Impact of Prolonged Exposure to Sour Service on the Mechanical Properties and Corrosion Mechanism of NACE Carbon Steel Material Used in Wet Sour Gas Multiphase Pipeline

Round 1

Reviewer 1 Report

The article entitled “Impact of prolonged exposure to sour service on the mechanical properties and corrosion mechanism of NACE carbon steel material used in wet sour gas multiphase pipeline” authored by Yadav et al. reports the comparison of micostructure and mechanical properties of corroded and non corroded section of steel pipes employed in service. The article has 13 figures, 7 tables and 33 references. The authors established their claims with the aid of OM, SEM, EDS, and XPS analysis. Though the authors are appreciated for undertaking an experimental study, the following queries needs to be addressed before considering for publication.

1. The content of the whole article is already available in the form of a thesis. https://qspace.qu.edu.qa/bitstream/handle/10576/15315/Manoj%20Yadav_OGS%20Approved%20Thesis.pdf?sequence=1&isAllowed=y
2. How this study is different from Ref.11. What is novel in the present study.
3. The major concern is level of corrosion varies at different locations why? 
4. Use of SI units is recommended.
5. Quality of micrographs are very poor. Demands big improvements.
6. Fig.2 is not a micrograph. Fig.3 is not clear, Scale bars are to be included.
7. The authors merely presented their results. In a research article it is recommended to add more discussions based on their results and compare their results with published literature. The article lacks in all aspects.
8. Older references (before 2000) should be replaced with latest references (last three years).

Author Response

We do thank the reviewer for his/her precious comments which enriched the manuscript. We have done all the corrections listed below and highlighted that in the manuscript.

1. The content of the whole article is already available in the form of a thesis. https://qspace.qu.edu.qa/bitstream/handle/10576/15315/Manoj%20Yadav_OGS%20Approved%20Thesis.pdf?sequence=1&isAllowed=y

Response 1: The manuscript is apart from a master thesis of the first author under the supervision of Prof Aboubakr Abdullah (one of the Co-authors). Also, more analyses were added such as the EIS and the XPS. However, the presented case study has not been studied at all in literature yet, which saves the novelty and the rights for the authors to publish it in MDPI with acknowledging the thesis work.  

1. How this study is different from Ref.11. What is novel in the present study.

Response 2: Ref. 11 compares mechanical and corrosion-mechanical properties of ferrite-pearlite X52 steel after service in the onshore section of a gas trunkline without any influence of any media. This study focused on pitting-initiated hydrogen embrittlement and stress corrosion cracking as the main reason for the failure. Meanwhile, the authors in our manuscript have established three main mechanisms which can be used to explain the reasons of the failure in sour media. These are Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), and Adsorption Induced Dislocation Emission (AIDE)

1. The major concern is level of corrosion varies at different locations why? 

Response 3: The authors appreciate the reviewer's comment, and the failed pipeline was in service for 15 years before removing it based on the severe localized thickness loss. It is worth mentioning that the failed sample was a part of the 2” piping spool, which is associated with a slug catcher inlet pipeline of a sour wet gas plant. Consequently, a countless number of noticeable corrosion forms were reported, and the authors tried to comprise all types and generate a corrosion mechanism which can include all forms.   

1. Use of SI units is recommended.

Response 4: The authors appreciate the reviewer comment, and SI units have been taken in consideration for any recent measurements. Meanwhile, the manufacturer measurements were kept by its forum as it related to the industry.

1. Quality of micrographs are very poor. Demands big improvements.

Response 5: The authors agree with the reviewer comments and the resolution for All figures were improved.

1. Fig.2 is not a micrograph. Fig.3 is not clear, Scale bars are to be included.

Response 6: Figure 2 and Figure 3 were modified

1. The authors merely presented their results. In a research article it is recommended to add more discussions based on their results and compare their results with published literature. The article lacks in all aspects.

Response 7: The authors agrees with the reviewer comment and results and discussion part was revised and results were compared with published literature to improve the scientific expressions

1. Older references (before 2000) should be replaced with the latest references (last three years).

Response 8: The authors are grateful for the reviewer's comment and older references were replaced with recent references

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper analyzed the corrosion mechanic of carbon steel under wet sour gas, and its structure, content, experiments design are reasonable. However, the theme is not so innovative for there have been lots of research related to carbon steel corrosion, and some research even with field tests. Therefore, from this point, it is not so meaningful. 

Author Response

The authors appreciate the reviewer for his/her valuable point view. However, the authors would like to highlight that the mentioned case study has been investigated mechanically and chemically at different position with noticing different corrosion mechanism at the same time with highligting three main mechanisms which can be used to explain the reasons of the failure in sour media. These are Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), and Adsorption Induced Dislocation Emission (AIDE)

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper studied the corrosion behaviour of pipeline steel in wet sour gas environment. The work has some interesting points and could be recommended for publication. However, some issues should be improved.

1. The grammar of the paper is very poor, which should be improved.
2.  Authors should distinguish the words of “pit” and “pitting”.
3. In Figure 8, why the elastic modulus of stress-strain curves is different? The reasonable explanation should provided.
4. In Figure 9, all pictures exhibit dimples, indicating ductile fracture. I guess the location which the authors observed was wrong. Please check it carefully.
5. In Figure 11, the fitting results for XPS curve are not good enough. 
6. All electrochemical reaction equations print garbled characters. Please modify them.
7. The authors state the hydrogen embrittlement mechanism. Is the fracture caused by hydrogen embrittlement?
8. In my opinion, the corrosion behavior needs to be analyzed from cross-sections of pipeline steel, such as the microstructure of the material or the corrosion components at the bottom of the pits.

Author Response

We do thank the reviewer for his/her precious comments which enriched the manuscript. We have done all the corrections listed below and highlighted that in the manuscript.

1. The grammar of the paper is very poor, which should be improved.

Response 1: The authors appreciate the reviewer's comment, and the manuscript has been proofread for grammatical errors

1.  Authors should distinguish the words of “pit” and “pitting”.

Response 2: Done

1. In Figure 8, why the elastic modulus of stress-strain curves is different? The reasonable explanation should provided.

Response 3: the difference in the elastic modulus of stress-strain curves is due to the resistance of the sample to elastic deformation; hence the samples with higher elastic modulus are harder than samples with lower elongated length.

1. In Figure 9, all pictures exhibit dimples, indicating ductile fracture. I guess the location which the authors observed was wrong. Please check it carefully.

Response 4: The authors agree with the reviewer's comment and the SEM analysis for the fractured samples T2 and T4 has been checked carefully.

1. In Figure 11, the fitting results for the XPS curve are not good enough. 

Response 5: XPS curves has been fitted again.

1. All electrochemical reaction equations print garbled characters. Please modify them.

Response 6: Done

1. The authors state the hydrogen embrittlement mechanism. Is the fracture caused by hydrogen embrittlement?

Response 7: The authors concluded that hydrogen embrittlement is one of the main reasons of the corrosion mechanism. There are mainly three principal mechanisms of hydrogen embrittlement (HE) and Hydrogen induced sulfide stress corrosion cracking, which can be used to explain the observed results during this research. These are Hydrogen Enhanced Localized Plasticity (HELP), Hydrogen Enhanced Decohesion (HEDE), and Adsorption Induced Dislocation Emission (AIDE).

1. In my opinion, the corrosion behavior needs to be analyzed from cross-sections of pipeline steel, such as the microstructure of the material or the corrosion components at the bottom of the pits.

Response 8: The authors agree with the reviewer's comment, which would clarify the corrosion behavior of the failed sample in sour media. However, the authors are planning to conduct a deep investigation on the microstructure of the material and the corrosion components at the bottom of the pits, which would be published in later manuscript.

Author Response File: Author Response.pdf

Reviewer 4 Report

Manuscript ID: sustainability-1683068

Recommendation: Minor Revision

The paper reports the mechanical properties and corrosion mechanism of a pipeline after 15 years of service, aiming to understand the effect of prolonged exposure of sour environment on the piping material. The research was mainly based on the OM, SEM/EDS, XPS, EIS and Tensile test, Microhardness results. While this work has certain scientific significance for readers and researchers, the analysis and discussion are weak. However, the manuscript should undergo revision before further consideration.

1. The English writing of the paper is poor. It should be improved taking help from a native English speaker.
2. The equation1 and 2 is garbled, recommending to use the formula editor (such Math-Type) to modify.
3. The specific test conditions of electrochemical impedance are not clearly written in the experimental part, and the fitting circuit diagram is not seen in the result of Electrochemical measurements, which should be supplemented.
4. Fig. 3 is not clear enough, and the text in the picture is small and difficult to identify.
5. In correlating of surface analysis results written “The third possibility is the combination of the above two explained reactions, where ferrous ions react both at the surface and the solution, thus causing the formation of porous, non-adherent, and non-protective FeS layer.” How to explain this phenomenon.

Consequently, my recommendation is to revise the present manuscript with the suggested comments and resubmit before acceptance.

Author Response

The authors are thankful to the esteemed reviewer for acknowledging our work and encouraging remarks. The comments have been taken on board to improve and clarify the manuscript. The following are the point-wise response to the reviewer's comments.

1. The English writing of the paper is poor. It should be improved taking help from a native English speaker.

Response 1: The authors appreciate the reviewer's comment, and the manuscript has been proofread for grammatical errors

1. The equation1 and 2 is garbled, recommending to use the formula editor (such Math-Type) to modify.

Response 2: Done

1. The specific test conditions of electrochemical impedance are not clearly written in the experimental part, and the fitting circuit diagram is not seen in the result of Electrochemical measurements, which should be supplemented.

Response 3: Electrochemical measurement was explained in details and the proposed fitting circuit was amended as Figure 13

1. Fig. 3 is not clear enough, and the text in the picture is small and difficult to identify.

Response 4: Figure 3 has been modified

1. In correlating of surface analysis results written “The third possibility is the combination of the above two explained reactions, where ferrous ions react both at the surface and the solution, thus causing the formation of porous, non-adherent, and non-protective FeS layer.” How to explain this phenomenon.

Response 5: Alternatively, ferrous ions can react at both the surface and the solution, resulting in the formation of a porous, non-adherent, and non-protective FeS layer. Besides enabling cathodic reactions, this corrosion layer also facilitates anodic dissolution of Fe which can be considered as a galvanic corrosion interaction

Author Response File: Author Response.pdf

Reviewer 5 Report

In this paper, the effect of long-term exposure to sour environment on pipeline materials was investigated. The materials selected in this research are part of a pipeline in service for 15 years and meet NACE standards. Optical microscopy, SEM and EDS were used to observe the microstructure and understand the deposits' morphology. XPS analysis was also carried out on the samples, which proved the presence of a significant content of sulfur compound. The microhardness of the samples was measured to investigate hardness variation from the inner diameter to the outer diameter of the piping. In addition, tensile test and impact test were carried out on the samples. This paper contributes to understanding the corrosion mechanism of pipelines exposed to sour environment for the long term. However, there are some points that should be improved and revised before it is considered for publication.

1. In the Abstract, the sentence “XPS analysis improves the presence of a significant content of sulfur compound” is difficult to understand. Is the word “proves” wrongly written as “improves”?
2. The “Results and discussion” part is too messy, making it difficult for readers to understand what you want to express. Please improve this part.
3. The “Conclusion”part is tedious, and the relevant part should be revised and refined.
4. The figures in your manuscript are very blurred,which has brought great interference to the understanding of this paper. Please improve them.
5. In XPS analysis, the sampling positions of samples A1-A3 and B1-B4 should be given so that readers can easily understand your paper.
6. There are some spelling and grammar errors in the manuscript. For example, on page 4, line 112, “@” would be “at” and on page 6, line 163, “depict” would be “depicts”. Please check your manuscript carefully and correct these errors.
7. Please include the recent literature in materials forming and processes: Highly mechanical and high-temperature properties of Cu–Cu joints using citrate-coated nanosized Ag paste in air  Cu-Cu joining using citrate coated ultra-small nano-silver pastes

Author Response

The authors appreciate the esteemed reviewer for acknowledging our work and encouraging remarks. The comments have been taken on board to improve and clarify the manuscript. The following are the point-wise response to the reviewer's comments.

1. In the Abstract, the sentence “XPS analysis improves the presence of a significant content of sulfur compound” is difficult to understand. Is the word “proves” wrongly written as “improves”?

Response 1: Done

1. The “Results and discussion” part is too messy, making it difficult for readers to understand what you want to express. Please improve this part.

Response 2: The authors agree with the reviewer comment and Results and discussion part was revised to improve the scientific expressions

1. The “Conclusion “part is tedious, and the relevant part should be revised and refined.

Response 3: The authors endorse the reviewer's comment and the conclusion part was revised to improve it.

1. The figures in your manuscript are very blurred, which has brought great interference to the understanding of this paper. Please improve them.

Response 4: Done.

1. In XPS analysis, the sampling positions of samples A1-A3 and B1-B4 should be given so that readers can easily understand your paper.

Response 5: The authors appreciate the reviewer's comment. However, the XPS analysis has investigated the different failure locations with different morphology, which not include A2, B2 and B4 as it has the same features with the presented samples.

1. There are some spelling and grammar errors in the manuscript. For example, on page 4, line 112, “@” would be “at” and on page 6, line 163, “depict” would be “depicts”. Please check your manuscript carefully and correct these errors.

Response 6: The authors appreciate the reviewer's comment, and the manuscript has been proofread for grammatical errors.

1. Please include the recent literature in materials forming and processes: Highly mechanical and high-temperature properties of Cu–Cu joints using citrate-coated nanosized Ag paste in air Cu-Cu joining using citrate coated ultra-small nano-silver pastes

Response 7: Done

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The article is recommended for publication