USA (Bartlett, IL) Division

• 100+ years Manufacturing Experience• Six Sigma Black Belt (2)• 350,000 Sq. Ft. Manufacturing & Office• Total Program Development & Management• Product Development & Test Facilities• Product Testing: Cycle/Leak/Stress Testing

USA (Bartlett, IL) Division

Manufacturing Expertise

• Welding: TIG, MIG, Laser, Resistance

• Forming: Hydroforming, Stamping , Folding, Flexible Tubing making (Bend-A-Flex)

• Cleaning: Aqueous, Solvent, Flushing, Clean Room Environment

• Brazing: Furnace, Induction, Manual

• Heat Treat: Vacuum, Atmosphere

Prototype Laboratory• 15,000 Sq. Ft. of Floor Space

• Production Representative

Equipment

• Full-Time Laboratory Tech’s

Test Laboratory• 24,000 Sq. Ft of Floor Space• Cycle Life Testing• Thermal Fatigue Testing • Full Test Engineering Staff

Senior Flexonics Business Unit

• Medical (Cryogenics, Endoscopic Tools - Bend-A-Flex Tubing & Heat Exchangers products)

• Semiconductor (Vacuum Components – Bellows, Bend-A-Flex Tubing products)

• Power (Stationary Engines, Gas Turbines, and Fuel Cells –Bellows, Bend-A-Flex Tubing & Heat Exchanger products)

• Petrochemical (Gas Lift, Oil & Gas Exploration –Bellows)

• General Industrial (Instrument & Controls, Valves, Electrical Switch Gear -Bellows)

Gas-Lift Bellows

ApplicationFunctional Requirements

• Pressure: typical operating 800 psi -1600 psi, 1800 psi max.

– Bellows design pressure 1” valve = 721 psi– Bellows design pressure 1-1/2” valve = 260 psi

• Stroke: valve full travel based on port size, but typically rated close to bellows design spec.

– Bellows design stroke for 1” valve = .167”– Bellows design stroke for 1-1/2” valve = .287”

• Temperature: typically based on elastomers used in valve. Std valve 250 degF, max 400 degF. Monel meets this requirement.

• Cycle Life: New multi-level API/ISO specification under development . Highest level would require life cycle testing and certification.

Bellows Design 101

Question: How do you design a bellows?

Answer: Very Carefully

Calculation Methods

• Flexonics equations• EJMA equations• ASME Section VIII equations • ASME B31.1 and B31.3 equations• ASME Section III equations

EJMAExpansion Joint Manufacturers Association

• Industry group composed of 7 manufacturers of expansion joints (including Senior Flexonics)

• Current standard is the 7th edition

Bellows Design Inputs

• outer diameter - OD• inner diameter - ID• wall thickness - t• number of plys - n• pitch - q• number of convolutions - N• material type

Bellows Operating Conditions

• Temperature• Pressure• Motion

– axial– lateral– angular

Bellows Design Characteristics

• Pressure Rating• Spring Rate• Effective Area• Cycle Life• Natural Frequency

Pressure Rating

• Bellows can be internally or externally pressurized.

• Internally pressurized bellows are subject to squirm (instability).

• Internally pressurized bellows exert pressure thrust force on mating hardware and components.

• Pressure rating proportional to thickness to the 2.0 power

Comments on Pressure• Considered only for internally pressurized

bellows.• Two types of instability

– column instability called squirm– in-plane instability called tilt

• Squirm is gross lateral shift of center section of bellows while ends remain fixed

• Tilt is when convolutions become non parallel to each other.

• Flexonics equation is less conservative

Spring Rate• Bellows have elastic properties similar to a

spring.• Bellows can be deflected by pressure as

well as mechanical loading• Spring rate is not linear but varies over

loading range and bellows deformation• Proportional to the wall thickness to the

2.7 power.

Comments on Spring Rate• EJMA equations can over predict spring

rate.• Flexonics has empirical data on spring

rates for standard size bellows. • If spring rate is an important design

consideration, always verify calculated number with empirical data and check spring rate on individual bellows as part of manufacturing process.

Effective Area

• Area of circle lying midway between bellows ID and OD

• Similar to piston exterting same thrust as bellows when subjected to same pressure

Cycle Life

• Determined from S-N curves for various materials

• Calculate deflection stress using EJMA equations.

• Stress is fictitious stress based on elastic formulas - plastic deformation is not considered.

Flexonics Cycle Life

• In 1968 Flexonics developed a SST S-N curve based on bellows and coupon testing.

• In 1971 similar curves were derived for other alloys.

• These curves can be used with the total stress from EJMA to predict cycle life.

Comments about Cycle Life

• The only way to confirm a cycle life prediction is to perform cycle testing of bellows.

• Cycling pressure and motion is more severe than constant pressure and motion cycling.

• Predicted cycle life is affected by operating temperature.

Comments about Vibration

• To avoid resonance the bellows natural frequency shall be lower or at least 50% higher than the system frequency

• Flow induced vibration of bellows can occur with high velocity flow. An internal liner must be used to reduce this phenomenon.

Nmin = 7.9E6, Inner surface of the outer ply.

DesignMaximum Stress & Fatigue Life

σmax

Data Aquisitionfor Model Verification

Von Mises Stresses

Inner & Outer Stresses of Multi Ply Bellow

2-Ply 26 Corrs w/ 85 mm OD, 75 mm ID 0.2032 mm THK,7.112 mm Pitch, 321 S. S.

Bellows Model

General Processof Making Gas-Lift Bellows

• Seam-welding & cutting of the 3 tubes (plies)• Draw processing to get tubes to their final wall

thickness• Tubes are telescoped together to form one 3-ply

tube• Bulge formed• Roll forming – we now have a functional bellows• Trimming the ends• Circumference weld• Leak Test• Final Inspection

Tube Welding

Welded Tubes

Tubes Awaiting Cleaning

Telescoping – 3 tubes into 1

Tube Bulging

Roll Forming

Trimming

Trimming

Circle Welding the Plies

Mass SpectrometerLeak Testing

Typical Failure Modes and Causes

• During Manufacturing– Inadequate circle welds on plies– Found at final Leak Test Operation

• From the Field– Fatigue Failure– Over Pressurization

Over Pressurization

Over Pressurization

Possible Bellows Performance Improvements

• Inconel Bellows• Valve redesign to minimize over

pressurization