Effect of Temperature and Immersion Time on Corrosion of Pipeline Steel Caused by Sulfate-Reducing Bacteria

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Line 39-44: It would be good to add the type/composition of the medium that is transported via pipelines.

Line 93-95: The description of the test material does not include the grade of steel being tested and its copper content. The grade of steel is indicated in the conclusions, in Line 450: steel L450. Please add the steel grade at this paragraph as well. Acc. to API Specification 5L, steel L450 contains max. 0.5% Cu, but typically approx. 0.1% Cu (acc. to Table 1 in Shuai Wang, Cheng Hou, Bin Wang, Guiyi Wu, Xueling Fan, He Xue “Mechanical responses of L450 steel under biaxial loading in the presence of the stress discontinuity”).

Table 1: There is no Cu content in steel. Please add it, definitely! Theis is the main reason for conducting the research. How can the influence of copper on corrosion be assessed if the Authors did not indicate its content in the steel?

4. Discussion+5.Conclusions: The discussion and conclusions do not include a comparison of the results obtained with those for steel with and without copper. The aim of the research was to demonstrate how the Cu affects corrosion (acc. to Line 85-90). The lack of a reference sample without copper makes it impossible to compare the results and demonstrate differences. There is no conclusion in CONCLUSIONS regarding the effect of Cu on corrosion, apart from a general sentence at the end of the CONCLUSIONS (Line 470-471). This is a big drawback of this work.

Author Response

Responses to the reviewer’s and editor’s comments

 

Thank you for your arduous work in revising our manuscript entitled “Temperature and immersion time effects on Cu-containing pipeline steel corrosion caused by sulfate-reducing bacteria”, and providing constructive comments and valuable suggestions, which have helped us to improve the quality and readability of our manuscript. We have studied the comments very carefully and have revised the manuscript exactly according to the reviewers’comments. We hope this revision will meet with approval. The main revisions corresponding to the reviewers’ comments are as follows.

 

Reviewer #1: 

1. Line 39-44: It would be good to add the type/composition of the medium that is transported via pipelines.

 

Response:

Thank you for your kind advice. 

We added the type/composition of the medium that is transported via pipelines. (lines 39-41, page 1)

 

2. Line 93-95: The description of the test material does not include the grade of steel being tested and its copper content. The grade of steel is indicated in the conclusions, in Line 450: steel L450. Please add the steel grade at this paragraph as well. Acc. to API Specification 5L, steel L450 contains max. 0.5% Cu, but typically approx. 0.1% Cu (acc. to Table 1 in Shuai Wang, Cheng Hou, Bin Wang, Guiyi Wu, Xueling Fan, He Xue “Mechanical responses of L450 steel under biaxial loading in the presence of the stress discontinuity”).

 

Response:

Thank you for your kind advice. 

The pipe steel used in this manuscript is BG L450OQO-RCB, which is the grade of PSL 2 steel pipe steel on the condition of Maritime service. We revised the description of the test material to be BG L450OQO-RCB. The pipe steel produced by Baoshan Iron & Steel Co., Ltd., is developed by optimizing the element composition and content, especially adding the copper element, to improves the MIC resistance on the basis of the steel L450. The average chemical composition of the pipeline steel is as following.

 

Table 1. The average chemical composition of the BG L450OQO-RCB pipeline steel (wt.%).

 

 

3. Table 1: There is no Cu content in steel. Please add it, definitely! Theis is the main reason for conducting the research. How can the influence of copper on corrosion be assessed if the Authors did not indicate its content in the steel?

 

Response:

The average chemical composition of the BG L450OQO-RCB is show in table 1. The Cu content is 0.587 wt.%.

 

4. Discussion+5.Conclusions: The discussion and conclusions do not include a comparison of the results obtained with those for steel with and without copper. The aim of the research was to demonstrate how the Cu affects corrosion (acc. to Line 85-90). The lack of a reference sample without copper makes it impossible to compare the results and demonstrate differences. There is no conclusion in CONCLUSIONS regarding the effect of Cu on corrosion, apart from a general sentence at the end of the CONCLUSIONS (Line 470-471). This is a big drawback of this work.

 

Response:

   The object of the research is to clarify the influence of temperature and immersion time on Cu-containing pipeline steel corrosion caused by sulfate-reducing bacteria. The average chemical composition of the BG L450OQO-RCB is show in table 1. The influence of Cu on corrosion was introduced in our other paper (3029945) in the coating journal. Whereas, to avoid confusion, the title is change into “Temperature and immersion time effects on a pipeline steel corrosion caused by sulfate-reducing bacteria”. The pipe steel used in this manuscript is described to be BG L450OQO-RCB.

 

 

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript  is devoted to the study of morphology and elemental composition of corrosion products, corrosion rate, corrosion solution composition, and electrochemical performance at different temperatures and immersion times of Cu-containing pipeline steel. The dependence on immersion time and temperature during the sulfate-reducing bacteria corrosion revealed the formation of three types of morphologies on the surfaces of steel samples.

 

Remarks

1.      Fig 1. It would be useful to provide an image of the surface before the onset of corrosion processes.

 

2.      There is no information about the grain size of pipeline steel, and whether the location of corrosion products is in any way related to grain boundaries.

 

3.      Figures 2, 5. In most EDS mapping images nothing is actually visible. It is clear that the image has low intensity, but the reader cannot see anything at all. It is not advisable to provide such figures. You should either significantly improve the quality of the figures by increasing the brightness and contrast, or remove the figures and replace them with descriptions. This especially applies to figures Fig.2 a (Cl, P,S), Fig.2b (P,S), Fig.2 c (P).

 

4.      In EDS studies, the thickness of near-surface corrosion products and its effect on the signal amplitude are not discussed. No data is provided on the accelerating voltage during EDS analysis, which allows us to at least estimate the depth of electron penetration and the size of the region forming the signal.

 

5.      A more detailed discussion of the EDS data on corrosion products should be added. It is necessary to discuss which elements noted in the spectra belong to the corrosion products and which belong to the substrate. It is not indicated from what area the signal was obtained during EDS analysis.

 

6.      The authors investigate a corrosion in Cu-containing pipeline steel. The composition of this steel is given in Table 1. However, this table does not contain information about the copper content. It is also not indicated in what units the average chemical composition is given in the table. This data must be provided

 

7.      The type of electrons that was used to form SEM images (backscattered oг secondary electrons) is not indicated.

Author Response

Responses to the reviewer’s and editor’s comments

 

Thank you for your arduous work in revising our manuscript entitled “Temperature and immersion time effects on Cu-containing pipeline steel corrosion caused by sulfate-reducing bacteria”, and providing constructive comments and valuable suggestions, which have helped us to improve the quality and readability of our manuscript. We have studied the comments very carefully and have revised the manuscript exactly according to the reviewers’comments. We hope this revision will meet with approval. The main revisions corresponding to the reviewers’ comments are as follows.

 

Reviewer #1: 

1. Fig 1. It would be useful to provide an image of the surface before the onset of corrosion processes.

 

Response:

The optical microstructure (OM) of the original specimen is shown in figure 1. The microstructure all of the sample is composed by ferrtic and globular cementite. The average grain size is 7.8mm. (lines 103-106 in page 3)

1. There is no information about the grain size of pipeline steel, and whether the location of corrosion products is in any way related to grain boundaries.

 

 Response:

The grain size of the pipe steel is 7.8mm, which is calculated from figure 1. The location of corrosion products is a random distribution.

 

2. Figures 2, 5. In most EDS mapping images nothing is actually visible. It is clear that the image has low intensity, but the reader cannot see anything at all. It is not advisable to provide such figures. You should either significantly improve the quality of the figures by increasing the brightness and contrast, or remove the figures and replace them with descriptions. This especially applies to figures Fig.2 a (Cl, P,S), Fig.2b (P,S), Fig.2 c (P).

 

 Response:

We improved the quality of the figures 3, 6.(in the revised manuscript) by increasing the brightness and contrast. The brightness in the element distribution maps corresponded to higher element content. The different corrosion products contain different elements and content. Therefore, the maps of elements with black color are also significant.  

 

3. In EDS studies, the thickness of near-surface corrosion products and its effect on the signal amplitude are not discussed. No data is provided on the accelerating voltage during EDS analysis, which allows us to at least estimate the depth of electron penetration and the size of the region forming the signal.

 

Response:

   The thickness of near-surface corrosion products is thin due to the low initial concentration of SRB. The accelerating voltage is 20KV,which less effect on the signal amplitude.

 

4. A more detailed discussion of the EDS data on corrosion products should be added. It is necessary to discuss which elements noted in the spectra belong to the corrosion products and which belong to the substrate. It is not indicated from what area the signal was obtained during EDS analysis.

 

Response:

The distribution of the elements C, Fe, O, P and S are obtained. Among these elements, C, Fe, O, P and S belong to the SRB corrosion products. The elements C has the possibility of be originated from the substrate. The elements distribution of C in the substrate is uniform，and the brightness of these elements is similar. The figures of EDS element mapping (figures 3 and 6) is obtained through the SEM pictures in the left side of figures 3 and 5. A more detailed discussion of the EDS data on corrosion products is shown in lines 205-217,page 7 and lines 312-315 and 325-328, page 12.

 

6. The authors investigate a corrosion in Cu-containing pipeline steel. The composition of this steel is given in Table 1. However, this table does not contain information about the copper content. It is also not indicated in what units the average chemical composition is given in the table. This data must be provided

 

Response:

The average chemical composition of the BG L450OQO-RCB pipeline steel (wt.%) is shown in table 1. .

7. The type of electrons that was used to form SEM images (backscattered oг secondary electrons) is not indicated.

 

Response:

The type of electrons that was used to form SEM images is secondary electrons.(line 145, page4) 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Line 98-99: Please check this sentence: “The average chemical composition of the Cu-containing pipeline steThe microstructure all of the sample is composed by ferrtic and globular cementite”.

Line 455-456: Please add steel grade or change in sentence: “The present study delved into the SRB corrosion of Cu-containing L450 (BG L450OQO-RCB) pipeline steel in terms of …” or “The present study delved into the SRB corrosion of Cu-containing BG L450OQO-RCB pipeline steel in terms of …”.

Author Response

 

Comments 1: Line 98-99: Please check this sentence: “The average chemical composition of the Cu-containing pipeline steThe microstructure all of the sample is composed by ferrtic and globular cementite”.

 

Response:

It is our mistake. The problem was revised.

The average chemical composition of this steel is introduced in detail in Table 1. (line 99,page 3) 

The optical microstructure (OM) of the sample is shown in figure 1. The microstructure all of the sample is composed by ferrtic and globular cementite. The average grain size is 7.8 mm. (lines 101-103, page 3)

 

Comments 2: Line 455-456: Please add steel grade or change in sentence: “The present study delved into the SRB corrosion of Cu-containing L450 (BG L450OQO-RCB) pipeline steel in terms of …” or “The present study delved into the SRB corrosion of Cu-containing BG L450OQO-RCB pipeline steel in terms of …”.

 

Response:

Thank you for your kind advice. 

    The sentence was changed into “The present study delved into the SRB corrosion of Cu-containing L450 (BG L450OQO-RCB) pipeline steel in terms of …”.(lines 464-465, page 18)

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The latest version of the article looks much better. The article may be published in its present form.

Author Response

We received your review report. Thank you.