Finite Element Analysis of the Limit Load of Straight Pipes with Local Wall-Thinning Defects under Complex Loads
Round 1
Reviewer 1 Report
The paper presents a methodology of calculations of the limit state of the pipes under internal pressure with local thinning. The pipes are loaded by combined loads like bending, torsion and axial force.
In the Introduction, the descriptions of the References [1, 2, 3] are incorrect. For example, it is not true that the authors of the paper [2] invented the definition of the limit load. At least, the description of the definition claims it. The descriptions of the other references contain such generalisations as well.
When describing the finite element model, the authors do not show the method of applying the loading placed at the nozzle and via the nozzle to the pipe. The model is not described well.
Equation (14) is not an empirical equation.
In general, the results presented in Figs 10 and 12 are correct.
In fact, the analysis of the pipes requires
considering the shakedown and the local effects like the presence of the openings and stress concentrations. However, the authors do not mention it in the text. They should refer to the problems in the text.
The authors did not express any novelty in the research. In other words, it should be explained what new is in the research explicitly.
The paper can be interesting for engineers and designers. In particular for the engineers who still may not be happy with the use of the finite element method in the design of the pipes. In other words, again, for the engineers who prefer to rely on semi-empirical, empirical, or analytical solutions.
I think if the authors introduce the remarks, the paper can be published.
Author Response
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for their very useful comments, which have helped us to improve the manuscript. Indeed, we appreciated all the comments made by the reviewers. We have read the comments carefully and we agree with those remarks. Therefore, we have made corrections/modifications in order to improve the content of the manuscript.
In the following paragraphs, we address carefully all reviewers’ comments:
Point 1: In the Introduction, the descriptions of the References [1, 2, 3] are incorrect. For example, it is not true that the authors of the paper [2] invented the definition of the limit load. At least, the description of the definition claims it. The descriptions of the other references contain such generalisations as well.
Response 1: Thank you for your comment. As the limit load is a common terminology in structual integrity. The relative references have been deleted.
Point 2: When describing the finite element model, the authors do not show the method of applying the loading placed at the nozzle and via the nozzle to the pipe. The model is not described well.
Response 2: Thank you for your comment. In Section 2.1, “The load application method is shown in Section 2.2. ” is added. In Section 2.2, the method of loads and the constraints are described in detail. As described in the article, “As shown in Figure 2 (a), the internal pressure is applied on the inner wall of the straight pipe and the axial equivalent head load is applied on the left end face in z direction of the straight pipe. The axial equivalent head load is calculated by Eq. (1).
Meanwhile, a node is established at the center of the left end face of the straight pipe in the z direction, which is used for MASS21 mass element. This node is coupled with all nodes of the straight pipe end face to form a rigid region. As shown in Figure 2 (b)-(c), the bending moment in the y direction and the torque in the z direction are applied on this node. And the axial force in the z direction is applied on this node in the same direction as the axial equivalent surface load Pc, which is shown in Figure 2 (d). Circumferential and axial constraints are applied on the right end face of the straight pipe in z direction.”
The above two paragraphs are marked red in the revision.
Point 3: Equation (14) is not an empirical equation. In general, the results presented in Figs 10 and 12 are correct.
Response 3: Thank you for your comment. Equation (14) is the limit load equation summarized in Reference (28). It is modified in the article that the word of “empirical” is deleted.
Point 4: In fact, the analysis of the pipes requires considering the shakedown and the local effects like the presence of the openings and stress concentrations. However, the authors do not mention it in the text. They should refer to the problems in the text.
Response 4: Thank you for your comment. The problems have be mentioned in line 29~32, and line 88~90 as following.
“Although ratcheting and fatigue should also be considered in the pipeline integrity assessment, the limit load which determines the load bearing capacity of structures is the basic parameter for structural integrity assessment corresponding to primary stress. ”
“It should also be mentioned that the methodlogy discuused can be used for other pipeline componemts such as elbow and tee which covers openings and other stress concentrations. ”
Point 5: The authors did not express any novelty in the research. In other words, it should be explained what new is in the research explicitly.
Response 5: Thank you for your comment. The novelty in the research is described in the last paragraph of intorduction(line 76-80).
The previous works mainly analyzed the limit load of SPLWT under internal pressure, bending moment, axial force and their combinations. The limit load has not been systematically studied for SPLWT under the combination of internal pressure, bending moment, torque and axial force together. This paper mainly uses finite element analysis to analyze the limit load of SPLWT under internal pressure, bending moment, torque, axial force and their combinations.
It has been marked red in the revision.
In general, the authors would like to thank the reviewers from the bottom of the heart for critically reviewing the article. The time spent by the reviewers on this paper has to be sincerely appreciated. All necessary changes have now been carried out as said by the experts. The authors feel that the quality appearance of the paper has completely been made professional. We would also like to thank the Editor for identifying such reviewers. Thanks again.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article lacks a comparison of the results obtained with a real straight pipe!
Do authors need to specify the reasons that conditioned their research using FE analysis?
I consider the topic original in the field. It addresses a specific gap in the field.
The authors added to the subject area FE analysis of the limit load of straight pipe with local wall-thinning defect under complex loads compared with other published materials.
The references are appropriately selected and cover the research area.
The conclusions are accurate and consistent with the evidence and arguments presented.
The tables and figures are clear and easy to read.
Author Response
Dear Editor and Reviewers:
First of all, we would like to express our thanks to the editor for providing a chance to review our work and to the reviewers for their very useful comments, which have helped us to improve the manuscript. Indeed, we appreciated all the comments made by the reviewers. We have read the comments carefully and we agree with those remarks. Therefore, we have made corrections/modifications in order to improve the content of the manuscript.
In the following paragraphs, we address carefully all reviewers’ comments:
Point 1: The article lacks a comparison of the results obtained with a real straight pipe!
Response 1: Thank you for your comment. In Section 4.4, the limit load curves of straight pipe with local wall-thinning defect under the combination of internal pressure and bending moment in this paper are compared with those in Reference 28.
Point 2: Do authors need to specify the reasons that conditioned their research using FE analysis?
Response 2: Thank you for your comment. The relative sentences have been deleted.
In general, the authors would like to thank the reviewers from the bottom of the heart for critically reviewing the article. The time spent by the reviewers on this paper has to be sincerely appreciated. All necessary changes have now been carried out as said by the experts. The authors feel that the quality appearance of the paper has completely been made professional. We would also like to thank the Editor for identifying such reviewers. Thanks again.
Author Response File: Author Response.docx
