Fracture Toughness Of Pipe Material Research Articles

Time dependent reliability analysis for cast iron pipes subjected to pitting corrosion

In this paper, a method is developed to evaluate the probability of fracture failure of pressurized cast iron pipes subjected to pitting corrosion. A new model for corrosion pit depth is developed which considers the correlation between model parameters. The first passage probability method is employed to quantify the probability of fracture failure where the failure criterion is established based on fracture mechanics and the stress intensity factor is modeled as a nonstationary lognormal process. A case study is presented to illustrate the proposed method, followed by a sensitivity analysis to investigate the effects of contributing factors on the probability of fracture failure. It is found in the paper that the developed model for corrosion pit depth is able to reproduce the evolution of the pit depth growth in cast iron pipes in a short period of corrosion time (<10 years) and predict the growth of pit depth for a longer corrosion time (>10 years). It is also found that the risk of pipe fracture failure increases with the increase of corrosion pit depth and the decrease of fracture toughness of pipe material and that the corrosion depth and internal pressure have the most influence on the probability of fracture failure compared with other parameters. Furthermore, the contribution of each variable to the failure probability of pipe varies with exposure time. The method presented in this paper can assist pipe engineers and asset managers in developing a risk-informed strategy for pipe maintenance, repair, and replacement.

The influence of torsion effect on fracture behavior of Pipe Ring Notched Bend specimen (PRNB)

Through the time, researches realize the problem of inability to measure the fracture toughness of pipe material in some cases, because of inability of producing standard specimens from pipe wall. This problem is especially expressed in thin walled pipes. In that sense, a lot of alternative procedures and nonstandard specimens are proposed but with no notable success. One of the latest and the most convenient one is Pipe Ring Notched Bend specimen (PRNB) proposed by Gubeljak and Matvienko (Patent No. RU 2564696 C1, 10.10.2015.: Matvienko Y.G. and Gubeljak N., Model for Determination of Crack – Resistance of the Pipes). Lot of research are made on the PRNB specimen and this paper presents further analysis of such a specimen. Due to the specific geometry of PRNB specimen and loading which is three – point bending, torsion effect occurs in the region of crack. This paper deals with analysis of influence of this torsion effect on fracture behavior of PRNB specimen. In order to obtain more detailed analysis of torsion effect influence, J – integral versus thickness of the specimen curves are presented for the specimen with and without torsion effect and for various a/W ratios. Further, comparison of maximal J – integral values (at half of wall thickness B/2) for specimens with and without torsion effect in relation to the a/W ratio has been analyzed.

Correlation of Pipe Ring Notched Bend (PRNB) specimen and Single Edge Notch Bend (SENB) specimen in determination of fracture toughness of pipe material

AbstractIt is well known that pipes or tubes due to their geometry are not suitable for producing standard specimens for fracture toughness testing (e. g. Single Edge Notched Bend (SENB) specimens or Compact Tension specimens. This is especially evident in thin walled pipes or tubes. We propose a new type of specimen, called Pipe Ring Notched Bend (PRNB) specimen, which is ideal for pipes or tubes due to its ring geometry. In the recent years, the authors have made a lot of research on this type of specimen, but cut out from a plate, not from pipes, where some imperfections in the geometry, material, residual stresses, etc. are present. Within this paper, two PRNB specimens (designations PRNB1 and PRNB2) are cut out from pipe which is used in boilers and made from 16Mo3 steel. From the same pipe, four SENB specimens (designations SENB1, SENB2, SENB3 and SENB4) are also made in order to compare the fracture behaviour of standard SENB and newly proposed PRNB specimens.

Study on the Load Separation Method of SENT Specimens for Fracture Toughness Assessment

In view of low constraint properties, single edged notched tension(SENT) specimens are gradually applied for the assessment on fracture toughness of pipe materials. Detailed analyses for the stress intensity factor, incremental plastic work and plastic factor used in the J-integral computation are conducted. The precision and validity are confirmed through the comparison between formulas obtained and references. Systematic investigation on the estimation of J resistance curves for SENT specimens is carried out on the basis of normalization method which concludes in the non-dimensional load separation method. The establishment of the load separation for SENT specimen is verified by finite element analysis. 30Cr2Ni4MoV used for steam turbine low pressure rotors, T92 pipe steel and 5083-H112 aluminum alloy are employed to experimentally complete the estimation of J resistance curves of SENT specimens by using the normalization method of non-dimensional load separation and reasonable fracture toughness values are acquired.