Abstract Bolted pipe flange connections with metallic flat gaskets or ring type joint (RTJ) gaskets are used under higher pressure and higher temperature. However, a sealing mechanism is not known and a design method is not established how to determine bolt preload for preventing leakage from the connection with metallic gaskets. In addition, the characteristics of the connection are not known when oval and octagonal gaskets are used. In previous paper, when the contact stress of metallic flat gasket reaches the stress at plastic deformation inflection point, the leak rate is decreased rapidly. However, the leak rate could be measured up to 1.0 × 10 −5 Pa · m 3 /s level. The objectives of the paper are to measure the leak rate of the metallic flat gasket of which the contact stress is over the stress at plastic deformation inflection point, and to measure the leak rate of 1.0 × 10 −9∼10 Pa · m 3 /s level in the flat metallic gasket in the platen tests and the connection with RTJ gaskets. In addition, the characteristics of the connection are examined when oval and octagonal gaskets are used. As a result, it is found that the leak rate for the metallic flat gasket can be measured around 1.0 × 10 −9∼10 Pa · m 3 /s in the platen tests when the contact stress of aluminum gasket reaches the stress at plastic deformation inflection point and more while the leak rate of SUS 304 flat gasket is around 1.0 × 10 −7∼8 Pa · m 3 /s even if the contact stress is over 1.3 times of the stress at plastic deformation inflection point. In addition, the sealing characteristics of the connection with oval gasket are shown to be better than that with octagonal gasket. From a laser microscope observation, it is found that the contact area of oval gasket in the connection is smaller than that of octagonal gasket in the connection.

Abstract The objective of the present paper is to examine the effect of tightening procedure on scatter in axial bolt forces and the bolt forces distribution in bolted gasketed pipe flange connections where spiral-wound gaskets and PTFE blended gaskets are used. The scatter in the axial bolt forces was examined by several tightening procedures which are JIS B 2251, ASME PCC-1 legacy, ASME alternative #1, #2, #3 and 3 rounds method procedures in ASME 24“ bolted gasketed pipe flanged connection. The leak rate of the tightened bolted flanged connections was also measured. Furthermore, the assembly efficiency based on both axial bolt forces and the tightness parameters of the bolted pipe flange connections was calculated and compared. The obtained results are as following. First, the leak rate of the connection tightened by JIS procedure is the lowest of all the tightening procedures. Second, the assembly efficiency based on axial bolt forces tightened by JIS procedure is the highest, and the assembly efficiency based on tightness parameters according to JIS procedure is also the highest. Third, the assembly efficiency based on tightness parameters is smaller than that based on the axial bolt forces. As a conclusion, the JIS B 2251 procedure is the most efficient tightening procedure of all the tightening procedures tested in the present study and the assembly efficiency based on the tightness parameters is suggested to design bolted connections for more safety.

Abstract In the valve industry, there is combined demand from the end-users for fugitive emissions reduction and energy efficiency improvement through the reduction of stem/packing friction forces. These two different goals will involve opposite trends on the load to be applied on the packing i.e. high load for good tightness and low load for low friction. Thus, the ability to define optimal ranges of packing tightening is important. Nevertheless, no standardized method for packing calculation nor packing full characterization (mechanical, friction, sealing performance vs. packing load,..) exists in Europe, as for bolted flange joints and associated gasket with EN1591-1 [1] and EN13555 [2]. In collaboration with ESA (European Sealing Association, www.europeansealing.com ) and FSA (Fluid Sealing Association, www.fluidsealing.com ), the Fluid Equipment Committee of CETIM has developed a tool for the optimization of packing. A set of tests enables to get the packing characteristics needed for the calculation. These tests can also be used for the comparison of packing materials and/or installation procedures performances in defined test conditions. This paper details the proposed calculation method and describes the associated test rigs and procedures. First test results and a calculation example are also given to show how the method works.

Abstract The thread ring block heat exchangers, served at the high temperature and pressure, are the key equipment in the petrochemical industry. Due to the severe operational conditions and unsuitable assemble, internal leakage problem commonly occurs, especially for the seal gasket between the tube sheet and shell. Many failed gaskets are collected. Through a series of experiments including chemical composition, metallographic analysis, SEM and fracture analysis, the gasket damage and leakage causes are analyzed. For further interpretation, the gasket stress analysis is completed by the finite element method. It shows that the gasket stress is a main factor that affects the sealing performance for the thread ring block heat exchanger. Under long term operation at high temperature and pressure, the gasket stress between the tube sheet and shell becomes loose and creep. The gasket material also deteriorates with increasing time. Therefore, in order to prevent the internal leakage, the stress should be controlled in an appropriate range. And periodical inspection must be performed.

Abstract There are currently no industry accepted methods for calculating sealing effectiveness of flange connections at the research and development phase of a project. As there are many different designs of bolted piping connectors being widely used in the oil and gas industry, operators and regulators could benefit greatly from a more accurate comparison and estimate of expected flange tightness level, based on design calculations only. This paper will propose a new methodology for sealing effectiveness estimation of bolted connections based on leak rate calculations. The methodology will combine practical simplicity and advance theory to get a simple but effective engineering/designing tool to assess the seal tightness. A new proposed method will be based on the contact stress pattern (FEA results), material properties (code specification) and surface finish/roughness (manufacture requirements) as inputs and leak rate estimation as an output. The Representative Surface Element concept will be introduced and presented. In this paper, the general methodology principles will be presented and followed by an engineering example.

Abstract Most vacuum vessels are bodies of revolution that are cylindrical or spherical. A square vacuum vessel was developed for a specialized application that needed to be suitable for repeated, rapid sealing and unsealing, and operation at mild vacuum (∼0.5 bara). This paper discusses the challenges that we faced in fabrication and testing of the vacuum vessel. The vacuum vessel was initially tested in a test rig. A second set of challenges was encountered when the vessel was tested mounted in the system. It captures the lessons learned from fabrication, rework, and modifications that were necessary to get the vessel to pass leakage testing.

Abstract Regular pigging operation of the pipeline inspection gauges (PIGs) is crucial for pipeline transportation. However, the PIG is often stuck when it runs in the oil and gas pipeline due to the interaction between spherical sealing cup and dent inside the pipe. The stress and strain distribution of the outer edge of the spherical sealing cup can provide a reference to the problem of understanding the blockage. In this study, numerical simulation of a PIG with spherical sealing cups runs through a pipe with dented wall is presented using MSC Marc 2016. Effects of the interference (δ) of the spherical sealing cup on the stress and strain distribution on the outer edge of the cup were discussed based on the model. Simulation results indicate that the smaller the thickness of the spherical sealing cup, the greater the effect of the interference of the cup on the stress. And the thickness of the cup should not be too small, an example of the failure of pigging due to the small thickness of the cup and the increase in the interference is given. The conclusions obtained in this study can contribute to the optimization design of the PIGs.

Abstract Bolted joint and gasket designers currently calculate spiral wound gasket stress in one of three ways. The differences lie in gasket area determination. The first is the historical Boiler & Pressure Vessel Code calculation method of using an effective sealing width which is half or less of the full dimensional width. Found to be inadequate for creating consistently acceptable sealing performance, those promoting and affecting lower leaks rates and emissions opt to use a gasket’s full width to determine gasket area and stress. The full width of a spiral wound gasket is currently being determined in two different ways among industry participants. Most use the dimensioned outer diameter which includes the bead of winding wire that does not contact the flange surface. Some exclude the width of the bead. Inclusion or exclusion of the bead has a significant impact on gasket seating stress for sealing elements of narrow width as the width of the bead represents a large percentage of the overall dimensions. In this paper, all three methods will be discussed focusing on gasket stresses for NPS calculated from the preferred method of full width comparing the inclusion and exclusion of the bead width.

Abstract PTFE is used in a variety of applications that goes from wiring in aerospace to non-stick coating in cookware. Some of the PTFE properties, such as high chemical stability and good conformability, makes it excellent for use as a gasket material, especially with aggressive media, pharma and food applications. The scope of this paper is to present an innovative PTFE gasket manufacturing method for sealing aggressive media. The patented technology represents a unique production process that improves reliability, reduces cost and material waste when compared to traditional production methods. The gasket can be tailored to meet specific needs making it possible for customizations such as radial density variations, assorted colors compositions according to the gasket region and properties, or even use of distinctive fillers along its radius. Comparative data are reported among the developed technology and traditional processes.

Abstract The V26 containment vessel was procured by the Project Manager, Non-Stockpile Chemical Materiel (PMNSCM) for use on the Phase-2 Explosive Destruction Systems. The vessel was fabricated under Code Case 2564 of the ASME Boiler and Pressure Vessel Code, which provides rules for the design of impulsively loaded vessels. The explosive rating for the vessel, based on the Code Case, is nine (9) pounds TNT-equivalent for up to 637 detonations, limited only by fatigue crack growth calculations initiated from a minimum detectable crack depth. The vessel consists of a cylindrical cup, a flat cover or door, and clamps to secure the door. The vessel is sealed with a metal gasket. The body is a deep cylindrical cup machined from a 316 stainless steel forging. The door is also machined from a 316 stainless steel forging. The closure clamps are secured with four 17-4 PH steel threaded rods with 4140 alloy steel threadednuts on one end and hydraulic nuts on the other. A flange with four high-voltage electrical feedthroughs is bolted to the door and sealed with a small metal gasket. These feedthroughs conduct the firing signals for the high-voltage Exploding Bridge-wire detonators. Small blast plates on the inside of the door protect fluidic components and electrical feedthroughs. A large blast plate provides additional protection. Both vessel door and feedthrough flange employ O-ring seals outside the metal seals in order to provide a mechanism for helium leak checks of the volume just outside the metal seal surface before and after detonation. In previous papers (References 2 and 3), the authors describe results from testing of the vessel body and ends under qualification loads, determining the effective TNT equivalency of Composition C4 (EDS Containment Vessel TNT Equivalence Testing) and analyzing the effects of distributed explosive charges versus unitary charges (EDS Containment Vessel Explosive Test and Analysis). In addition to measurements made on the vessel body and ends as reported previously, bulk motion and deformation of the door and clamping system was made. Strain gauges were positioned at various locations on the inner and outer surface of the clamping system and on the vessel door surface. Digital Image Correlation was employed during both hydrostatic testing and dynamic testing under full-load explosive detonation to determine bulk and bending motion of the door relative to the vessel body and clamping system. Some limited hydrocode and finite element code analysis was performed on the clamping system for comparison. The purpose of this analysis was to determine the likelihood of a change in the static sealing efficacy of the metal clamping system and to evaluate the possibility of dynamic burping of vessel contents during detonation. Those results will be reported in this paper.

The quantities of leak rate through sealing systems are being regulated because of the global concern on the hazardous pollutants being released into the atmosphere and their consequences on the environment and health. The maximum tolerated leak is becoming a design criterion, and the leak rate for an application under specific conditions is required to be estimated with reasonable accuracy. In this respect, experimental and theoretical studies are being conducted to characterize the gas flow through gaskets and packing rings. The amount of the total leak that is present in a gasketed joint or a valve stem packing is the sum of the permeation leak through the sealing material and the interfacial leak at the mating surfaces between the sealing element and mechanical clamp assembly. The existing models used to predict leakage do not separate these two types of leaks. This paper deals with a study based on experimental testing that quantifies the amount of these two types of leaks in bolted gasketed joints and packed stuffing boxes. It shows the contribution of interfacial leak for low and high contact surface stresses and the influence of the surface finish as a result of a 32 and 250 micro-inch RAAH phonographic finish in the case of a bolted flange joint. The results indicate that most of the leak is interfacial reaching 99% at the low stress while the interfacial leak is in the same order of magnitude of the permeation leak at high stress reaching 10 −6 and 10 −8 mg/s in both packing and gaskets, respectively.

In December 2013, a new version of EN 1591-1 (1) was issued. Apart from several other modifications, the treatment of external loads was included in this calculation standard for circular bolted flanged joints. In the former standard, only axial forces and bending moments resulting from the piping system were considered; in the new issue lateral forces and shear moments can also be treated. There are two possibilities to counterbalance the lateral forces and the shear moments: firstly by metallic contact of the flanges and secondly by friction between the gasket and the flange surfaces. While the first option cannot occur in the type of flange connection (with a floating gasket between the flanges) covered by EN 1591-1, the lateral displacement of the flanges can only be prevented by friction between the gasket and flange surfaces. Therefore, the friction factor μ G was introduced in the calculation procedure. In an informative annex of EN 1591-1 (Annex E), some friction factors are published exemplarily. These factors are based on values published in the German nuclear codes KTA 3201.2 (2) and KTA 3211.2 (3). The origin of these values can’t be retraced anymore. For this reason, it is stated in Annex E that these values are probably very conservative, and that an experimental determination of the factors should be preferentially used. Incidentally, overly conservative friction factors lead to higher required bolt forces to counterbalance the external loads, which may result in an overstressing of the components of the bolted flanged joint. Therefore, the European Sealing Association (ESA) decided to determine generic data for different types of gaskets which could be published in the next revision of EN 1591-1. In this paper the results of this project are presented.

Bolted flange joints (BFJs) are widely used in the process industries, and there is a large proportion served in the high temperature environment. During the long term service at high temperature, the creep relaxation of each component of BFJ will cause the decline of the residual gasket stress, which will further affect the sealing effect. So, it is very important to make sure the change rule of the leakage rate of BFJ during the long term service at high temperature. Firstly, according to constructing the relationship between the leakage rate and the service time, the leakage rate calculation method of BFJ during the long term service at high temperature was proposed. Secondly, the stress distributions of the gasket during the long term service at high temperature, which was time-dependent, were calculated at the tightness level T2 and T3 by using the numerical simulation method. Finally, based on the time-dependent average gasket stress and maximum gasket stress, the change rule of the time-dependent leakage rate of BFJ during the long term service at high temperature was obtained. The research results will play an important role in mastering the attenuation rule of the leakage rate of BFJ and supporting the leakage rate control of BFJ during the long term service at high temperature.

Gaskets incorporating polytetrafluoroethylene (PTFE) are one of the most common in use today where soft sealing material is needed in bolted joints. Over the years, various types of gaskets have been developed including those using skived, expanded, filled, or molded PTFE sheet. Still other PTFE gaskets have been fabricated, incorporating some type of metal insert. Although many of the key benefits (e.g., chemical resistance, application in a broad range of flange types, higher maximum temperature and stress levels than most elastomers, indefinite shelf life, etc.) remain, the performance of the gasket will vary significantly according to the type of PTFE gasket employed. These variations in accordance with PTFE gasket styles are presented and discussed with an emphasis on such criteria as relaxation, gasket tightness / leak rate, and safe reserve operating temperature. For estimating tightness and predicted leak rates, the previously reported “Fugitive Emissions Calculator” (FEC) model has been used which employs Room Temperature Testing (ROTT) data and an ASME / PVRC draft empirical equations set. Published test data have also been compiled to support conclusions concerning relative capabilities for selected PTFE gasket categories. The differences in analytical and leak rate performance criteria have been used to suggest appropriate applications for various subtypes of PTFE gaskets.

The sealing performance prediction of bolted pipe flange connections with gaskets is important factor. However, it is known that the sealing performance of the larger nominal diameter connection is worse than that with smaller nominal diameter connection due to the flange rotation. Furthermore, recently PTFE blended gaskets were developed newly and the excellent sealing performance in the bolted pipe flange connection with smaller nominal diameter is found. So, it is necessary to examine the sealing performance and the mechanical characteristics of pipe flange connections with larger nominal diameter under internal pressure. The objectives of present study are to examine the mechanical characteristics of the pipe flange connection with PTFE blended gasket under internal pressure such as the load factor, the contact gasket stress distribution and the sealing performance using FEM and experiments. Using the obtained contact gasket stress distribution and the fundamental leak rate for smaller PTFE gasket, the leak rate of the connection is predicted under internal pressure. In the FEM calculation, the effects of the nominal diameter of pip flange connections on the mechanical characteristics are shown. In the experiments, ASME class 300 24” pipe flange connections is used and the gasket is chosen as No.GF300 in PTFE blended gaskets. The FEM results of the axial bolt forces are in a fairly good agreement with the experimental results. In addition, the leak rate obtained from the FEM calculations are fairly coincided with the measured results. The mechanical characteristics of pipe flange connection with PTFE blended gasket are compared with those with spiral wound gasket.

The paper discusses the development of sealing technology within the organisation with particular emphasis on the gasket manufactured by profiled winding wire. This will be referred to as a PWG. The paper is a continuation of the paper presented in Paris PVP2013-97050 and follow up in PVP2014-28948. It discusses further laboratory testing and briefly describes 4 related field service case studies. The paper details tests which include: Thermal cycle, sealing performance, compression and recovery testing carried out in both laboratory and field conditions. The 4 related studies are based around the use on large flanges, the use in oxygen rich environment, the use in a thermal cyclic environment and on problematic flange corrosion.

Polytetrafluoroethylene (PTFE) products have been widely used for industrial sealing applications due to their outstanding chemical resistance as well as their electrical, anti-stick, impact resistance and low friction properties. Diverse PTFE flat gaskets production methods are available in the industry, which include the combination of a selected Resin Type and a determined manufacturing process, being able to provide a wide range of several types of PTFE gaskets, with different mechanical characteristics. The production method has significant impact on the mechanical properties of the PTFE gaskets, especially the creep relaxation property at elevated temperatures. Therefore, the gasket behavior at high temperatures and, consequently, the bolted flanged joint (BFJ) performance, directly depends on both selected Resin Type and gasket manufacturing process. One of the most used PTFE gasket types is produced from multiaxially expanded PTFE sheets. As it is known, different types of stretching, among other factors, confer to the gasket particular mechanical characteristics. This type of gasket exhibits a very low gasket seating stress, and it is the preferred type for most low bolt load flanges. This paper presents a study of the creep relaxation property at room and elevated temperatures of expanded PTFE gaskets manufactured by different Resin Types and processes of expanding PTFE materials. Experimental results are presented comparing EN 13555 [1] Q smax , P QR and Δ e Gc parameters of the produced PTFE gaskets.

With Oil and Gas exploration and production in low temperature arctic environment, new concerns arise concerning the application of the existing design rules for these conditions. Most codes and standards for bolted flange calculation do not include specific rules concerning application at low temperature. Especially, gasket performances under low temperature are neither tabulated nor easily available from other public sources. In this context, in collaboration with TOTAL, SCHLUMBERGER and SAIPEM sponsors, the CETIM has performed a program called ARCTICSEAL to characterize the flange gasket behavior in arctic environment. The goal is to check that gasket references, commonly used by these companies, are still usable under low temperature arctic conditions without main performance loss. The test program involves mechanical and sealing tests performed on 4 gasket types (sheet fiber based, sheet PTFE based, sheet graphite based and graphite spiral wound) with both NPS 8 and NPS 16 gasket sizes. Gasket performances are determined at −60°C, after loading at −25°C. Additional test involving hot/cold thermal cycling ageing (simulation of intermittent hot process fluid in the bolted flange) have also been performed. The result shows the ability of the tested gasket references to maintain good sealing behavior in most cases. Moreover, the hot/cold thermal cycling ageing improves the sealing performances for some of the tested gasket references. Moreover, a dedicated test stand has been developed to study the behavior of NPS 8 flange connection exposed to quick heat-up after exposure to low temperature environment.

Performance of a bolted flange joint (BFJ) is characterized mainly by its ‘strength’ and ‘sealing capability’. How to keep the ‘strength’ and ‘sealing capability’ for the BFJ serving at elevated temperature is a difficult problem in engineering applications. The variations of bolt stress and gasket contact stress play an important role on the structural integrity and sealing performance of BFJ in the bolt-up, pressurization and heat-up stages. In this paper, a three-dimensional elastic-plastic finite element model has been developed to investigate the performance of joint under combined internal pressure and elevated temperature. The thermal-structural coupling method has been used to analyze the variations of axial bolt force, maximum blot stress and gasket contact stress under steady-state and transient thermal loadings. The effects of internal pressure, temperature as well as the heating rate on the variations of bolt load, bolt stress and gasket contact stress have been evaluated. The results show that the maximum bolt stress increases while average gasket contact stress decreases with increasing the temperature under steady-state thermal loading. Besides, when the transient thermal loading is considered, heating rate has a significant effect on the maximum bolt stress and gasket contact stress. This research will contribute to the design of BFJ subjected to elevated temperature.

The use of segmented joint technology allows gasket manufacturers to fabricate and supply gaskets in discrete segments, rather than the conventional one-piece construction. Segmented gaskets are required when using sheet type gaskets for flange diameters larger than the available sheet size. Typical gasket sheets are 60” × 60” or 70” × 70” square, for instance. Flanges designed for these lower stress sheet gaskets that are larger than the available sheet size to fabricate the gaskets are typically fabricated as segmented gaskets. Segmented gaskets are also utilized in smaller flange applications to facilitate maintenance activities. When replacing the tube sheet gasket in a shell and tube exchanger the entire tube sheet must be removed in order to utilize a solid, one-piece ring gasket. In some cases this is not practical or desired, so a segmented gasket is utilized which only requires the tube sheet to be removed a short distance to allow access to the sealing surface. This same scenario exists with other common process piping and vessel flanges including thermowells, lance tubes, agitator or mixer shafts, etc. Valid concerns exist when using segmented gaskets as potential leak paths are created at every joint. If the gasket material and joint design are not correctly specified and fabricated the segmented gasket may not provide the same sealing performance and reliability as the solid, un-segmented gasket. This paper will discuss the research and data found that identifies the stress multiplier for segmented/jointed gaskets to achieve the same (similar) leak rate as their solid, unsegmented gasket counterpart. This assembly or design stress multiplier will be a dynamic number that will vary based upon the gasket material and the joining technology used. Two jointing methods are evaluated in this research; the industry standard “dovetail” and the Engineered Interference Tortuous Path (EITP) joint. In practice there is currently no guidance available to guide the design or assembly of these segmented gasket applications. The purpose of this paper is to provide guidance for both design and assembly purposes.