Factors Influencing Nut Factor Test Results

Nut Factor is used to establish a bolt load for a given applied torque in bolted joint assembly. In previous papers the effects of different factors influencing Nut Factor results were examined, which included the type of anti-seize, bolt and nut material, bolt diameter and amount of anti-seize applied. This paper examines those factors further and then includes additional factors which have been shown to have significant effect on the measured Nut Factor. The knowledge of these factors has been used to adjust the proposed ASTM specification for determining Nut Factor. It is also relevant to application in the field and to ensure that any testing conducted in a laboratory will be applicable in the field.

Investigation of Smooth Pipe Bends Under the Effect of In-Plane Bending

Pipe bends are frequently used to change the direction in pipeline systems and they are considered one of the critical components as well. Bending moments acting on the pipe bends result from the surrounding environment, such as thermal expansions, soil deformations, and external loads. As a result of these bending moments, the initially circular cross-section of the pipe bend deforms into an oval shape. This consequently changes the pipe bend’s flexibility leading to higher stresses compared to straight pipes. Past studies considered the case of a closing in-plane bending moment on 90-degree pipe bends and proposed factors that account for the increased flexibility and high-stress levels. These factors are currently presented in the design codes and known as the flexibility and stress intensification factors (SIF). This paper covers the behaviour of an initially circular cross-sectional smooth pipe bend of uniform thickness subjected to in-plane opening/closing bending moment. ABAQUS FEA software is used in this study to model pipe bends with different nominal pipe sizes, bend angles, and various bend radius to cross-sectional pipe radius ratios. A comparison between the CSA-Z662 code and the FEA results is conducted to investigate the applicability of the currently used SIF factor presented in the design code for different loading cases. The study showed that the in-plane bending moment direction acting on the pipe has a significant effect on the stress distribution and the flexibility of the pipe bend. The variation of bend angle and bend radius showed that it affects the maximum stress drastically and should be considered as a parameter in the flexibility and SIF factors. Moreover, the CSA results are found to be un-conservative in some cases depending on the bend angle and direction of the applied bending moment.

Temperature Measurement of an Array of Heated Rods Subjected to Vacuum Drying Conditions

During vacuum drying of used nuclear fuel canister, helium pressure is decreased to as low as 67 Pa to promote evaporation and removal of water remaining in the canister following draining operation. At low pressures associated with vacuum drying, there is a temperature jump (thermal resistance) between the solid surfaces and helium in contact with them. This temperature jump increases as the pressure decreases (rarefied condition), which contributes to the fuel assembly’s temperature increase. It is important to keep the temperature of the fuel assemblies below 400°C during vacuum drying to ensure their safety for transport and storage. In this work, an experimental apparatus consisting of a 7×7 array of electrically heated rods maintained between two spacer plates and enclosed inside a square cross-section stainless steel pressure vessel is constructed to evaluate the temperature of the heater rods at different pressures. This geometry is relevant to a BWR fuel assembly between two consecutive spacer plates. Thermocouples are installed in each of the 49 heater rods, spacer plates and enclosure walls. They provide a complete temperature profile of the experiment. Different pressures and heat generation relevant to vacuum drying conditions are tested. The results showed that the maximum temperature of the heater rods increases as the pressure decreases. The results from these experiments will be compared to computational fluid dynamics simulations in a separate work.

Load Factors for Concrete Wall Pipe Penetrations With a Wall Mounted Welded Plate

The bending moments imposed on welded plate anchors that are part of embedded pipe wall penetrations are often overestimated in the structural evaluations of these penetrations. For this type of restraint, the pipe is embedded in a concrete wall penetration with a welded plate mounted on the surface of the wall. This penetration is typically modeled with a single 6 degree of freedom (DOF) restraint at the plate in the pipe stress analysis. This approach can lead to overestimated loads on the welded plate and the mounting anchor bolts because no credit is taken for reaction on the embedded portion of the pipe. A significant portion of the bending moments from piping on both sides of the penetration is transferred directly to the concrete wall by the normal reaction on a fully grouted pipe, thus reducing loads on the steel plate and the mounting anchored bolts. The objective of this study is to determine load factors for bending moments from both sides of the pipe penetration on the anchored steel plate. A parametric study is performed using ANSYS models of a pipe fully embedded in a concrete wall penetration with a welded plate mounted on one side of the wall by anchor bolts. Various pipe diameters, concrete wall thicknesses and plate thicknesses are considered. For each model, the loading on the plate is compared to the loading applied at the free end of the pipe. Load factors are developed for use in the structural evaluation of the welded plate and the mounting anchor bolts. The maximum compressive bearing pressure at the concrete wall is also calculated for use in the structural evaluation of these types of pipe supports.

Additive Manufacturing of Pressure Vessels (With Plating)

Additive manufacturing (AM) allows for product development with light weight, fewer machining constraints, and reduced costs depending on the application. While AM is an emerging field, there is limited research on the use of AM for pressure vessels or implementation in high stress environments. Depending on the design approach and limitations of traditional material-removal fabrication techniques, AM parts can achieve high strength-to-weight ratios with reduced manufacturing efforts. Coupling AM with alternative metal and composite materials allows for unique designs that have high strength-to-weight ratios for pressure-based applications. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has conducted research on a number of these composite designs, focusing on the use of carbon fiber or metal plating with the AM materials. Before implementing AM in field tested prototypes, JHU/APL performed strength limitation tests on AM pressure vessels (PVs) in the laboratory to prove their effectiveness. PVs constructed with varying thicknesses and coating techniques were divided into three groups, each with a uniform wall thickness that provided a congruent surface area to withstand higher pressures. These PVs were then paired with one of three coating/plating technologies, forming a trade matrix of varying AM thicknesses and plating techniques. Once fabricated and plated, these test PVs were hydro-statically tested at increasing pressure levels. This pressure testing demonstrates that the use of AM to create PVs, when paired with specific plating techniques, can result in structures with significant strength capabilities at lighter than normal PV weights. Furthermore, JHU/APL has begun to test the AM PVs in a number of research projects. Such testing is desired because these unique parts can be easily manufactured in shapes and volumes that were previously unattainable through common manufacturing techniques. AM parts are now commonly used in air-frames; however, in higher pressure underwater scenarios AM’s capabilities are unproven. JHU/APL has begun to apply this new and emergent field to the effective design of AM PVs, which can play a significant role in the field of underwater vehicles and similar projects.

Fatigue Life and Reliability Consideration During Field Repair of Coke Drum and Piping

Aging coke drums and their connected overhead piping in delayed coking units experience fatigue cracks which most commonly occur at the skirt junction and high stress pipe welds. This paper presents 2-case studies of this new cost-effective repair methodology with fatigue resistant design upgrade. The first case study applies to coke drum weld build-up solid skirt crack repair and the second for overhead vapor line weld crack repair. This paper presents new field repair methodology which could also improve long term fatigue resistance. It also suggests optimizing the thermal operation & thermal gradients of coke drums for further reliability improvement. Based on FEA, successful field execution and our experience, these case studies demonstrate a long term improvement in reliability and fatigue life of the order of 2.5 to 3 or higher especially if combined with thermal operation optimization.

Experimentally Benchmarked Computational Fluid Dynamics Simulations of a 7×7 Array of Heated Rods Within a Square-Cross-Section Enclosure Filled With Rarefied Helium

Computational fluid dynamics simulations of a 7×7 array of heated rods within a square-cross-section enclosure filled with rarefied helium are performed for heat generation rates of 50 W and 100 W and various helium pressures ranging from 105 to 50 Pa. The model represents a section of nuclear fuel assembly between two consecutive spacer plates inside a nuclear canister subjected to during vacuum drying process. A temperature jump model is applied at the solid-gas interface to incorporate the effects of gas rarefaction at low pressures. The temperature predictions from simulations are compared to measured temperatures. The results showed that when helium pressure decreased from 105 to 50 Pa, the maximum temperature of the heater rod array increased by about 14 °C. The temperatures of the hottest rod predicted by simulations are within 4°C of the measured values for all pressures. The random difference of simulated rod temperatures from the measured rod temperatures are 3.33 °C and 2.62 °C for 100 W and 50 W heat generation rate.

Vibration Testing of Compression Joints

The use of compression joints in ASME Nuclear Class 2 and 3 small diameter piping systems has become increasingly popular because their installation does not require welding, and therefore saves time, money, and radiation dose. An important question is whether these types of joints can be a practical alternative to socket welds in piping systems subject to vibration. There have been numerous operating experience events where socket welds have developed cracks due to high cycle fatigue. On the other hand, parts of compression joints plastically deform the pipe to grip and create their sealing connection; the application of a high cycle vibration load to an already plastically strained pipe might lead to premature failure. It is desired to know whether at least one type of compression joint would perform better or worse than socket welds in such an environment. In this paper, a testing methodology is described, in which one supplier’s coupling joint design was tested for vibration loading in tubing assemblies of varying sizes. The intended application for these joints is in an Electro-Hydraulic Control system at a northeastern Boiling Water Reactor plant. Industry experience reports have identified past vibration problems in this system at other plants. A test setup was devised, in which multiple specimens could be tested simultaneously by adjusting specimen natural frequency, shake table speed, and input acceleration. Fatigue Strength Reduction Factors were derived, allowing the resistance to fatigue failure to be quantified. Both compression joints and socket welds were tested using the same procedures, in order that the fatigue damage resistance could be compared between the two types of joints.

Acceptable Levels of Corrosion for Pressure Boundary Bolted Joints

This paper outlines recent work in the field of pressure boundary bolted joint integrity and the effect of corrosion on bolted joint components. It summarizes recent analysis and testing which determined the risk to joint integrity or catastrophic failure associated with corrosion of the joint components; bolts, nuts and flanges. The paper details, at a high level, the work performed and outlines the limits to corrosion that can be applied in the field for each component as an inspection limit to trigger planned replacement or emergency shut down.

Benchmarking of Explicit Dynamic Finite Element Analysis for Storage and Transportation Casks Under Impact Loading Conditions

Impact analyses for storage and transportation cask drop tests were performed using the explicit dynamic finite element analysis code to demonstrate analytical accuracy and benchmark the analytical code. The test series for this benchmarking were provided by Sandia National Laboratories (SNL) as the Structural Evaluation Unit Benchmark Problem Statement. 30 foot and 120 foot drop test cases in which the test unit was dropped from 30 feet and 120 feet onto an essentially rigid target were selected as the benchmarking problems. A comparison of deformation and acceleration between the actual cask drop tests and those predicted by explicit dynamic finite element analysis performed using LS-DYNA was performed in this paper. The simulation results showed reasonably good agreement with respect to deformation and acceleration between the calculated and the measured result by adjusting the material properties of the impact limiter to match the amount of crush.