Application of Plastic Region Bolt Tightening to Flange Joint Assembly: Behavior of Large Diameter Flange

In the past study the plastic region tightening has been applied to the bolted flange joint with smaller nominal diameter and its advantages have been demonstrated, however, behavior of the bolted flange joint with larger diameter is not investigated. Flange rotation of the bolted flange joint with large diameter increases when the internal pressure is applied. Gasket stress is not uniform and it may cause leak accident. So, it is necessary to investigate the behavior of the larger diameter flange. The present paper describes the behavior of bolted flange joint with large diameter under plastic region tightening. Firstly, API 20-inch flange joint tightened to the plastic region by bolt with a smaller diameter and superiority in the uniformity of the axial bolt force is demonstrated. And then the internal pressure is applied to the bolted flange joint and the behavior of the additional axial bolt force is demonstrated. The axial bolt force decreases with increasing the internal pressure, and the load factor is negative due to increasing of the flange rotation. However, the load factor of the bolted flange joint tightened to the plastic region by using the bolt with the smaller diameter approached zero. Using the bolts with smaller diameter is advantageous to the flange joint with the larger diamter, whose load factor is negative, to prevent the leakage. Additionally, the leak rate from the bolted flange joint is measured and the sufficient sealing performance is obtained.

Superheated Steam Test Rig for Compressed Non-Asbestos Gaskets Evaluation

This paper presents a Superheated Steam Test Rig and a Test Procedure for Compressed Non-Asbestos (CNA) Gaskets qualification. The Test Rig is a versatile assembly that can use different flange sizes and heating systems. It simulates a Superheated Steam Boiler with a water feed pump, pressurized water tank, pressure relief valve, condenser and the flange pair acting as the Steam generation unit. Heating can be provided by an oven or heating element bands. The Test Protocol enables the evaluation of the gasket performance in Superheated Steam in severe operational conditions like high pressure and temperature with thermal cycling. Different types of non-asbestos compressed gaskets were tested monitoring the leak rate and bolt load at each thermal cycle.

Recent Advances in Lower Bound Shakedown Analysis

The special interest in lower bound shakedown analysis is that it provides, at least in principle, safe operating conditions for sensitive structures or structural elements under fluctuating thermo-mechanical loading as to be found in power- and process engineering. In this paper achievements obtained over the last years to introduce more sophisticated material models into the framework of shakedown analysis are developed. Also new algorithms will be presented that allow using the addressed numerical methods as post-processor for commercial finite element codes. Examples from practical engineering will illustrate the potential of the methodology.

Numerical Simulations of Dynamic Fracture in Thin Pipes

We present a meshless methodology for large scale computations of fractureing thin shell structures subjected to internal pressure loads. The contribution is the first step of an efficient numerical methodology for such kind of events. In this paper, numerical simulations of large deformation dynamic fracture in thin shell structures using 3-D meshfree methods is presented. Due to the smoothness of the meshfree shape functions, they are well suited to simulate large deformation of thin shell structures while avoiding ill-conditioning as well as stiffening in numerical computations. The 3D meshfree representation allows high flexibility since thin structures as well as thick structures can be studied by the same methodology. The meshfree approach makes the methodology more flexible and independent as compared to finite elements, i.e. there is no need for creation of mesh. Dynamic fracture is modeled by a simple criterion, i.e. removing connectivity between adjacent nodes once a fracture criterion is met. The main advantage of such a 3-D meshfree continuum approach is its simplicity in both formulation and implementation as compared to shell theory approach, or degenerated continuum approach. Moreover, it is believed that the accuracy of the computation may increase because of using 3-D exact formulation.

Gas Leakage Correlation

A project has been carried out on the correlation of leakage measurements of different gases in specific conditions in bolted flanged assembly. The objectives were: • to check if the relationship between the leakage measurements of Helium, CO2, refrigerant R134a and CH4 would be similar to results of calculations that can be found when using correlation formulas, • to compare emissions of a typical laboratory fluid (Helium) with process fluids like methane, used in petrochemical plants, as well as CO2 and R134a, used in the refrigeration industry. Referring to TA Luft and VDI 2440, which specify a unique test for the certification of gaskets, the configurations of the testing installation used consist of flanges assembled with either PTFE based, graphite or fibre based gaskets. Different gasket loads and internal pressure were applied in order to simulate molecular, intermediate or laminar leakage flow rates. This article describes the test configurations and shows the leakage measurement results. It also compares the ratios between the leakage values and the results that would be obtained by predicting the leakage of another gas and/or in other pressure conditions, using Poiseuille or Knudsen laws.

Analysis of Contact Pressure Distribution on 3-Bolt Self-Energized Connector Seals

A novel design using 3 bolts for a self-energized seal connector is proposed for quick assembly applications. Contact pressure distribution on the surface of the seal ring during initial bolt-up and subsequent operating pressure is analyzed for 3″ and 10″ connectors using Finite Element Analysis. FEA is performed on a 3″ and 10″ ANSI RF flange assembly and contact pressure distribution on the RF gasket is compared with the tapered seal ring assemblies. Hydrostatic tests are carried out for the tapered seal and ANSI bolted connectors to evaluate maximum pressure at which leak occurs for both size assemblies.

Analysis of the Compression Behavior of Spiral Wound Gaskets

Recent updates to the ASME B16.20 standard for spiral wound gaskets now require inner rings on all flexible graphite and PTFE filler spiral wound gaskets [1]. This new requirement is intended to prevent the occurrence of inward buckling; however the addition of an inner ring can have significant impact on the spiral wound gasket compression behavior and possibly its sealing performance. This paper explores the compression behavior and sealing performance of spiral wound gaskets, with and without inner rings, and thus provides a better understanding of their performance capabilities in ASME B16.5 flanges, as well as their design and performance within ASME Boiler & Pressure Vessel Code Appendix 2 flanges [2].

Stress Analysis and a Design Method for Bolted Pipe Flanged Joints Subjected to Internal Pressure

This paper deals with the stress analysis of a pipe flange connection with a spiral wound gasket using the elasto-plastic finite element method when an internal pressure is applied to the pipe flange connections with the different nominal diameters from 2″ to 20″. The effects of the nominal diameter of the pipe flange on the contact stress distributions at the interfaces and the hub stress are examined. Leakage tests of the pipe flange connections with 3″ and 20″ nominal diameters were conducted and measurement of the axial bolt force was also performed. The results by the finite element analysis are fairly consistent with the experimental results concerning the variation in the axial bolt force (Load factor). By using the contact stress distributions and the results of the leakage test, the modified gasket constants are proposed and compared with PVRC values. As a result, it is found that the variations in the contact stress distributions are substantial due to the flange rotation in the pipe flange connections with the larger nominal diameter. The hub stress has been overestimated by ASME method. In addition, a method to determine the bolt preload for a given tightness parameter and a rational design method for pipe flange connections are demonstrated.

Investigation of Pressure Stress Concentration Factors for Intersecting Elliptic Bores With Circular Bores in Blocks

Stress concentration factors due to intersecting elliptic bores as well as circular bores in blocks have been thoroughly investigated by Badr [1] and Sorem et al [2]. Results of these investigations indicated that intersecting elliptic crossbores generate lower stress concentration factors than those due to intersecting circular crossbores. In this study, we investigate stress concentration factors for crossbores in blocks (cubical and rectangular) emanating from intersecting elliptic with circular holes. Comparing these results with those generated by Badr [1] for elliptic hole intersections; it was found that crossbores due to intersecting elliptic with circular bores generate higher hoop stress concentration factors. A regression analysis was also performed to determine a relationship between the stress concentration factors, the bore ratio (a2/a1) and the tilt angle θ.

Improved Construction of End Closure Seal Using D-Shaped Shearing Bolted Connection for Pressure Vessels

This paper describes a new improved structural type of end closure with use of D-shaped shearing bolts by which the head can be opened and closed easily & quickly, and use of metallic self-energized C-ring or O-ring as its sealing gaskets for pressure vessels. Strength analysis and calculation methods for its key components are recommended. This new structure has reliable safety, compact, easy assembly and cost effective in materials etc. Its size and operating pressure should be unlimited, so it can be widely used in industries.