Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions When - - PowerPoint PPT Presentation

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Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions When and When Not Anita Bausman, P.E. Senior Applications Engineer VSP Technologies Kingsport, TN Bolted Connectors: Re-Torquing to Reduce Fugitive 4/3/2018 Page 1

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4/3/2018 Page 1 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Anita Bausman, P.E. Senior Applications Engineer VSP Technologies Kingsport, TN

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4/3/2018 Page 2 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Retorque: Why or Why Not?

  • Consequences of Low Operational Bolt Load
  • Causes of Low Operational Bolt Load
  • Overcoming Operational Bolt Load Losses
  • Gasket Selection/Optimization
  • Joint Design
  • Over-Torquing
  • Optimized Assembly
  • Re-Torque
  • When
  • Dwell time after assembly
  • Resources/Guidance
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4/3/2018 Page 3 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Definitions:

RETORQUE:

  • Any Subsequent Re-Application Of Bolt Load After Initial Flange

Assembly PURPOSE:

  • Re-Establish Assembly or Operating Bolt Loads and Gasket

Stresses

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4/3/2018 Page 4 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Consequences Of Low Operational Bolt Load or Gasket Stress

1. Gasket Blow-Out 2. Visible, Gross Leakage (gasket still intact) 3. Low Operating Margin Against Failure

  • Mechanical Integrity
  • Equipment Reliability
  • Safety
  • Environmental

4. Excessive Emissions, Permeation, External Corrosion

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4/3/2018 Page 5 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Excessive Emissions with Reduced Bolt Load

Comparison of PTFE Gaskets - NPS 3 x 150 flanges at 50psig using Relaxation @300°F per HOBTC Graphs

Using Tightness Parameter at Assembly Using Operating Tightness Parameter

Material Selected

Tp Kg/Yr Tp Estimated Emissions Kg/Yr Emissions

  • Incr. After
  • Gasket. Stress

Loss

Composites - ePTFE w/ encapsulated corrugated metal

18951 8.60E-07 15091 1.36E-06 58%

Composites - ePTFE with Tang Core (1/8")

399 1.94E-03 338 2.71E-03 40%

PTFE Expanded Sheet - (1/8'')

923 3.63E-04 695 6.39E-04 76%

PTFE Filled HS-10 Sheet - BaSO4 filled - Off-white (1/8'')

1470 1.43E-04 868 4.10E-04 187%

PTFE Filled HS-10 Sheet - Glass Microsphere filled - Blue (1/8'')

1403 1.57E-04 585 9.01E-04 474%

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4/3/2018 Page 6 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Causes of Low Operational Bolt Load:

1) Bolt Load Losses From Gasket Changes:

  • Gasket Creep
  • Example: PTFE gaskets
  • Settling/Compaction of Gaskets
  • Example: Compressed NonAsbestos (CNA),

Spiral Wound gaskets

  • Thermal/Aging Degradation of Gaskets
  • Example: Elastomer, CNA, Flexible Graphite

gaskets

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4/3/2018 Page 7 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Causes of Low Operational Bolt Load:

2) Bolt Load Losses Due to Piping or Joint Design and/or System Operating Losses:

  • PTFE liner and HDPE Flange/Liner Creep
  • Soft Joint Piping Thermal Expansion Effects

from Additional Gasket Compression

  • Short Effective Bolt Length
  • Tapped Bolt Holes
  • Minimal Assembly Elongation
  • Rigid (stiff) Flanged Joint
  • B16.47 Series A (stiff) vs. Series B (flexible)
  • Stiff flanges more susceptible to bolt load loss
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4/3/2018 Page 8 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Causes of Low Operational Bolt Load:

3) Equipment with Known Low Gasket Assembly Stress / Marginally Available Bolt Load

  • Limited assembly bolt load
  • Stainless steel bolts
  • Glass lined steel flanges
  • Weak flanges
  • FRP
  • Lap Joint flanges
  • Under-Bolted Flanges
  • Hinged Manways
  • Many Appendix 2 Designed Flanges
  • Full Face Gaskets
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4/3/2018 Page 9 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Causes of Low Operational Bolt Load:

4) Questionable / Undocumented Assembly Practices / Torque Values

  • Elastic interaction
  • Questionable skills/capabilities of assembly crews
  • Impact wrench assembly
  • Unlubricated fasteners
  • Used or damaged fasteners
  • Unknown or undocumented assembly torque levels
  • Unknown or undocumented assembly patterns/procedures/tools
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4/3/2018 Page 10 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Causes of Low Operational Bolt Load:

5) Joint Design:

  • Pressure Energized Manways/Drum Doors
  • Operational pressure supplies significant additional gasket compression
  • Assembly bolt load is completely lost
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4/3/2018 Page 11 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Summary: Causes Of Low Operational Bolt Load

  • r Gasket Stress
  • 1. Gasket Creep (ex. PTFE), Liner

Creep (ex. PTFE/PE), Flange Creep (ex. HDPE)

  • 2. Gasket Settling/Compaction (PTFE,

CNA, Flexible Graphite, Spiral Wound

  • 3. Gasket Degradation (thickness loss)

– CNA, Flexible Graphite @ T > 600°F

  • 4. Hydrostatic Unloading of Gasket

(larger diameter connections, high pressure)

  • 5. System Pressure Energized

Compression of Gasket (Drum Doors/Internal sealing Manways)

  • 6. Piping System Thermal Expansion

(Spiral Wound Gaskets)

  • 7. Poor Assembly Practice/Guidance
  • 8. In-Adequate Assembly Load or

Gasket Stress (FRP, Glass Lined, Hinged Manways, etc.)

  • 9. Low Assembly bolt load or bolt strain
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4/3/2018 Page 12 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Overcoming Operational Bolt Load Loss

(without a Re-Torque) Gasket Selection / Optimization Joint Design Over Shoot Torque Optimized Assembly

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4/3/2018 Page 13 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Gasket Selection & Optimization

PTFE Gaskets:

  • More creep-resistant material
  • Thinner gasket
  • Gasket design
  • Reduced area = higher stress
  • Spring inserted = live load

PVRC Project No. 96-12G – Long Duration Mechanical Performance of PTFE Based Gasket Materials

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Gasket Selection & Optimization:

Compressed Non- Asbestos (CNA) Fiber Gaskets:

  • Thinner seals

better

  • 250°F Maximum

Temperature Thermal Degradation: Compressed, Non-Asbestos (CNA)

Thermal Degradation Of The Rubber Binder Creates Porosity and Stress Relaxation Example: “High Temp” CNA Steam Pressure Aging @ 320 °C 40 Days Exposure: Gasket Stress 44 MPa – 31 MPa = 30% Loss Steam Pressure 180 Bar – 15 Bar

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4/3/2018 Page 17 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Gasket Selection & Optimization:

Flexible Graphite (FG) and Corrugated Metal Graphite-faced Gaskets:

  • 600°F Maximum

temperature

  • Specify Oxidation

Inhibited FG

  • Failure Mode is Oxidation

@ T >600°F (for a 5yr life)

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4/3/2018 Page 18 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Flanged Joint Arrangements / Design:

Hard Joint = Metal to Metal contact Soft Joint = No metal to metal contact (soft gasket between) Hard Joints are Less Susceptible to Load Loss

Soft Joints with Sheet Gaskets:

  • Subject to creep, degradation, bolt

load loss

  • Belleville washers for more flexibility

Hard Joints w/SW with Inner and Outer Rings:

  • IF Fully Compressed During Assembly,
  • therwise can further compress
  • Cammprofile
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4/3/2018 Page 19 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Deliberate Overshoot Torque:

Knowing there will be Bolt Load Loss from Gasket Creep, Settling/Compaction, and Operational Lossess….

  • Compensate for Expected Losses by Increasing Intial Assembly Load
  • Within the Flange and Bolting Allowable Stresses at Operating

Conditions

  • FEA/Flange Analysis is Often Required
  • Gasket Maximum Stress
  • Flange Maximum Stress
  • Bolting Maximum Stress
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Consider PTFE Relaxation with Temperature:

Blow-Out, Increased Leakage If Residual Stress Too Low Higher Assembly Bolt Loads Shifts The Relaxation Curve Up Cycles To Ambient

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4/3/2018 Page 21 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Optimize Assembly:

  • Overcome Flange Bolt Interactions (“Cross Talk”)
  • Achieves Target Assembly Bolt Load
  • Use Slower Assembly
  • 5 (or more) passes instead of 3
  • Multiple final rotational passes
  • Recoup Gasket Creep Losses During Assembly Process
  • (Retorque During Assembly)
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Bolt Load Distribution During Assembly

NPS 4 Class 900, Weld-Neck Flange 100% Bolt Load Not Achieved Until 3 Final Circular Passes

Load after 3 Star Pattern Passes Load after 6 Passes (3 Star + 3 Rotational)

*Bolt #4 data not included due to strain gauge malfunction

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Retorque to:

AS-6117B Column Torque Body Flange # 5

100 200 300 400 1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81

Bolt Number Ft - Lbs Torque

Bolt Torque

287.6 Average Torque

Note: Initial Torque 370 Ft-Lbs

Glass Column Body Joint PTFE Envelope Gasket 300 °F Operation, 6 Month Torque Check Star-Pattern Assembly, (1) Final Rotational Pass Assembly Torque = 370 Ft-Lb Average Residual Torque = 288 Ft-Lb

Retorque Necessary 370 ft-lb Assembly Torque

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AS-6117A Column Torque Body Flange # 1 12/14/09 Through 2/15/10

100 200 300 400 1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81

Bolt Number Ft - Lbs Torque

316.0 Average Torque

Initial Torque 320 Ft-Lbs

Glass Column Body Joint Expanded PTFE Envelope Gasket 300 °F Operation, 6 Month Torque Check Star-Pattern Assembly, Multiple Final Rotational Passes

Assembly Torque = 320 Ft-Lb Average Residual Torque = 316 Ft-Lb Retorque Not Necessary 320 Ft-Lb Assembly Torque

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4/3/2018 Page 25 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

If Component, Design or Assembly Improvements Are Not Possible:

THEN Re-Torque – Timing Options:

  • Ambient Temperature Re-Torque Prior To Start-Up
  • Re-Torque 2 – 24 Hours After Assembly, But Before Start-Up
  • Dwell-time based primarily on GASKET creep properties
  • Ambient Temperature Re-Torque After Operation/Process Cycle
  • Re-Torque After Operation/Cycle, While Vessel Is At Ambient Temperature & Pressure
  • Start-Up Hot Torque
  • Re-Torque While Vessel Is Coming Up To Temperature
  • Not recommended for PTFE based gaskets
  • On-Line Re-Torque (Hot Re-Torque)
  • Re-Torque After Operation, While Vessel Is At Temperature, Preferably At Low or Ambient

Pressure

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4/3/2018 Page 26 Bolted Connectors: Re-Torquing to Reduce Fugitive Emissions – When and When Not

Guidance & Resources:

ASME Post Construction Committee

  • PCC-1-2013
  • Section 10.4 Start-Up Re-Torque
  • Appendix B Definitions & Guidance on Hot Bolting, Half Bolting, and Live Tightening
  • PCC-2-2015
  • Article 3.10 Hot Bolting (still under development)
  • Note: Hot bolting can also be used to check residual bolt stress after a period of operation
  • r to retighten loose bolts. Hot bolting for these purposes is beyond the scope of PCC-2.

Plastics Pipe Institute

  • TN-38 - July 2011 – Bolt torques for Polyethylene flanged joints

Gasket Manufacturer, 3rd Party Test Data

  • HOBTC (Hot Blowout with Thermal Cycles) test

BFC Engineering & Component Suppliers