Control valve packing considerations for ldar and enhanced ldar programs
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Control Valve Packing Considerations for LDAR and Enhanced LDAR Programs. Blake Coleman Sales Engineer. Meet Low-E requirements without compromising control valve performance. Control Valve Packing Needs Industry Fugitive Emission Standards Packing Technology Packing Principles

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Control Valve Packing Considerations for LDAR and Enhanced LDAR Programs

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Control valve packing considerations for ldar and enhanced ldar programs

Control Valve Packing Considerations for LDAR and Enhanced LDAR Programs

Blake Coleman

Sales Engineer

Meet Low-E requirements without compromising control valve performance


Control valve packing considerations for ldar and enhanced ldar programs

Control Valve Packing Needs

Industry Fugitive Emission Standards

Packing Technology

Packing Principles

Applying Principles

Agenda


Control valve considerations

Control Valve Considerations

What drives control valve packing selection?

High cycle demand of control valve applications

Low emissions for compliance with LDAR and Enhanced LDAR requirements

Minimal maintenance between turnarounds

Maintaining dynamic performance for loop control


Control valve fugitive emission standards

Control Valve Fugitive Emission Standards

  • Address high cycle and low emission requirements through leakage and cycle classes

  • ISO 15848-1

    • Isolation Valves (on-off)

      • 500-2500 cycles required

    • Control Valves

      • 20,000-100,000 cycles

    • Valve specific type testing (e.g. ENVIRO-SEAL packing in a Fisher valve)

  • ANSI/FCI 91-1

    • Exclusively written for control valve packing

    • High Cycle

    • Valve specific type testing (e.g. ENVIRO-SEAL packing in a Fisher valve)

A direct comparison of FCI 91-1 and ISO 15848-1 requirements is not possible.


Historical perspective

Historical Perspective

Traditional packing approach at the time

“the more packing rings, the better”

“just tighten the packing if it begins to leak…if the valve can still stroke it’s okay”

leakage vs. friction


Control valve packing design

Control Valve Packing Design

  • In light of 1990 Clean Air Act, LDAR, and lower control valve emission requirements:

    • Fisher initiated a packing development and testing program to address these challenges

    • Testing revealed several important observations

      • Traditional approach of trying various materials and arrangements would not stand up to new leakage criteria

    • Development

      • Through empirical laboratory studies and research, Fisher identified 5 control valve packing design principles used today


Identified 5 packing design principles

Identified 5 packing design principles

Controlled packing stress

Minimized packing arrangement

Packing ring containment and support

Stem guiding and alignment

Stem surface finish

Slide 7

Emerson Confidential


Design principle 1 controlled packing stress

Design Principle 1 – Controlled Packing Stress

Creating a seal

Resilient packing material placed between stem and bonnet

Deformed (stressed) to fill any voids

Limitations

Stationary follower relies solely on resiliency of packing itself to establish and maintain stress

Volume loss due to compression and filling voids causes stress to decrease

Must re-tighten packing nuts to re-establish stress

Maintenance intensive

Difficult to ensure correct stress is applied initially or at later maintenance stage

Insufficient stress = weak seal

Too tight = overstress and increase in excessive packing loss by extrusion or wear

Torque packing nuts to load packing flange

Creates axial load on follower and stress in packing

Packing stress transmits into radial load, creating seal between stem and packing box

Traditional Packing Approach

Slide 8

Emerson Confidential


Design principle 1 controlled packing stress1

Design Principle 1 – Controlled Packing Stress

Spring stack between packing flange and follower to establish and maintain a controlled load and stress on packing (live-load)

Benefits

Packing stress is maintained via Bellevilles even as packing volume and height is lost through friction, extrusion, or consolidation,

Slight reduction in spring force as packing consolidates, but will not compromise seal integrity because springs and packing are properly paired

Reduces effects of thermal cycling

Less maintenance (re-tightening)

Additional considerations

Must be used in conjunction with anti-extrusion system to prevent loss by extrusion via constant stress

Stem alignment control is crucial

Torque packing nuts to load packing flange

Compresses Belleville springs which live-load follower axially and create constant stress in packing

Packing stress transmits into radial load, creating seal between stem and packing box

Solution: Live-Loading

Slide 9

Emerson Confidential


Design principle 2 minimized packing arrangement

Design Principle 2 – Minimized Packing Arrangement

Quality and position of the seal depends on

Ability of packing to deform under compressive load

Friction between the packing and stem

Understanding where sealing occurs

Slide 10

Emerson Confidential


Consolidation

Consolidation

Packing consists of stacked rings

Air is trapped between the rings when first installed

As packing is stressed, the air is compressed and forced out of the packing

As air leaves, the effective volume of packing decreases, e.g. “consolidates”

Stationary follower: consolidation reduces stress and radial deformation (seal)

Must be re-tightened

Live-loading: consolidation minimally reduces packing stress

Springs take up lost height from consolidation

Consolidation further minimized by

Minimizing number of packing rings needed to create a seal

Packing ring design that minimizes voids

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Emerson Confidential


Friction

Friction

The greater the area of contact between packing and stem (more rings), the greater the friction

Graphite packing has high friction

Additional rings only increase friction

Requires larger actuator

Slow stem movement

Poor control

Slide 12

Emerson Confidential


Where sealing occurs

Where Sealing Occurs

Key takeaway: one ring seals

Additional packing rings provide no improvement in sealing force

Consider packing material behavior under axial pressure…

If packing acted as a fluid:

Uniform radial pressure and seal

If packing acted as a solid:

Little or no axial load transmitted to radial pressure to deform packing and create seal

Solution: Utilize minimum number of packing rings

Actual PTFE packing behavior

Non-uniform radial load with maximum stress near the middle of the packing set

-Design Principle 2

Actual Graphite packing behavior

Non-uniform radial load with maximum stress near the top due to high friction between the packing and stem countering the downward load

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Design principle 3 packing ring containment and support

Design Principle 3: Packing Ring Containment and Support

PTFE has 2 deficiencies

Coefficient of thermal expansion is 10x that of steel

Tends to cold flow when stressed

As PTFE packing heats, it tries to expand

Increases stress in packing

Flow (extrude) past retaining rings and out of the packing box

More PTFE packing = more expansion force = more difficult to retain

As PTFE cools, the amount lost to extrusion will reduce the sealing stress

Requires re-tightening and maintenance program

As a result, thermal cycling is a major cause of packing loss, leakage, and short service life

Extrusion of PTFE

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Emerson Confidential


Control valve packing considerations for ldar and enhanced ldar programs

Packing Retention and Anti-Extrusion

Packing lost via 2 mechanisms

Wear caused by friction (Graphite)

Extrusion (PTFE)

Live-loading can moderate stress reductions from packing loss, but it cannot prevent extrusion altogether

Solution: anti-extrusion rings

Less pliable material than packing “seals” the packing, not the leakage

Efficient load transfer from follower to packing

Tight fit to stem to prevent extrusion without scratching stem surface

Design Principle 3: Packing Ring Containment and Support

Slide 15

Emerson Confidential


Design principle 4 stem guiding and alignment

Design Principle 4: Stem Guiding and Alignment

Valve stems and shafts experience radial movement

Bending stress

Imperfect alignment of actuator

High packing loads

Leads to non-uniform packing stress around the stem

Guiding and alignment controls

Solution: Close fitting follower to serve as guide bushing

PTFE lined for tight clearance and reduced friction when temperature allows

Hard carbon bushing rings for graphite packing systems

Belleville springs centered around the stem or shaft reduce alignment issues as opposed to being installed under each packing stud where differences in packing nut torque have greater influence

Slide 16

Emerson Confidential


Design principle 5 stem surface finish

Design Principle 5: Stem Surface Finish

Solution: Smooth, polished stem finish

Reduces packing erosion and friction

Enhances anti-extrusion ring effectiveness


Applying design principles enviro seal ptfe

Applying Design Principles: ENVIRO-SEAL PTFE

PTFE packing rings stressed and load maintained via live-loading with adequate spring compression remaining to compensate for expansion

Optimal packing stress derived by lab testing

Minimize the number of packing rings

Confirmed by lab testing

Employ special anti-extrusion rings to contain PTFE and protect against extrusion and consolidation

V-shaped packing ring and anti-extrusion ring shapes to closely match and reduce packing ring voids

Add anti-extrusion washers to further contain the anti-extrusion rings

PTFE lined packing follower serves as bushing and stem alignment

Polished valve stem

Slide 18

Emerson Confidential


Control valve packing considerations for ldar and enhanced ldar programs

ENVIRO-SEAL PTFE – Sliding Stem

Design Principle 4: Guiding

Design Principle 1: Live-loading

Packing Follower

(Stainless Steel)

Springs

(N07718)

Design Principle 3

Anti-Extrusion Ring

(Filled PTFE)

Design Principle 3

Anti-Extrusion

Washers

Lantern Rings

(Stainless Steel)

Packing Box Ring

(Stainless Steel)

Design Principle 2: Optimized Minimal Packing

Packing Ring

(PTFE)

Design Principle 5: Polished stem finish


Enviro seal graphite ulf

ENVIRO-SEAL Graphite ULF

Design Principle 1: Live Loading

Springs

(N07718)

Design Principle 4:

Guide Bushing

(Carbon)

Design Principle 3: Containment

Packing Ring

(Composite)

Design Principle 2: Optimized Minimal Packing

Packing Ring

(Flexible Graphite)

Packing Washer

Packing Box Ring

(Stainless Steel)

Design Principle 4:

Guide Bushing

(Carbon)

Design Principle 5: Polished stem finish


Considerations for control valve packing

Considerations for control valve packing

Does packing solutions meet control valve fugitive emission standards?

ANSI/FCI 91-1

ISO 15848-1

Does it use design principles to meet leakage and control valve cycle requirements with minimal maintenance?

Controlled packing stress

Minimized packing arrangement

Packing ring containment and support

Stem guiding and alignment

Stem surface finish

Does it meet LDAR (500ppm) and Low-E/Low-leaking (100ppm)?

Does it maintain dynamic performance required of control valve applications?

ENVIRO-SEAL…designed, tested, and validated to fugitive emissions standards to meet Low-E requirements

Slide 21

Emerson Confidential


Questions

Questions?


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