Reliability Digest, February 2015 Fault Diagnostic .
Reliability Digest, February 2015Fault Diagnostic Opportunitiesfor Solenoid Operated Valvesusing Physics-of-Failure AnalysisN. Jordan Jameson* (jjameson@calce.umd.edu)Michael H. Azarian (mazarian@calce.umd.edu)Michael Pecht (pecht@calce.umd.edu)Center for Advanced Life Cycle EngineeringUniversity of MarylandCollege Park, MD[3], [4], and the control of automobile transmissions [5]. Inthe process and nuclear industry, solenoid valves are used forprocess fulid control and in critical safety instrumentedfunctions (SIF). Approximately 2–4% of all solenoid valvesin a typical chemical plant are part of a SIF [6]. Moreover,safety valves are generally the most important components inthe safety loop [7]. Thus, their reliability and availability arecritical.Due to the pervasive use of SOVs in a variety ofindustries, interest continues to grow in estimating theirhealth and remaining useful life (RUL). Understanding theunderlying physics of their failure mechanisms can yieldinsight into the measurement techniques that may produceuseful results for health estimation. This is referred to as thephysics of failure (PoF) approach to diagnostics andprognostics. The first step in this process is to identify andanalyze the hardware of the system. This yields anunderstanding of how the components connect and theirfunctional relationships, which can be used in identifyingloading conditions applied to system components. Theloading conditions are a direct result of the life-cycledemands of the system. However, in a system where there isheavy interaction between the components, as seen in theSOV, life-cycle loads and demands can produce stresses thatinteract among the components. These stresses may beclassified as mechanical, electrical, chemical, thermal, orenvironmental radiation. The presence of any particular loadin the life-cycle depends on the specific application of theSOV. The next step is to perform a failure modes,mechanisms, and effects analysis (FMMEA) on the system.This, combined with a criticality analysis, is useful foridentifying and prioritizing the failure mechanisms of thesystem. With an understanding of the failure mechanisms, asystem can be designed to monitor key parameters in order toperform system diagnostics and prognostics.The purpose of this paper is to identify the criticalcomponents and failure mechanisms of the solenoid valvesystem, and then explore existing and potential methods ofperforming health diagnostics and prognostics.Abstract—Solenoid operated valves are vitalcomponents in many process control systems. They arecomponents that are often critical to safety. Solenoidvalve degradation is difficult to detect in situ, leading tofailures, which are often sudden and unexpected. Thispaper reviews some of the common causes of solenoidvalve degradation, presents strategies that leverage thesemechanisms to detect and diagnose faults before theylead to failure, and discusses research opportunitiesaimed at improving solenoid valve diagnostics andprognostics.Keywords-solenoid valve; diagnostics; electrical coil;fault detectionI.INTRODUCTIONThe Transocean Deepwater Horizon disaster in 2010 wasa major incident resulting in 11 lives lost and an estimated4.9 million barrels of oil discharged into the Gulf of Mexico.Tests performed by Transocean Ltd. and CameronInternational after the incident revealed that the coil of asolenoid valve failed to energize, suggesting an electricalcoil fault. The investigation team found no evidence tosuggest that this fault was a result of the incident. Rather,they concluded that the electrical fault(s) likely existed priorto the accident [1]. Had the solenoid valve been workingproperly, it could have yielded at least a partial closure ofthe blind shear rams, resulting in a far less serious incident.Solenoid operated valves (SOVs) are utilized to shut off,discharge, dose, allocate, or combine fluids. This action isaccomplished by passing an electric current through a coiledwire, thereby producing a magnetic field, which magnetizesthe plunger resulting in a position change. The position of theplunger controls the flow of the process fluid(s).SOVs are integral components of many systems. Theirpopularity is primarily due to their simple and ruggedconstruction, and their inexpensive cost. Within theautomotive industry, solenoid valves are used to achieveintelligent control in electro-pneumatic braking systems ofmotor vehicles [2], control in diesel fuel injection systemsII.HARDWARE ANALYSISSolenoid operated valves are used in many differentoperating environments and thus can have a variety ofdesigns. The fundamental differences can usually beunderstood using the following terms: normally open versus27
Reliability Digest, February 2015normally closed; direct-acting versus pilot-controlled; andtwo-way versus three-way versus four-way. Normally open(closed) refers to a valve where the inlet port is open (closed)when the valve is de-energized. A direct-acting valve is onewhere all flow passes through an orifice that is openeddirectly by an electromagnet and plunger. Pilot-controlledrefers to a solenoid valve that operates by means of aminimum and maximum pressure differential and uses anelectromagnet and plunger to open or close a small orificethus controlling the pressure differential across a piston ordiaphragm. A two-way valve, as shown in Figure 2.1, is onewhere there are two ports and a single orifice that can beopened or closed. Two-way valves are used to control asingle working fluid. In a three-way valve, there are threeports and two orifices, similar to what is shown in Figure 2.2.Three-way valves can have several possible functions. Theyare commonly used to alternately apply pressure to andexhaust pressure from the diaphragm operator of a controlvalve, single-acting cylinder, or rotary actuator. It canoperate with an inlet port, an outlet port, and an exhaust portfor operating a single acting cylinder; one inlet port and twooutlet ports for selecting or diverting flow; or two inlet portsand one outlet port for mixing fluids. Four-way valves aregenerally used to operate double-acting cylinders oractuators. They have four or five pipe connections: onepressure, two cylinder, and one or two exhausts. In thispaper, a two-way, direct-acting solenoid valve will beanalyzed, not because it is necessarily the most common, butbecause it provides an opportunity to analyze componentsand loading conditions that are common to the valvespreviously mentioned.Figure 2.2. Three-way, direct-acting solenoid valveIn a two-way valve design, the spring, core, and coretube are exposed to the process fluid. This type of design iscommon, though there are available designs where thesecomponents are separated from the process fluid by amembrane, used with ultra-pure or extremely aggressiveprocess fluids.III.LOADING CONDITIONSIn order to assess the reliability of a SOV, environmentaland operational loads must be understood. For mostapplications, there are chemical and contamination loadsarising from the process fluid and airborne environment, andthermal loads arising from the process fluid and theelectrical coil. Further, due to the interaction of thecomponents, friction and impacts will be present during thelifetime of the SOV. Each component in the valve will besubjected to a different combination of loads. A less generalload is radiation loading, in the case where a SOV is used ina nuclear facility. In providing an FMMEA for SOVs,motivation is given for further research into diagnostic andprognostic methods for SOVs.IV.FAILURE MODES, MECHANISMS, AND EFFECTSANALYSISFailure modes, mechanisms, and effects analysis(FMMEA) is a systematic methodology of finding rootcause failure mechanisms of a given product [8]–[10]. Aneffect is the observable result of a failure on the product.Failure mode is a way in which a component, system, orsubsystem may fail to meet its intended function. Failuremechanism is the mechanical, chemical, thermodynamic orother physical process or combination of processes thatresult in a failure. FMMEA helps to identify potential failuremechanisms and models for expected failure modes andprioritize them. An important result from FMMEA is anunderstanding of possible parameters to be monitored fordiagnostics and prognostic purposes.A. Potential Failure ModesThe major components of the solenoid valve are selectedfrom the analysis of hardware given in Section 2 for atwo-way, direct-acting solenoid valve. An overview of thepotential failure modes, mechanisms, and effects is given inTable 4.1.Figure 2.1. Two-way, direct-acting normally opensolenoid valve1) Valve BodyThe valve body is exposed to the process fluid and musttherefore be resistant to corrosion and contamination. Thematerials used to construct the valve body are mostcommonly brass, bronze, cast iron, or stainless steel. Somealternative materials are used in specialized applications.Polyvinylidene fluoride (PVDF) is suitable for valves inacidic and solvent applications. Polyether ether ketone(PEEK) has desirable mechanical properties but issusceptible to attack by nitric and sulphuric acid.The failure of the valve body will be evidenced byleakage of the process fluid. This could be caused byloosening of the outside connections or, in extreme cases,plastic deformation of the valve body. In cases where thereis a mechanical loading, such as vibration or impacts,applied to the valve body, the failure mechanisms are fatigue28
Reliability Digest, February 2015leading to fracture or overstress fracture. However, sincecontaminants and corrosive media are present in mostsolenoid valve applications, the expected failure mechanismfor the valve body is corrosion fatigue or corrosion fracture,depending upon the ambient environment.The coil housing performs three functions for the SOV: itcompletes the electromagnetic flux path of the solenoid,provides protection from contact with the coil, and protectsthe coil against environmental conditions. For this reason, itis generally constructed using a soft ferromagnetic stainlesssteel.The housing will be directly exposed to the environmentalconditions. If the SOV were used in extreme environments,the combination of corrosion and temperature from theprocess fluid and electrical coil could produce a loss ofmaterial resulting in the decrease of magnetic flux. Inenvironments with high hydrogen concentration, hydrogenembrittlement could potentially be a failure mechanism.2) SealThe seal is used to control the flow of the process fluidthrough the valve. Implied by this function is therequirement to prevent leakage from the input to the outputinside the valve, referred to as seal leakage. Since the seal isexposed to the process fluid, there are several differentmaterials used for seal construction. Some examples are:NBR (nitrile butadiene rubber), EPDM (ethylene propylenediene monomer rubber), FPM (fluorocarbon rubber), andFFPM (perfluorinated elastomer).The seal will experience impact loading from the core andwill also experience chemical loading from the process fluid.Further, the process fluid or the electrical coil could causethe temperature of the seal to increase. Some valve designslocate the seal on the tip of the core, exposing the seal tofriction. A failure of the seal would result in seal leakage.This could be caused by a combination of mechanisms:corrosion, embrittlement, erosion of the seal material causedby the process fluid, impacts from the core and friction, andfatigue caused by impacts from the core.6) Core TubeThe core tube functions as a barrier between the core andthe electrical coil. It helps to protect the coil from theprocess fluid and direct the magnetic flux into the coreinstead of around the core. Most designs call for the coretube to be constructed of aluminum or paramagneticstainless steel. (A ferromagnetic core tube would provide ashunt path for the magnetic field lines, which would reducethe efficiency of the SOV.)Aggressive process fluids and friction produced byinteraction with the moving core result in wear of the coretube. This produces wear particles that can inhibit themovement of the core.3) Core SpringThe function of the core spring is to return the core to itsdefault position when de-energized. In many valve designs,the core spring is exposed to the process fluid and must beresistant to corrosion from the process fluid. Thus, it isgenerally constructed from paramagnetic stainless steel.As the spring is subjected to cyclic motions, the stiffnesswill decrease over time. Further, as the spring is commonlyexposed to the process fluid, it could corrode and furtherfatigue. This loss of stiffness will cause the valve toimproperly meter the process fluid, as the orifice will not beproperly plugged or fully opened. If allowed to continue inoperation, the spring could eventually fracture, resulting in atotal loss of function.7) Electrical CoilThe electrical coil is responsible for producing themagnetic field that magnetizes the core and produces thenecessary motion of the valve. The wire used is generallyreferred to as magnet wire and is usually constructed ofcopper. Within the solenoid valve field, there are three maintypes of insulation used to coat the wire. Class E insulationis rated for temperatures up to 120 C; class F is rated fortemperatures up to 155 C; and class H is rated fortemperatures up to 180 C. Electrical coil construction isgenerally divided into two methods: tape wrapped coils andencapsulated coils. Tape wrapped coils are manufactured bywinding wire around a spool or bobbin, and then protectingthe winding with insulation tape. Encapsulated coils alsohave a wire wound around a spool or bobbin, but the wire isthen encapsulated or molded over with a suitable resin.As an electric current is passed through the wire, Jouleheating causes an increase in the wire temperature. If thetemperature is too great, the dielectric material between thewires could degrade, fail, and two neighboring wires wouldform an electrical connection, producing a turn-to-turn orlayer-to-layer short. These shorts cause the coil resistance todecrease, thus pulling a greater current into the valve. At thelocation of the short, a hot spot can form, where the localtemperature is great enough to cause the wire to burn out,resulting in an open circuit. Corrosion can also play a role inthe failure of the electrical coil by causing necking and lossof material in the wire.4) Core/plungerThe core/plunger is responsible for allowing or preventingthe flow of process fluid through the solenoid valve. Incommon designs, the core is exposed to the process fluid.The core must be a soft ferromagnetic material in order toperform the functions necessary for the valve. The mostcommon material used for this purpose is stainless steel430F, a low carbon, high chromium stainless steel, whichwas developed specifically for solenoid plunger applicationsin corrosive environments.As the core is often exposed to the process fluid,corrosion frequently acts on the core material. Additionally,the core is in contact with the core tube, which introducesfriction, wear, and material loss. This will be evidenced bystick slip behavior or a failure to fully seal the valve whenclosed. The core is also exposed to the magnetic fieldcreated by the electrical coil. Prolonged exposure to thisfield can result in permanent magnetization of the plunger,resulting in improper behavior of the core, and impropermetering of the process fluid.B. Prioritization of Potential Failure MechanismsIn order to prioritize the potential failure mechanisms ofthe SOV, one must utilize past experience, stress analysis,accelerated tests, and engineering judgment. In 1987, OakRidge National Laboratory (ORNL) gathered and analyzeddata taken from the Nuclear Plant Reliability Data System5) Coil Housing29
Reliability Digest, February 2015(NPRDS) records of the Institute of Nuclear PowerOperations (INPO) for SOVs, covering September 5,1978-July 11, 1984, and the NRC Licensee Event Reporting(LER) system records for January 26, 1981-July 11, 1984[11]. The data showed that over 50% of SOV failuresresulted from 4 sources: worn or degraded parts,contamination by foreign materials, short circuit in the SOVcoil, and open circuits in the SOV coil. The remainingfailures were attributed to manufacturing defects, improperinstallation, incorrect assembly, corroded parts, loose ormisaligned parts, or their failure source was unspecified.Overall, the dominant failure source was shorts in theelectrical coil, followed by foreign material contamination,and then electrical coil open. Importantly, there was nofurther breakdown into specified failure sites for the cases ofworn, degraded, or broken parts and foreign materials.Table 4.1. Potential Failure Effects, Modes, andMechanisms of Solenoid Operated ValvesFailuresiteValvebodyPotentialfailure effectBody leakageSealImpropermedia flow(e.g. sealleakage),noiseLoosening ordeterioration ofseal, impactswith core,frictionPolymerembrittlement, erosion,overstress,fatigueCorespringImpropermedia flowWeakening ofspring strength,spring breakage,material /plungerIrregularmovement,seal leakageLoss of material,stick slipWear, ion ofmagnetic fluxpath (reducedmagneticefficiency)Loss ordiscontinuity ofmaterial inhousing fromcorrosion oroverstressCorrosion,overstressCore tubeIrregular coremovementresulting inseal leakageDebris coilSOV unable tooperate (coilopen),leakageresulting fromreducedmagnetic fieldstrength (coilshort)Fracturing ornecking of wire;degradedinsulation fromtemperature,conductorthermalexpansion, orelectricaltransients;material ress ofconductor,fatiguefractureFailure modeLoosening ofconnectionseals, openingin overstressfractureA study in 2009 by Angadi et al. [5], [12] revealed l-thermo-mechanical failure mechanisms. Inparticular, they emphasized the role of Joule heating in thethermal expansion of the magnet wire, causing thedegradation and failure of the insulation between the wires.This mechanism results in a turn-to-turn short, andultimately in a coil burnout.With these cases, and the variety of failure mechanismsacting on each component, in mind, it is difficult to drawconclusions on the prioritization of failure mechanisms withrespect to failure sites. However, it is clear that electricalfaults and valve contamination are prevalent and critical tothe health of the SOV.30
Reliability Digest, February 2015In this circuit, RL is the series resistance of the coil, L isthe coil inductance, C is the distributed capacitance of thecoil, Rc1 is the series resistance due to the distributedcapacitance, and Rc2 is the parallel resistance due to thedistributed capacitance. For their simulations, the resistancesRc1 and Rc2 were neglected. They tested a healthy solenoidvalve and a solenoid valve with approximately 6 percent ofits turns shorted. The test consisted of measuring the voltageresponse of the valves after stepping down to 0V DC from30V DC. The equivalent circuit model was able to reproducethe response of the healthy valve, as it behaved like adamped oscillator system. However, the response of thefaulty valve was not reproduced using the equivalent circuitmodel. An expected advantage of this approach was theability to detect faults in the valve that were undetectableusing other methods, since the ECM could take advantage ofdirect electrical measurements and observe any faultsexisting only in the coil. As the equivalent circuit could notaccurately reproduce the response of the faulty valve, thismethod was deemed as having low promise in the field.The state-of-the-art in solenoid valve fault detection ispartial stroke testing (PST) [7]. In
Reliability Digest, February 2015 27 Fault Diagnostic Opportunities for Solenoid Operated Valves using Physics-of-Failure Analysis N. Jordan Jameson* (jjameson@calce.umd.edu) Michael H. Azarian (mazarian@calce.umd.edu) Michael Pecht (pecht@calce.umd.edu) Center for Advanced Life
Test-Retest Reliability Alternate Form Reliability Criterion-Referenced Reliability Inter-rater reliability 4. Reliability of Composite Scores Reliability of Sum of Scores Reliability of Difference Scores Reliability
CDS G3 Fault List (Numerical Order) Fault codes may be classified as sticky or not sticky: Type of fault Method to clear Not sticky Clears immediately after the fault is resolved Sticky Requires a key cycle (off and on) after the fault is resolved to clear. CDS G3 Fault Tables 90-8M0086113 SEPTEMBER 2013 Page 2G-3
Capacitors 5 – 6 Fault Finding & Testing Diodes,Varistors, EMC capacitors & Recifiers 7 – 10 Fault Finding & Testing Rotors 11 – 12 Fault Finding & Testing Stators 13 – 14 Fault Finding & Testing DC Welders 15 – 20 Fault Finding & Testing 3 Phase Alternators 21 – 26 Fault Finding & Testing
illustrated in Figure 3. This is a fault occurring with phase A to ground fault at 8 km measured from the sending bus as depicted in Figure 1. The fault signals generated using ATP/EMTP are interfaced to the MATLAB for the fault detection algorithm. (a) Sending end (b) Receiving end Figure 3. Example of ATP/EMTP simulated fault signals for AG fault
In this paper, the calculation of double line to ground fault on 66/33 kV transmission line is emphasized. Figure 3. Double-Line-to-Ground Fault 2.4 Three-Phase Fault In this case, falling tower, failure of equipment or . ground fault, fault current on phase a is I a 0. Fault voltages at phase b and c are: V b .
Real Property Value/Acre 0 50,000 100,000 150,000 200,000 250,000 300,000 350,000 400,000 2010 2014 2016 2019 Net M&O Digest Residential Digest Commercial Digest Industrial Digest Combined Near West Air Cities Based on data from Georgia Dept. of Revenue Tax Digest Consolidated Summary 20
Extracting the RC4 secret key of the Open Smart Grid Protocol (OSGP) 9 OSGP data integrity For each message, generate a digest (hash value) using the secret "Open Media Access Key" (OMAK): OSGP-Digest-plaintext message Algorithm 12-byte OMAK 8-byte digest Data Concentrator (DC) Device Transmit message and its digest: plaintext digest OMAK OMAK
Cambridge International Examinations Cambridge Secondary 1 Checkpoint ENGLISH 1111/02 Paper 2 Fiction For Examination from 2018 SPECIMEN MARK SCHEME 1 hour plus 10 minutes’ reading time MAXIMUM MARK: 50 www.exam-mate.com
