simulate Rigidity, Active Bolt Length, Bolt Stretch, and Gasket Stress Of Many Auxiliary Connections On Pressure Cars
Fixture Assembly Procedure and Location Of Strain-Gauged Bolts VSP Assembly Procedure for Gasket Material Re-Torque Testing - 07/01/05 5 2 7 3 4 Location of Strain Gage #1 Location of Strain Gage #2 8 1 6 1.) Make Sure all Bearing Surfaces are Lubricated before Each Application 2.) Snug all Bolts 3.) 1st Pass, Follow Star Pattern Sequence with Torque Set at 30 ft-lbs 4.) 2nd Pass, Follow Star Pattern Sequence with Torque Set at 60 ft-lbs 5.) 3rd Pass, Follow Star Pattern Sequence with Torque Set at 90 ft-lbs 6.) 4th Pass, Follow Star Pattern Sequence with Torque Set at 120 ft-lbs 7.) 5th Pass, Rotational Pass with Torque Set at 120 ft-lbs, No Overlap 8.) Record Data on Excel Spread Sheet at appropriate times 9.) ReTorque at either 24 Hr or 2 Hr, with a single rotational pass 10.) Continue Recording Data on Excel Spread Sheet at appropriate times
Sample Data Sheet 24hr Retorque Expanded PTFE #1 Time (min.) Dial # 1 Dial # 2 Average 0 0.00450 0.00450 0.00450 15 30 45 60 0.00430 0.00420 0.00410 0.00408 0.00420 0.00410 0.00410 0.00405 0.00425 0.00415 0.00410 0.00407 Each Gasket Tested Twice @ Each Re-Torque Dwell Period 120 180 240 0.00395 0.00388 0.00380 0.00400 0.00390 0.00385 0.00398 0.00389 0.00383 Residual Bolt Elongation Recorded Periodically During Test 720 1,440 1,441 1,455 0.00370 0.00368 0.00410 0.00408 0.00370 0.00369 0.00410 0.00406 0.00370 0.00369 0.00410 0.00407 Bolt Elongation Measurements Were Averaged For Analysis 1,470 1,485 0.00407 0.00405 0.00404 0.00400 0.00406 0.00403 Test Duration: 24 Hours Beyond Re-Torque 1,500 0.00405 0.00400 0.00403 1,560 0.00402 0.00395 0.00399 1,620 0.00400 0.00392 0.00396 1,680 0.00398 0.00391 0.00395 1,800 0.00395 0.00390 0.00393 2,460 0.00390 0.00380 0.00385 2,880 0.00390 0.00380 0.00385
Data Summary: All Materials, 24 Hour Re-Torque Dwell Period 0.00600 Re-Torque Testing 2" x 300# WN/Blind Raised Face Flanges - 120 Ft.-lbs 24 Hour Re-Torque Dwell Period. 0.00500 2nd Gen. eptfe Bolt Elongation (in.) 0.00400 0.00300 0.00200 0.00100 1st Gen. eptfe eptfe W/Corr. Insert eptfe W/Corr. Insert Barium Sulphate Filled PTFE Virgin Skived PTFE GF PTFE (white) GF PTFE (blue) Note The Broad Range Of Final Bolt Elongation (Residual Load) 0.00000 0 500 1,000 1,500 2,000 2,500 3,000 3,500 Time (min.)
0.006 0.005 Re-Torque Testing 2" x 300# Welding Neck/Blind Raised Face Flanges - 120 Ft.-lbs. Different Behaviors Noticed: Bolt Elongation (in.) 0.004 0.003 0.002 Expanded PTFE w/corr. Insert-1 2 hr Expanded PTFE w/corr. Insert-2 24 hr Expanded PTFE w/corr. Insert-1 24 hr Residual Elongation After 2 Hour Re-Torque Dwell Period Noticeably Less Than After 24 Hour Re-Torque Dwell Period 0.001 0 0 500 1000 1500 2000 2500 3000 3500 Time (min.) 0.006 Re-Torque Testing 2" x 300# Welding Neck/Blind Raised Face Flanges - 120 Ft.-lbs. Bolt Elongation (in.) 0.005 0.004 0.003 0.002 2nd Gen. eptfe-1, 2 hr 1st Gen. eptfe-2, 24 hr 1st Gen. eptfe-2, 2 hr 2nd Gen. eptfe-1, 24 hr 1st Gen. eptfe-1, 24 hr Residual Elongation After 2 Hour Re-Torque Dwell Period Equivalent To 24 Hour Re-Torque Dwell Period 0.001 0 0 500 1000 1500 2000 2500 3000 3500 Time (min.)
Load Loss Prior To 1 st Re-Torque 80 70 60 50 40 30 20 10 0 Percent Load Loss 1st 24 Hours Percent Bolt Load Loss V PTFE GF White GF Blue HS-10 BS Micro-Cell eptfe/corr eptfe 1st eptfe 2nd Key Indicator Of Which Material Types Truly REQUIRE A Re-Torque
Average Creep Rate (Lb/Min.) Creep Rate During Final 800 Minutes After Re-Torque 1.8 1.6 1.4 1.2 0.8 1 0.6 0.4 0.2 0 After 2 Hour Re- Torque Dwell After 24 Hour Re- Torque Dwell V PTFE GF White GF Blue HS-10 BS Micro-Cell eptfe/corr eptfe 1st eptfe 2nd Key Indicator Of The Effect Of Dwell Period On The Material s CREEP RATE
Percent Bolt Load Loss 60 50 40 30 20 10 0 V PTFE Total Relaxation After Re-Torque GF White GF Blue HS-10 BS Micro-Cell eptfe/corr eptfe 1st After 2 Hour Re- Torque Dwell After 24 Hour Re- Torque Dwell eptfe 2nd An Indicator Of The Residual CREEP POTENTIAL Remaining In The Material After Each Dwell Period
Cumulative Load Loss Before and After 24 Hour Re-Torque Dwell Period Cumulative Percent Bolt Load Loss 140 120 100 80 60 40 20 0 V PTFE Total Relaxation Of PTFE Materials GF White GF Blue HS-10 BS Micro-Cell eptfe/corr eptfe 1st eptfe 2nd Percent Relaxation 24 Hours After Re- Torque (24 Hour Dwell) Percent Relaxation 1st 24 Hours An Indicator Of The Material s CREEP STABILITY and RE-TORQUE & DWELL PERIOD EFFECTIVENESS
Post-Test Visual Analysis Of Gaskets Creep Rate Stability, and Need For Re-Torque Conclusions Are Supported By The Visual Condition (physical flow) Of The Gaskets
Conclusions: 1) All materials tested, with the exception of expanded PTFE, exhibit significant relaxation and should be re-torqued after assembly 2) A two hour re-torque dwell period appears inadequate for half of the materials tested 3) A two hour re-torque dwell period appears suitable for the following materials: White, Glass Filled, Skived PTFE HS-10 Process, Barium Sulphate Filled PTFE Expanded PTFE w/ Corrugated Insert 1 st Generation Expanded PTFE Future Studies: 1) Four hour and eight hour re-torque dwell periods 2) Different flange stiffness 2) Longer duration after re-torque 3) Lower initial assembly stress