Braided Packing An Old technology With a Modern Twist. March 10, 2016

Transcription

1 Braided Packing An Old technology With a Modern Twist March 10, 2016

2 What is Compression Packing? A material made from soft, pliable ingredients that is cut or formed into rings and compressed in an annular cavity to seal around a moving shaft. Compression packings are contained and compressed within a cavity called a stuffing box by a packing gland. Applications include pumps, valves, mixers and other unique types of equipment.

3 An Old Technology Perception

4 Motion Packing Seals Reciprocating Motion Helical Motion

5 Types of Packing Constructions Braided Twisted Wrapped, Rolled and Folded Extruded Laminated Bulk Die Formed

6 Braided Mechanical Packing Braided Mechanical Packing is a system made of Fibers Braid Style Lubricants Break-in Blocking Corrosion Inhibitors Some general requirements for packing Resilience Chemical Resistance Strength Temperature Resistance

7 Types of Braided Packing Square braided (plaited) Usually soft Uses fewer, larger diameter diameter yarns Large percentage of of lubricants Used in high-speed rotary rotary service at low low pressures Used in old and worn worn equipment Used for small cross cross sections 2 -Track Structure

8 Types of Braided Packing Inter-braided Even distribution of yarn density yarn density throughout throughout Uses more strands of smaller smaller diameter than square braid 3-Track Structure 4-Track Structure

9 Braid Design Different Braiding Machines and Styles Interbraid Square Braid 1/8 1/2 cross sections Highest coating pick-up percentage Square Braid

10 Bulk Material Flexible graphite can be molded to make solid rings Other material are used in extrusion, die forming, or molding PTFE Elastomers Buna-N Ethylene-Propylene Neoprene FKM Silicone

11 Carbon or Graphite Fiber Carbon and graphite fibers are inert to most chemicals and have low frictional coefficients. ph range 0-14 except for strong oxidizers Advantages Temperature Heat Transfer Chemical Resistance Low Friction Disadvantages Price Cleanliness

12 eptfe/graphite Fiber eptfe/graphite fiber is a fiber that combines the properties of PTFE and graphite. It is limited only by the temperature range of the PTFE - ph range 0-14 Advantages Heat Transfer Chemical Resistance Low Friction Good tensile strength Disadvantages Temperature Range

13 The Main Properties of Flexible Graphite Material Density: Is light in weight and has compressibility & recovery Purity: 98% to 99% purity High & Low temperature: From -245 C to 850 C Corrosion resistant: Chemically inert except strong oxidizers Excellent thermal conductivity Low thermal expansion Impermeability Self lubricating Flexible High compressibility Resilient

14 Exfoliated Natural Graphite Flake (Enlarged View)

15 Braided Flexible Graphite Flexible Graphite by itself does not have enough tensile strength to braid. To create a braidable yarn, manufacturers use a carrier or support to give the material the mechanical strength that by itself it lacks.

16 Outer Jacket Graphite Tape Yarn Encapsulated in an Inconnel Wire Mesh 4532 F (2500 C) max temperature 0 to 14 ph range Low Friction Outer Jacket Core Corners (x4)

17 Metals Some metal wires are used for fiber reinforcement Stainless steel Inconel Copper Brass Monel Some metals are used in foils Lead Aluminum Copper

18 Lubricants Packing Lubricants - Compression packings generally contain lubricants - Lubricants provide resiliency that allows the packing to deform and recover under slight mechanical deficiencies such as shaft movement or flexing. Some lubricants can also be called blocking agents. - Many packing manufacturers offer blends of materials. As a result, limitations and properties vary.

19 Lubricants Materials - Colloidal Polytetrafluoroethylene - Animal & Vegetable Lubricants - Petroleum (Mineral) Lubricants, (petrolatum) - Solid Lubricants: - Graphite powder or flake - molybdenum disulfide - Boron Nitride - Silicone oil - Bio-lubricants (environmental implications)

20 Coating Formulation Individual strands must be coated prior to braiding Greatest challenge: Flexibility Adhesion Permeability Sample Formulations Flexibility Testing

21 Coating Application Wet-Braiding Coat the packing while it s being braided Higher coating content between the strands Wet-Braiding on Inverted Braider Machine

22 Valve Packing Characteristics Square-Braid Design Small cross-sections High coating content Outer Jacket Anti-extrusion capabilities Coatings act as a fluid barrier to enhance sealing Core Internal spring characteristics Wet-Braiding High coating content Low permeability Coating Emission capability

23 Testing & Validation API-622 Test

24 Testing and Validation Testing of packing in a fixture such as that specified by API 622 is not a guarantee that the same emission level will be achieved in a given valve. Factors such as surface finishes, concentricity, tolerances on diameters, bolt stress, and deformation under load all affect emission results Tests must be done first to qualify the packing and then to qualify the valve with the packing

25 Testing & Validation No Longer an Old Technology ISO and API-624 Testing

26 Packing Behavior Study Typical case and assumptions Packing Rings Packing Ring Size Bolt Lubricant Packing Gland Bolt Torque Applied Gland Stress Applied 5 Cut Rings 1.0 (ID) x 1.5 (OD) x 0.25 (CS) Sliding Paste (0.18 nut factor) 40 ft.-lbs 8,575 psi

27 Packing Behavior Study CONTEXT Increasing demand from the end-users Reduction of fugitive emissions Reduction of opening/closing forces Need for the differentiation from different packing types No standardized method for packing calculation nor packing full characterization (mechanical, friction, sealing performance vs. packing load,..) Existing standards for bolted flange joints with gasket with EN1591 and EN13555 => FSA and ESA joined with CETIM and its industrial partners to work on the creation of a packing design tool, based on the system developed for bolted flanges

28 Study Test Equipment Page /03 SEALING TEST CELL Compression press gland load application Sealing test cell (room temperature) To spectrometer He Stem movement transmission equipped with load sensor or torque meter Stem movement (translation or rotation) generation

29 Page /03 SEALING TEST CELL Vacuum chamber - (Stuffing box/gland sealing) Pressurized chamber (Stuffing box/stem sealing)

30 Page /03 Mechanical test cell Gland Strain gauges Stuffing box

31 Test Equipment Design Verification

32 déformation circonférentielle Test Equipment Design Verification Page /03 Stuffing box design: Stuffing box thickness : 10 mm Materials: P295 GH (EN ) Load case2 (min stress) P=10 MPa, Length= 3 mm, T=20 C 1.20E E E E E-06 cas n E E E P=10 MPa position suivant la hauteur (mm) 3mm Results Deformation peak 1 E-05=> OK for gauges => stuffing box thin enough

33 déformation circonférentielle deformation Test Equipment Design Verification Page /03 Contact pressure on internal diameter vs. Circumferential deformation 4.00E E E-06 variable packing/stufing-box contact length (3 to 12 mm) Constant contact pressure of 1 MPa 12mm 12mm 4.00E E E E-06 max def (1 MPa) y = 3.074E-07x E-07 R² = 9.989E E E-06 max def 2.00E E-06 3mm 3mm 1.50E E-06 Linéaire (max def) 1.00E E E E-07 position suivant la hauteur (mm) effort 3 mm effort 5 mm effort 8 mm effort 10 mm effort 12 mm 5.00E E Contact length [mm] Proportionnal to contact length on internal diameter for a given contact pressure level

34 déformation circonférentielle Test Equipment Design Verification Page /03 Check of distance between gages strain gage chain (10 gages at 1mm distance each) 1.2E-05 Load case2: P=10MPa over 3mm => 1.0E-05 signal «flat» enough for a 1mm grid 8.0E E E-06 maillage 2.0E E E position suivant la hauteur (mm)

35 Test Equipment Design Verification Page /03 Experimental calibration using elastomeric rings Hypothesis: K=1 Test on a dedicated compression press using the mechanical cell

36 Test Equipment Design Verification Page /03 Experimental calibration using elastomeric rings µm ChA Jauge 01 µm ChB Jauge 01 µm ChC Jauge A,B,C Gauges (position angle 120 ), same axial position => good alignement

37 max deformation[µe] Test Equipment Design Verification Page /03 Experimental calibration using elastomeric rings Test max deformation mesuré (µ ) Force de fond [N] max deformation calculée (µe) pour H =9mm max deformation calculée (µe) pour H =10mm max deformation calculée (µe) pour H =11mm max deformation calculée (µe) pour H =12mm => Good order of magnitude for measurmement and calculation (initial uncompressed packing height 12.7 = 2*6.35mm

38 Packing Behavior Study Page /03 SEALING TEST PROCEDURE 1 Apply initial axial stress of 1 MPa (reference) 2 Apply (and maintain) an axial stress of Q A 3 Apply M stem movements (translation or rotation) handling an axial stress of Q A (M=30) 4 Connect He spectrometer (check of vacuum and leakage level without He) 5 Pressurize (and maintain) with Helium at pressure level P 6 Leakage measurement over 2 hours 7 Unload to stress level Q Leakage measurement over 2 hours 7 Unload to stress level Q 2.

39 Axial stress [MPa] -He Pressure [bar] Test Results Page /03 SEALING TEST CURVE EXAMPLE Sealing test curve example (Q A =80MPa, 4 graphite rings, 10 bar He, translation) He spectrometer connection Pressurization 1.0E E E E E E E E E Time [hr] Stress [MPa] Leakage Leakage Leakage Leakage Leakage Pressure [bar] Leakage [atm.cm3/s]

40 Leakage [mg/s/m of stem perimeter] Test Results Page / E E E E E E-05 Leakage diagram (4 graphite rings, 10 bar He, translation) 40MPa_10b_1 40MPa_10b_2 60MPa_10b_1 60MPa_10b_2 80MPa_10b_2 A B C 1.00E E TIGHTNESS CLASS Initial packing stress QA [MPa] LEAKAGE [mg/s/m] C 1.00E-02 20/- 27/31 26 B 1.00E A 1.00E Packing axial stress [MPa]

41 On-Going Work Testing continues Different packing formulations must be tested to determine their behavior Algorithms will need to be developed Standardization will be essential

42 Conclusions The performance demands are higher than ever The products have higher performance than ever Compression Packing formulation, design, and testing use some old technology but also state of the art engineering tools Parameters such as compressive loads and friction will no longer just be based on experience and occasional verification Compression packing emission sealing is a modern technology