High Strength Pressure Vessel Research Articles

Freeze casting of porous monolithic composites for hydrogen storage

Freeze casting of composite PIM-1 and activated carbon hydrogen adsorbent monoliths, from chloroform, toward high-strength pressure vessel inserts.

Integrity and Life Assessment of Welded Joints Made of Micro-Alloyed High Strength Steels

Structural integrity and life of welded joints made of a micro-alloyed low-carbon fine-grained normalised high strength pressure vessel steel, P460NL1 is presented [1]. The researach performed within the scope of this topic involved a large number of experiments, including tensile and bending tests, hardness and toughness, as well as metallography and fractography tests, in order to determine the mechanical properties of the materials and the welded joints in detail, along with their microstructures and their influence on the obtained test results. Specimens cut out of a welded plate with dimensions of 500x500x14 mm were used for the experiments, whereas certain tests required the making of notches in the specimens, inside the heat affected zone, and this welded joint region was the focus of the research. Fatigue experimental tests were based on the assumption that fatigue crack growth rate changes depending on the regions through which the crack passed during its propagation. For this purpose, specimens used in toughness and fatigue tests were divided into four groups, depending on the part of the plate from which they were taken. Numerical calculations were performed using the extended finite element method (XFEM) [2]. Simulations were based on the experimentally determined values of Paris law coefficients, C i m [3-5], for every region through which the crack propagated during each test. Obtained results have indicated good agreement with the experimental ones, which verified the application of extended finite element method in this case.

Evaluating the fracture toughness of layered pressure vessel steels

This paper describes testing conducted on dis-assembled layered pressure vessels to determine the fracture toughness properties of the component structural steels used in their construction. These vessels are part of a large number of similar vessels used at NASA laboratory facilities which were constructed during the 1950s and 1960s to support the then expanding space program. Fracture toughness properties are determined for the ferritic structural steels according to the ASTM standards E1820 and E1921 and the intention is to use the properties obtained from a small number of sacrificed vessels to assure the safety of the remaining vessels. This paper describes the NASA program briefly and the preliminary data obtained more extensively. The steels used to construct the vessels are no longer used in pressure vessel construction but are present in many structures that exist throughout the world that date from the same time period. The properties are hence important and useful beyond the more narrow NASA application. A discussion is also included on the applicability of the modern ASTM fracture toughness tests to evaluate the fracture toughness properties of these early high strength pressure vessel steels.

Research on the Mechanical Properties and Weldability of Wh630e Plate with VN Micro-Alloying

Stable VN micro-alloying for WH630E steel plate can be achieved by utilization of blowing nitrogen at the bottom of BOF and refining process. Steel plate WH630E with thickness of 8-25mm was rolled by TMCP process and was treated by normalizing. By comparing mechanical properties and microstructure changes in as-rolled plate and normalized plates, it was found out that ferrite grain size can be refined by normalizing process and the low temperature impact energy can be improved by normalizing. The main Strengthening mechanism for normalized WH630E steel plate was ferrite grain refining, grain refining plays a more stronger role than V(CN) precipitation strengthening. Cold crack and reheated crack can be avoided by preheating treatment with no more than 170 ̊C before welding WH630E plate, strength and toughness for welded joint can have good match with the base metal by the process of 15∼35kJ/cm welding heat input energy and 500∼580 ̊C SR(stress relief)heat treatment. Yield strength of normalized high strength pressure vessel steel plate can be improved by VN micro-alloying, and then the wall thickness of pressure vessel can be thinned or operating pressure can be increased, therefore overall weight of transportable pressure vessel can be reduced, and there will be significant economic and social benefits for the application of this kind pressure vessel steel plate.

Mechanical and Physical Properties of a High Strength Pressure Vessel Steel 12Cr2Mo1R

12Cr2Mo1R is a high strength pressure vessel steel used in the petrochemical industry. The mechanical and physical properties of the steel 12Cr2Mo1R which was developed in Wuhan Iron and Steel (Group) Company, were investigated in the present work. Test results showed that the steel 12Cr2Mo1R exhibits a high strength at room temperature and high temperature, high strength along Z-direction, and also has very good impact toughness at lower temperatures. The density, linear expansion coefficient and elasticity modulus were also measured. The measured values are all higher than the corresponding specifications of national standards. The uniform mechanical properties and physical properties is attributed to homogeneous microstructure through steel plates.

Post-Autofrettage Thermal Treatment and Its Effect on Reyielding of High Strength Pressure Vessel Steels

The autofrettage process of a thick walled pressure vessel involves applying tensile plastic strain at the bore of the vessel, which reverses during unloading and results in favorable compressive residual stresses at the bore and prolongs the fatigue life of the component. In thick walled pressure vessels this process can be accomplished with either a hydraulic or mechanical overloading process. The Bauschinger effect, which is observed in many of the materials used in thick walled pressure vessels, is a phenomenon, which results in lower compressive residual stresses than those predicted with classic ideal isotropic hardening. The phenomenon is a strong function of the amount of prior tensile plastic strain. A novel idea, which involves a multiple autofrettage processes, has been proposed by the present authors. This process requires a low temperature post-autofrettage thermal treatment, which effectively returns the material to its original yield conditions with minimal effect on its residual stress state. Details of this low temperature thermal treatment are proprietary. A subsequent second autofrettage process generates a significantly lower amount of plastic strain during the tensile reloading and results in higher compressive residual stresses. This paper reports the details of the exploratory tests involving tensile and compressive loading of a test coupon, followed by a low temperature post-plastic straining thermal treatment, and subsequent reloading in tension and compression. Finally results of a full scale safe maximum pressure (SMP) test of pressure vessels are presented; these tests indicate a significant increase (11%) in SMP.

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第2報)

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第2報)

高温庄力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第4報)

高温庄力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第4報)

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第3報)

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第3報)

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第1報)

高温圧力容器用高強度Cr-Mo鋼の技術基準と諸特性 (第1報)

Finite Element Investigation of Bauschinger Effect in High-Strength A723 Pressure Vessel Steel

The Bauschinger effect has been evaluated in high-strength pressure vessels. A simple initial test suggested that a biaxial Bauschinger effect was present and that it was different from previously published uniaxial Bauschinger results. The difference was believed to be significant, so further investigation was undertaken. Several full-size A723 steel gun sections were heavily overstrained and subjected to slit tests in order to measure opening angles and displacements. These geometries were then modeled with finite element (FE) analysis using both ideal autofrettage stresses and Bauschinger modified stresses, which were based on previously published uniaxial Bauschinger test results. Because techniques available for predicting reverse yielding for overstrained pressure vessels were limited, a simple methodology for predicting the yield surface upon reverse yielding from a series of uniaxial Bauschinger test data was developed and is presented. This methodology, when used in the FE predictions, compares favorably with analytical predictions made previously. Comparisons of slit-opening results measured from pressure vessel sections with FE calculations using uniaxial Bauschinger data are made. The opening displacements comparison between the uniaxial predictions and those measured from the heavily overstrained sections with biaxial stresses are so subtle (<1mm) that the tests appear to be inconclusive.

Mechanisms and Modeling Comparing HB7 and A723 High Strength Pressure Vessel Steels

HB7, an ultra-clean, high strength pressure vessel steel manufactured in France, is compared to A723 steel. This steel, suggested as an improved pressure vessel material is currently being proposed for critical applications, and will likely be used more frequently as design engineers discover its capabilities. This paper includes comparisons of strength, fracture toughness, fatigue properties and composition of the two steels, followed by an in-depth comparison and modeling of environmental cracking resistance, Bauschinger-modified residual stresses and fatigue lives. Results indicate that in all critical areas, with the exception of Bauschinger-reduced residual stress, the HB7 is superior to the A723 steel. Particularly for small amounts of autofrettage, near-bore residual stresses are reduced for HB7 steel compared to those for A723 steel at the same strength level. The greatest improvement of the HB7 over the A723 is in environmental cracking resistance. The HB7, when tested in concentrated sulfuric acid, exhibits five orders of magnitude longer crack incubation times and three orders of magnitude slower crack growth rates, when compared to A723 steel at the same strength level.

평균응력을 동반하는 2.2Ni-lCr-0.5Mo강의 피로수명과 변형률에너지 밀도와의 상관관계

Fatigue damage of 2.2Ni-1Cr-0.5Mo steel used fir high strength pressure tubes and vessels was evaluated using uniaxial specimens subjected to strain-controlled fatigue loading. Based on the fatigue test results from different strain ratios of -2. -i 0, 0.5, 0.75, the fatigue damage of the steel was represented by using a cyclic strain energy density. Mean stress relaxation depended on the magnitude of the applied strain amplitude. The high pressure vessel steel exhibited the cyclic softening behavior. Total strain energy density consisting of the plastic strain energy density and the elastic tensile strain energy density described fairly well the fatigue life of the steel, taking the mean stress effects into account. Compared to other fatigue damage parameters, fatigue life prediction by the cyclic strain energy density showed a good correlation with the experimental fatigue lift within a factor of 3.

Effect of heat treatment of preform on the mechanical properties of flow formed AISI 4130 Steel Tubes—a theoretical and experimental assessment

Flow forming is an advanced eco-friendly chipless metal forming process, which employs an incremental rotary point deformation technique. Flow forming offers a remarkable increase in tensile properties due to strain hardening and provides excellent dimensional accuracy and surface finish for the formed part. This paper presents the results of a study on the effect of heat treatment of preform material on the mechanical properties of the flow formed part and the validity of using empirical relations in predicting the properties of the flow formed components. The strength coefficient K and strain hardening exponent n of equation σ= Kε n are determined from stress–strain curves under different heat treatment conditions for AISI 4130 steel. The effect of cold work on mechanical properties of flow formed part for a given reduction in area (RA) is predicted using empirical relations published in literature. In order to validate the hypothesis of prediction of cold worked material properties after flow forming, a few flow forming experiments are carried out. The preform dimensions are worked out based on constant volume principle. A three pass flow forming sequence was followed and the properties are measured for about 88–90% thickness reduction. Comparison of the experimental results and the properties of the flow formed tubes predicted using empirical relations shows that empirical relations can be used for predicting the properties of flow formed tubes with reasonable accuracy. Preforms processed through hardening and tempering route give better performance. These results are used for design of performs for manufacturing of large number of high strength pressure vessels successfully.

Experimental studies on bursting pressure of thin-walled flow formed pressure vessels

The design of pressure vessels for critical high-pressure applications has to consider two failure modes. The first mode of failure can occur when deformation becomes excessive and permanent deformation might occur. The second type of failure occurs at higher magnitudes of pressure resulting in bursting of tubes and catastrophic failure. Hence predicting the bursting pressure of thrust chambers is an important consideration in their design and gives a more realistic indication of the factor of safety than the value that can be provided based on the yield pressure value. The burst pressure gives an indication of the margin of safety available over the maximum expected operating pressure (MEOP). The assessment of burst pressure is very important for pressure vessels which are used for critical applications. In this paper an attempt has been made to study the suitability of the burst pressure prediction formula available in literature and its modification for thin-walled high strength pressure vessels manufactured by a flow forming technique.

Effects of acute and chronic treatment of haloperidol, clozapine and sulpiride on c-fos mRNA expression in rat forebrain regions

Stable VN micro-alloying for WH630E steel plate can be achieved by utilization of blowing nitrogen at the bottom of BOF and refining process. Steel plate WH630E with thickness of 8-25 mm was rolled by TMCP process and was treated by normalizing. By comparing mechanical properties and microstructure changes in as-rolled plate and normalized plates, it was found out that ferrite grain size can be refined by normalizing process and the low temperature impact energy can be improved by normalizing. The main Strengthening mechanism for normalized WH630E steel plate was ferrite grain refining, grain refining plays a more stronger role than V(CN) precipitation strengthening. Cold crack and reheated crack can be avoided by preheating treatment with no more than 170 ̊C before welding WH630E plate, strength and toughness for welded joint can have good match with the base metal by the process of 15∼35 kJ/cm welding heat input energy and 500∼580 ̊C SR(stress relief)heat treatment. Yield strength of normalized high strength pressure vessel steel plate can be improved by VN micro-alloying, and then the wall thickness of pressure vessel can be thinned or operating pressure can be increased, therefore overall weight of transportable pressure vessel can be reduced, and there will be significant economic and social benefits for the application of this kind pressure vessel steel plate.

The mechanical properties of high-strength steel weldments

In order to develop good mechanical properties in highstrength weldments, selection of a welding process, weld consumables, and postweld heat treatment compatible with the intended service is of major importance. This paper illustrates how these selections can influence the properties of the weld metal, heataffected zone and base metal for six highstrength pressure vessel steels. In each case, the balance of strength and toughness achieved is indicated and the effect of process variables reported. The steels studied include those intended for high- and lowtemperature services, as well as those intended for general purpose applications.

Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part II: Variable Amplitude Block Loading Effects

To investigate load sequencing effects in fatigue-crack growth, surface flaw or part-through crack (PTC) specimens of a high-strength pressure vessel steel were subjected to variable-amplitude cyclic loading. Blocks of different load sequences and stress-ratio (R) patterns and cyclic lengths were employed. Crack-growth rate (da/dN) data were analyzed within the framework of linear elastic fracture mechanics using the stress-intensity range parameter, ΔK. The da/dN data were found to correlate well with a seauence-independent formulation of ΔK derived using nominal mean stress, σm, for the loading blocks studied. However, it proved necessary to utilize the normalizing relationship discussed in “Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude”, to account for stress-ratio effects observed under the variable-amplitude block loading. Only the sequential block pattern of high-low-intermediate produced a significant crackgrowth retardation. Predictions made using the sequence-independent normalizing procedure compare favorably with those using the Willenborg model. It is concluded that useful predictions for structural life under variable-amplitude cyclic loading sequences can be made for a wide variety of high-strength pressure vessel applications using sequence-independent analysis procedures.

Analysis of Fatigue-Crack Growth in a High-Strength Steel—Part I: Stress Level and Stress Ratio Effects at Constant Amplitude

High-strength pressure vessel steel surface flaw or part-through crack (PTC) specimens were selected for studies of fatigue crack growth rate (da/dN) under constant amplitude cycling to assess the effects of varied stress ratio R (minimum nominal stress/maximum nominal stress, σmin/σmax) and stress level (maximum nominal stress/yield stress, σmax/σys). Analyzed within the framework of linear elastic fracture mechanics, these studies warrant the following conclusions regarding fatigue-crack growth in this material: • Crack growth does not appear to be influenced by stress level, per se, even for stress levels approaching net section yield. • It is moderately influenced by both positive (tension-tension) and negative (tension-compression) stress ratios. • It is principally related to the tensile range of cyclic stress as expressed by the fracture mechanics stress-intensity range parameter, ΔK. Utilizing the results of this investigation, a normalizing relationship expressing da/dN as a function of both ΔK and R, which is applicable to both positive and negative values, is discussed. It is concluded that the stress-intensity range ΔK provides a viable analytical approach to fatigue crack-growth analyses relevant to high-strength pressure vessels.

Fracture Toughness and Pressure Vessel Performance

Criteria for predicting pressure vessel performance based on fracture toughness are reviewed in general terms. Experimental studies of small pressure vessels fabricated of high toughness, high strength steel 4330V (Mod + Si) are described. Data presented include fatigue life in presence of a small part-through-crack and burst properties of the fatigue cracked cylinders. Interpretation of the fatigue data is based on Paris’ relationship dadN=K4M. The failure stresses are discussed in relation to the stress elevating effect of local bulging on the apparent fracture toughness. The behavior observed in testing full scale high strength pressure vessels fabricated from materials having intermediate fracture toughness, namely, D6A steel at 200,000-psi yield strength and 300M steel at 230,000-psi yield strength and materials having limited fracture toughness, namely, twenty percent nickel maraging steel at 280,000-psi yield strength, are discussed in relation to the ratio of fracture toughness to plane-strain fracture toughness based on the part-through-crack model. Precautions necessary for fabrication and inspection to insure reliable performance are discussed.