Jae Sil Park

Evaluation of Fatigue Characteristic of a Real Waterworks Pipe

The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many researches have reported that test results of standard specimens are very different from those of real structures or components. One reason for this difference is the constraint effects according to the geometrical difference. Therefore, to calculate more accurate fatigue life, the constraint effect must be considered by comparing test results of standard specimens with those of real structures or components. Another reason for this difference is the surface condition. All surfaces of a standard specimen are polished to obtain similar conditions in a fatigue test. However, in a piping system, surface conditions of components are different from each other and very different from that of a standard specimen. Because fatigue life is effected by a surface condition, to evaluate the fatigue life of a piping system, fatigue tests must be conducted with a specimen extracted from a pipe with the same surface condition. The objective of this paper is to evaluate the fatigue characteristic of a real waterworks pipe by conducting fatigue tests with standard specimens and non-standard specimens of base metal and weld metal. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks. Also, fatigue tests of pipes used in water service were carried out and then compared with those of standard specimens and non-standard specimens. From these results the relation between the S-N diagram of a specimen and that of a pipe specimen was evaluated.

FATIGUE CHARACTERISTICS OF SM490A WELDED JOINTS

We compared the fatigue characteristics of weld metal with those of base metal heat-treated and non heat-treated. Also, we examined the influence of bead on fatigue life. From the experimental results of this study, it has been seen that the fatigue characteristics of welded specimens grinded the toe of bead are slightly better than those of welded specimens not grinded. Fatigue life is affected more by the stress concentration due to the profile change in the weld toe rather than by the residual stress, and heat-treatment had almost no influence on the fatigue characteristics.

Evaluation of Pipe Fracture Characteristics for SA312 TP304L Stainless Steel

In order to perform elastic-plastic fracture mechanical analyses, fracture resistance curves for concerned materials are required. A standard CT specimen was used to obtain fracture resistance curves. However the fracture resistance curve by the standard CT specimen was very conservative to evaluate the integrity of the structure. Also the fracture resistance curve was affected by the specimen geometry, crack plane orientation, reverse cyclic loading and dynamic strain aging. The objective of this paper is to be certain the conservativeness of the fracture resistance curve by the standard CT specimen. For these purpose, fracture tests using the real-scale pipe specimen and standard CT specimen test were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method was used to measure the crack extension and the length for the pipe test. From the result of the pipe and the standard CT specimen tests, it was observed that the fracture resistance curve of the standard CT specimen test was conservative compare to that of the pipe specimen test.

FATIGUE LIFE CHARACTERISTICS OF WATERWORKS PIPE WELDS

The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many test results of standard specimens are very different from those of real structures or components because of geometrical effect, surface condition and so on. In this study, fatigue tests with specimens and pipes were carried out to evaluate the fatigue characteristic of a real waterworks pipe. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks system. Also, fatigue tests of real pipes used in water service were carried out. This result was compared with that of standard specimens and non-standard specimens. To evaluate pipes fatigue characteristics based on life distribution, the statistical analysis method was introduced. Probability density functions of the specimen based on the normal distribution function were obtained from fatigue tests at particular stress levels. These functions were then transformed to probability density functions based on a specific number of cycles to failure. This procedure was also adapted to the pipes test results. From these results, the fatigue characteristic of waterworks pipe was evaluated.

The Evaluation of Tensile Properties at High Temperatures Using a Ring Specimen

In the case of inner pressurized pipe, the hoop stress mainly causes the failure of pipe. For evaluating the hoop tensile properties of pipes, a ring test is used although it has an inevitable shortcoming of disturbance by the bending. Arsene suggested a central piece-inserted ring test for reducing the bending. At high temperatures, the friction between the specimen and the central piece exerts a serious influence on the results, so an effect on friction should be considered in the analysis. In this study, for the evaluation of the hoop properties using the central piece-inserted ring model of Arsene, we performed the ring tensile tests at several temperatures. From the ring tensile tests and numerical analysis the load-displacement conversion relationship of ring specimen (LCRR) was determined. We could obtain the hoop tensile properties by means of applying the LCRR to the results of the ring tensile test. From the result, it was observed that the strength decreased as the temperature increased, and the elongation dropped a little around 400°C.

Measurement Methods of Crack Length for Real-Scale Pipe Specimen

Fracture resistance curves for concerned materials are required in order to perform the elastic-plastic fracture mechanical analyses for a piping system. The fracture resistance curve is built with J-integral values and crack extension values. The objective of this paper is to apply the load ratio method to the measurement of crack length for a real-scale pipe specimen. For these, the fracture test using a real-scale pipe specimen and finite element analyses were performed. The direct current potential drop method and the load ratio method were used to measure the crack extension and the crack length for a real-scale pipe specimen test. Finite element analyses about the compliance of a pipe specimen were executed for applying the load ratio method according to the crack length. Introduction The fracture toughness was required to evaluate the fractural integrity of a piping system. So, the fracture toughness derived from the fracture test of a standard specimen was used for the fracture toughness for the material of the piping. Also, it is used to analyze the structure and the fracture characteristics of the total structure being evaluated. The fracture resistance curve, J-R curve is a plot of the crack extension resistance as a function of the stable crack extension. It is used to determine the plane-strain fracture toughness, JIC and to evaluate the elastic-plastic fracture mechanical integrity. The fracture resistance test for a piping material must be conducted to yield the fracture resistance curve. However, the results from standard specimens are affected by constraint effect, reverse cyclic load, dynamic strain aging and so on. Also, in the case of a large pipe, the effect is better. So, the experimental test results of pipes are necessary to prove the property of fracture for the piping system. For the production of the fracture resistance curve by the pipe experiment, J-integral value and crack length are necessary. To calculate the crack extension, the unloading compliance method was proposed in the standard test method, ASTM E1820 [1] about a standard specimen. Also, alternative methods of measuring the crack extension, such as the electric potential drop method, the load ratio method and load normalization method, are allowed. However the unloading compliance and the electric potential drop method need precise measurement equipment and the great experience of a test operator. Also, these methods are difficult to apply to high or low temperature conditions and to dynamic loading conditions. Especially in the direct current potential drop (DCPD) method, the electromagnetic inductive phenomenon dramatically decreases the reliability of the measured potential difference and rapidly changes the measured voltage [2]. Therefore many researchers have investigated the calculating method of a crack extension directly from the load – load-line displacement record, such as key curve method [3], load normalization method [4-5], load ratio method [6-7] and etc. These methods are applied to calculate the crack length on the fracture resistance test for not only the standard specimens but also specimens of various types [8-10]. Also among these, the load normalization method was proposed to calculate the crack length under the dynamic loading condition in the standard test method [1] that modified recently. In this study the DCPD method and the load ratio method are proposed to measure the crack length in a pipe experiment and to confirm the applicability of the load ratio method. To apply the Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 944-949 doi:10.4028/www.scientific.net/KEM.270-273.944

Fatigue Characteristic of High Impact Polystyrene(HR-1360) Materials

In recent times, there has been considerable interest in HIPS (High Impact Polystyrene) materials for their use in construction of office equipments, home electronics, housing for electronics appliances, packing containers, etc. However, these materials suffer from problems caused by fatigue fracture. Further, their strength is substantially affected by environmental conditions. Therefore, in this study, the effect of temperature was analyzed by performing a tensile test and a fatigue test. It was observed that the yield strength, the ultimate strength, and the fatigue life decreased relatively with an increase in temperature. Further, an S-N curve can be predicted by using the results of the tensile test and a micro-Vickers hardness test.

A Study on the Estimation of Fracture Behaviour for a Circumferentially Through-Wall Cracked Pipe

It is known that fracture characteristics are changed due to the geometric configuration. Also, it is known that toughness data obtained from the standard specimen test are conservative to predict fracture behavior of the real piping. Thus fracture behavior by tests of pipes would to be applied to the integrity evaluation for the piping system. However, fracture test with real pipe is not only difficult to perform but also very expensive, and requires lots of experience. So an estimation method of pipe’s fracture behavior is necessary to solve this problem. The objective of this thesis is to propose a method to estimate the fracture behavior of a pipe from the result of the standard specimen fracture test. For this, fracture tests for standard specimens and pipes are conducted. The resultant load - load-line displacement record of the standard specimen was transformed to that of a pipe by load separation method. To begin with, the load versus load-line displacement curve of a standard specimen extracted from a pipe is normalized by a geometry function of the CT specimen. Then this normalized curve was converted to pipe’s load versus displacement curve by a geometry function of pipe. To verify the constraint factor and the geometric function of pipe, finite element analyses were performed. To demonstrate the proposed method, experimental results of pipes are compared with predicted results. Calculated results from CT specimens are similar to experimental results of pipes. Therefore the transformability from a CT specimen to a pipe by load separation method is proved. Consequently the applicability of the proposed method was proved.

Evaluation of the Ductile-Brittle Transition Behaviour of Aging Specimens by the Fracture Toughness Test

The safety and reliability of industrial machineries and structures used in various, and severe conditions has become an increasing concern. This study proposes ductile-brittle transition temperature (DBTT) evaluation technique by the sub-sized specimen test to prevent cleavage fracture. Four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared. The fracture toughness tests were performed on sub-sized specimens both at room and low temperatures. The results of the fracture toughness tests were analyzed to obtain the DBT behaviours of the specimen materials

A Study on Estimation of the Pipe Fracture Characteristics

In order to analyze the elastic-plastic fracture behavior of a structure, the fracture resistance curve of the material should be known. However, it is difficult to evaluate the fracture characteristics with an experiment on the piping system. Instead, the fracture toughness obtained from standard specimen tests is used to analyze the structure and assess the fracture characteristics of the total structure. It is known that toughness data from the standard specimen test are conservative to predict fracture behavior of the real piping. Thus the fracture resistance curve by the fracture test of the real scaled pipe specimen would be applied to the integrity evaluation for the piping system. However, it is not only difficult to perform but also very expensive to perform full-scale pipe tests. The objective of this thesis is to propose a method to estimate the fracture resistance curve of a pipe from the result of standard specimen fracture test. To estimate the fracture resistance curve for a pipe specimen, load – load-line displacement records of a standard specimen were transformed to those of the pipe specimen. The load ratio method was proposed in order to calculate the crack length from load – crack mouth opening displacement records for the pipe specimen. To prove the validity of this estimation results, fracture tests for pipe specimens were performed. Consequently the applicability of the proposed method was investigated by comparing estimated results with tested results.