B. Medjo

API J55 Steel Casing Pipe with an Initial Surface Crack under Internal Pressure - Determination of Fracture Parameters

Seam casing pipe used in an oil drilling rig, manufactured by high frequency (HF) contact welding of API J55 steel, is tested. The influence of an initial defect (machined surface crack) is analysed, by performing pressure test of a pipe segment closed at both ends. Besides the damages at the internal surface, casing pipes are exposed to damage at the external surface, which is why such configuration is analysed here. Measurement of strains and crack mouth opening displacement (CMOD) enabled the application of direct method for J integral evaluation. This procedure is based on the path independence of the J integral and can be applied both in laboratory conditions (on specimens) and on structures. However, it requires a demanding experimental - computational procedure, which is accomplished here using the developed routine. Additionally, the behaviour of the pipe under internal pressure, including fracture mechanics parameters determination, is modelled numerically (by finite element method) in software package Abaqus. The pressure is applied as distributed load acting on the inner surface of the three-dimensional model, and axial tension is applied at the end of the pipe to simulate the closed end. J integral values determined numerically and using direct method are used for estimation of the critical pressure corresponding to the crack growth initiation. Additionally, plastic limit load, i.e. pressure which causes yielding of the ligament, is determined. Based on the results, criteria for pipe integrity assessment are discussed

Influence of Crack Length on Ductile Fracture Initiation in Welded Joints with one and Two Weld Metals

Among various micromechanical models for ductile fracture analysis using local approach, those based on the Gurson plastic flow criterion have been intensively developed in the past three decades. However, their application is still subject of many researches, with the aim to improve the assessment of ductile fracture in various, mainly metallic, materials. In this work, Gurson criterion is applied to welded joints produced with one or two different weld metals (one of these is overmatched, while the other is undermatched). Welded single-edge notched bend (SENB) specimens are examined, with an initial pre-crack located in the symmetry plane of each joint. Local approach is chosen for assessment of behaviour of the joints under the external loading, to capture the effect of material inhomogeneity and initial crack length on deformation and ductile fracture initiation in analysed specimens.

Project Management Software for Distributed Industrial Companies

This paper gives an overview of the development of a new software solution for project management, intended mainly to use in industrial environment. The main concern of the proposed solution is application in everyday engineering practice in various, mainly distributed industrial companies. Having this in mind, special care has been devoted to development of appropriate tools for tracking, storing and analysis of the information about the project, and in-time delivering to the right team members or other responsible persons. The proposed solution is Internet-based and uses LAMP/WAMP (Linux or Windows - Apache - MySQL - PHP) platform, because of its stability, versatility, open source technology and simple maintenance. Modular structure of the software makes it easy for customization according to client specific needs, with a very short implementation period. Its main advantages are simple usage, quick implementation, easy system maintenance, short training and only basic computer skills needed for operators.

Seam pipes for process industry - fracture analysis by using ring-shaped specimens

Pipelines are commonly used in process industry for transport of fluids, as well as granular solids, due to their numerous advantages in comparison to other transportation means. Pipe integrity is essential for a reliable work of the entire plant, as well as for safety assurance. Also, serious ecological consequences may follow the pipeline failure in some cases, i.e. due to the leak of toxic, flammable or otherwise dangerous fluids in a chemical or some other plant. Therefore, it is very important to examine the fracture behaviour of pipelines, which is done here by testing the recently proposed ring-shaped specimens exposed to bending. The specimens were fabricated from a seam pipe for pressure applications (allowed for usage on temperatures up to 300 °C). Initial defects, very narrow notches, were machined either in the base metal and weld metal (seam) or in the base metal only. Regardless of the defect position, ductile fracture mechanism is observed in all specimens. The results show that the ring-shaped specimen can be successfully used for fracture characterisation of pipeline material, especially for thin-walled pipes which are not suitable for production of standard fracture mechanics specimens due to the insufficient wall thickness.

Structural integrity assurance of casing pipes in the oil and gas industry

The exploitation of casing steel pipes used in oil and gas drilling rigs typically involves a corrosive atmosphere, high pressures and elevated temperatures. These conditions can affect the initiation and development of defects in the material, which can jeopardi ze the safe service of the system. In this work, an assessment of the integrity of a damaged pipe, manufactured by high frequency contact welding (HF) of API J55 steel, is presented. The influence of an initial defect (machined surface crack) on the pipe structural integrity is analysed. Besides the defects at the internal surface, which is in contact with the transported fluid, casing pipes are also exposed to damage at the external surface, which is why such configuration is examined here. The analysed surface crack is in an axial direction, bearing in mind that this type of defect is the most severe for the cylindrical pressurised components. Internal pressure testing is conducted on a pipe closed by dished ends. The values of fracture parameters, crack mouth opening displacement CMOD and J integral, were tracked during the experiment. The applied procedure for J integral determination (so-called direct measurement) can be applied both on standard specimens and on structures. It includes the use of combined experimental – computational procedure. Finite element analysis is used for determining the criteria for the pipe failure, regarding both crack growth initiation and plastic collapse of the ligament. The size of the crack is varied in the finite element models, in order to determine the influence of its size on the maximum loading. Simplified 2D models are also examined, with the aim of

Micromechanical Analysis of Ductile Fracture Initiation in Mismatched and Double Mismatched Welded Joints

The aim of this paper is prediction of ductile fracture initiation in mismatched and double mismatched welded joints. The micromechanical approach is very well-suited for this purpose, because it describes the process of fracture in a way close to the actual phenomena in the material. Micromechanical models based on the Gurson plastic flow criterion are often used for ductile fracture analysis. One of these models, the Complete Gurson Model (CGM) is used here, because the critical value of the damage parameter can be calculated during the analysis. In many other models, the value of this parameter must be predefined. Experimental and numerical analysis of ductile fracture of pre-cracked single-edge notched bend (SENB) specimens is presented. These specimens contain mismatched or double mismatched (undermatched - OM, and overmatched - UM) welded joints. The crack is located in the weld metal (WM), and in case of double mismatched joints it runs through both weld metals. Numerical analysis is conducted using ABAQUS, with user material subroutine for the CGM created by Z.L. Zhang. Three-dimensional models of double mismatched welded joints are analysed, because they cannot be regarded as plane strain or plane stress. To attain the best possible computational efficiency, the submodelling technique is used in the crack front region. With submodelling, it is possible to have sufficiently refined mesh around the crack front (which is very important, as will be discussed in the paper), without excessive computational cost. Microstructural observation is used to quantify the volume fractions of non-metallic inclusions in base metal (BM) and overmatched and undermatched weld metals. Based on these data, initial void volume fractions and mean free paths between the inclusions for all materials are determined. Crack tip opening displacement (CTOD) at the crack growth initiation is measured experimentally and calculated using the CGM, and different values are obtained in overmatched weld metal in comparison with the undermatched weld metal (for double mismatched joints). The size of the elements near the crack tip strongly influences the prediction of the crack growth initiation, and the best results are obtained for the size of the element similar to the mean free path between non-metallic inclusions. The results are also sensitive to the change of the initial void volume fraction, and the best agreement with the experimental data is obtained for the value determined by quantitative microstructural analysis. It is concluded that the CGM enables determination of the crack growth initiation in analysed welded joints and successfully captures the effect of the inhomogeneity.Copyright

Evaluation of Damage of Steam Pipeline Steel Using Local Approach to Fracture

In the paper, the level of damage of steam pipeline steel after about 100,000 hours at 540°C (1004 °F) under pressure of 42 bars (609 PSI) is analyzed. Material degradation is estimated using a combined experimental and numerical procedure based on micromechanical or local approach to fracture. Detailed analysis is conducted on the samples taken from exploited – used steel and from unused – new steel of the same designation. Damage parameter – void growth ratio – is determined using round notched specimens, (including various notch radii). A comparison of the values for critical void growth ratio, computed for tested steels is made. Based on the values obtained, the possibility of prolongation of the operating life of used steel is discussed.Copyright