Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

see attatched

Comments for author File: Comments.pdf

Comments on the Quality of English Language

see attatched

Author Response

The authors are grateful for the constructive comments, which have enhanced the quality of our research. All comments have been addressed in the responses below, and the manuscript has been revised accordingly where possible, with changes highlighted in green.

Reviewer's general comment:

This paper analyzes in detail the deflection change, debonding mechanism and other key issues of discontinuous IRP system under lateral loading by using finite element method. The article is logically rigorous and informative. The four-point bending finite element model of the pipe is also verified by experimental analysis. The conclusions are objective and meticulous. The review comments are set out below:

The overall work content of the article is worth admiring, with suggested changes as appropriate.

Reviewer's specific comments:

Reviewer's Comment 1:

Is it possible that Figure 6 can be represented as the initial state when an IRP system is added to the main pipe? If yes, then can it be considered that the finite element simulation experiment is more suitable for the analysis process of the force after adding IRP system to the pipe under no load, rather than the analysis process of adding IRP to the aging pipe under lateral loading?

Author’s Response 1:

Figure 4 and Figure 6 illustrate the initial setup and the finite element analysis (FEA) model of the 12.7 mm (0.5 inch) discontinuous IRP system, respectively. Additionally, Figure 7 provides the comparison of load versus displacement between the FEA and experimental results, where the deflection load ranges from 0 (initial state) to a maximum of 69.1 kN (15.5 kip).

Reviewer's Comment 2:

It seems that the article lacks the description of the exact implementation process and the measurement of deflection for the experiments with the addition of IRP system shown in Tables 5 and 6, preferring to give the experimental results directly.

Author's Response 2:

The experimental setup was originally described in Section 2.1.1, "Four-Point Bending Deflection Modelling" (page 3). Additional details have now been included in the revised manuscript (lines 117–120).

Reviewer's Comment 3:

The first paragraph of the introduction is based on the state of natural gas with the greatest degree of aging, but according to the introduction of the meaning of the experimental method and results can also be used in the oil pipeline, the first part of the introduction of natural gas and the oil pipeline should be a trade-off, otherwise it is easy to mislead the reader;

Author's Response 3:

The rehabilitation of legacy oil and gas pipelines using IRP is the primary focus of this research. The introduction has been revised slightly to emphasise this focus, with changes made in lines 33-37.

Reviewer's Comment 4:

The introduction of the impact of the research content of the role of the slightly polite, perhaps for the subsequent research work how to carry out, the construction of simulation scenarios, the actual optimization of the scenarios and other issues to develop a specific narrative;

Author's Response 4:

The significance of the research is discussed in the abstract (lines 18–28) and the introduction (lines 95–100). Recommendations for optimal design and future development are provided in the concluding remarks (lines 714–763).

Reviewer's Comment 5:

The last paragraph of the introduction is too concise, and it is not easy to directly grasp the overall pulse of the article.

Author's Response 5:

We have elaborated on the last paragraph to provide a clearer and more detailed overview of the research. Please refer to lines 91-100 for the revised content.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a very interesting study and I have followed the work of authors for quite some time. 

1) What distinguishes this publication from the others by the same authors? In other words, what has specifically been addressed in this study, that hasn't been explicitly discussed elsewhere?

2) P3L141: How is the 1 million cylces related to a service life of 50 years? It would be interesting for the readers to know.

3) Table 1: Did the authors do the chemical composition themselves or as I would assume, this is based on the ASTM A48 Class 20 requirements? In the latter case, the table should be cross-referenced to the ASTM standard.

4) How was the cast iron modeled in the FEA? There is no information about the stress-strain behavior of the gray cast iron, which is essential for reproducing the results by other researchers. Also, was the pipe pressurized in the initial verification? Please clarify.

5) What was the contact definition and interaction between the different parts of the model shown in Fig. 2? Please elaborate all components.

6) Section 2.1.2. Can the authors show a comparison between load-deflection from the test and obtained through the FEA? Also, it would be good to add a qualitative comparison between the FEA and test at the final stage. 

7) P7L207: Typo in the unit of acceleration (m/s2).

8) For the four-point bending deflection modelling and validation, a gray cast iron pipe was used, while for the IRP validation a steel pipe was used. Is this correct? Why did the host pipe material change?

9) For the IRP modelling and validation, only the nonlinear material properties (stress-strain curve) of the ALTRA10 is provided.  How about the nonlinear material behavior of the epoxy or the steel? How were they modeled in Ansys, specially the adhesive? 

10) What are the interaction properties between the IRP, adhesive, and steel host pipe? Did you consider debonding possibility? 

11) P20L447-449: "Utilizing the S-N curve of ALTRA10 [25], as depicted in Figure 23, and the normal stress concentration data from Figure 22, Table 9 shows the minimum life cycles to failure of a 12.7 mm (0.5-inch) discontinuous IRP system with varying levels of adhesive bonding shear strengths". Can you please elaborate more on how this fatigue performance and FEA were integrated? It's not well defined. How do you show the degradation of the material and introduce it into the FEA?

 

Author Response

The authors are grateful for the constructive comments, which have enhanced the quality of our research. All comments have been addressed in the responses below, and the manuscript has been revised accordingly where possible, with changes highlighted in green.

Reviewer's general comments

This is a very interesting study and I have followed the work of authors for quite some time. 

Reviewer's specific comments

Reviewer's comment 1:

What distinguishes this publication from the others by the same authors? In other words, what has specifically been addressed in this study, that hasn't been explicitly discussed elsewhere?

Author's response 1:

To the best of our knowledge, this study offers new and valuable insights into improving trenchless repair techniques, which in turn enhance system performance and extend service life. The three key contributions are: 1) the demonstration of the critical role adhesive strength plays in the overall performance of the repair system, 2) the examination of varying adhesive strengths resulting from different surface preparation methods (unclean, cleaned, and ablated), and 3) optimizing adhesive strength leads to more efficient, cost-effective, and durable infrastructure maintenance solutions.

Reviewer's comment 2:

P3L141: How is the 1 million cylces related to a service life of 50 years? It would be interesting for the readers to know.

Author's response 2:

The revised version (lines 130-136) now clarifies this point as follows: By applying this load, the stresses and deformations experienced by the pipeline represent worst-case scenarios under vibrational loading, aiming to achieve a design fatigue life of 1 million cycles, which corresponds to a 50-year service life as introduced by O’Rourke et al. in 1985 [18,19]. The 1 million cycles over a 50-year period equates to approximately 20,000 cycles per year. This fatigue life estimate was rounded up from the original value of 780,000 cycles based on the expected number of heavy truck crossings over 50 years.

Reviewer's comment 3:

Table 1: Did the authors do the chemical composition themselves or as I would assume, this is based on the ASTM A48 Class 20 requirements? In the latter case, the table should be cross-referenced to the ASTM standard.

Author's response 3:

A cross-reference to the ASTM A48 has been added (lines 123 and 143).

Reviewer's comment 4:

How was the cast iron modeled in the FEA? There is no information about the stress-strain behavior of the gray cast iron, which is essential for reproducing the results by other researchers. Also, was the pipe pressurized in the initial verification? Please clarify.

Author's response 4:

A clarification has been provided in the revised version (lines 144-146): A linear static structural FEA was conducted on a single cast iron pipe during a four-point bending test to validate the analytical approach using linear solution methods. The mechanical properties of the cast iron pipe are described in lines 123-124. Additionally, the pipe was not pressurised during the deflection validation of the single cast iron pipe.

Reviewer's comment 5:

What was the contact definition and interaction between the different parts of the model shown in Fig. 2? Please elaborate all components.

Author's response 5:

The contact definitions and interactions between the different components of the model shown in Fig. 2 have been initially outlined and further elaborated in response to the comments in the revised version (see lines 144-159).

Reviewer's comment 6:

Section 2.1.2. Can the authors show a comparison between load-deflection from the test and obtained through the FEA? Also, it would be good to add a qualitative comparison between the FEA and test at the final stage.

Author's response 6:

We understand that modelling a four-point bending test on a large pipe, such as the one discussed in this work, poses significant challenges for finite element analysis (FEA). Therefore, validation is crucial, whether achieved through theoretical methods, experimental approaches, or a combination of both. In this research, we employed an established theoretical approach for validation of single cast iron pipe, optimising the use of experimental resources and enabling a more comprehensive validation of the internal replacement pipe (IRP) system.

Reviewer's comment 7:

P7L207: Typo in the unit of acceleration (m/s2).

Author's response 7:

The typo has been corrected in the revised manuscript (line 200).

Reviewer's comment 8:

For the four-point bending deflection modelling and validation, a gray cast iron pipe was used, while for the IRP validation a steel pipe was used. Is this correct? Why did the host pipe material change?

Author's response 8:

Yes, that is correct. The modeling and validation of the four-point bending deflection were performed using a gray cast iron pipe to align with the pioneering work of O’Rourke et al., which reported a deflection of 1.78 mm (0.07 inches) over 1 million cycles, corresponding to a 50-year service life. This rationale has been elaborated upon in the revised manuscript (lines 130-136).

The experimental data for the IRP system is only available for steel pipes; therefore, a steel pipe was used for the IRP system, leveraging the confidence gained from the earlier validated four-point bending test setup.

Reviewer's comment 9:

For the IRP modelling and validation, only the nonlinear material properties (stress-strain curve) of the ALTRA10 is provided.  How about the nonlinear material behavior of the epoxy or the steel? How were they modeled in Ansys, specially the adhesive?

Author's response 9:
Further clarification on the FEA modelling of the steel and adhesive is provided in lines 213-214. The mechanical properties of both the steel components and the epoxy adhesive were modelled as linear materials.

Reviewer's comment 10:

What are the interaction properties between the IRP, adhesive, and steel host pipe? Did you consider debonding possibility? 

Author's response 10:

In the FEA modelling, the contact conditions between the adhesive and the host pipe, as well as between the adhesive and the IRP, were assumed to be fully bonded. Additional details regarding the adhesive bonding have been provided in lines 192-193 and 312-313.

Reviewer's comment 11:

P20L447-449: "Utilizing the S-N curve of ALTRA10 [25], as depicted in Figure 23, and the normal stress concentration data from Figure 22, Table 9 shows the minimum life cycles to failure of a 12.7 mm (0.5-inch) discontinuous IRP system with varying levels of adhesive bonding shear strengths". Can you please elaborate more on how this fatigue performance and FEA were integrated? It's not well defined. How do you show the degradation of the material and introduce it into the FEA?

Author's response 11:

We have expanded the explanation on how the S-N curve for ALTRA10 was integrated with FEA results to assess the fatigue performance of the IRP system (see lines 443-449). This study focuses specifically on structural weakening due to adhesive debonding between the host pipe and the IRP, rather than material degradation.

Reviewer 3 Report

Comments and Suggestions for Authors

The study proposed by the authors includes both experimental and numerical work. The topic is relevant to the journal's scope. However, further improvements are required before reaching acceptance.

1.      The introduction part does not clearly identify the major contribution of the presented research study.

2.      The authors should include more review papers and research on pipelines to update the current state of the art such as “Evaluating the reliability and integrity of composite pipelines in the oil and gas sector: A scientometric and systematic analysis” and “Machine learning-based Shapley Additive Explanations approach for corroded pipeline failure mode identification” and “A comprehensive review of corrosion protection and control techniques for metallic pipelines”.

3.      Could the authors elaborate on the parameters utilized in the FEA? And how will this affect the outcomes analysis!

4.      Use a flowchart to describe the research paper's structure.

5.      Improve figures quality.

6.      Check the headings. As an example: Surface preparation and its effect should be Surface preparation and impact or something similar.

7.      Improve the discussion. Figure 14.

8.      The authors mentioned that the results can be helpful for reliability analysis! How?

9.      The conclusion should discuss limitations and future directions.

Comments on the Quality of English Language

Please give the manuscript another read to eliminate all mistakes and typos. 

Author Response

The authors are grateful for the constructive comments, which have enhanced the quality of our research. All comments have been addressed in the responses below, and the manuscript has been revised accordingly where possible, with changes highlighted in green.

Reviewer's general comments

The study proposed by the authors includes both experimental and numerical work. The topic is relevant to the journal's scope. However, further improvements are required before reaching acceptance.

Reviewer's specific comments

Reviewer's comment 1:

The introduction part does not clearly identify the major contribution of the presented research study.

Author's response 1:

The revised version (lines 91-100) now clarifies this point. This study provides valuable insights into enhancing trenchless repair techniques, which improve system performance and extend service life. The key contributions are: 1) demonstrating the critical role of adhesive strength in the overall performance of the repair system, 2) examining the impact of different surface preparation methods (unclean, cleaned, and ablated) on adhesive strength, and 3) optimising adhesive strength to achieve more efficient, cost-effective, and durable infrastructure maintenance solutions.

Reviewer's comment 2:

The authors should include more review papers and research on pipelines to update the current state of the art such as “Evaluating the reliability and integrity of composite pipelines in the oil and gas sector: A scientometric and systematic analysis” and “Machine learning-based Shapley Additive Explanations approach for corroded pipeline failure mode identification” and “A comprehensive review of corrosion protection and control techniques for metallic pipelines”.

Author's response 2:

We have added the recommended reference, “Evaluating the Reliability and Integrity of Composite Pipelines in the Oil and Gas Sector: A Scientometric and Systematic Analysis,” in line 59. This reference reinforces the benefits of using Internal Replacement Pipe (IRP) technology for oil and gas pipeline repair.

Reviewer's comment 3:

Could the authors elaborate on the parameters utilized in the FEA? And how will this affect the outcomes analysis!

Author's response 3:

We have expanded the explanation on how the S-N curve for ALTRA10 was integrated with FEA results to assess the fatigue performance of the IRP system (see lines 443-449).

Reviewer's comment 4:

Use a flowchart to describe the research paper's structure.

Author's response 4:

A description of the paper's structure has been added on lines 101–105.

Reviewer's comment 5:

Improve figures quality.

Author's response 5:

The quality of the figures has been improved where possible, specifically in Figures 2–4, 6, 7, 11–13, and 17.

Reviewer's comment 6:

Check the headings. As an example: Surface preparation and its effect should be Surface preparation and impact or something similar.

Author's response 6:
The title of Section 3 has been revised to "Surface preparation and its impact on debonding".

Reviewer's comment 7:

Improve the discussion. Figure 14.

Author's response 7:

The discussion of Figure 14 has been enhanced (see lines 323–328) to better explain the debonding phenomena observed in the lap-shear validation, comparing the FEA and experimental results.

Reviewer's comment 8:

The authors mentioned that the results can be helpful for reliability analysis! How?

Author's response 8:

The sentence on line 750 has been revised to clarify the meaning. The authors were referring to the fidelity of the findings, rather than a formal reliability analysis.

Reviewer's comment 9:

The conclusion should discuss limitations and future directions.

Author's response 9:

A discussion of the limitations and future directions of the current method has been added (see lines 758-763).