Residual ultimate strength investigation of offshore pipeline with pitting corrosion

2021 ◽  
Vol 117 ◽  
pp. 102869
Author(s):  
Liang Feng ◽  
Dingyu Huang ◽  
Xuguang Chen ◽  
Hongda Shi ◽  
Shuqing Wang
Keyword(s):  
Ultimate Strength ◽  
Pitting Corrosion ◽  
Offshore Pipeline

Visual Assessment of Corroded Condition of Plates With Pitting Corrosion Taking Into Account Residual Strength: In the Case of Webs of Hold Frames of Bulk Carriers

2007 ◽  
Author(s):  
Tatsuro Nakai ◽  
Hisao Matsushita ◽  
Norio Yamamoto
Keyword(s):  
Ultimate Strength ◽  
Pitting Corrosion ◽  
Residual Strength ◽  
Steel Plates ◽  
Average Thickness ◽  
Loading Conditions ◽  
Equivalent Thickness ◽  
Thickness Loss ◽  
Minimum Cross Section ◽  
Corrosion Pits

Corrosion pits with a conical shape are typically observed in hold frames in way of cargo holds of bulk carriers which carry coal and iron ore. The ratio of the diameter to the depth of the typical corrosion pits is in the range between 8–1 and 10–1 and its diameter might become up to 50mm. The evaluation of residual strength of members with large uneven pitting corrosion is difficult compared with that of members with general corrosion. Therefore, it is of crucial importance to develop a method for the evaluation of residual strength of pitted members. The purpose of the present study is to investigate the effect of pitting corrosion on the ultimate strength of steel plates under various loading conditions and explore a method for the evaluation of residual thickness of pitted plates. In the present study, a series of non-linear FE-analyses has been conducted with steel plates with a variety of random pit distributions under various loading conditions such as uni-axial compression, bi-axial compression, shear and combination of these. In these analyses, random pit distributions were calculated by the previously developed corrosion model. It has been shown that equivalent thickness loss, which is defined as thickness loss of uniformly corroded plates with the same ultimate strength as the randomly pitted plates, is smaller than or equal to 1.25 times the average thickness loss. It has been also revealed that the equivalent thickness loss for the ultimate strength under the above-mentioned loading conditions is smaller than average thickness loss at the minimum cross section, where the average thickness loss at the minimum cross section almost corresponds to the equivalent thickness loss for the tensile strength. Based on these findings, a method for the estimation of equivalent thickness loss of pitted plates has been discussed using the thickness diminution-DOP relationship, where DOP (Degree of Pitting Intensity) is defined as the ratio of the pitted surface area to the total surface area.

Ultimate Strength of Typical Stiffened Panels in Container Ships Under Localized Pitting Corrosion

2016 ◽  
Author(s):  
Jinju Cui ◽  
Deyu Wang ◽  
Ning Ma
Keyword(s):  
Life Cycle ◽  
Ultimate Strength ◽  
Pitting Corrosion ◽  
Load Capacity ◽  
Uniform Corrosion ◽  
Ship Structures ◽  
Element Analysis ◽  
Stiffened Panels ◽  
Transverse Loads ◽  
Structural Capacity

In the life cycle of ships, corrosion exists and deteriorates ship structures, resulting in the degradation of ship structural capacity. Based on practical observations, non-uniform corrosion takes place instead of uniform corrosion which is adopted widely in design rules. So it is necessary to study the load capacity of ship structures under non-uniform corrosion. In this paper, the ultimate strength of typical bottom panels in container ships under localized pitting corrosion is studied by Nonlinear Finite Element Analysis (NFEA). The pitting corrosion is supposed to be of normally distributed circular shapes whose radius is in accordance with observational statistics. Different pitting corrosion densities with perforation in both the stiffener and panel plate are considered. Structural ultimate strengths under pitting corrosion are studied under longitudinal loads, transverse loads and combination of both, and the results are compared with that from equivalent uniform corrosion. Finally, the probabilistic characteristics of structural ultimate strength under pitting corrosion in life cycle are studied.

scholarly journals Progressive Collapse Analysis of an FPSO Vessel Hull Girder Under Vertical Bending Considering Different Corrosion Models

2020 ◽  
Author(s):  
Zorareh Nouri ◽  
Mohammad Reza Khedmati
Keyword(s):  
Ultimate Strength ◽  
Pitting Corrosion ◽  
Progressive Collapse ◽  
Relative Reduction ◽  
Uniform Corrosion ◽  
Hull Girder ◽  
Operational Life ◽  
Collapse Analysis ◽  
Corrosion Model ◽  
Progressive Collapse Analysis

Abstract Nowadays, with the increasing operational life of ships, the aging effects on their structural behavior need to be investigated precisely. With the corrosive marine environment taken into consideration, one of the important effects of aging that must be studied is thickness degradation. In this paper, with the use of previously proposed equivalent thickness formulations for corroded plates, the progressive collapse analysis software HULLST is enhanced, and then, the effects of different corrosion models of uniform, random, pitting, and tanker pattern types on the ultimate and residual strengths of a floating production, storage, and offloading vessel hull girder are evaluated for the ages of 0 to 25 years. Results reveal that the uniform corrosion and random corrosion models have close outcomes. The value of relative reduction in the ultimate strength of ship hull girder (compared with the intact condition) ranges roughly from 6% for the age of 5 years to 17% for the age of 25 years in the hogging mode. The relative reduction in the ultimate strength ranges from 4% to 16% in the sagging mode. Pitting corrosion and tanker pattern (random) corrosion models lead to higher relative reductions in ultimate strength. The pitting corrosion model leads to a 16%–32% relative reduction in the ultimate strength for the ages of 5–25 years of the ship in either hogging or sagging. The tanker pattern (random) corrosion model leads to a 6%–37% relative reduction in the ultimate strength in the hogging mode and 3%–31% in the sagging mode at ship ages of 5 to 25 years.

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