Characterization of Piezoelectric Material Properties Using Atomistic Simulations

Damage monitoring in pipes and pressure vessels are important to ensure safety and reliability of these structures. Structural damage monitoring based on an actuator-sensor system is a promising technology to obtain real-time information for structural condition. Since piezoelectric materials in electromechanical systems can detect mechanical responses such stress and deformation as a sensor or perform a defined work as an actuator, piezoelectric actuators/sensors are extensively used in damage detection. In the design of piezoelectric actuators and sensors, it is important to know the properties of the piezoelectric material, in particular, piezoelectric constants to predict its actuation/sensing performance. In this study we determine a piezoelectric constant of ZnO using molecular dynamics simulations. We introduced a shell degree of freedom to the core-only atomic potential to enable polarization of the ion caused by an electric field. This modeling technique allowed for accurate piezoelectric response of the molecular structure.

Bolt Strength in Sectional Body Construction of Valves

ASME B16.34-2017 Section 6.4.2 provides requirements for valves with bolted body joints and threaded body joints. The section states that valves with bodies of sectional construction such that bolted or threaded body joints are subject to piping mechanical loads in addition to the pressure rating for which the valve is designed, shall satisfy the following requirements. For bolted joints, the requirement is a simple formula where the product of pressure rating class designation and ratio of area bounded by the effective outside periphery of a gasket or O-ring or other seal-effective periphery and total effective bolt tensile stress area are less than a certain constant. For bolts of strength less than 137.9 MPa, the value of constant reduces as a multiple of 50.76 times the bolt tensile strength in MPa required or provided in a sectional construction. Section 6.4.3 cautions that the minimum requirements of ASME B16.34 may fall short in scenarios due to valve design, special gaskets, high temperature service, creep characteristics etc. This paper reviews and studies this ASME B16.34 requirement which was triggered by failure of a valve with section body construction in the field. Traditionally valves have been considered as rigid bodies when analyzing a piping system for stresses, support loads, terminal point loads and deflections. The rigid modelling assumes the strength of the valve is much higher than an equivalent straight length of pipe. Some computer programs have a provision that permits modeling the valve as a multiple like 3- or 4-times pipe section modulus. This paper compares the strength of piping and valves based on inherent valve body thickness, body sectional bolting provided and strength of the equivalent piping flanges. The paper makes conclusions for the user to be aware of so that pre-emptive actions can be taken when using valves with sectional body construction.

Evaluation of Flange Calculations Using Strain-Based Acceptance Criteria

The Nuclear Power Plant KKG in Gösgen, Switzerland was designed according to the ASME Boiler and Pressure Vessel Code. The ASME BPVC, Section III, Appendix 11 regulates the flange calculation for class 2 and 3 components, it is also used for class 1 flanges. A standard for the determination of the required gasket characteristics is not well established which leads to a lack of clarity. As a hint different y and m values for different kinds of gasket are invented in ASME BPVC Section III [1]. The KTA 3201.2[2] and KTA 3211.2[3] regulate the calculation of bolted flanged joints in German nuclear power plants. The gasket characteristics required for these calculation methods are based on DIN 28090-1[4], they can be determined experimentally. In Europe, the calculation code EN 1591-1 [5] and the gasket characteristics according to EN 13555[6] are used for flange calculations. Because these calculation algorithms provide not only a stress analysis but also a tightness proof, it would be preferable to use them also in the NPP’s in Switzerland. Additionally, for regulatory approval also the requirements of the ASME BPVC must be fullfilled. For determining the bolting up torque moment of flanges several tables for different nominal diameters of flanges using different gaskets and different combinations of bolt and flange material were established. As leading criteria for an allowable state, the gasket surface pressure, the allowable elastic stress of the bolts and the strain in the flange should be a good and conservative basis for determining allowable torque moments. The herein established tables show only a small part according to a previous paper [7] where different calculation methods for determining bolting up moments were compared to each other. In this paper the bolting-up torque moments determined with the European standard EN 1591-1 for the flange, are assessed on the strain-based acceptance criteria in ASME BPVC, Section III, Appendices EE and FF. The assessment of the torque moment of the bolts remains elastically which should lead to a more conservative insight of the behavior of the flanges.

Evaluation of Bolt Strength Characteristics in Bolted Joints Using an Optical Fiber Sensor System

Bolted joints are used in many industrial products such as mechanical structures, automobiles, airplanes, chemical plants, and so on. In many cases, after the design of new products is finished, various tests on the bolt and bolted joints are carried out using actual parts to prevent accidents due to bolt loosening and fracture. At the same time, in the strength tests, external force measurement, axial bolt force measurement and so on are included. However, there are no advanced tests in which axial bolt strain distribution or bolt elongation in actual parts and so on are measured. Therefore, in this research, a new method for evaluating bolt strength characteristics using an optical fiber sensor system capable of measuring actual parts is demonstrated. First, a tensile strength test using an optical fiber sensor is carried out to measure strain distribution in a bolt, and a maximum strain value position in the measured clamp load-strain curve is shown. Then, the elongation at each part of the bolt is shown. Next, yield clamp bolt force is found using this sensor system in torque/clamp force testing. In addition, the measured yield clamp bolt force is compared with the values in the conventional measurement method and in the estimation formula. Also, discussed is the effective cross section area by which the stress at the engaged threads is calculated under tensile load. Finally, another case where an optical fiber sensor system is used for bolt fastening evaluation is discussed.

Leak Behavior and Prediction of Metal Ring Joint Gaskets in Simplified Leak Test With Grooved Platen

Pipe flange connection with metal gasket is used under high temperature and pressure in place required high sealing performance. It has been known that gasket compressive force, which is closely related the leakage decreases by internal pressure action. Since the pressure is very high in metal gaskets, the sealing performance evaluation in internal pressure action is important. However, there is little research that evaluates a little leakage, metal gasket is empirically used up to the present time. Therefore, evaluated sealing performance of metal gasket, it is necessary to clarify the sealing mechanism. In this study, evaluated effect that decreasing of gasket compressive force affects leakage in both octagonal type and oval type in ring joint gasket by simplified leak test using grooved platen and finite element method stress analysis, evaluation method of leakage in metal gasket is proposed. Based on this evaluation method, decision method of initial tightening force that guaranteed one amount of leakage to design internal pressure is shown in pipe flange connection with metal gasket.

A Novel Methodology to Optimize the Tightening Sequence in Bolted Flange Joints

Bolted flange joints are the most complex structural components of pressure vessels and piping equipment. Their assembly is a delicate task that determines their successful operation during the service life. During bolt tightening, it is very difficult to achieve uniformity of the target bolt preload due to elastic interaction and criss-cross talk. The risk of leakage failure under service loading is consequently increased because of the scatter of the bolt preload. In previous work, an analytical model based on the theory of circular beams on linear elastic foundation was proposed to predict the bolt tension change due to elastic interaction. Based on this model, this paper presents a novel methodology for the optimization of the tightening sequence. The target preload and the load to be applied to each bolt in each pass can be calculated to achieve uniform final preload and avoid bolt tension reaching yield under a number of specified tightening passes. The validity of the approach is supported by experimental tests conducted on a NPS 4 class 900 welding neck flange joint and by finite element analysis on this bolted joint using the criss-cross tightening and sequential patterns. This study provides guidelines for bolted flange joints assembly and enhances its safety and reliability by minimizing bolt tension scatter due to elastic interaction.

Optimum Design of Composite Pressure Vessel Based on 3-Dimensional Failure Criteria

Anisotropic composite cylinders and pressure vessels have been widely employed in automotive, aerospace, chemical and other engineering areas due to high strength/stiffness-to-weight ratio, exceptional corrosion resistance, and superb thermal performance. Pipes, fuel tanks, chemical containers, rocket motor cases and aircraft and ship elements are a few examples of structural application of fiber reinforced composites (FRCs) for pressure vessels/pipes. Since the performance of composite materials replies on the tensile and compressive strengths of the fiber directions, the optimum design of composite laminates with varying fiber orientations is desired to minimize the damage of the structure. In this study, a complete mathematical 3D elasticity solution was developed, which can accurately compute stresses of a thick multilayered anisotropic fiber reinforced pressure vessel under force and pressure loadings. A rotational variable is introduced in the formalism to treat torsional loading in addition to force and pressure loadings. Then, the three-dimensional Tsai-Wu criterion is used based on the analytical solution to predict the failure. Finally, a global optimization algorithm is used to find the optimum fiber orientation and their best combination through the thickness direction.

Study of Simplified Assembly Patterns With Load-Based Feedback and Preemptive Elastic Interaction Compensation

A total of 12 flange assemblies, spanning both class 300 and 600 were instrumented with ultrasonic transducers and observed following differing assembly patterns to gain insight into the BFJ elastic interactions. Each flange assembly was additionally tested to multiple load targets to monitor the overall sensitivity of interaction to load. Analytical work following the data collection led to the development of a simplified installation method and sequencing that dramatically reduces the work effort required to effectively close a joint while being independent of fastener condition or tool selection. The range of validity for the simplified method is further extended with linear multivariate solving techniques and accelerated joint “snugging” to promote joint stiffness. Limits on the acceptable load achievement was set to < 5% error on the average load and < 10% normalized standard deviation to be considered acceptable when targeting Appendix-O calculated loads of ASME PCC-1. Validation of the proposed method was undertaken by the University of Houston at the Bechtel WATC facility with support of Carber Engineering which included full size pressure testing following joint assembly. The observations made from the 60+ full size trials then served to validate FEA work towards the analysis of the remaining sizes of class 300/600 from 4″ to 24″.

New Leakage Requirements for ASME B16.20 and Current Generation Spiral Wound Gaskets

The ASME B16.20 Metallic Gaskets for Pipe Flanges standard was extensively revised in 2017 [1]. One of the significant changes is the introduction of maximum permissible leakage rate. This marks a landmark introduction of an actual leakage performance criterion into ASME B16.20, a most welcome advance. A common maximum permissible leakage rate of 0.0137 mg/s-m (7.67E−10 lb/s-in) is specified for all sizes and pressure classes of finished spiral wound gaskets, that is, including the windings and any or no gauge rings for that particular gasket. Test conditions are defined — ambient temperature and calibration gas with a known methane concentration and flow rate of 1 L/min. The test pressure is defined by the pressure class: 20 bar (290 psi) for Class 150 and 40 bar (580 psi) for Class 300 and above. The qualification parameters listed in B16.20-2017 include prescribed gasket seating stress targets which also vary by pressure class. These gasket seating stress requirements are defined as 35 MPa (5,000 psi) for Class 150, 56 MPa (8,000 psi) for Class 300 and Class 400, and 70 MPa (10,000 psi) for Class 600 and above. Three questions will be explored in this paper. First, to what tightness does the new B16.20 spiral wound gasket leakage rate criterion correspond? Second, do current generation spiral wound gaskets meet this criterion? Several commercially available spiral wound gaskets will be analyzed and compared to the new B16.20 requirements. Leak rates and tightness at the new B16.20 performance qualification test conditions can be determined using publicly available, published Room Temperature Tightness (ROTT) test constants for these gaskets. Finally, an exploration of Assembly Tightness compared to Operating Tightness for a selection of spiral wound gaskets will be presented and compared to the new B16.20 Performance Testing requirements. This exploration of the new maximum leakage performance criterion in ASME B16.20-2017 will help to familiarize the end user with a valuable new aspect of this gasket standard as well as how the current generation of spiral wound gaskets meets that criterion using publicly available ROTT performance data.

Estimating Collapse Pressure of Centralizer Subs From Machine Learning Models

Centralizer subs are run in conjunction with the casing strings in the oil/gas wells to ensure that the casing is centralized while it is installed down hole. Centralizer subs are fabricated of stronger material than the casing strings and designed such that it can sustain a higher collapse pressure than the attached tubing string. A typical centralizer sub is a tube with some complex geometrical features, so the collapse pressure of a centralizer sub can only be estimated by conducting a finite element analysis or subjecting it to a collapse pressure test. Both the options are time consuming and expensive. In this work, a machine learning based regression model is used to derive a parametric equation for calculating the collapse pressure of a centralizer sub. The data needed to train and cross validate the regression model is obtained from finite element analysis (FEA). This machine learning based equation provides a closer estimate of the collapse pressure of the centralizer subs to the results obtained from the FEA than the existing collapse prediction equations from API RP 1111. This machine learning based estimation of collapse pressure will help in correctly predicting the collapse rating of the centralizer sub without performing FEA or testing for each individual subs. This approach of building machine learning models from data generated from FEA can be used for analysis of other equipment as well. With the availability of past data collected/generated through years, the recent advances in machine learning can be used to save time and resources.