Modeling Gas-Liquid Head Performance of Electrical Submersible Pumps

This study presents a new gas-liquid model to predict Electrical Submersible Pumps (ESP) head performance. The newly derived approach based on gas-liquid momentum equations along pump channels has improved the Sachdeva model [1, 2] in the petroleum industry and generalized the Minemura model [3] in the nuclear industry. The new two-phase model includes novel approaches for wall frictional losses for each phase using a gas-liquid stratified assumption and existing correlations, a new shock loss model incorporating rotational speeds, a new correlation for drag coefficient and interfacial characteristic length effects by fitting the model results with experimental data, and an algorithm to solve the model equations. The model can predict pressure and void fraction distributions along impellers and diffusers in addition to the pump head performance curve under different fluid properties, pump intake conditions, and rotational speeds.

An Approach for Cost Effective Assessment in Risk-Based Maintenance as a Life-Cycle Maintenance (LCM) Model

For aged power plants in Japan, the life extension with retaining the safety and cost-effective beyond the original design lifetime is proposed. Therefore it is important to minimise the risk and maintenance cost to keep operating the plants. Life-Cycle Maintenance (LCM) is proposed for optimising maintenance plan with reliability in the life of the plants. Risk Based Maintenance (RBM) is included in the LCM to assess the risk of components in the plants. LCC and the investment assessment may be also conducted to decide the most cost effective maintenance strategy, if several maintenance strategies are proposed in RBM. In this paper, concept and an application of the LCM are described to optimise maintenance plan in the lifetime of a plant. It was found that the LCM is quite useful method to plan the most cost effective maintenance strategies in the lifetime of the plant.

On the Governing Contingency for Pressure-Relief Device Sizing

Equipment and piping systems that operate under pressure need to be protected from excessive overpressure. This is accomplished with the installation of pressure-relief devices, which must be properly sized and specified for the intended service conditions. To adequately size a pressure-relief device to provide overpressure protection for equipment and piping, several relief event scenarios always should be considered. Ultimately, overpressure protection is provided with the installation of pressure-relief devices that are specifically sized, specified and installed for the postulated governing overpressure contingency. Too often, pressure-relief devices are sized based on the possibly erroneous presumption that fire exposure will be the most likely governing contingency. Historically, the fire exposure contingency has been emphasized to such an extent that pressure-relief devices often are assessed solely on the basis of fire exposure. Substantiation of this presumption, however, is not obvious in the literature. In fact, one can argue that there are many relief contingencies other than fire exposure which may govern the relief device size. Furthermore, neglecting consideration of other relief contingencies can present a potentially dangerous situation. This paper presents results from a study intended to examine which overpressure relief contingency, if any, most often governs the size of relief devices that are used to protect equipment and piping systems. From previous related work, seven relief contingencies are described and emphasized by the author. For this study, relief device sizing data was compiled from a number of chemical and petrochemical project applications to provide a reasonable sample of contingencies that governed the sizes of existing and new safety-relief valves and rupture discs [1,2,3].

High Pressure Fluctuations Induced by Safety Valves Operating With Liquids at Very Low Lift

This paper deals with the valve disc vibrations occurring during safety valve opening transient. These vibrations always induce pressure fluctuations that are not damped if pressure is not sufficiently increased. The tests, performed on three different safety valves, showed heavy pressure fluctuations in the valve inlet connecting pipe. For connecting pipe lengths over 0.7 m, excessive pressure fluctuations were measured even in the protected device. The analysis of vibration inception and development is presented, showing that the phenomenon is driven by an harmonic self-exited motion of the valve disc coupled to a standing wave system in the connecting pipe. Vibration frequencies always strongly exceeded the spring-disc natural frequency, meaning that the disc movement occurred between a fixed position of the stem head and the disc seat on the nozzle. No impact on this latter surface was ever detected. On the contrary, significant damages of the stem-disc coupling were observed. Finally, the influence of plant and valve parameters that affect the pressure fluctuation amplitude is presented and discussed.

The Assignment of SIL Targets to Overpressure Protection in Reactive Systems

The assignment of performance targets, or target Safety Integrity Levels (SILs), is a critical step in the application of the Safety Instrumented System (SIS) standards, i.e., ANSI/ISA S84.0.01-1996, IEC 61508 and IEC61511. Although the SIL is a key concept in the implementation of the standards, the development and application of a method for determining the target SIL has been left to the owner/operator. The standards do, however, provide guidance on this topic and present a number of techniques that can be considered, including risk matrix, risk graph, and Layers of Protection Analysis (LOPA). Generally, the methods for SIL assignment are qualitative or semi-quantitative risk assessment methods that are based upon the judgments of an assignment team. In most cases the methods based on expert opinion and limited historical data are adequate. However, in the case of overpressure protection for reactive systems, the number and complexity of the scenarios often overwhelms these simplified approaches. There are warning signs that can aid in the identification of cases where the simplified methods may break down and provide non-conservative results. In cases such as this, a quantitative assessment should be conducted to evaluate the likelihood of SIF demands, the risk reduction supplied by the other protection layers, with the aim of determining the risk reduction required from the instrumented overpressure protection system.

Field Vibration Tests and Dynamic Stability Analysis of a Full-Scaled Tainter-Gate

This study presents results from in-air and in-water field vibration tests of a 29-ton full-scaled Tainter-gate installed on a river in Japan. These tests were conducted to confirm the validity of our theoretical analyses especially for a large value of Froude number. First, with the gate raised, an in-air experimental modal analyses, using an impact hammer and accelerometers, was conducted to determine the natural frequencies and the damping ratios for two modes of gate vibration. These two modes corresponded to the rigid body vibration of the whole gate around the trunnion pin and the streamwise rotational vibration of the skinplate. Subsequently, with the gate again lowered and exposed to flowing water, the gate vibration characteristics were carefully measured. Only weak, unsynchronized vibrations were recorded and the gate was found to be dynamically stable. A theoretical analysis developed to predict the hydrodynamic pressure, the vibration frequency ratios and the dynamic stability were applied to the full-scaled gate. The theoretical analysis correctly predicted both the measured frequency ratios and the gate’s dynamic stability.

Theoretical Investigation on Flow Rate at the Maximum Efficiency Point in the Design of Impeller Blade in Centrifugal Pump

This paper presents a theoretical investigation of the flow rate at the maximum efficiency point in the design of impeller blade in centrifugal pump. An energy balance was performed at the trailing edge of impeller outlet in the rotating flow passage of centrifugal pump. The evaluation shows that, when the fluid particles straight forward tangential velocity is one third of the impeller blade’s peripheral velocity and the fluid particles circular forward tangential velocity is two third of the impeller blade’s peripheral velocity at the trailing edge of the impeller outlet, the maximum hydraulic energy output, that is, the maximum efficiency point is obtained.

An Integrated Approach for the Structural Reliability Evaluation of Fast Breeder Reactor Components

For the improvement of structural design of fast breeder reactors, a new method for the optimization of structural reliability is proposed. This method approximates failure probability of a component by a linear formulation of various design variables. The formulation is obtained by a theoretical calculation extended by numerical considerations based on Monte Carlo simulation. This method allows a designer to optimize reliability without trial-and-error type calculations.

Developing an Efficient, Predictive, Risk Based Inspection/Maintenance Program for Recovery and Power Boilers

Risk Based Inspection (RBI) is intended to be a simple, logical, repeatable, documented method of determining equipment inspection frequencies and inspection scopes/methods. With consistent boiler tube thickness measurements, developed boiler tube engineering standards and well documented inspection/repair information, it is possible to set up an effective RBI program for predicting boiler component conditions and accurately plan boiler inspections/repairs far into the future. Inspection efforts are then concentrated, logically, on the documented ‘problem’ and high risk areas of the boiler. Inspection scopes and frequencies are reduced on the more benign, low risk areas. All boiler components will have documented and accepted justifications detailing how the component inspection scopes and frequencies were developed.

Reliability Analysis of the Tube Hydroforming Process Using Fuzzy Sets Theory

Tube hydroforming currently enjoys increasingly widespread application in industry, especially in the automotive industries, because of several advantages over traditional methods. Reliability analysis as a probabilistic method to deal with the probability of the failure of the structure or the system has been widely used in industry. A new reliability analysis approach for the tube hydroforming process using the fuzzy sets theory is presented in this paper. The stress of the hydroformed tube is related to several parameters, such as geometry, material properties, and process parameters. In most cases, it is difficult to express in a mathematical formula, and its relative parameters are not random variables, but the uncertain variables that have not only randomness but also fuzziness. In this paper, the finite element method is applied as a numerical experiment tool to find the statistical property of the stress directly by a fuzzy linear regression method. Based on the fuzzy stress-random strength interference model, the fuzzy reliability of the tube hydroforming process can be evaluated. A tube hydroforming process for cross-extrusion is then introduced as an example to illustrate the approach. The result shows that this approach can be extended to a wide range of practical tube hydroforming process.