Abstract Bolted flange joints (BFJs) are very common in the process industries, and they play an important role in equipment connection. A lot of BFJs are working at high temperature. The temperature and internal pressure will lead to gasket stress redistribution, and then affect time-dependent leakage rate of BFJs. In this paper, the effect of internal pressure on gasket stress and leakage rate of BFJ during the long term service at high temperature was discussed. The time-dependent gasket stresses of BFJ during the long term service at high temperature under two tightness levels and three internal pressures were calculated by using the finite element method. And then, based on the leakage rate prediction model of BFJ during the long term service at high temperature proposed, the corresponding time-dependent leakage rates of BFJ during the long term service at high temperature were acquired. The results showed that the internal pressure had a significant impact on the time-dependent gasket stresses and time-dependent leakage rates of BFJ during the long term service at high temperature. This research will help the engineers and technicians to understand the role of the internal pressure on the time-dependent gasket stresses and time-dependent leakage rates of BFJ during the long term service at high temperature.

Abstract A typical Fluid Catalytic Cracking Unit (FCCU) generates high temperature flue gas in the process of regenerating the catalyst. This flue gas is diverted to a stack after removal of catalyst fines and excess heat using a Waste Heat Recovery Unit (WHRU) or CO boiler. This flue gas line is a large diameter (1.2 m /2 m) piping and is a combination of Hot Wall (bare SS304H piping with external insulation) upstream of Orifice Chamber and Cold Wall (Carbon steel piping with internal refractory lining) for the downstream side. In a major revamp project, large portion of flue gas line was replaced with some dimensional and design changes. A crack was noticed at the SS304H side of hot wall to cold wall transition joint downstream of Orifice Chamber after approximately 2 years in operation. The line operates around 700 °C and 0.15 Bar(g) at the location of the crack. The initial crack was measured to be approximately 250 mm to 300 mm and grew to a full circumference crack in a short time resulting in minor flue gas leaking with catalyst fines. This paper discusses the details on how the issue was addressed on site and a temporary repair (i.e. welding of a box on high temperature piping) was carried out online safely, while the unit remained in operation. Further, the paper presents the root cause assessment and design modifications implemented for hot wall to cold wall transition joint during a scheduled turnaround.

Abstract A summary of testing related to bolt relaxation, which occurs at temperatures above 230°C (450°F) was presented in a previous paper. The work has since been extended to include lower temperature data for common bolting materials. This paper provides a summary of the additional work performed and further observations regarding the acceptable design limits for A193-B7 and A193-B7M bolt materials. In addition, a conclusion regarding the recommendations made in API RP751 comparing A193-B7 and A193-B7M relaxation is made.

Abstract Reformer furnaces are widely used in a hydrogen plant to obtain hydrogen from hydrocarbon. The radiantt coils tubes are the most critical components of a reformer furnace, which can be heated up to 850 °C or higher temperature for long time during service. The failure of tubes usually happened before the designed life due to over-heating or unexpected damage, which usually leads to unplanned shutdown of plant and great losses. Thus, it is important to assess the damage conditions and residual life of furnace tubes. This study is an attempt to investigate the property degradation and residual life for service exposed reformer tubes of a hydrogen reformer furnace after 6 years service. Microstructural and mechanical experiments were carried out to reveal the property degradation, included optical observations, scanning electron microscope (SEM) observations, room temperature tensile tests, high temperature tensile tests, and stress rupture tests. Finite element analysis was also used to investigated the influence factors on the stress of tubes. The residual life of furnace tube was estimated based on these experimental and simulation results.

Abstract Printed Circuit Heat Exchangers (PCHEs) are well-suited for Very High Temperature Reactors (VHTRs) due to high compactness and efficiency for heat transfer. The design of PCHE must be robust enough to withstand possible failure caused by cyclic loading during high temperature operation. The current rules in ASME Code Section III Division 5 to evaluate strain limits and creep-fatigue damage based on elastic analysis method have been deemed infeasible at temperatures above 650°C. Hence, these rules are inapplicable for temperatures ranging from 760–950°C for VHTRs. A full inelastic analysis method with complex constitutive material description as an alternative, on the other hand, is time consuming; hence impracticable. Therefore, the simplified Elastic-Perfectly Plastic (EPP) analysis methodology is used as a solution in ASME Code Section III Division 5. The current literature, however, lacks any study on the performance evaluation of PCHE through EPP analysis. To address these issues, this study initiates the pathway of EPP evaluation of an actual size PCHE starting with elastic orthotropic analysis in the global scale. Subsequently, preliminary planning for analyzing intermediate and local submodels are provided to determine channel level responses to evaluate PCHE performance against strain limits and creep-fatigue damage using Code Case-N861 and N862 respectively.

Abstract In our past paper, the new fracture surface was proposed considering the effects of hydrostatic stress in an elastic-plastic region and in a creep region. In this paper, the mechanism the dominant factors of local failure were studied in an elastic-plastic region. Experimental and analytical study were made using circular plate specimens with a nozzle. The material was a lead alloy (99% Pb-1% Sb). The fracture test was performed in an elastic-plastic region at room temperature. Both ductile fracture and local failure were observed at structural discontinuities, based on the stiffness differences between attached nozzles and plates. In this study, the proposed fracture surface in an elastic-plastic region showed the fracture location accurately, for the both failure modes. It was concluded that the proposed fracture surface is available and useful in order to predict the failure mode and the failure location.

Abstract The Concentrating Solar Power (CSP) Gen3 Demonstration Roadmap has recognized Supercritical carbon dioxide (sCO2) Brayton Cycle as the best-fit power cycle as it provides thermal efficiency benefits relative to the conventional Steam-Rankine cycles. However, to enable the integration of sCO2 Brayton Power Cycle, it is necessary to increase the outlet temperature of current molten salt CSP systems from 565°C to approximately 720°C. Increasing the temperature of the salt brings significant material and engineering challenges. Creep-fatigue damage accumulation and ratcheting deformation are important design considerations for receivers operating at high temperature due to frequent transient loads caused by diurnal cycling and thermal shocks from transitions between sun and cloud cover. In this work, a reference thermomechanical model of a Gen3 CSP receiver is developed to evaluate different creep-fatigue and ratcheting design approaches identified in Section III, Division 5, of ASME Boiler and Pressure Vessel Code. The design methods are then ordered based on design margin and ease of use. Design by elastic perfectly-plastic analysis is found to be the most conservative among the methods. Elastic analysis is the easiest to perform but the design calculations are extremely complicated. In contrast, design calculations are straight forward in inelastic analysis method but it requires developing a sophisticated inelastic constitutive model describing the material behavior. Several recommendations are made for developing creep-fatigue and ratcheting design rules for CSP systems.

Abstract Residual stresses within welded components can redistribute when exposed to high temperatures and large levels of loading. The ageing process for a specimen attempts to replicate the temperature regime experienced during typical service use of the component, redistributing stresses from the as-welded condition to post-ageing. The aim of this investigation was to study the effects of ageing on weld residual stress redistribution and to evaluate the changes in the residual stress profiles before and after the pipe had been aged. In this investigation the through thickness residual stresses within a narrow gap girth TIG welded stainless steel 316L pipe were measured. The ageing of the pipe specimen involved heating to 400°C for 3000 hours. To measure residual stress the incremental Deep-Hole Drilling (iDHD) method was employed; two measurements were taken, once before and after ageing. Analysis of the measured pre and post-ageing residual stresses showed a consistent reduction in the magnitude of approximately 50 MPa, corresponding to the change in the yield stress of the material at room and elevated (400°C) temperatures; the maximum residual stress, of 450 MPa, was measured at 4 mm from the external surface of the pipe.

Abstract The offshore oil and gas industry is drilling into and producing from wells in high-pressure, high-temperature (HPHT) environments. This has created a greater demand to develop more advanced tools and new technology to safely overcome the challenges in these operations. Due to the sensitivity and potential impact on the environment, the industry is striving to homogenize the design and acceptance criteria. The API 17G is the industry standard for offshore intervention operations. According to the standard, design verification is performed using finite element analysis (FEA). The standard provides three sets of criteria for determining capacities that adopt the methodologies from ASME Boiler Pressure Vessel Code (BPVC) Section VIII, Div. 3. The objective of this study is to evaluate tension, pressure, and bending moment capacities per the elastic-plastic analysis methodologies outlined in API 17G for a subsea intervention system connector. The global and local failure capacities are presented for yielding load, plastic collapse, and 2% strain methods. Results indicate that the plastic collapse method is the most conservative approach for evaluating the global capacity of the connector.

Abstract The American Petroleum Institute (API) is continuing to develop technical reports, guidelines and standards for the construction of high-pressure, high-temperature (HPHT) equipment for offshore oil and gas exploration and production. HPHT is considered to be equipment with a pressure rating greater than 103 MPa (15,000 psi) and/or a temperature rating greater than 177°C (350°F). One alternative in the evolving API standards is to use the analysis methodology in ASME Section VIII, Division 3, including fracture mechanics, for determination of the static pressure rating and the design fatigue life. However, detailed requirements for finite element analysis (FEA) parameters such as element type and mesh density are not specified. In addition, specific requirements for fracture mechanics analysis are not provided. This paper explores the effect of variations in those parameters on the calculated static pressure rating and the design fatigue life and gives recommendations for optimizing the parameters of the design itself (e.g. blend radii at transitions) and the analysis considering the required accuracy of the result, analysis time and cost.

Abstract Fatigue sensitive pressure containing components in the oil & gas industry requires a life cycle assessment. High Pressure High Temperature (HPHT) equipment designed using API 17TR8 and ASME Section VIII Division 3 are evaluated for cyclic fatigue crack growth per API 579/ASME FFS-1 fitness for service level 3 assessment. The level 3 assessment requires more advanced stress analysis to define the state of stress at critical locations and a defined initial flaw for cycle growth assessment. The cyclic crack growth in pressure containing equipment depends on the alternating crack tip stress intensity values for the defined load histogram. Therefore, in this paper, the stress intensity at crack tip is calculated using two approaches for 20 ksi pressure equipment. The first approach is to utilize linear elastic stresses obtained from a three-dimensional finite element evaluation, where the stress profiles are used as an input to Signal FFS (fitness for service) Quest software, to calculate stress intensity at crack tip. The second approach utilizes a J-integral based on fracture mechanics analysis considering a pressure penetration on cracked surfaces. Although there is a difficulty in representing the complete production load histogram applying the J-integral solution, this paper provides evaluation of the two methods for comparison of results. It also demonstrates the feasibility of application to pressure vessel equipment.

Abstract Bonded composite repairs are commonly used as both a temporary and permanent repair method to restore damaged pressure vessels and pipelines. This repair approach is used in a wide variety of industries, including the oil and gas industry. Design and qualification of repair method have been standardized by the ASME post-construction codes. Significant literature has been generated to understand the behavior of these repairs under a variety of loading conditions, both static and dynamic. However, this repair type has typically only been investigated at or near room temperature. As the application possibilities for these repairs expand, higher service temperatures have become a focus for both repair manufacturers and operators. High temperatures (> 250°F) have a number of impacts on polymer composites, including reducing the elastic modulus of the repair material, which tends to reduce the repair strength. Therefore, it is critical to understand the effect of temperature on both the individual composite components, as well as the overall composite repair system. The research presented here studies the influence of temperature on bonded composite repair systems at service pressure (3000 psi) and high temperature conditions. This high temperature is generated using a heating element inside the repaired vessel while contained inside an insulated oven. Strain measurements of the repair are also investigated during a quasi-static testing.

Abstract Composite materials are being used in many industrial applications such as automobile, aerospace, marine, oil and gas industries due to their high strength to weight ratio. The long-term effect of sustained loads and environmental factors that include exposure to UV light, temperature, and moisture have been under investigation by many researchers. The major objective of this study is to evaluate the effects of harsh environment (e.g. seawater and high temperature) on the structural properties of E-glass epoxy composite materials. These effects were studied in terms of seawater absorption, permeation of salt and contaminants, chemical and physical bonds at the interface and degradation in mechanical properties. Samples were immersed in seawater at room temperature (23°C), 65°C and 90°C for the duration of 6 months. Results show that seawater absorption increased with immersion time at 23°C and 65°C, whereas the weight of the specimens decreased at 90°C. The moisture causes swelling at 23°C and 65°C and breakdown of chemical bonds between fiber and matrix at 90°C. It is observed that high temperature accelerates the degradation of the E-glass epoxy composite. At 90°C, the tensile strength of E-glass epoxy sharply decreased by 72.92% but no significant change was observed in modulus of elasticity of the composite.

Abstract Austenitic materials with high sensitization resistance and high temperature strength are required for furnace and reaction tower of desulfurizing plants in the petroleum refinery industry. For these requirements, a new steel (LowC-18Cr-11Ni-3Cu-Mo-Nb-B-N) has been developed. The steel shows no intergranular stress corrosion cracking in polythionic acid environment after aging in the temperature range from 565 to 700 °C for up to 10,000 hours. This excellent PTA-SCC resistance is attributed to the prevention of M 23 C 6 carbide precipitation along grain boundary due to extra low carbon content with high ratio of niobium to carbon. The maximum allowable tensile stress of this steel is estimated to be more than 30% higher than that of ASME SA213 Type347H. This excellent strength is based on the precipitation strengthening effect due to fine precipitates of a copper rich phase which are coherent with the austenite matrix in addition to Z-phase (NbCrN). Moreover, boron addition improves creep strength and creep ductility of the steel. From these results, it is concluded that the newly developed steel is a promising material not only for refinery processes but also for other elevated temperature usages.

Abstract Nelson curve for carbon steel without post welding heat treatment (PWHT) was reconsidered in Annex F of API PR941 8th Edition because a lot of hydrogen damage cases of carbon steel for pressure vessels and pipes with weld joint were reported. However the mechanism of the damage initiation has not been extensively studied. For these reason, the purpose of this study was to clarify effect of residual stress on high temperature hydrogen attack (HTHA) and examine the mechanism in terms of microstructure. The specimens that were simulated welding residual stress by four point bending tool were exposed to high temperature and high pressure hydrogen gas to investigate relationship between damage initiation and condition of temperature and pressure. The frequency of damage occurred by residual stress under high temperature and low hydrogen pressure conditions was higher than that under low temperature and high pressure condition. The damage occurred on boundary of ferrite and pearlite. The grain reference orientation deviation (GROD) map obtained from EBSD measurement indicated the concentration of strain on the boundary generated by plastic deformation. Thus, the damage is most likely initiated by concentration of hydrogen on ferrite-pearlite boundary at which welding strain accumulated. Moreover the damage susceptibility of ferrite-pearlite structure was higher than that of bainite structure. The microstructures in base metal is ferrite-pearlite, but that in heat affected zone is bainite by reheating and cooling at welding. Hence, the base metal has higher damage susceptibility than HAZ.

Abstract The R5 procedures have been developed within the UK power generation industry to assess the integrity of nuclear and conventional plant operating at high temperatures. Within R5, there are specific procedures for assessing creep-fatigue crack initiation in initially defect-free components (Volume 2/3), components containing defects (Volume 4/5), dissimilar metal weldments (Volume 6) and similar metal ferritic weldments under steady loading (Volume 7). A key driver for continued developments in the R5 Procedure is the operational feedback from thirty years of operation of the UK Advanced Gas-Cooled Reactor (AGR) fleet. This experience from operation of the UK AGR fleet can be used to inform the design and operation of future high temperature reactors. Some of the lessons learnt from long-term operation of austenitic stainless steels at high temperatures are detailed briefly within this paper. Further, this paper briefly outlines the current R5 procedures and then focuses on two significant recent developments in these procedures: treatment of carburisation and its impact on creep-fatigue crack initiation and improved methods for predicting creep-fatigue crack growth under combined primary and secondary loads.

Abstract In recent years, there has been a growing interest of using Leak-Before-Break (LBB) concept in the refining industry. LBB methodology has been applied in the nuclear industry for decades, but generally for elimination of hardware for dynamic rupture control at the design stage. However, in the refining industry the purpose of the LBB application could be quite different than for the nuclear industry. In the refining industry the purpose of LBB is to show in-service leakage can be detected well ahead the potential for rupture allowing for ample time for safe replacement of piping. This paper explores conditions in which LBB can be applied to refinery piping. Initially, the analysis was conducted using a finite element model of a typical pipe system with its design boundary conditions under operating loadings, i.e., gravity, pressure, thermal and hanger loadings. The results with various circumferential crack sizes show a displacement-controlled manner (LBB is easy to satisfy) for the pipe system mainly due to higher secondary stresses, i.e., thermal loadings. However, the pipe system behaved in a load-controlled manner (LBB is harder to satisfy) when some of the boundary conditions were changed simulating a possible support failure and/or hanger failure. This paper investigates how boundary conditions can change a displacement-controlled LBB behavior to load-controlled LBB for a representative pipe system and the implications regarding leak rate detection capability. The effect of material’s toughness reduction due to high-temperature hydrogen-attack (HTHA) damage was also included in these analyses. The procedure outlined here can be applied to a piping system to identify piping supports that are critical for inspection to demonstrate LBB, and the anticipated leak rate before reaching critical flaw size.

Abstract The dissimilar metal weld (DMW) is widely used in fabrication and manufacturing in various industries. Joining between nickel-based alloy and ferritic steel tubing and piping is commonly employed for ASME Code compliant welds for high-temperature and corrosion resistance applications. A series of DMW samples between alloy 600 pipe and SA-106 Grade B pipe are fabricated using different welding processes, joint design and welding techniques. By detailed comparison, this paper provides insight into the effects of these different welding variables on mechanical properties (tensile properties and hardness of weld materials and heat affected zone), metallurgical properties (macro and microstructure examination) and chemistry (root pass alloying dilution etc.) It has been shown that an asymmetric joint bevel design in consideration of different heat dissipation, melting temperature of the two materials will promote good weld bead formation during the root pass welding. Different joint designs (such as with or without consumable insert) will create variations on weld dilution and Cr/Ni recovery in the root area. Other welding variables such as tungsten electrode location for root pass welding for DMW, machine Gas Tungsten Arc Welding (GTAW) using hot wire and cold wire, etc. are also discussed.

Abstract The governor valve is a very important component in steam turbine, which can change the power output of the steam turbine by controlling the amount of the inlet steam. The service conditions of governor valve is very complicated, which should suffer high temperatures, high pressure, erosion, water induction and so on. As we all know the fatigue and creep can significantly reduce valve life. However, the damage due to governor valve seat interference fits is also very important for the units’ safety operation. A compromised interference fit can lead to significant valve leakage and possibly catastrophic seat failure. This article bases on a real case from a STP’s SC unit, which is operating in the South Asia market. Simulating the behavior of the valve seat under service conditions by numerical method, to find out the root cause of the interference fit failure and the operational advice for the unit running.

Abstract Making light water reactor (LWR) components using additive manufacturing (AM) provides a high degree of design freedom to create complex near net shape geometries, with significant reduction in the deployment time. Since most of the current AM research focus on the refining of the fabrication variables, little information exists on the actual corrosion behavior (including general corrosion, localized corrosion and environmentally assisted cracking - EAC) of AM components. The most frequent operational material failure modes in LWR is EAC and debris fretting of fuel rods, therefore the objective of this work was to evaluate the environmental performance of AM type 316L SS in relation to the traditionally melted and forged wrought material. Stress corrosion cracking results show similar behavior between AM and wrought 316L SS in high temperature water. Ambient temperature electrochemical testing showed that the AM 316L SS was slightly more resistant to localized corrosion than the traditional wrought material and that AM material did not suffer sensitization during fabrication or heat treatment processes.