Proof Pressure Research Articles

Assessment on structural integrity of aluminium alloy AA6061 water tank used in satellite launch vehicles

AA 6061 is an age-hardenable aluminium alloy with 1wt% magnesium and 0.6wt% silicon as major alloying constituents and is used for manufacture of toroidal water tanks of earth storable liquid rocket engines of ISRO’s launch vehicles. These water tanks are used for storing water to generate steam in gas generator as well as for cooling various components of liquid rocket engine. As a part of the developmental efforts of a new source for fabrication of water tanks, a qualification test procedure was laid down, wherein a quarter portion of the water tank, namely the test article, is designed, fabricated and subjected to series of acceptance and qualification tests, including proof pressure test, cyclic pressure tests with intermediate non-destructive tests. These were finally followed by burst testing of the test article for conforming structural design margins and quality standards adopted for realizing the hardware. A burst test is a destructive test, performed to determine the overload capacity of the pressure vessels depicting margin of safety with respect to its mechanical strength limit. This work highlights the detailed manufacturing processes viz. forming, machining and welding including heat treatment of shells, metallurgical analysis carried out on the parent and weld specimens as well as results from proof pressure and pressure cyclic tests. Further, fractographic studies were carried out on the burst tested hardware, wherein specimens collected from different locations of the burst tested hardware were analyzed using optical scanning electron microscopy, to locate the origin of crack initiation and nature of the failure.

Design, analysis and fabrication of hydro fixture for testing of 32” and above size valve

A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant. Strength is usually tested by measuring permanent deformation of the container. Hydrostatic testing is the most common method employed for testing pipes and pressure vessels. Using this test helps maintain safety standards and durability of a vessel over time. Newly manufactured pieces are initially qualified using the hydrostatic test. They are then re-qualified at regular intervals using the proof pressure test which is also called the modified hydrostatic test .Testing of pressure vessels for transport and storage of gases is very important because such containers can explode if they fail under pressure. Hydrostatic tests are conducted under the constraints of either the industry's or the customer's specifications, or may be required by law. The vessel is filled with a nearly incompressible liquid - usually water or oil - pressurized to test pressure, and examined for leaks or permanent changes in shape. The test pressure is always considerably higher than the operating pressure to give a factor of safety.

Online structural integrity monitoring of high-performance composite rocket motor casing

Solid rocket motor (SRM) is one of the significant sub-systems for aerospace launch vehicles. The requirements of high range and high payload capabilities in aerospace systems demand the usage of high specific strength and high specific stiffness materials for rocket motor casings to minimize the inert weights. The present state-of-the-art technology is to realize stages of missile systems/launch vehicles with Composite Rocket Motor Casing (CRMC) to have a high-performance factor. CRMC is being designed with a marginal Factor of Safety (FOS) and mostly for a one-time use during its service life. CRMC is pressure tested to verify leak containment and its ability to sustain the Maximum Expected Operating Pressure (MEOP). Acoustic Emission Testing (AET), an online and global Structural Health Monitoring (SHM) technique along with strain and dilation measurement is used for observing the dynamic behavior of CRMC during the pressure test. Conventional Non-destructive Testing (NDT) such as Ultrasonic (UT) and Radiographic testing (RT) are employed to identify the type of defects. This unique capability of monitoring the dynamic behavior of active defects during real-time is of great significance for the acceptance of CRMC. The evolution of such an online system requires, first, identification of an appropriate process and next its adoption to meet the challenges posed by composite materials. There are various steps involved in the online SHM of CRMC. In this paper, various test practices, requirements, test parameters along with the details of strain and dilation measurements are given. This online inspection methodology and strain-dilation measurement during the Proof Pressure Test (PPT), along with a series of other inspection methods form the basis of CRMC acceptance for further use.

Finite Element Analysis of Gasket in Pressure Vessel

Abstract: Pressure vessel is a closed container designed to hold liquids or gases at a pressure which are higher than the surrounding atmospheric pressure. These pressure vessels are not made as a single component but manufacture with an assembly of many other components and connected through bolted joints or riveted joints or welded joints. These joints are susceptible to failure and cause leakage of the liquid or gas which are very dangerous and sometimes causes heavy loss of life, health and property. Hence proper care has to be taken during the design analysis processes by following ASME section VIII division 1 which specifies the design-by-formula approach while division 2 contains a set of alternative rules based on design by Analysis (FEA) to determine the expected deformation and stresses that may develop during operation. The ASME section-VIII division-2 standards are used for the design of pressure vessel. Leakage in gasketed flanged joints have always been a great problem for the process industry. The sealing performance of a gasketed flanged joints depends on its installation and applied loading conditions. The present project work involves the design procedure and stress analysis (Structural Analysis) for the leak proof pressure vessel at the gasket under three different gasket conditions. Keywords: 1. FEM, 2. ASME, 3. ANSYS, 4. Gasket,5. Displacement,6. Stress

Failure analysis of a steel pressure vessel with a composite wrap repair proposal

Two steel pressure vessels, part of an air compressor unit, failed during hydrostatic test at a pressure lower than proof pressure. Pressure drop and fluid leakage was noted during the test and later investigation revealed through-wall cracks on the shells of each vessel. Experimental and numerical investigation was employed to determine possible causes of failure and to propose a repair method for such vessels. Non-destructive testing (visual and ultrasonic) was performed to check the outer and inner surfaces of the vessel for possible cracks and to measure wall thickness. Optical and scanning electron microscopy was used to inspect crack surroundings and determine the size of the cracks. According to experimentally obtained results, excessive pitting corrosion at the bottom part of the vessel initiated cracks. In order to retain the functionality of the vessel, composite patch repair procedure is proposed. Numerical analysis was performed to determine pressure bearing capacity of the repaired vessel. Also, recommendations for avoidance of failure scenario for considered pressure vessels are given.

The requirements for the design and construction of a gas cylinders aimed for transportation of a compressed and liquefied gases

In this paper a typical requirements for the design and construction, workmanship and tests of a gas cylinders of water capacity between 150 l and 3000 l are described. This type of gas cylinder presents a refillable seamless steel tube aimed for transportation of compressed and liquefied gases exposed to extreme world-wide ambient temperatures. These tubes can be used alone or in batteries to equip trailers or multiple element gas containers (ISO modules or skids). When it comes about design requirements, the main focus is on the cylindrical shell thickness, which is calculated using the Lamé-von Mises formula. For some applications such as tubes assembled in batteries to equip trailers or skids (ISO modules) or MEGCs for the transportation and distribution of gases, it is important to calculate stresses associated with mounting the tube (bending stresses, torsional stresses, dynamic loadings etc.). Special attention must be paid to design of tube ends, which should be approximately hemispherical. To permit internal visual inspection of the tube, an adequate opening must be provided at the neck ends. The tubes are manufactured from seamless steel tubing, typically hot rolled, extended/extruded or forged. The ends of tube are hot formed using either forging or spinning methods. After manufacturing process, each tube must be inspected in terms of surface imperfections. Next, each tube must be ultrasonically examined for internal and external defects and laminar imperfections and to determine wall thickness. Batch tests for checking the quality of tubes includes mechanical testing, such as tensile and impact testing. Beside the batch tests, all tubes must be subjected to the following tests: a hydraulic proof pressure test or a volumetric expansion test, a hardness test, a visual inspection, a visual check of the stamp markings, a dimensional inspection and an ultrasonic non-destructive testing (NDT). At the end of this paper, the most commonly found manufacturing imperfections are pointed out.

Failure analysis of a ruptured compressor pressure vessel

This paper deals with failure analysis of a ruptured pressure vessel that served as a part of an air compressor. Pressure vessel failed during hydrostatic test when, at a pressure level lower than proof pressure, two cracks occurred on the shell and test fluid leakage was recorded. Experimental investigation methods were employed to determine possible causes of crack occurrence and vessel rupture. Liquid penetrate inspection was performed to check for other surface-breaking defects on the shell and locations of the cracks. Visual examination revealed the condition of the internal surface of the shell. Optical microscopy was used to inspect crack area while scanning electron microscopy examination at suitable magnification was employed to characterize fine microstructure of the fractured surface and to reveal flaws that served as rupture initiation points. Material’s chemical composition was determined using optical emission spectrometer with glow discharge source sample stimulation. Hardness test results were used to derive maximum tensile strength of the material. According to results obtained from performed investigations, it was concluded that excessive corrosion at the bottom part of the pressure vessel caused formation of pits that served as initiation points for leakage cracks. Recommendations for avoidance of such scenario with the rest of the user’s compressor pressure vessel were given. Also, ultrasonic testing of shell thickness was performed and results of the performed hydrostatic pressure test were recorded to be used in subsequent numerical failure analysis of the failed pressure vessel.

Estimation of Correct Long-Seam Mismatch Using FEA to Compare the Measured Strain in a Non-Destructive Testing of a Pressurant Tank

This paper discusses the design criterion of a pressurant steel tank made of HSLA 15CDV6 and proof pressure test (PPT) as a non-destructive examination. An inverse Ramberg-Osgood relation is used to represent the stress-strain curve of the material. Elasto-plastic finite element analysis (FEA) has been carried out to examine the adequacy of the design. Experimental stress analysis has been carried out from the measured strains and found maximum effective stress is at LS joint (max. measured strain location). Strain obtained from FEA is compared reasonably well with the proof pressure test (PPT) data at most of the strain gauge locations except at one long-seam (LS) joint. So, to explain the causes of difference in strains near one LS, parametric studies have been performed in a 3D FEA with varying LS mismatch to find the correct mismatch as a reverse engineering problem. It is found that a mismatch value of 0.9 mm will give the required strain at PPT, which is measured only 0.4 mm. The failure pressure estimated through nonlinear FEA/analytical expressions found to meet the design.

Acoustic emission examination of high strength steel M250 pressure vessels for aerospace applications

This paper deals at experiences with the Acoustic Emission (AE) monitoring of critical pressure vessels during qualification proof pressure test. Conventional Non Destructive Evaluation (NDE) methods have limitations in evaluating the vessel. There is a high probability that they may not provide information required to evaluate the quality of vessel. In contrary, Acoustic emission technique has a high probability of detecting the likely defects in pressure vessels prior to the failure. This technique has to be applied under pressure load. These pressure loads create stresses in the vessel. During increasing pressure loads AE signals are obtained from discontinuities and other locations of stress concentrations. AE is very useful in estimating the soundness of critical pressure vessels used by aerospace industry that is made up of high strength Maraging steels. AE Testing and result analysis was carried out according to standard procedures. During the tests, AE signals were recorded and post analysis was done to understand the response from the material. The experimentation revealed that the amplitude of AE signals were less than the corresponding AE signals for critical crack opening, during pressurization cycle. Also, at proof pressure, a 2 minutes hold time was observed with no increase in amplitude of signals. AE activity can detect any defect growth during proof pressure test. Inspection was carried-out in accordance with a set of acceptance criteria based on available literature and specimen level tests.

ON THE EXPERIMENTAL RATIONALE OF QUALITY INDICATORS OF FIRE-FIGHTING LAYFLAT DELIVERY HOSES FOR FIRE-RESCUE EQUIPME

The urgency of the necessity of experimental substantiation of quality indicators of the fire-fighting layflat hoses for fire – rescue equipment and methods of their estimation is noted, taking into account the modern approaches set out in European standards. The results of experimental researches of fire-fighting layflat hoses for fire – rescue equipment by quality indicators are presented: resistance of the hoses to the action of working hydraulic pressure, resistance of the hoses to the action of the proof hydraulic pressure, burst pressure and abrasion resistance. Delivery fire hoses are one of the main types of fire fighting equipment. Delivery fire hoses in the course of operation undergo mechanical wear, are exposed to the sun's rays, microbiological putrefactive processes, accidental ingress of chemically active substances, the influence of low and high temperatures, irreversible processes of material aging. All this causes the appearance of defects of different nature. Analysis of the causes of failure of delivery fire hoses showed that of all failures more than 60% are fistulas, as well as breaks and disruptions of heads - 30% and 10% respectively. The analysis of the presence and nature of defects during the regular testing of workers and decommissioned fire hoses showed that the defects are divided into: explicit (gusts and fistulas) that violate the tightness of the hoses; visible cuts, abrasions, missing and chemical corrosion from contamination of fuel and lubricants that do not violate the tightness of the hoses; hidden (unnoticed cuts, breaks in the threads of the power frame, etc.) that do not violate the tightness of the hoses. Studies have shown that only 75% of defects are detected during hydraulic testing, and undetected defects result in hoses failing in a fire. To date, requirements for assessing the quality of delivery fire hoses for fire - fighting equipment in Ukraine are set out in the standard DSTU 3810-98. At the same time, these requirements are to some extent obsolete and do not meet the current regulations of the leading countries in the world on this issue. In view of the above, it is urgent to experimentally justify the quality indicators of the fire-fighting layflat hoses for fire – rescue equipment and methods of their evaluation, taking into account the modern approaches set out in European standards. The results of the pilot studies will be used to justify the provisions of the draft national standard of Ukraine that will be developed and to improve the existing test base. Keywords: abrasion, burst pressure, experimental research, fire – rescue equipment, layflat delivery fire hoses,, proof pressure, quality indicators, technical requirements, specifications, working pressure

ANALYSIS OF THE TECHNICAL REQUIREMENTS FOR THE FIRE-FIGHTING DELIVERY HOSES USED TOGETHER WITH THE FIRE-RESCUE EQUIPMENT

The urgency of the issue of substantiation of technical requirements to fire-fighting layflat delivery hoses for fire-rescue equipment is given. Fire hoses are a significant component of fire fighting equipment. According to DSTU 2273, a fire hose is a flexible conduit fitted at the ends with connecting heads intended for the transport of extinguishing agents. Among the technical means intended for the transportation of extinguishing agents to the fire cell, the main role is certainly played by delivery fire hoses. According to DSTU 2273 delivery fire hoses (in EU countries they are classified as "layflat") are intended for transportation of extinguishing agents under excess pressure. At present, there are a number of standards in Ukraine and in the leading countries of the world that set the technical requirements for delivery fire hoses, in particular those used in conjunction with fire rescue equipment, namely DSTU 3810-98, DIN 14811, EN 14540: 2004 + A1: 2007, etc. In addition, a draft state standard is being developed in the Republic of Belarus. Considering the process of gradual integration of Ukraine into the European Union and the fact that the requirements of the current national standard DSTU 3810-98 do not meet the modern European requirements for layflat delivery hoses for fire-fighting equipment, a pressing issue is the justification such types of hoses. In order to assist in solving this problem, the Ukrainian Research Institute of Civil Protection is currently conducting a research work "Justification of fire hose test methods", within which a national standard will be developed, which regulates general technical requirements and test methods for the fire-fighting layflat hoses for fire – rescue vehicles. The basic technical requirements for the specified hoses, which meet the modern requirements of the EU and which, after appropriate experimental justification, can be considered in the draft national standard, which regulates the general technical requirements and test methods for the fire-fighting layflat hoses for fire – rescue vehicles to be developed. This publication lists six tables that provide basic specifications for delivery fire hoses. Keywords: abrasion, burst pressure, layflat delivery fire hoses, fire – rescue vehicles, proof pressure, technical requirements, specifications, working pressure.

Fabrication and Testing of the Cold Gas Propulsion System Flight Unit for the Adelis-SAMSON Nano-Satellites

Adelis-SAMSON is a nano-satellite mission aimed at performing geo-location of target signals on Earth using a tight three-satellite formation in space. To maintain formation, each nano-satellite is equipped with a cold gas propulsion system. The design, qualification, and integration of the Adelis-SAMSON nano-satellite propulsion system is presented in this paper. The cold gas propulsion system mass is approximately 2 kg, takes a volume of 2U, and generates a thrust of 80 mN from four thrusters using krypton as a propellant. We first present the propulsion system requirements and corresponding system configuration conceived to meet the mission requirements. Subsequently, we present the system architecture while listing all the components. We overview the particular role and qualification process of four of the propulsion system’s components: the propellant tank, thruster assembly, pressure regulators, and fill and vent valve. We detail the tests performed on each component, such as proof pressure tests, vibration tests, and external leak tests. Finally, we present the propulsion system level tests before delivery for satellite integration and discuss the propulsion system’s concept of operations.

Metamodel-assisted Kalai-Smorodinsky equilibria to solve a multicriteria optimization problem

The main idea of solving a multicriteria optimization problem (MOP) is to find non-dominated solutions belonging to the Pareto frontier (e.g., a compromise between the criteria). If we consider our criteria as players, we can remark that the obtained solutions are the result of a cooperation of the players to increase their profits which is the same principle of solving a bargaining problem (BP). The Kalai-Smorodinsky (KS) model suggests an attractive solution for the BP called KS equilibria that can be also a MOP solution without having to calculate the Pareto Frontier known to be computationally so expensive. In this paper, we propose an algorithm aimed to rapidly finding the KS solution. The idea is to make a coupling between the KS algorithm and a Radial Basis Function (RBF) metamodel called KS-RBF. In fact, the KS algorithm transforms the MOP into a succession of single objective problems (SOP); for our proposed algorithm, the objective function of each SOP will be replaced by an approximate one using a reliable RBF metamodel (SOP-RBF). The performance of the proposed approach is firstly validated by some well-known mathematical multicriteria problems (Tanaka, Poloni, and ConstMIN problems) by finding a KS solution belonging to the Pareto Frontier; then, we used it to solve a realistic industrial case, namely, shape optimization of the bottom of an aerosol can undergoing non-linear elasto-plastic deformation in order to simultaneously minimize the dome growth (DG) (e.g., displacement of can base) at a proof pressure and maximize the dome reversal pressure (DRP), a critical pressure at which the aerosol can’s bottom loses stability (e.g., initiates buckling). The KS solutions are compared with Pareto Frontier results previously suggested in other papers. The comparison leads us to confirm the performance of the KS-RBF coupling.

Fatigue Crack Growth Rate Studies on High-Strength Low-Alloy Steel under Different Loading Conditions

The fatigue crack growth rate of 0.3C–CrMoV (ESR) steel has been investigated on parent metal and weld under sinusoidal and block loading conditions to simulate the proof pressure testing and service conditions of rocket motor case. Parent metal exhibited higher resistance to fatigue crack propagation at lower stress intensities during sinusoidal loading, and as the stress intensity increased, the crack propagation rates in weld and parent were almost identical. Block loading introduced a plastic zone ahead of the crack tip, retarding the crack propagation rates. During block loading with continuous increase in stress intensity levels, crack growth rates were slow compared to the specimens tested at different ranges of initial stress intensity levels. The Paris’ law constants C and m were evaluated.

Structural Integrity Assessment of a Propellant tank in Presence of Welding Residual Stresses

Upper stage of India’s new generation launch vehicle makes use of cryogenic propellants with liquid hydrogen (LH2) and liquid oxygen (LOX) as fuel and oxidizer respectively. The propellants are stored in tanks fabricated of Aluminum alloy and contain various openings. As carrying out proof test at operating environment is not feasible, the tanks are subjected to proof pressure test at room temperature (RT). During the RT proof pressure test of LOX tank, high strains, greater than 8000με, were recorded by gauges at three locations where weld rework had been undertaken. From structural analysis, the maximum welding residual stress at these locations is evaluated to be 95N/mm2. From stress analysis point of view, positive margins were observed with respect to failure of the tank even in presence of these residual stresses.However, since the tank is operating at cryogenic temperature, though there is an increase in the yield and ultimate strengths of the tank material, there is a reduction in ductility (lower percentage elongation). Therefore, evaluation of structural integrity of the hardware from fracture point of view is of paramount importance. A study was undertaken to investigate the influence of residual stresses on integrity of the tank in presence of minimum detectable crack sizes using conventional NDE techniques. The location where maximum strains were observed, post proof test, is considered for fracture evaluation. Directional stresses at location of interest are predicted through detailed finite element analysis. Subsequently, generalized Failure Assessment Diagram was drawn based on Elasto-Plastic fracture mechanics principles and margin against ultimate load ensured. The tank was used in a launch vehicle which was successfully flown in June 2017.

Electrostatic assembly of superwetting porous nanofibrous membrane toward oil-in-water microemulsion separation

Creating a lotus-leaf-structured membrane surface with nano/microstructures plays a key role in the development of functional membranes for oil/water separation; however, fabrication of such membranes with uniform and compact nano/microstructures via an efficient and facile method have demonstrated to be challenging. Herein, a superwetting nanofibrous membrane with strong corrosive resistance was prepared via co-electrospinning of polyacrylonitrile/sulfonated polyethersulfone nanofibrous membrane (PAN/SPES NFM), amination of PAN and subsequent electrostatic assembly of lotus-leaf-structure by binding the negatively charged silica nanoparticles (SiO2 NPs). Benefiting from the changes in pore size distribution and surface structure of nanofibrous membrane, the optimal membrane is endowed with an intriguing superhydrophilicity of 0°, an underwater superoleophobicity of 161°, and an outstanding oil proof pressure of 95.5 kPa. These fantastic features inspired the membrane to effectively separate the surfactant-stabilized oil-in-water microemulsion with a high water flux of 1852 ± 158 L m−2 h−1 and a high separation efficiency of 99.6% when a vacuum driven pressure of 10 kPa was applied. The layer-by-layer assembly method utilized in the construction of membrane roughness is expected to be applicable to a wide range of other selective wetting separation fields.

Design, Development and Testing of Inconel Alloy IN718 Spherical Gas Bottle for Oxygen Storage

This paper describes the details of design, manufacture and testing of 200 mm diameter spherical gas bottle of Inconel 718 (IN718) with nominal wall thickness of 2.3 mm. Gas bottle was designed for the specified internal pressure loading with a thickness of 2.9 mm at the circumferential weld which was brought down to 2.3 mm at the membrane locations. Hemispherical forgings produced through closed-die hammer forging were machined and electron beam welded to produce a spherical gas bottle. Duly welded gas bottle was subjected to standard aging treatment to achieve the required tensile strength. Aged gas bottle was inspected for dimensions and other stringent quality requirements using various nondestructive testing techniques. After inspection, gas bottle was subjected to pressure test for maximum expected operating pressure and proof pressure of 25 and 37.5 MPa, respectively. Strain gauges were bonded at different locations on the gas bottle to monitor the strains during the pressure test and correlated with the predicted values. The predicted strain matched well with the experimental strain confirming the design and structural integrity.

Design and Development of a Pressure Transducer for High Hydrostatic Pressure Measurements up to 200 MPa

A number of pressure transducers, based on strain gauge, capacitance/inductance type, frequency resonators, are commercially available and are being used for sensing and producing an electrical output proportional to applied pressure. These sensors have their own advantages and limitations due to operational ease, measurement uncertainty and the costs. Strain gauge type transducers are now well established devices for accurate and precise measurement of pressure within measurement uncertainty up to 0.1 % of full scale. In the present research work, an indigenous strain gauge pressure transducer has been designed, developed, tested and calibrated for pressure measurement up to 200 MPa. The measurement uncertainty estimated using the pressure transducer was found better than 0.1 % of full scale. This transducer was developed using four foil type strain gauges, bonded, two in axial direction while other two in radial direction, to the controlled stress zones of a tubular maraging steel active cylinder working also as diaphragm. The strain gages were then connected to a Wheatstone bridge arrangement to measure stress generated strains. The pressure was applied through matching connector designed in the same tubular transducer active element. The threaded unique design in a single piece through collar, ferule and tubing arrangement provides leak proof pressure connections with external devices without using additional seals. The calibration and performance checking of the pressure transducer was carried out using dead weight type national pressure standard using the internationally accepted calibration procedure.

Experimental Evaluation of Overload Capability of an Annular Combustor Casing of a Gas Turbine Engine

For the aero engine, size and weight of the combustors are important considerations along with long operating life and its overload capability. The combustor which is considered for this research has an annular shape with a thickness of 2 mm. The combustor casing is manufactured out of forging by machining to a thickness of 2 mm. This method has the advantage of better control of the thickness so that the desired thickness can be maintained throughout the component. Structural analysis has been carried out for the overload condition which is taken as twice the maximum operating pressure and at engine operating temperature analytically. The strength of the combustor casing has been evaluated analytically before subjecting it to experimental test. It is a mandatory requirement from the airworthiness point of view to evaluate its overload capability and to validate the manufacturing methodology by means of full scale rig tests before it is declared fit to fly. Details of the test facility, test adaptors, adaptation of the combustor to the test facility, instrumentation and the testing are presented in this paper. The component is inspected before starting the test and at the end of the test. No cracks and no change in dimensions are observed as per the inspection reports. The combustor casing has withstood the proof pressure test and demonstrated its overload capability for its safe life. The manufacturing process, that is, manufacturing of the combustor out of forging is also validated by means of this test.

Failure Analysis of a Reactor after Explosion Accident

Burst of a reactor occurred in an explosion accident during the production of antistatic agent process. According to the results of site survey, the current regulations and standards as well as the requirements of the accident investigation group, the reason of burst was discussed by failure analysis of the shell and bolts. The shell strength was analyzed by visual inspection, thickness measurement, and strength verification as well as estimating of bursting pressure. It can be concluded that the tank strength met the requirements of design condition. The bolts of the reactor was broken in the accident, so the failure analysis of bolts was carried out in detail, including visual inspection, fracture examination, chemical composition analysis, mechanical testing and strength verification. According to the results of the measured mechanical properties, the strength of the bolts was verified. It can be concluded that the bolts could bear the proof pressure test safely. Fracture analysis shows that no obvious metallurgical defects were found, the bolts were broken due to extreme overload. According to the technical analysis of the shell and the bolts, it can be concluded that the reactor could service safely under normal operating conditions. The cause of the bursting was transient extreme overpressure.