Measurement and Simulation of Water Hammer in Piping Systems Including Junction Coupling

For the analysis of the effects of fluid-structure interaction (FSI) during water hammer in piping systems, a complex test facility was constructed. Resonance experiments with movable bends in two system configurations were carried out. The pressure and the displacement of the bend were recorded. The aim was to reproduce the results with two coupled codes: a one-dimensional solver based on the method of characteristics (MOC) for the hydraulic system and a three-dimensional solver based on the finite element method (FEM) working with one-dimensional beam elements for the structural system. The calculation included junction and friction coupling. The models were fine-tuned separately. For this purpose, special measurements were carried out. These included the determination of the structural damping, the friction factor, the influence of the bending of the anchorage, etc. After the validation of the models, the results of the coupled calculations were compared against the measurements, the performance of the coupled codes was evaluated and the most important physical effects were analyzed and are discussed.

Experience With Using Code Case 2564 to Design and Certify an Impulsively Loaded Vessel

Code Case 2564 for the design of impulsively loaded vessels was approved in January 2008. In 2010 the US Army Non-Stockpile Chemical Materiel Program, with support from Sandia National Laboratories, procured a vessel per this Code Case for use on the Explosive Destruction System (EDS). The vessel was delivered to the Army in August of 2010 and approved for use by the DoD Explosives Safety Board in 2012. Although others have used the methodology and design limits of the Code Case to analyze vessels, to our knowledge, this was the first vessel to receive an ASME explosive rating with a U3 stamp. This paper discusses lessons learned in the process. Of particular interest were issues related to defining the design basis in the User Design Specification and explosive qualification testing required for regulatory approval. Specifying and testing an impulsively loaded vessel is more complicated than a static pressure vessel because the loads depend on the size, shape, and location of the explosive charges in the vessel and on the kind of explosives used and the point of detonation. Historically the US Department of Defense and Department of Energy have required an explosive test. Currently the Code Case does not address testing requirements, but it would be beneficial if it did since having vetted, third party standards for explosive qualification testing would simplify the process for regulatory approval.

Towards the Development of Filament Wound Composite Structures Submitted to Very High Internal Pressure, Based on Complex Geometry Shapes

Industrial applications, especially composite structures bearing high internal pressure, and fabricated using the filament winding process face certain difficulties like the reinforcement of complex shapes, as well as the correct placement of fibers over the surface of a mandrel. In some cases the definition of the manufacturing parameters respond more to cost or time criteria rather than engineering standards, reducing largely the advantages of the said manufacturing process. In order to overcome these obstacles, this research aims to propose a solution that permits to fabricate complex shapes with the desired winding angles at a certain region of complex-shaped mandrels. A numerical tool that simulates the placement of fiber tows over the surface of complex geometries is developed and validated by means of the fabrication of convex and concave composite structures using detachable mandrels. Previous results show that it is feasible to wind complex geometries with good accuracy.

Image Quality Assessment of Four Different Computed Radiography Systems for NDT Applications

Computed radiography (CR) is a digital radiographic technique, which uses very similar equipment to conventional radiography except that in place of a film to create the latent image, an imaging plate (IP) made of a photostimulable phosphor is used [1]. CR systems are commonly used in medical applications since they have proven reliability over more than two decades. Conversely, the NDT community has discussed the efficacy of film replacement by CR for more than 15 years. Though some standards were introduced in 2005 (ASTM E 2033, CEN EN 14784-2) and others are on the way (PR ISO 17636-2), CR is actually not included within the French RCCM, while the technique is commonly used in US for nuclear applications according to ASME (Section V, article 2). Since 2006, AREVA has been evaluating the performance of CR in comparison to conventional RT in the framework of EN 14784 for the digital part and the RCCM for the conventional part. The objective was to build a technical justification report to eventually support introduction of CR into the RCCM. In 2009 the subject gave rise to collaboration between AREVA NP – NETEC and EDF-CEIDRE, for a joint project to establish performance limits of CR towards EN 14784 specifications and RCCM image quality indicator (IQI) requirements [2]. In this paper, we present performance comparison results of four different CR systems. The measurements were conducted in 2012 and they demonstrate the current state of achievable image quality in CR. The performance has been evaluated for steel with a thickness range of 20÷60 mm using an Iridium 192 gamma source. Image quality has been assessed in terms of EN 462 and ASTM (E 747, E 1742) IQI. The results have been scored considering the PR ISO 17636-2, RCCM 2007, and ASME V-2010. This also permitted comparison among the different standard requirements.

Experimental Study of Two-Phase Flow Induced by Cavitation Through a Safety Relief Valve

The goal of this study is to understand the behavior of a safety relief valve in presence of a two-phase flow induced by cavitation, in which the mass flux tends to be reduced. Two distinct safety relief valves are tested: an API 2J3 type and a transparent model based on an API 1 1/2G3 type. Instead of using a spring, the design of both valves allows the adjustment of the disk at any desired lift. Tests are conducted with water at ambient temperature. Results show a similar influence of cavitation on the flow characteristics of both valves. The liquid pressure recovery factor FL, which is normally used to identify a choked flow condition in a control valve, is experimentally determined in a safety relief valve. The existence of a local minimum located at a height position L/D = 0.14 indicates in this position, a change on the flow characteristics of both valves. It is verified that the existence of a local minimum in the liquid recovery factor is related to the minimum cross section of the flow, which does not remain constant for every lift positions. Furthermore, it is remarked that in the case of the 2J3 safety valve, the blow down ring adjustment has significant influence on the location of the minimum cross sections of the flow.

On the Adequacy of Shell Models for Predicting Stresses and Strains in Thick-Walled Tubes Subjected to Detonation Loading

This paper analyzes the adequacy of shell models for predicting stresses and strains in thick-walled tubes subjected to detonation loads. Of particular interest are the large axial strains which are produced at the inner and outer surfaces of the tube due to bending along the tube axis. First, comparisons between simple shell theory and a static finite element model are used to show that the axial strain varies proportionally with wall thickness and inversely with the square of the axial wavelength. For small wavelengths, this comparison demonstrates nonlinear behavior and a breakdown of the shell model. Second, a dynamic finite element model is used to evaluate the performance of transient shell equations. This comparison is used to quantify the error of the shell model with increasing wall thickness and show that shell models can be inaccurate near the load front where the axial curvature is high. Finally, the results of these analyses are used to show that the large axial strains which are sometimes observed in experiments cannot be attributed to through-wall bending and appear to be caused instead by non-ideal conditions present in the experiments.

Deep Well Drilling Applications

The majority of oilfield Wellhead and Tree equipment has been designed with guidance from codes API 6A and 17D. However, their design methods are not the most appropriate for the new High Pressure High Temperature (HPHT) applications; equipment rated above 15 ksi (103 MPa) Working Pressure and/or above 350 °F (177 °C). This paper discusses the limitations of established design methods and presents more suitable methods for HPHT applications. FEA is well established as a stress analysis method for use in conventional Pressure Vessel design; however it is not so well established for load bearing interfaces. This leaves a gap in our Design Methods, since load bearing interfaces are intrinsic to Wellhead Equipment Pressure Vessel design. Intrinsic because many of our Pressure Vessels are “capped” by hangers and connectors instead of flanges; if a hanger Load Shoulder fails then the Pressure Vessel above it has failed. Unique to the oilfield are infrequent but extremely high loads. These loads are much higher than the Working Condition and in most cases they stem from field testing and emergency situations. If the established ASME methods are used for these cases certain projects may not be viable.

Microstructural Modelling of P91 Martensitic Steel Under Uniaxial Loading Conditions

The changing face of power generation requires an improved understanding of the deformation and failure response of power plant materials. Important insights can be obtained through microstructurally motivated modelling studies. This paper deals with the comparisons of predictions of the mechanical response of a power plant steel (P91), obtained from a model with a measured microstructure with those obtained from a numerically simulated microstructure. Electron backscatter diffraction (EBSD) is employed to obtain the orientation of the martensitic grain structure of the steel. This information is incorporated within a representative volume element (RVE) to represent the material microstructure. A non-linear, rate dependent, finite strain crystal plasticity model is used to represent the deformation of the material, with the orientation of each finite-element integration point determined from the EBSD analysis. The deformation under uniaxial tension is analysed. Due to the inhomogeneous microstructure strong strain gradients are generated within the RVE even under remote homogenous strain states. It is seen that peak stress/strain states are associated with particular features of the microstructure. The results taken from the model are compared with those obtained with an equiaxed microstructure generated using the Voronoi tessellation method.

Effect of the Loading Rate on Failure of Composite Pressure Vessel

A multi-scale model has been successfully applied to the simulation of the effects of pressurisation rate on damage accumulation in carbon fibre/epoxy plates and composite pressure vessels. The results of the simulations agree with experimental results and reveal that the point at which the structures become unstable in a monotonic pressurisation test depends on the speed of loading. The faster the loading rate the higher the applied stress at which the composite structure becomes unstable. The mechanism which governs this behaviour is seen to be the viscoelastic nature of the matrix material through which stresses are transferred from broken to neighbouring intact fibres. At loading rates that allow greater relaxation of the resin around fibre breaks neighbouring fibres are subjected to increased loads over a significantly greater length, leading to further earlier breaks.

A Novel Procedure for Measuring the Dynamic Fracture Toughness Using Direct Tension Hopkinson Bar

In this paper a technique for determining the dynamic fracture toughness is presented. The proposed experimental method is based on the use of the direct tension Hopkinson bar allowing accurate control of the generated tensile stress pulse and avoiding limitations showed by other similar configurations. The sample geometry investigated here is the circumferentially cracked bar in tension (CCB(T)). This geometry does not require special fixtures to be hold between the bars and does not suffer loss of contact during dynamic loading. Numerical simulation showed that, at least for high toughness materials, the relative displacement of the bars can be used to have a direct measure of the CTOD that can be used to derive the corresponding J-integral value.