Three-Dimensional Ultrasonic Reverse-Time Migration Imaging of Submarine Pipeline Nondestructive Testing in Cylindrical Coordinates

Round 1

Reviewer 1 Report

The article presents a numerical model for 3D visualization of defects in the pipeline. The idea is to describe the propagation of ultrasonic waves in cylindrical coordinates, and to characterize the structural defect by analyzing the reflected, scattered and diffracted ultrasound signals. The introduction of the manuscript is well written, unfortunately there are no more good sections. The manuscript needs significant revision and cannot be accepted in this form. A few key notes that may help authors are listed below.

In Section 2.

All the equations given in the manuscript are useless. How they were applied in numerical simulations is a big question. It is not clear what the authors want to demonstrate with equations (1) and (2). This is the classical description of the Heimholtz equation in cylindrical coordinates. But in the next step (page 3 line 116) the authors propose the simulation methods with Cartesian coordinate system (reference 50).

Equation 3 raises more questions (Page 4 line 137). Attenuation factor is d(x) or d(l)? What direction of attenuation is being used; R- Z- or θ-direction? The descriptions of symbols are not definite. “x is the distance from the boundary of the model.” From the boundary to … what; is x the distance? Figures 1 and 2 are not informative and could be deleted from the text.

In section 3.

Why defect modeling is given in Cartesian coordinates?

What does mean the numbers 1, 2 and 3 in the table 1 (Page 7 line 214). Is it the values of sound speed and density of in the regions 1, 2 and 3 of figure 5? In this case, why does the delamination (2) that is an extended air or void inclusion, have such atypical characteristics? Moreover the description of Figure 5b is wrong.

What does characteristics of the modeled wave (frequency, wide of signal etc.). Is it a plane wave, spherical or cylindrical?

In section 4. The big question is the comparison of numerical and experimental results. The authors have shown the experimental results of the propagation of Rayleigh surface waves; however, all numerical calculations are presented for bulk longitudinal waves.

Some terms have a double or unclear meaning

Author Response

Please see the attachment.

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The work seems sound, although I am not sure how practical the technique will be for real pipelines due to the high data density required (not to mention the difficulties of field inspecting subsea pipelines in general). Still, probably worth pursuing in case the other problems are solved or an alternative application is found. A couple of minor points:

eq1, eq2: Please declare all your variables in your initial equations.

P4: given your boundary conditions, would your model ignore helical modes? Does this matter? Perhaps they are outside the time windows used anyway.

Ln 197: Horizontally placed? Are those lines not circumferentially placed?

P7: I do not understand why the density and velocity parameters are varied so wildly in the models. Well beyond the range of materials subsea pipelines are made of. perhaps I am misunderstanding the reasons, but maybe other people would also misunderstand so you could clarify.

Almost all fine. A couple of minor points:

missing comma and incorrect plural, ln 39

Ln 49, consider revising sentence structure.

Ln 61: "methods"

ln 70-71: "considering"

Author Response

Please see the attachment.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The proposed method is destined to detect three types of defects in submarine pipelines, i.e., a hole, a delamination defect, and a slag inclusion.

What about welding defects, such as: stress concentration and discontinuities ?

These topics must be considered, since submarine pipelines are often welded. 

Others parameters must be considered in the analysis method, such as: the deep into the water, and superficial condition of submarine pipes.

Minor revision is required.

Author Response

Please see the attachment.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

In the present study is proposed a reverse time migration imaging algorithm to be applied in the obtention of 3D imaging of pipelines.

The topic of the paper is very interesting, the structure of the paper is well organized and well written, and it is easy to follow.

In the reviewer opinion, the present paper meets all requirements for the published in Journal of Marine Science and Engineering after the follow comments have been considered.

Comments:

1. Page 3, from line 117 to 119

Correspondence between the physical quantities and the symbols must be done.

2. Page 4, line 137

Must exist coherence in the variable that indicates the distance from the boundary of the model. There is “x” in the text and “l” in the equation (3).

3. Page 5, eq. (4)

The variable "I" must identified in the text.

4. Page 6, line 196

Details about the geophones used should be provided.

5. Page 6, line 200

The authors speak here about “sensors”. The sensors are geophones? Please clarify.

6. Page 7, line 213

Details about “vp” and “ro” in table 1 must be provided. What is vp velocity? Is phase velocity?  What is the relation with each one of the defects of figure 5?

7. Page 8, Fig. 228

Grammatical typo.

8. Page 10, line 225, legend of Fig. 7

Is not clear how fig. 7 to 9 were obtained and what is physical meaning of the horizontal axis called Trace/No. Previous explanation about this should be made in the text.

Author Response

Please see the attachment.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks for the replies that have been carefully reviewed. The text comprehension become more clearly but I still have some doubt the correct description of experiment data. Nevertheless, after the minor revision the manuscript can be recommended to publication.

1. Section 3.2. Please improve the signal width 0-2MHz (Page 11, line255).  Bandwidth is usually described as width of spectrum at half amplitude (6dB decrease).So according to figure 6b it is around 0.83 MHz

2. Rice. 8-11 are still difficult to understand, first of all, how they were obtained. I assume that they were formed in the reflected mode during the double passage of an elastic wave from the outer boundary to the inner boundary of the pipelines and back. Whether this is true or not remains a mystery. Then, firstly, the figures names are “Synthetic R- direction records…”. Is it mean the cross section in  R-θ coordinates (Line θ1- θ3) and R-Z coordinates (line Z1-Z3)? Secondly, were these cross sections obtained by one source of ultrasound waves or by compilation of signals generated by all sources depicted in Figure 4? If it was one, then where were the other sources used? Third, each figure has a space in the central part. Better explain it. Please highlight all these points in the text.

3. It is better not to use the word delamination, since you are talking about the same slag inclusions but of different orientation. May be better use the phrases: vertical and horizontal slag defect (inclusion). Please remove “delamination” from the manuscript.

Author Response

Please see the attachment.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Authors have made the main suggested modifications.

Author Response

Thank you so much for your professional suggestion, which can greatly improve the quality of our manuscript, as well as the important guiding significance to our researches.

 

Round 3

Reviewer 1 Report

Thanks for the answers, all improvements are made.