Stress Intensity Factor Solutions for Crack-Like Anomalies in ERW Seam Welded Pipe

2017 ◽  
Author(s):  
Jennifer O’Brian ◽  
Richard Olson ◽  
Bruce Young
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Transportation Safety ◽  
Department Of Transportation ◽  
Axial Crack ◽  
Resistance Weld ◽  
Welded Pipe ◽  
Weld Corrosion ◽  
Longitudinal Seam

In response to the National Transportation Safety Board (NTSB) Recommendation P-09-1, the Department of Transportation (DOT) Pipeline and Hazardous Material Safety Administration (PHMSA) initiated a comprehensive study to identify actions that could be implemented by pipeline operators to significantly reduce longitudinal seam failures in electric resistance weld (ERW) pipe. As part of the project, Task 3 in Phase II was designed to determine more appropriate stress intensity factor solutions for non-standard, axial, crack-like anomalies in ERW seam-welded pipe. The purpose of this paper is to provide an overview of the normalized stress intensity factor solutions for cold weld (CW), selected seam-weld corrosion (SSWC), and hook crack type anomalies. ERW seams with and without weld caps are also included. The limitations on design space are discussed in the context of presenting results and interpolation and extrapolation schemes beyond that space with infinitely long solutions used as a boundary value. Results are presented in the form of surface plots for various combinations of parameters. The reports generated during the project are publicly available and are located on the following PHMSA website: http://primis.phmsa.dot.gov/matrix/PrjHome. rdm?prj=390.

Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds

2008 ◽  
Author(s):  
Mayumi Ochi ◽  
Kiminobu Hojo ◽  
Itaru Muroya ◽  
Kazuo Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Extension ◽  
Crack Depth ◽  
Alloy 600 ◽  
Intensity Factors ◽  
Axial Crack ◽  
Extension Analysis

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.

Evaluation of Constraint Effect due to Crack Location and Bottom Head Shape

2016 ◽  
Author(s):  
Shin-Beom Choi ◽  
Han-Bum Surh ◽  
Jong-Wook Kim
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Head Shape ◽  
Constraint Effect ◽  
Crack Location ◽  
Spherical Bottom ◽  
Axial Crack ◽  
Elliptical Bottom ◽  
The Difference

The aim of this paper is to evaluate the constraint effect due to the crack location and bottom head shape. To do so, two types of bottom head shape such as a semi-spherical bottom head and semi-elliptical bottom head were considered. In addition, five types of axial crack and two types of circumferential crack, classified by location, were adopted to conduct FE analyses. As a result, the bottom head shape does not affect the stress intensity factor of the circumferential flaw. Moreover, the crack location is not a sensitive parameter of the stress intensity factor for an axial crack located at the semi-spherical bottom head. In contrast, the crack location should be considered when the stress intensity factor of an axial crack located at the semi-elliptical bottom head is calculated. In addition, a heatup curve and cooldown curve were derived from the FE analysis results. As a result, the constraint effect owing to a crack location, except for the transition area, is not shown in the case of a semi-spherical bottom head. In the case of a semi-elliptical bottom head, the difference between each crack location is shown. These results will be helpful to enhance the understanding of the constraint effect and P-T limit curve.

Simplified Stress Intensity Factor Equation for SCC Propagation in the Pipe Welds (Step 2)

2009 ◽  
Author(s):  
Mayumi Ochi ◽  
Kiminobu Hojo ◽  
Kazuo Ogawa ◽  
Naoki Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Depth ◽  
Element Model ◽  
Dissimilar Welding ◽  
Intensity Factors ◽  
Propagation Behavior ◽  
Influence Coefficients ◽  
Axial Crack

Considering characteristics of PWSCC’s propagation behavior of the dissimilar welding joint of the safe end nozzles, an axial crack was modeled in a FE (Finite Element) model as a rectangular shape with larger aspect ratio. The stress intensity factors at the deepest point of the crack were calculated with change of crack depth. Using the influence coefficients, the simplified equation of stress intensity factor with parameters of radius/thickness and thickness/weld width was proposed. The contents of this paper is revised from the paper already presented [1] by further investigation for the shallow cracks with less than 20% thickness.

Simulating Natural Axial Crack Growth in Dissimilar Metal Welds due to Primary Water Stress Corrosion Cracking

2013 ◽  
Author(s):  
D. Rudland ◽  
D.-J. Shim ◽  
S. Xu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Crack Growth ◽  
Wall Thickness ◽  
Influence Functions ◽  
Dissimilar Metal ◽  
Primary Water ◽  
Axial Crack ◽  
Growth Analyses

For axial subcritical crack growth in dissimilar metal (DM) welds due to Primary Water Stress Corrosion Cracking (PWSCC), the crack growth in the length direction is limited to the weld width since the base materials are not susceptible to this type of cracking mechanism. However, the crack may continue to grow in the depth direction until it penetrates the wall thickness. Since the weld width can be much less than the pipe wall thickness, axial cracks have the potential of growing much deeper than they are long. Published stress intensity factor influence functions for semi-elliptical axial cracks in pipe suggest that as the half crack length (c) becomes smaller than the crack depth (a), the stress intensity factor at the deepest point of the crack begins to decrease. These solutions suggest that in many cases, these types of cracks may arrest before penetrating the wall thickness. However, natural flaw growth using the Advanced Finite Element Method (AFEA) suggests that these cracks will not arrest and the stress intensity factor does not decrease in a manner suggested by idealized flaw growth analyses using semi-elliptical crack influence functions. In this paper, modifications to idealized flaw growth analyses are proposed to predict the natural PWSCC axial crack growth within DM welds. A series of modified flaw growth predictions are presented and compared to published AFEA results. The simplistic rules developed in the paper allow the use of standard influence functions in predicting the time to leakage for axial cracks in DM welds without having to conduct the more complex AFEA analyses.

Evaluation of Stress Intensity Factor for Transverse Cracks in Weld Joint of BWR Shroud Support and Its Application to the Evaluation of Trapezoidal Crack

2008 ◽  
Author(s):  
Masao Itatani ◽  
Toshiyuki Saito ◽  
Takahiro Hayashi ◽  
Chihiro Narazaki ◽  
Kazuo Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Weld Metal ◽  
Evaluation Method ◽  
Base Alloy ◽  
Elliptical Crack ◽  
Transverse Cracks ◽  
Axial Crack ◽  
Front Shape

Since the weld joints of BWR shroud support are made of Ni-base weld metal that has susceptibility to SCC in the BWR water, the SCC crack prefers to grow in weld metal rather than base metal of Ni-base alloys. It is important to prepare the evaluation method for SCC crack initiated in these alloys. To develop the flaw evaluation method for shroud support, stress intensity factor of postulated axial cracks in H10 weld of shroud support in BWR were analyzed by FEM. Results were compared with simplified SIF solutions in codes and standards to confirm the applicability of these simplified methods. It was understood that these simplified methods were available to evaluate the SIFs of axial crack in H10 weld although the thickness of H10 weld is not constant and is tapered. In the present study, SIF for trapezoidal crack was also analyzed because the front shape of stress corrosion crack in the weld metal of Ni-base alloy is not always semi-elliptical and is thought to have complex shape. It was found that the trapezoidal crack could be substituted by elliptical crack for conservative evaluation when the crack is deep and the ratio of upper base 2d to lower base 2c is small. Based on this result, the authors analyzed SIF for more number of trapezoidal cracks in a plate and compared with SIF of semi-elliptical crack which has the same depth a and surface length 2c of trapezoidal crack to investigate the effective range of substitution by an elliptical crack. It was found that the SIF of deepest point KA of semi-elliptical crack becomes larger than that of trapezoidal crack when d/c becomes smaller than about 0.37. These results show the substitution of trapezoidal crack with small d/c by semi-elliptical crack makes conservative SIF evaluation and it is very useful because the SIF solutions for semi-elliptical crack provided in many codes and handbooks can be applied.

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