Presentation on theme: "MOV/Gearbox Overtorque Protection"— Presentation transcript:
1 MOV/Gearbox Overtorque Protection (Ex: Limitorque Actuators)Power GenerationBest Practice’s MeetingOctober 31, 2007The topic of this presentation is overtorque protection of motor operated valves and gearboxes, such as Limitorque actuators.Presented By: Denise Lane Mech. Engineer Agua Fria Generating Station
2 Presentation Elements MOV/Gearbox Safety Concern RefresherCrystal RiverCommon Causes of FailureValve Wrench/Cheater Bar UsageMechanical Overload Protection DeviceOperating PrincipleInformation & CalculationsInstallation & CostIn the first segment of the presentation, I’ll remind you of the safety concerns by discussing the incident at Crystal River, the common causes of failure, and the use of valve wrenches and cheater bars.In the second part of the presentation, I’ll discuss a mechanical overload protection device to prevent failure. I’ll show a film clip on how the device works; touch on the information and calculations needed to buy the protectors; and briefly discuss the installation process and protector cost.
3 MOV/Gearbox Safety Concerns Crystal River - 01/2004BFP Iso ValveKilled 20 Yr. EmployeeValve Wrench To CloseGears Cranking to OpenCracked Actuator HousingMost of us are familiar with the Crystal River fatality that occurred in An employee that had worked at Progress Energy for 20 years was killed when part of an actuator housing ejected and flew through the air with line pressure momentum; hitting the employee.The root cause was determined to be from a feedwater pump requiring maintenance.An upstream valve was used to isolate the pump, but the actuator couldn’t completely shut it off so a valve wrench was used.Several days later, after the pump had been fixed, the operators attempted to open the valve with the actuator, but the attempt failed.While discussing alternative methods, the valve wrench’s seating force combined with the cranking torque of the gears that were still trying to open the valve. These forces cracked the metal casing and the projectile was set in motion.
4 MOV/Gearbox Safety Concerns Valve Failure Root CausesUsing a Valve Wrench/Cheater Bar on the HandwheelHolding In the Motor Control ContactorSetting the Torque Switch Too HighBeating on Valve Body to Unseat ValveRemoving Stem Locknut Under PressureElectrical ShockBecause of this, a couple of years ago, AFGS hired Pinnacle Actuation to provide safety training for these types of equipment. In the training, we were instructed on the top (6) causes of failure. They are:Using a Valve Wrench &/or Cheater Bar on the HandwheelHolding in the Motor Control ContactorSetting the Torque Limit Switch Too HighBeating on the Valve Body to Unseat the ValveRemoving the Stem Locknut While the Line is Under PressureAnd Electrical ShockThe use of valve wrenches and/or cheater bars has been determined to be the #1 cause of the failures.
5 Safety – Handwheels & Valve Wrenches Handwheel Torque > Motor TorqueWheel Radius & Max. Hand Forces Limit TorqueDesigned for Max. Allowable Actuator RatingThere are (2) facts that need to be considered in the use of valve wrenches and/or cheater bars.The first is that use of the actuator handwheel can achieve a greater torque than the motor.This is a specific safety measure incorporated by the actuator manufacturer to prevent normal operation stresses.The second fact is that the wheel radii and hand forces are the limiting factors in allowable actuator torques and should not be exceeded. Within these (2) facts lies the problem.
6 Safety – Handwheels & Valve Wrenches Valve Wrenches/Cheater BarsBenefit - Decreases Hand Force Needed to Seat or Unseat ValvesDrawback - Uncontrolled Length Increases Induced Weak Link StressDrawback – “Slipping” Safety ConcernBecause hand force is used as the limiting factor, a high average force of approx. 150 lbs is used in wheel radius determination.Quite often, an employee can not apply this force or the handwheel is not in the greatest location for force application.Therefore, a valve wrench is needed to fully close a valve.Because a wrench provides a longer force arm, less hand force is needed to seat the valve.On the other hand, if the wrench is too long, an over-stressed housing scenario can easily develop.There have also been instances noted where the valve wrench or cheater bar has dislodged and caused personnel injuries.
7 Safety Concerns Weak Links Can Stretch & Separate Yoke & Actuator Housing Cover BoltsCauses Actuator &/or Valve Housing Ejection“Missile” Safety ConcernNot Just LimitorqueMore Often NowOver-stressed areas can cause bolts to stretch and then, ultimately, separate.This creates an immediate missile safety concern as evidenced by the Crystal River employee’s death.I spoke with Pinnacle Actuation recently and they reported that they are seeing this scenario a lot more in recent inspections and that it’s not just limited to Limitorque valves anymore.
8 Overtorque Protection Collar – How It Works Since we can’t easily control what length of valve wrench an employee uses, Aunspach Controls is one of a few companies that have created overload protection devices.They have graciously provided a film clip that details handwheel and valve stem overload protectors and how they work.
9 Protection Collar – Other Styles Top Mounted D82Model D82TM-INTSMB-000Aunspach Controls offers different styles of collars available to suit most needs.For instance, In the handwheel collar line, they offer a top-mounted model and an integrated model for the Limitorque specific model SMB-000.Integral part of Limitorque actuator
10 Protection Collar – Information Needed ValvesMake & Model/StyleStem Diameter & Threads/InchActuatorsShaft DiameterKeywaysWidth x Length x DepthLength Extended Through Handwheel Collar?Extruded or Inlaid?To order the collars, the following information is needed:For the Valves, you’ll need to know the make, model, stem diameter and threads/inchFor the Actuators, you’ll also need to know the make, model, shaft diameter, and keyway information.The keyway information includes the width, length, and depthThe length that the keyway extends through the handwheel collar. For instance does it extend all the way through or just part of the way through?And, lastly, is the keyway extruded or inlaid on the shaft?
11 Protection Collar – Calculations Needed -Formula Derivation – (4) StepsParker/Winsmith Gear Speed ReducersLimitorque SMB-00 Actuator SupplierPinnacle ActuationMOV/Gearbox Safety TrainingSRP EngineeringThe next several screens will show the required calculations. I’ll show the more important calculations on the screen and mention some important facts. If someone wants more in-depth details, they are more than welcome to access this presentation and an existing excel spreadsheet to aid in the calculations; just give me a call.There are (4) steps needed in handwheel collar sizing calculations. These formulas were derived by Parker/Winsmith, a manufacturer of gear speed reducers and a Limitorque supplier, Pinnacle Actuation, and SRP engineering.
12 Protection Collar – Calculations Needed Determine Actuator ParametersLimitorque SMB-00 = 260 ft*lbs Max. InputAura Motor = 260 x 0.6 = 156 ft*lbs Max.rpm = hp x 5252/TorqueMin. Angular Speed < Step 3 Ensures Max Torque Not ExceededThe first step determines the minimum stem speed that can be supplied to open or close the valve.
13 Protection Collar – Step 1 Information Actuator Nameplate Service FactorMaximum Allowable Torque InputMotor Manufacturer Safety FactorStep 1 calculations require information regarding the actuator nameplate service factor, the maximum allowable actuator torque input, and the safety factor included by the actuator motor manufacturer.
14 Protection Collar – Calculations Needed Gear Output = Min. Torque to Open/Close ValveWedge Diameter = Valve DiameterSeating Force = Line Pressure x Seating Area x Valve Turning Hardness FactorRequired Output = Total Thrust x Stem RadiusThe second step calculates the minimum system torque required to open and close the valve.
15 Protection Collar – Step 2 Information System Line PressureValve Internal DiameterValve Stem DiameterValve Friction Coefficient:Gate = 0.3Packing Friction CoefficientGraphite = 3,000 psig incl. S.F.Step 2 calculations require valve and system data. You will need to know the line pressure, the valve internal diameter, the valve stem diameter, and valve and packing friction coefficients.
16 Protection Collar – Calculations Needed Supplied Gear Output = Max. Actuator TorqueInput = hp x 5252/rpmStem Speed = rpm/Drive Sleeve Bevel Gear RatioMust be > Step 1 Min. Calculated Speed InputGear Torque = Output hp x 5252/Stem SpeedThe third step calculates the maximum stem speed and torque that the actuator motor can supply.The actuator’s maximum allowable torque value could also be used instead of this calculated value.But if the equipment is not new and you don’t know the current stressed state, using the maximum motor-based torque value will provide a good safety factor.The minimum and maximum torque parameters have now been established.
17 Protection Collar – Step 3 Information Motor hpMotor rpmMotor EfficiencyDrive Sleeve Bevel Gear RatioStep 3 calculations require motor and gear data. You will need to know motor hp, rpm, and efficiency along with the gear ratio.
18 Protection Collar – Calculations Needed Required Torque < Overload Protection Cutoff < Max. Actuator TorqueVector = Moment Arm Length About System C.G.Hand Force = Cutoff Torque x VectorMax. Bar Length Allowed =Cutoff Torque - Avail. Hand Torque_____Hand Force Needed – Avail. Hand TorqueThe last step calculates a maximum valve wrench length so the collar does not disengage from the stem and cause operation frustration.In the example that I’ve been showing, the minimum torque was 88 ft lbs and the maximum was 106 ft lbs.I chose 95 ft lbs because other valves could use this same collar size.By using this value as the maximum, I could increase the torque value of the collar to accommodate more valves without having to worry about exceeding the maximum allowable torque.This also allowed the manufacturer to reduce the manufacturing time and provide a discount for using the same setup.
19 Protection Collar – Ease of Installation/Pricing Dependent onQty. & StyleGreg Bennett –“Relatively Easy”Kirk Mason –“Very Easy”“Piece of Cake”Successfully TestedIn the last screen, we discussed minimizing the cost of the collars.So, what is the cost? We ordered a total of (17) handwheel collars in (4) sizes. Our total cost was approx. $16,000.We saved approx. $5,000 or 25% because we minimized the size changes and maximized the qty.At any rate, the collars are relatively inexpensive compared to the possible consequences.“How easy are they to install?” First, the keyed handwheel is removed. Second, the collar is slid along the keyway and tightened onto the shaft perimeter with bolts. Lastly, the handwheel is re-installed, but on the collar shaft instead. It’s that easy.Do they work? The collars are adequate for the job.We tested the collars and found that they allowed closing and opening of the valve; that they disengaged when they should; and that they automatically reset for another attempt if needed.
20 Collar Installed on FWH Extraction Valves Here, you can see a visual of before and after collar installation. The collar length is sufficiently small to avoid interference with close quarter equipment.No CollarsCollars