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Charpy specimen
This study presents selected data from an extensive testing program on steel taken from the Kulluk that was carried out to characterize the present-day mechanical properties. The program investigated the tensile and failure behaviours as well as the fracture energies and ductile-to-brittle transition temperature of steel from two hull locations. These locations were selected based on the following criteria: exposure to seawater and temperature fluctuations, experience of high ice loads, level of plastic deformation, and steel grades. The two selected pieces were made of EH II and DHN grades. The initial results showed that the steels still meet the design requirements as per the ABS rules.
- North America > Canada > Newfoundland and Labrador (0.29)
- North America > United States > Texas > Harris County > Houston (0.16)
Study of the Mechanical Properties and Fracture Morphology of Niobium Microalloyed 80 ksi Class Thick Plates Produced by Controlled Rolling Followed by Accelerated Cooling
Viana, R. T. (Gerdau Ouro Branco) | Gorni, A. A. (Gerdau Ouro Branco) | da Silveira, J.H.D. (Gerdau Ouro Branco) | Camey, K. (Gerdau Ouro Branco) | de Faria, R. J. (Gerdau Ouro Branco)
Abstract This paper describes the first production trials of 80 ksi class thermomechanically controlled processing (TMCP) thick plates at the new Gerdau Ouro Branco plate mill. These trials were very successful, as the product fully satisfied the mechanical properties requirements for such grade, enabling the start of commercial delivery of this material. In addition, experience gained in this process will promote further technological improvement of this class of products, as well more sophisticated plates. The occurrence of separations in the fractured surface of Charpy specimens was considered with detail.
High strength pipeline steels have different plastic properties in each direction. This anisotropy is developed by TMCP processes in a heavy plate mill. The process may also lead to anisotropic ductility and toughness of the plate. The purpose of this study is to develop a constitutive model integrating anisotropic behavior and ductile damage for a high strength pipeline steel. The model is based on a set of experiments on various smooth, notched and cracked specimens and on a careful fractographic examination of the damage mechanisms. The model is also based on an extension of GTN model which includes plastic anisotropy. Provided brittle delamination is not triggered, the developed model can accurately describe the plastic and damage behavior of the steel. The developed model is then used as a numerical tool to investigate the effect of plastic anisotropy on ductile crack extension. It is shown in particular that it is not possible to obtain a unified description of rupture properties for notched and cracked specimens tested along different directions without accounting for plastic anisotropy. INTRODUCTION Economic studies have shown that development of oil and gas transportation over long distances requires the use of high grade steels whose mechanical properties allow to substantially increase the internal pressure for a given pipe thickness. Research projects have then been focused on the development of API grades X80 and X100 (Hillenbrand et al., 2004; Okatsu et al., 2002) and more recently to grades X120 (Hillenbrand et al., 2004). Their mechanical behaviour needs to be characterized both in terms of plastic behaviour and crack growth resistance. In particular resistance to ductile crack initiation and longitudinal propagation needs to be evaluated to assess the high-grade pipelines structural integrity. In practice, standards recommend the use of Charpy-V or drop weight tear tests in relation with semi-empirical correlations to predict the outcome of full-scale burst tests of pipelines (Civallero et al., 1981; Maxey, 1981; Wiedenhoff et al., 1984). These correlations have been established on lower grade steels. Results of recent full-scale testing campaigns (Vogt et al., 1993; Demofonti et al., 2003) have shown that these correlations no longer hold for the new grades.
- Asia > Japan (0.46)
- North America > Canada (0.28)
ABSTRACT A threaded coupling in the production tubing string in an oil well at a tension leg platform in the Gulf of Mexico failed in June 1999. The coupling was a 110 grade, 15Cr martensitic stainless steel. The fracture was longitudinal, through-wall, the entire length of the coupling, and intergranular. Neither harm to personnel nor release of hydrocarbons to the environment occurred because of this failure. This paper presents and discusses the results of a laboratory failure analysis from which it was determined that the fracture was caused by the heat treatment. The fracture was not caused by the production environment or by any other well-bore fluids. The fracture mode was duplicated in unused product in the laboratory. The QA/QC in place for the order did not detect this problem. INTRODUCTION In June 1999, a premium threaded coupling of a 5-½ inch (140 mm), 22.54 lbs/ft production tubing failed during service in an oil well at a tension leg platform in the Gulf of Mexico. The well environment was sweet. The tubing and the coupling were made from the same material, a quenched and tempered, 110 grade, 15Cr martensitic stainless steel with a nominal composition of 0.1C-14.5Cr- 1.7Ni-0.4Mo (a subset of UNS $42500). It was the first such use for this grade of this material. The well fluids were safely contained within the riser and no hydrocarbons were released to the environment. The well was shut in and the tubing string was recovered for evaluation. The well had been in service for a short period of time when the failure occurred.
ABSTRACT Toughness of simulated HAZ was evaluated by means of CTOD and instrumented pre-crack Charpy tests. While the CTOD transition temperature represents brittle fracture initiation toughness, pre-crack Charpy transition temperature is strongly influenced by brittle fracture arrest toughness. The both transition temperatures are controlled by different microsturcutal parameters. INTRODUCTION Property requirements for the steels used for offshore platforms are becoming increasingly severe. In particular, toughness of welded joints is one of the severest requirements to achieve. Offshore platform steel specifications, like API-RP-2Z (1992) and EEMUA 150 (1987), require the heat-affected zone (HAZ) CTOD test in addition to the conventional Charpy-V impact test. CTOD property is very sensitive to the local brittle zones (LBZ) in the HAZ (Haze et al, 1988a). HAZ CTOD value has a large scatter because size of the LBZ is small and it is difficult for fatigue pre-crack-tip to sample the LBZ with high probability.(Toyoda et al,1991). Because of this nature of HAZ CTOD, post- test examination on the sampling of the LBZ is required. In addition to the inherent difficulty in sampling the LBZ, HAZ CTOD value is also influenced by welding conditions even if steel is welded at constant heat input; local toughness of the LBZ changes with thermal cycles of the subsequent welding passes and also size and distribution of the LBZs change with them. All of these factors are influenced by welding bead placement even under constant heat input. On the stage of steel development, simulated HAZ toughness tests may be conducted. They have no ambiguity in terms of the notch location relative to the LBZ and of the variability of welding condition, although large scatter is still observed due to inherent toughness variability, which is a result of a character of the weakest-link brittle cleavage fracture (Lin et al,1987; Tagawa et al,1993).
- North America > United States (0.46)
- Asia > Japan (0.28)
- Energy (0.69)
- Materials > Metals & Mining > Steel (0.68)
Summary The toughness behavior of API Grades E and G pipe was studied by use of the instrumented impact test on Charpy V-notch specimens. This study was done at various locations in the pipes, including the upset, nonupset, and transition from upset to nonupset regions. The use of instrumented impact testing made it possible to distinguish the stage of crack initiation from that of propagation during the impact tests. The study revealed that the Grade E pipe possessed poor toughness as evidenced by the low energy values required to propagate the crack. The toughness behavior varied from upset to nonupset regions in the Grade E pipe. The Grade G pipe, on the other hand, exhibited superior toughness uniformly throughout its length as revealed by the high energy values required for crack propagation. Scanning electron microscope (SEM) and metallographic techniques were used to explain the fracture behavior of both types of pipe. The toughness of Grade E pipe, and therefore its tolerance to the pipe. The toughness of Grade E pipe, and therefore its tolerance to the presence of defects, can be improved by adopting a quench-and-temper heat presence of defects, can be improved by adopting a quench-and-temper heat treatment. Introduction Several field failures involving API Grade E drillpipes have been investigated recently at our laboratory. Many of these failures occurred in the nominal wall region of the pipe about 76 to 102 mm [3 to 4 in.] from the end of the upset into the nonupset region of the pipes. Analysis of these failures at this laboratory and elsewhere showed that they were the result of either fatigue or corrosion fatigue. In many instances, relatively new pipes were reported to have failed after only a short service life. According to API Spec. 5A, the Grade E pipe should possess a minimum yield strength of 517 MPa [75,000 possess a minimum yield strength of 517 MPa [75,000 psi] and a minimum ultimate tensile strength of 689 MPa psi] and a minimum ultimate tensile strength of 689 MPa [100,000 psi]. API Grade E pipes are typically normalized and tempered, and exhibit a microstructure consisting of bainite and ferrite. The high-strength pipes Grades G and S are typically quench-and-temper heat-treated during manufacturing and exhibit a tempered martensitic microstructure. According to API Spec. 5AX, Grade G pipe should possess a minimum yield strength of 724 MPa pipe should possess a minimum yield strength of 724 MPa [105,000 psi] and a minimum ultimate tensile strength of 793 MPa [115,000 psi]. Both ends of the Grades E and G pipes are upset and the upsets are typically 76 to 102 mm [3 to 4 in.] long. In the vast majority of failures reported, the cracking occurred about 76 to 102 mm [3 to 4 in.] from the end of the upset region into the nonupset region of the pipes. Examination of this region showed the presence of several fatigue cracks in many of the broken pipes. No such frequent premature fatigue failures were reported in the quench-and-temper Grade G pipes that were used in even greater depths and severe environments. An earlier study involving quench-and-temper steels showed that those steels exhibiting better fracture toughness also exhibit longer fatigue life compared with the other steels. Hertzberg and Goodenow studied the fracture toughness and fatigue crack propagation in a quench-and-temper alloy steel and a hot-rolled microalloyed steel. They also observed a similar relationship between fracture toughness and fatigue crack propagation, in that the quench-and-temper steel that had better fracture toughness also showed lower fatigue crack growth rates (more fatigue resistance) in the longitudinal direction. The fracture-toughness measurements in Refs. 5 and 6 correlated well with Charpy impact tests: steels that possessed better fracture toughness also showed higher Charpy impact energy absorbed (or lower impact transition temperatures). The purpose of this investigation was to use the instrumented impact tests to study the toughness behavior of this region (about 76 to 102 mm [3 to 4 in.]) in relation to the upset region, the transition zone from the upset to nonupset regions, and the nominal wall of the pipe. The behavior of a Grade G pipe was also studied for comparison with the Grade E pipe. Also, the toughness behavior of the Grade E pipe in the quench-and-temper condition was studied.
- Well Drilling > Drillstring Design > Drill pipe selection (1.00)
- Well Completion > Hydraulic Fracturing (1.00)
ABSTRACT In current practice of platform and drilling vessel construction, a steel is considered as having adequate fracture toughness if the transition temperature of the steel is below the minimum service temperature. Plates from the material used in construction of several fixed platforms and semi submersible drilling vessels have been collected to obtain basic data for establishing the ductility transition temperature of various widely used grades of structural steels.. The steels were produced by both U. S. and European mills. Specimens taken from these steel plates were subjected to Chary V-notch tests and drop weight tests. For each grade of steel investigated, these tests have determined the nil ductility temperature as well as the variation with temperature of impact energy, fracture appearance, and lateral expansion. The transition temperatures of each grade of steel were established by various criteria. The test data presented in this paper will provide a basis for the selection of steels to meet the minimum fracture toughness requirements for offshore platform or drilling vessel construction. The use of several previously published criteria for establishing the minimum fracture toughness requirements for a particular application are discussed, as well as the need for more specific methods for dealing with fracture toughness requirements for fabricated structures which may contain defects. Examples are also given to illustrate the use of these data to establish the safe service temperature for a platform or drilling vessel. INTRODUCTION The purpose of this paper is to present approaches useful in the selection of material for both floating and fixed offshore structures. These approaches involve the treatment of fracture toughness in quantitative terms useful to the designer rather than the more conventional terms used by the metallurgist. The paper also contains a number of Chary transition curves representing steel produced in the last few years by several suppliers. There are situations in which engineers are asked to comment on the suitability of a structure for a particular location and function. Often there is no fracture toughness data available on the material(s) used to fabricate the structure. In these instances, the availability of properties for multiple heats of the particular grade of steel is of considerable benefit over a single "typical" transition curve. It is recognized that the data presented in this paper is not as large a sample as would be desirable, but it is believed to be a better approach than using a "typical curvy" Practical Measurements of Fracture Toughness Fracture toughness is a critical design parameter that is often neglected by the design engineer. Brittle materials are rather intolerant of defects or stress concentrations any may fail at gross stresses well below the yield strength. This brittle behavior is a function of temperature. Nearly all common structural steels exhibit a marked change from ductile to brittle behavior at temperatures below the transition temperature. There are, however, many different transition temperatures for a given material since the transition temperature is particularly sensitive to material thickness, strain rate and notch acuity.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)