Deflected Stress Corrosion Cracks in the Pipeline Steel

2004 ◽  
Author(s):  
Robert Sutherby ◽  
Weixing Chen
Keyword(s):  
Stress Corrosion ◽  
Hoop Stress ◽  
Pipe Wall ◽  
Pipeline Steel ◽  
Maximum Shear Stress ◽  
Mechanical Damage ◽  
Wall Material ◽  
Corrosion Attack ◽  
Pipeline Steels ◽  
Pipe Surface

This research reports a special case of stress corrosion cracks (SCC) in the pipeline steels that had propagated in the direction deviated from the pipe radial direction. It was characterized that the cracks were intergranular in nature with relatively wide crack crevice. Most of crack being characterized consisted of two segments: a crack segment near pipe surface that is normal to the axis of hoop stress, and the subsequent segment that is inclined to the axis of the hoop stress. The segment near the surface was usually less than 1.5 mm long, and the inclined one was up to 10 mm in length. The angle of the inclined segment was dominantly in the range of 30° to 60°. To understand the mechanisms related to the deflected crack growth, the microstructure of the pipeline steels was studied. It was found that The pipeline steel is characterized with a sandwich-like microstructure, for which it is harder at the surface (∼ 1.5 mm thick) and progressively softer towards the center of the wall. This particular structure might have caused a complex loading condition to the pipe wall material such that yielding of the soft material become possible, particularly when crack has propagated into the soft region of the pipe wall. As a result, corrosion attack may take place in a direction consistent with the maximum shear stress, and cracking preceded by the concurrent interaction between corrosion attack and mechanical damage.

The Role of Pressure and Pressure Fluctuations in the Growth of Stress Corrosion Cracks in Line Pipe Steels

1998 ◽  
Author(s):  
Martyn J. Wilmott ◽  
Robert L. Sutherby
Keyword(s):  
Stress Corrosion ◽  
Hoop Stress ◽  
Pipeline Steel ◽  
Pressure Fluctuations ◽  
Operating Pressure ◽  
Pipeline Steels ◽  
Cyclic Stresses ◽  
Neutral Ph ◽  
The Impact

Stress corrosion cracking of pipeline steels involves the interaction of a susceptible material with a corrosive environment under appropriate loading conditions. The stress exerted on pipeline steel is a combination of the internal operating or hoop stress, cyclic stresses due to pressure fluctuations within the pipe, residual stresses developed during pipe manufacture and pipeline construction, as well as other sources of stress such as stress concentrators like corrosion defects and geotechnical stresses. As the internal pressure of an operating pipeline is never static the fluctuations in pressure result in cyclic loading of the pipeline material. Whilst there are many stresses acting on a pipeline the predominant stress is the hoop stress created as a result of the internal operating pressure. In this paper experiments are described which are aimed at determining the effect of pipeline hoop stress on the growth of stress corrosion cracks under neutral pH conditions. The propagation of stress corrosion cracks in pipeline steels at near neutral pH was studied under realistic environmental conditions. The impact of hoop stress on the growth of shallow surface cracks in an X60 pipeline steel was investigated at 40%, 70% and 100% of the specified minimum yield strength of the material. Crack growth rate is shown to be independent of the applied stress in the range studied for these shallow cracks. Cyclic stresses appear to be more important for crack propagation under neutral pH SCC conditions. In light of the results obtained in this test program an attempt was made to characterize the pressure changes occurring on an operating gas pipeline. A computer program was developed to enable characterization of the pressure fluctuations for operating gas pipelines. The results of characterization of pressure histories from a number of operating pipelines are presented.

Understanding Magnetic Flux Leakage Signals From Gouges

2010 ◽  
Author(s):  
Lynann Clapham ◽  
Vijay Babbar ◽  
Jian Dien Chen ◽  
Chris Alexander
Keyword(s):  
Magnetic Flux ◽  
Pipe Wall ◽  
Mechanical Damage ◽  
Internal Surface ◽  
Magnetic Flux Leakage ◽  
Wall Surface ◽  
Pipe Surface ◽  
Early Results ◽  
Flux Leakage ◽  
Wall Geometry

The Magnetic Flux Leakage (MFL) technique is sensitive both to pipe wall geometry and pipe wall strain, therefore MFL inspection tools have the potential to locate and characterize mechanical damage in pipelines. The present work is the first stage of a study focused on developing an understanding of how MFL signals arise from pipeline gouges. A defect set of 10 gouges were introduced into sections of 12″diameter, 5m long, end capped and pressurized X60 grade pipe sections. The gouging tool displacement ranged (before tool removal) between 2.5 to 12.5mm. Gouges were approximately 50mm in length. The shallowest indentation created only a very slight scratch on the pipe surface, the deepest created a very significant gouge. All gouges were axially oriented. Experimental MFL measurements were made on the external pipe wall surface (pressurized) as well as the internal surface (unpressurized). The early results of the experimental MFL studies, and a hypothesis for the origin of the MFLaxial signal “dipole” are discussed in this paper.

STRESS CORROSION CRACK INITIATION BEHAVIOR FOR THE X70 PIPELINE STEEL BENEATH A DISBONDED COATING

2012 ◽  
Vol 48 (10) ◽  
pp. 1267 ◽  
Author(s):  
Zhiying WANG ◽  
Jianqiu WANG ◽  
En-hou HAN ◽  
Wei KE ◽  
Maocheng YAN ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Stress Corrosion ◽  
Stress Corrosion Crack ◽  
Pipeline Steel ◽  
X70 Pipeline Steel ◽  
Disbonded Coating

scholarly journals Finite Element Analysis of Composite Repair for Damaged Steel Pipeline

Coatings ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 301
Author(s):  
Jiaqi Chen ◽  
Hao Wang ◽  
Milad Salemi ◽  
Perumalsamy N. Balaguru
Keyword(s):  
Finite Element ◽  
Shear Stress ◽  
Hoop Stress ◽  
Pipe Wall ◽  
Von Mises Stress ◽  
Repair System ◽  
Composite Repair ◽  
Steel Pipeline ◽  
Von Mises ◽  
Infill Material

Carbon fiber reinforced polymer (CFRP) matrix composite overwrap repair systems have been introduced and accepted as an alternative repair system for steel pipeline. This paper aimed to evaluate the mechanical behavior of damaged steel pipeline with CFRP repair using finite element (FE) analysis. Two different repair strategies, namely wrap repair and patch repair, were considered. The mechanical responses of pipeline with the composite repair system under the maximum allowable operating pressure (MAOP) was analyzed using the validated FE models. The design parameters of the CFRP repair system were analyzed, including patch/wrap size and thickness, defect size, interface bonding, and the material properties of the infill material. The results show that both the stress in the pipe wall and CFRP could be reduced by using a thicker CFRP. With the increase in patch size in the hoop direction, the maximum von Mises stress in the pipe wall generally decreased as the maximum hoop stress in the CFRP increased. The reinforcement of the CFRP repair system could be enhanced by using infill material with a higher elastic modulus. The CFRP patch tended to cause higher interface shear stress than CFRP wrap, but the shear stress could be reduced by using a thicker CFRP. Compared with the fully bonded condition, the frictional interface causes a decrease in hoop stress in the CFRP but an increase in von Mises stress in the steel. The study results indicate the feasibility of composite repair for damaged steel pipeline.

scholarly journals The Pitting Susceptibility Investigation of Passive Films Formed on X70, X80, and X100 Pipeline Steels by Electrochemical Noise and Mott-Schottky Measurements

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Yang Zhao ◽  
Ping Liang ◽  
Yanhua Shi ◽  
Yunxia Zhang ◽  
Tao Yang
Keyword(s):  
Distribution Function ◽  
Electrochemical Noise ◽  
Pipeline Steel ◽  
Stochastic Theory ◽  
Gumbel Distribution ◽  
Passive Films ◽  
Initiation Rate ◽  
Pipeline Steels ◽  
X100 Pipeline Steel ◽  
Pit Initiation

The pitting susceptibility of passive films formed on X70, X80, and X100 pipeline steels was investigated by means of electrochemical noise (EN) and Mott-Schottky measurements. The EN results were analyzed according to the shot-noise theory and stochastic theory. Pit initiation process was analyzed quantitatively using the Weibull distribution function. Pit growth process was simulated by Gumbel distribution function. The experimental results of Mott-Schottky plots showed that the passive films formed on the three pipeline steels displayed an n-type semiconductor character, and the passive film for X100 pipeline steel has the lowest donor density (ND) among the three passive films. The EN results demonstrated that X100 pipeline steel had the lowest pit initiation rate and pit growth probability, which implied that the X100 pipeline steel had the lowest pitting susceptibility.

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