Abstract
The experimental part in this companion paper revealed that the macroscopic mechanical performance of corroded pipes follows a decreasing trend with the increasing corrosion rate. Inspired by the surface topology by scanning electronic microscopy (SEM) and the scattered distribution of test data, a computational procedure based on the Monte Carlo simulation method was developed in this paper to understand the randomness of the crack propagation process and the performance degradation mechanism of the corroded pipelines. A total of 2700 random samples, which contain three corrosion rates of 15%, 45%, and 70% with each corrosion rate having three variances of 0.02 mm, 0.06 mm, and 0.10 mm, were generated and then were mapped to the shell section of the FE model. In the application of the material model considering the damage, a series of “numerical” tensile experiments were carried out. The simulation analysis indicated that the corrosion rate and the standard variance of the thickness collaboratively dominated the mechanical performance of the corroded specimen. Under the same standard deviation, the wall corresponding to the higher corrosion rate is more likely to cause stress concentration in the weak position, which makes the pipe more prone to fail. Furthermore, under the same corrosion rate, the increase of the standard deviation will aggravate the unevenness of the wall thickness distribution, and then the lower tensile load will cause damage at weak locations and lead to randomness of the crack propagation path, thereby reducing the pipe’s macroscopic strength and fracture strain. The analytical methods in this paper have the potential of being a useful tool for structural reliability assessments of aged pipelines and the full life cycle design of new pipeline networks.
Highlights
Owing to its large transportation volume, continuity, and economic efficiency, metal pipelines have become the artery of modern industrial fluid transport
It is interesting to note that when the variance is the same and the corrosion rate is different, the yield stress and ultimate strength are quite different. is is because even if the variance is the same, the higher the corrosion rate, the smaller the overall wall thickness of the element, and the lower the ability to resist crack generation and development. is implies that the corrosion rate has an important influence on the performance of the pipe when the variance of the wall thickness distribution is the same
A total of 2,700 numerical pipeline models, which have three corrosion rates and three standard variances, were subjected to tensile tests. e following main conclusions can be drawn: (1) e dispersion of wall thickness caused by environmental erosion will lead to stress concentration at the weak position of the pipeline and induce the randomness of the crack propagation, which gives a reasonable explanation for the experimental failure mode of the corroded pipe
Summary
Owing to its large transportation volume, continuity, and economic efficiency, metal pipelines have become the artery of modern industrial fluid transport. Research studies by Ossai [1], Fekete and Varga [2], and Pilkey et al [3] showed that corrosion is becoming a severe threat to the safety of pipelines. Extensive research on the performance of corroded pipelines focuses on the burst pressure [4,5,6,7,8,9] and bending capacity [10,11,12,13,14,15,16], and there are few studies on their tensile behavior. E observation based on the fracture patterns of corroded pipelines shows that the corrosion transits the fracture mode from the transverse crack in the middle of the specimen to a multiple fracture mode in which the position and angle are randomly distributed.
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