Fracture Of Pressure Vessels Research Articles

Study on the Fracture of Pressure Vessels for Hydrogen Filling by Semi-elliptical Cracks

Study on the Fracture of Pressure Vessels for Hydrogen Filling by Semi-elliptical Cracks

Omega and CTOA for dynamic steady-state fracture propagation and their dependency to fracture speed

Dynamic ductile fracture in pressure vessels is an increasingly important topic. Recent catastrophic pressurised pipeline failures highlighted the critical needs of reliable pipeline infrastructures. The ability for line pipe steels to resist fracture is a critical design factor for governing the severity level of fracture failures given that it determines if fracture propagates for several kilometres or is arrested quickly. Developing a reliable fracture toughness test to systematically evaluate new steel products’ quality is therefore important. In the current work, a novel small-scale fracture toughness parameter Omega was implemented and compared to the well-established parameter CTOA, with respect to their performance of characterizing steady-state fracture propagation and their dependencies to Fracture Speed. The current experimental data were collected from a 3-point bend dynamic Drop Weight Tear Test (DWTT) for 9 line pipe steels with different thicknesses and impact conditions. It was found that the Omega gives significantly better description for steady-state fracture propagation; and it is found to be independent of the Fracture Speed. The current study confirmed that in DWTT, CTOA values decrease with increasing Fracture Speed. Finally, a simple analytical model is proposed to describe this dependency (CTOA-Fracture Speed) from a geometrical standpoint.

Modelling of fracture in pressure vessels by thin shell isogeometric analysis

Modelling of fracture in pressure vessels by thin shell isogeometric analysis

Modelling of fracture in pressure vessels by thin shell isogeometric analysis

We aim to model fracture on pressure vessel surfaces so that its rupture can be avoided. It is well known that pressure vessels have wide-spread applications in almost all industries. They are often subjected to high pressures and extreme temperatures and in some typical applications they even carry highly flammable or hazardous substances. In the presence of cracks, the state of stress near the fracture zone becomes very high, due to the phenomenon of stress singularity at the crack tips. This greatly reduces the strength of the material and can lead to early failure. In this paper, the geometry of pressure vessels is discretised using splines which are used as the basis for isogeometric analysis (IGA). Initially, the stress analysis of thin pressure vessel is carried out in the absence of cracks by implementing IGA-based Kirchhoff-Love shell theory, and the results are compared with analytical or standard available solutions. The crack is assumed to cross the entire thickness and is introduced either in axial or circumferential direction.

Managing Cold Temperature and Brittle Fracture Hazards in Pressure Vessels

Brittle fractures of pressure vessels can be both catastrophic and costly. The intent of this article is to provide guidance in avoiding such failures by identifying some of the causes for cold embrittlement hazards and brittle fracture in pressure vessels. Selected examples will help illustrate the main factors that contribute to brittle fracture, through identifying brittle fracture features, and demonstrating the importance of coordination of materials and potential operating condition. This article also discusses how to assess existing equipment pressure vessels subject to cold conditions and brittle fracture concerns using the guidelines of API 579-1/ASME FFS-1, Part 3.

A pressure vessel fracture mechanics study of the aluminum beverage can

Two fracture mechanics studies were conducted using two different aluminum beverage containers (wall thicknesses of 0.0044 in. [0.112 mm] and 0.0039 in. [0.099 mm]). The first study involved a 1.25 in. (31.75 mm) wide center-cracked panel specimen to measure the axial fracture resistance of the containers. Factors contributing to beverage container fracture resistance are discussed, including the thickness and rolling direction orientation. Due to the extremely thin nature of these containers, a reduced specimen thickness leads to a reduced fracture resistance. This resistance is also seen to increase as the orientation to the material rolling direction becomes perpendicular. The second study was a full-scale, leak-before-break rupture test. Each container had a crack of a known length and depth machined in the exterior wall. The stress intensity factor of these cracks upon failure gives excellent correlation to the center-cracked panel specimens as well as to other models for predicting pressure vessel rupture.

How to obtain a complete dependence curve of impact toughness or fracture toughness vs temperature on nuclear pressure vessel steels by using only one Charpy-size specimen

Considering the re-utilization of parts of the broken Charpy-size specimens used in nuclear pressure vessel fracture toughness surveillance programs, this paper has investigated how to evaluate the dependence curve of impact toughness or fracture toughness vs temperature for a nuclear pressure vessel A508CL3 steel by using one standard Charpy-size specimen and the eight reconstituted Charpy-size specimens which are manufactured from the two broken halves of the tested standard Charpy-size specimen. The research results indicate that by this means a reliable and complete dependence curve of impact toughness or fracture toughness vs temperature on nuclear pressure vessel steels can be obtained by using only one standard Charpy-size specimen. This, in a nuclear surveillance program, is equivalent to getting the complete dependence curve of material property vs temperature from only one Charpy-size specimen that is taken out of a reactor core; this would be very valuable for improving the reliability of surveillance programmes on nuclear pressure vessel embrittlement due to neutron irradiation. Especially this method is extremely important for the life-time prediction and safety surveillance of a nuclear pressure vessel which has been operated for a long-time and for which there is left only a few surveillance specimens in it.

Crack initiation under creep and creep-fatigue on CT specimens of an austenitic stainless steel

In the nuclear industry, some methods for calculating the time of crack initiation from pre-existing defects are needed. For this purpose, a correlation is checked between T i (initiation time) or N i (initiation cycles) and local parameters at a characteristic finite distance d from the crack-tip ( α d criterion) (D. Moulin, B. Drubay and D. Acker, PVP-Vol. 223 (1992), Pressure Vessel Fracture, Fatigue and Life Management, ASME, 1992.) For fatigue tests, relevance of σ d criterion is observed when using finite element code for calculating axial stress range Δσ d. For creep tests, experimental points corroborate σ d criterion when no stress relaxation at the crack tip is supposed. Finite element code with plane strain or plane stress conditions gives a large value of axial stress at 50 μm from the crack tip. Crack initiation prediction is then conservative. Further, a remarkable T i -C h ∗ correlation was observed for creep tests. Both criterions are compared. For creep-fatigue tests, crack initiation prediction is conservative, but comparison of σ d criterion with other approaches is still in progress. Fracture surface examinations show that both creep and creep-fatigue specimens revealed the same intergranular surface aspect, whereas pure fatigue specimens presented transgranular cracking.

Heavy-section steel technology program overview

This paper presents a status review of ongoing HSST program tasks aimed at refining the technology used in analysis of reactor pressure vessel fracture margins under pressurized thermal-shock (PTS) loading. Specific fracture-technology issues addressed include vessel flaw density and distribution, shallow flaws, fractures-toughness data transfer, circumferential cracks, ductile tearing and the influence of low-tearing toughness in stainless steel cladding. Preliminary results from the analysis and test programs are presented, together with interim assessments of their potential impact on a reactor vessel PTS analysis.

Phenomena of material degradation with time relevant to reactor pressure vessels

The knowledge regarding specific technical and regulatory issues which arise in assessing long-term integrity and lifetime management of reactor pressure vessels are reviewed. The major failure risk of the reactor pressure vessel arises from material degradation due to fast neutron irradiation during the service of the plant. Better understanding of the irradiation damage of reactor pressure vessel materials is important in improving and validating the engineering methodologies for the assessment of the reactor pressure vessel integrity and safe service life. The fracture mechanics issues and their impact on the reactor pressure vessel pressurized thermal shock analysis are also discussed, including the effects of cladding on the reactor pressure vessel fracture. Since failure of the reactor pressure vessel might initiate from crack-like defects at critical locations in the vessel wall, the purpose of this presentation is also to review the design, inspection and monitoring practices as well as the occurrence of stress corrosion cracking/fatigue cracks in operating nuclear pressure vessels. Recommendations will also be provided to address the material degradation related concerns in operating nuclear power plants.

Effects of residual welding stresses on fracture of pressure vessels

Effects of residual welding stresses on fracture of pressure vessels

Estimates of brittle fracture probability using reactor surveillance capsule data

This work is part of an expanding effort to construct sound methodology for calculating estimates of brittle fracture of pressure vessels. These estimates are generated from material data on the class of steels being used and from calculated operating characteristics, and involve the structuring of K IC and ΔRT NDT as random variables. Three sources of variability are inherent in material data of the type involved here: (a) measurement variability, (b) variability arising from local inhomogeneities in a plate, and (c) variability from gross differences among plates. Generic data reflect all three, while vessel-specific data limit the third to those plates that are actually used in fabricating a given vessel. We have devised a procedure that combines the data sets with weights that reflect the variance composition and would agree with the limiting cases above should one of them be true. Vessel specific data come from two sources: 1. (1) preoperational tests — these are Charpy V-notch tests from the exact steel plates which are used in fabricating the pressure vessel. Before a plate is used in vessel fabrication, specimens are machined from it and Charpy tests run. Only those plates with acceptable Charpy values are used. 2. (2) Surveillance capsules — in order periodically to monitor the characteristics of an operating pressure vessel, surveillance capsules are placed in the reactor prior to start-up. Each capsule contains specimens machined from the steel plates used in fabricating the vessel. These capsules are removed periodically during scheduled plant shutdowns and tensile, Charpy and fracture toughness tests are run. These are very valuable data since they have been irradiated in the specific reactor of interest. In this paper we present a method for estimating the brittle fracture probability using the HSST and vessel-specific data. The method is general enough so that data from all surveillance capsules removed from a vessel to date can be included for the purpose of updating estimates of brittle rupture probability at the instances of scheduled shutdowns.

Use of probability with linear elastic fracture mechanics in studying brittle fracture in pressure vessels

This paper deals with one phase in the development of statistical methodology for a fracture mechanics analysis of the failure of nuclear steam supply system components, in particular that of brittle fracture in the beltline region of the pressure vessel resulting from various transients. It introduces a probability structure into the deterministic linear elastic fracture mechanics calculations. The resulting estimates of probability of brittle fracture reflect not only variation due to heterogeneity of vessel material but also uncertainties in the effect of embrittlement of the vessel steel due to neutron irradiation. Using importance sampling in conjunction with Monte Carlo simulation we estimate that, for the operational transients considered, the probability of brittle fracture conditional on the presence of an Appendix G flaw is less than 2 × 10 −10 .