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Pressurized equipments maybe deform partially or wholly, and the mechanical properties of the construction material would be degraded due to a fire event. Fitness for service assessment can help to minimize reconstruction costs and allow safe resumption of unit operation as fast as possible. A propylene heat exchanger was exposed to overheating for about 3 hours due to a fire accident five or six meters far away. A fitness for service assessment was conducted according to API 579-1/ASME FFS-1. The material of the propylene heat exchanger is 09MnNiDR. The possible damage was examined by dimensional checks, hardness testing, in-situ field metallography, ultrasonic testing and magnetic particle testing. The heat exposure temperature of the propylene heat exchanger during the fire accident was estimated through the comparison between the results of in-situ field metallography examination and heat exposure simulation experiments. The heat exposure zones were identified based on the results of visual inspection and conjectural heat exposure temperature. The level 2 assessment was adopted to evaluate the heat exposure zones of V and VI. The approximate ultimate tensile strengths for the shell and the eastern head were converted from the hardness testing results. The caculated MAWP of the shell side is higher than the design pressure of the heat exchanger. The finite element method was adopted to evaluate the influence of the bulge in the upper part of the shell. The analytical results showed that the bulge had no significant effect on the operation of the heat exchanger before next inspection.

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.

Quenched and tempered high strength steel 07MnMoVR provides an excellent combination of strength and toughness potentially providing significant cost savings in petrochemical industry. Exposure to fire will subject steel to thermal conditions that may alter the material’s microstructure and properties. The extent of the fire damage and the potential reusability of the components can be evaluated by fitness-for-service (FFS) assessment after a fire event. According to API 579-1/ASME FFS-1, metallurgical investigation and mechanical testing are the chief means for the assessment of fire damage. This paper presents the details of an experimental investigation on the post-fire metallographic structure and hardness of 07MnMoVR steel. Metallographic analyses and hardness testing were performed on coupons exposed to elevated temperatures varying from 550°C to 850°C for half an hour to 8 hours and then naturally cooled in air or cooled by water. The results show that the microstructure of as-received 07MnMoVR steel consisted of tempered sorbite and bainite. With increasing heat exposure temperature, bainite disappeared gradually. The recovery and recrystallization of ferrite began to occur after heat exposure at 650°C for 5hrs. When the heat exposure temperature exceeded 750°C, the effects of duration time and cooling rate on microstructure were both significant. A linear correlation is indicated by fitting the ultimate tensile strength and hardness. Due to the drastically degradation of impact toughness of 07MnMoVR steel after heat exposure exceeded 650°C, it is suggested that the removal and testing of material samples shall be utilized to evaluate the fire damage of components, besides replication or in-situ field metallography and hardness testing. This study can provide basis data and guidelines for the fitness-for-service assessment of 07MnMoVR steel suffered from a fire event.

Quenched and tempered high strength steel 07MnMoVR with a better combination of mechanical properties and low susceptibility to welding crack has attracted attention for applications in engineering fields. Exposure to fire will subject steel to thermally induced environmental conditions that may alter the material’s properties. The residual strength after a fire event is important to assess the extent of the fire damage and the potential reusability of the vessel. This paper presents the details of an experimental investigation on the post-fire mechanical properties of 07MnMoVR steel. Uniaxial tension tests and Charpy impact tests were performed on coupons exposed to elevated temperatures varying from 550°C to 850°C for half an hour to 8 hours and then naturally cooled in air or cooled by water. The post-fire stress-strain curves, strength, ductility and impact toughness of 07MnMoVR steel are discussed. The results show that the yield plateau in post-fire stress-strain curves disappears when the exposure temperature is higher than 700°C. The residual yield strength and ultimate strength decrease firstly and increase afterward with increasing exposure temperature. The influences of duration time on the residual strength are considerable for exposure at 650°C. The post-fire impact toughness of 07MnMoVR steel at −20°C degrades drastically with increasing duration time when the exposure temperature reaches 700°C. The effects of cooling methods on strength and toughness become significant when the exposure temperature exceeds 750°C. The critical tempetature for the mechanical properties deterioration is 650°C. This study can provide basis data and guidelines for the fitness for service assessment of 07MnMoVR steel suffered from fire accident.

Small specimen creep test techniques have been widely applied in the creep properties assessment of materials for the equipment in-service. In order to acquire the creep data accurately and conveniently, the creep test method with small cantilever beam specimens is proposed. On the basis of Norton-Bailey creep law, analytical creep model for the cantilever beam specimen is derived. With this model, the load can be converted to equivalent uniaxial stress and the displacement rate can be converted to equivalent uniaxial strain rate. The creep properties of Cr-Mo steel are assessed by the cantilever beam specimens creep tests. And the creep parameters are evaluated, which are compared to the uniaxial creep parameters. The results show that parameters obtained from the cantilever beam tests correspond reasonably well with those from uniaxial tests. It proves that the primary and secondary creep properties can be assessed by the cantilever beam specimen tests.

Partial safety factor (PSF) is a reliability approach for considering the variance of parameters in flaw assessment procedure in major fitness-for-service (FFS) codes, such as recent API579 and BS7910 codes, but is still not adopted in Chinese FFS code GB/T 19624-2005. This study investigated the derivation method for PSFs based on GB/T 19624 procedure. The limit state equations for PSFs calculation were proposed based on GB/T 19624 level 2 failure assessment diagram (FAD). The distribution of random variables was determined according to China’s domestic features. The first order reliability method (FORM) and second order reliability method (SORM) were employed as reliability analysis methods, and the calculated results were both compared with that simulated using Monte Carlo method. The PSFs at different target reliability levels were established and compared with that in API 579 and BS 7910. The method proposed in this study provides a basis for introducing PSF approach into Chinese FFS code.

Remaining life prediction model of ethylene cracking tubes (ECT) suffered joint damage of carburizing and creep have been set up in this study. Materials employed in this work were cut from Cr35Ni45-type radiation section of ECT. Layered structure, including oxide layer, carburized layer and carburizing transition layer, have been found from inside to outside of the tubes in scanning electron microscopy (SEM) images. However, no abrupt transition occurs between carburized layer and the base material. Both carburizing related layers caused the damage of the tubes, together with oxide layer. In order to facilitate the life prediction accuracy, carburizing transition layer was considered as a part of the damage layer. The remaining life of ECT was investigated by review of the microstructure and stress-rupture tests. Stress-rupture tests have been finished to obtained the rupture life of the tubes at 1000°C, 1040°C, 1080°C and 1125°C under six loading stresses (10MPa, 15MPa, 17MPa, 20MPa, 25MPa and 30MPa, respectively). In the results of stress-rupture tests, the combination of testing temperature at 1040°C and loading stress with 15MPa got the highest rupture life of 830h. Finally, a modified Larson-Miller remaining life prediction model of ECT, considering the comprehensive effect of carburizing and creep damage, has been established.Copyright © 2015 by ASME

The degeneration of mechanical properties is one of the main concerns in assessment of fire damaged pressure vessels. This study investigates the influence of fire exposure on mechanical properties of Q345R steel which is widely used for pressure vessels in China. Heat treatment with different temperatures and holding times was conducted to simulate various heat exposure conditions in fire event. Hardness testing, metallographic analysis and tensile tests were carried out to investigate the effects of fire exposure temperature and duration. The experimental results indicate that the inflection temperature for mechanical property degeneration of Q345R steel is 700 °C. The decline of hardness, yield and tensile strengths due to spheroidization become more obvious with increasing heat exposure duration. A linear correlation is indicated by fitting the tensile strength and hardness. For the assessment of fire damaged component, the mechanical properties of Q345R steel at room temperature can be determined combining on-situ field metallographic examination and hardness testing with.

A crack was observed on an outlet elbow of the pre-converter in coal gasification unit during operation. This paper details the investigation into the failure and highlights the most probable cause of failure based on available documents and experimental analysis. Visual examination, chemical components analysis, energy spectrum analysis, fracture analysis, metallurgical analysis, mechanical properties test and residual stress measurement were performed. The experimental results show that the primary crack initiated from inside and propagated to outer surface of the elbow. The content of titanium element was lower than the requirement in GB/T 14976-2002. Corrosion products were rich in O and S elements. Amounts of secondary cracks and strain induced martensite were observed. Furthermore, the residual stress on the inner surface near the crack tip was extremely high. According to the experiment results and the analysis of operating condition and history, the failure mechanism of the elbow is stress corrosion cracking. Sensitization of the stainless steel due to low Ti content and the faulty heat treatment contributed to the intergranular stress corrosion cracking.Copyright © 2015 by ASME

In a scheduled maintenance inspection of a fertilizer power station, a series of circumferential cracks were found in shift gas heat transfer tubes. In order to get an understanding of the failure mechanism, a failure analysis was performed on the leak-off shift gas tubes in this paper. The tubes were observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The fractography and metallurgical examination results showed that the crack initiated along grain boundaries and propagated through grain boundaries and the crack tips were oxide filled and not branched. Typical fatigue striations were observed on the fracture surfaces. The surface intergranular corrosion cracks caused by sensitization resulted in stress concentration. Fatigue cracks propagated along slip plane of grains under varying load. Moreover, the oxides on the surface of slip planes reduced the cohesive strength of steel substrate on both sides of slip planes. The synergistic effect of corrosion and fatigue, herein referred to as corrosion-fatigue, was the dominant mechanism of the failure. The vibration analysis of the tubes was carried out, and the results indicated that the vibration was induced by Karman vortex shedding and wobbling turbulent flow. In addition, prevention methods have been proposed to avoid corrosion-fatigue of the tubes.

When pressure vessels are subjected to fire damage, they maybe deform partially and the mechanical properties of materials would be degraded. Fitness for service assessment can help to minimize reconstruction costs and allow safe resumption of unit operation as fast as possible. The safety of a packed column subjected to fire damage due to spontaneous combustion of FeS during a shutdown period is assessed according to API 579-1/ASME FFS-1. First, the highest temperature during the fire accident was estimated. The possible damage was examined by hardness test, dimensional checks, in-situ field metallography, ultrasonic test and penetration test. The Heat Exposure Zones were defined based on the results of visual inspection and test. The plates containing Widmanstatten or localized distortions were replaced. The column leaned with the vertical deviation of 85mm which could not satisfy the requirement of the national standard GB 50461-2008. The finite element method is adopted to analyze the influence of the vertical deviation with the consideration of wind loading. The analytical results show that the vertical deviation of 85mm has no significant effect on the safe operation of the column before the next inspection.Copyright © 2014 by ASME

The fitness-for-service assessment is widely used to demonstrate whether identified defects or in-service deterioration threaten the structure integrity of the pressure equipment. This article introduces the development of the Chinese national safety assessment standard. The assessment procedure and assessment techniques of current Chinese national safety assessment standard GB/T 19624-2004 are demonstrated, and the improvement is proposed. In order to maintain availability of aging equipment and enhance the long-term economic performance of in service pressure equipment, a new Chinese national safety assessment standard system is methodology proposed based on the analysis of some international structure integrity procedures or standards. A new national standard fitness-for-service which focuses on the evaluation of in-service damage and degeneration will be established while GB/T 19624 is applicable for general defects.Copyright © 2013 by ASME

In the condition of the earthquake force and wind loads, there are many failure modes for the spherical tanks, such as the structure damage of the supports, uniform foundation settlement, displacement or upset, and the fracture of pipelines attached to the tank, etc. In this paper, more precise stress distribution of spherical tanks under wind loads and seismic force was obtained by finite element analysis. The safety assessment is carried out on a spherical tank. The weakness components of the spherical tank were found and the wind-proof performance and earthquake-proof performance of the spherical tanks could be improved.