Field Inspection of High-Density Polyethylene (HDPE) Storage Tanks Using Infrared Thermography and Ultrasonic Methods

Round 1

Reviewer 1 Report

A comprehensive article describing the use if infrared thermography for the detection of defects in HDPE tanks. Very good citation of prior art.

The article, in the abstract and introduction, the use of both infrared thermography (IRT) and ultrasonic testing (UT) for field inspection of HDPE tanks, which gives an impression that the techniques are combined to enhance their merits. However, it is understood from the article that the major contribution is in IRT, and the use of phased array ultrasonic testing (PAUT) is a complementary method. Therefore, the contribution of PAUT to the article is disputable. It might be removed for clarity.

The manually created defects are drilled circular holes. The efficiency of the method for cracks is not mentioned. Yet, there is no discussion on the severity of the crack that requires immediate replacement of the tank to prevent rupture.  

While length and temperature units are presented in "metric (imperial)" format, volumes are given as "imperial (metric)" (as in lines 34-35).

line 203 PUAT -> PAUT

Several missing figure and table references.

Author Response

Response letter to Reviewer 1’s comments: The authors wish to thank the editor and reviewers for their time and effort in reviewing the manuscript and hope the changes listed make the manuscript suitable for possible publication. The comments and the concerns of the reviewer were noticed carefully and addressed point-to-point.
A comprehensive article describing the use if infrared thermography for the detection of defects in HDPE tanks. Very good citation of prior art. The article, in the abstract and introduction, the use of both infrared thermography (IRT) and ultrasonic testing (UT) for field inspection of HDPE tanks, which gives an impression that the techniques are combined to enhance their merits. However, it is understood from the article that the major contribution is in IRT, and the use of phased array ultrasonic testing (PAUT) is a complementary method. Therefore, the contribution of PAUT to the article is disputable. It might be removed for clarity. Response: The authors appreciate your impression of our work. We kept PAUT in this paper since this work was in continuation of our previous work and experiments conducted in the laboratory. In the previous work, we showed that both IRT and PAUT are useful techniques to detect subsurface defects. In this work, we tried to transfer both techniques to the field and wanted to highlight the challenges that an inspector may see in the field. Therefore, we had to show both IRT and PAUT results to list the challenges in the field and based on the identified challenges, develop a guideline for the inspectors.
The manually created defects are drilled circular holes. The efficiency of the method for cracks is not mentioned.
Response: Thanks for your comment. Your concern is valid. We have discussed the effectiveness of IRT on crack detection in our previous work which is in press (Reference 9 in our manuscript). We have added a sentence in Lines 661 to 662.
“IRT is not able to detect non-leaking cracks propagated from the internal side of the AST towards the surface. This has been discussed in more detail in Ref [9].”
[9] A. Behravan, T.Q. Tran, A. Hernandez, M.M. DeJong, A.S. Brand, Evaluating the integrity of high-density polyethylene (HDPE) storage tanks, J. Mater. Civ. Eng. in press (2022).
Yet, there is no discussion on the severity of the crack that requires immediate replacement of the tank to prevent rupture. Response: Thanks for your great point. In fact, the brine tanks store highly concentrated brine solution which in case of a failure impact the environment severely. Therefore, as far as the authors are aware, state DOTs remove the brine tanks from the service immediately after observing a crack to prevent catastrophic failure. The authors do not have information from other industries that use HDPE storage tanks and their policies. Therefore, the authors are unable to recommend a time frame for removing the tank from the service. It totally depends on the industry, the stored solution, the policy of the owner, and the environmental obligations. While length and temperature units are presented in "metric (imperial)" format, volumes are given as "imperial (metric)" (as in lines 34-35). Response: Thanks for your detailed review. We switched the units to be consistent throughout our paper. line 203 PUAT -> PAUT Response: Thanks for your detailed review. We fixed it.
Several missing figure and table references.
Response: All missed figures and tables are shown in the supplementary document that was uploaded and submitted along with the manuscript.

Reviewer 2 Report

There are errors in the article "Error! Reference source not 80 found" with respect to the cited literature.
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I propose to label Figure 2 and Table 5 and Table 6 in more detail. I believe that it is not fully understood by the reader.
Figure 3 I propose to mark in detail on the drawing possible defects in the tank.

I think that the research should continue and expand all diagnostic possibilities, maybe it is also worth considering changes in the frequency of ultrasound heads.

Author Response

Response letter to Reviewer 2’s comments:

The authors wish to thank the editor and reviewers for their time and effort in reviewing the manuscript and hope the changes listed make the manuscript suitable for possible publication. The comments and the concerns of the reviewer were noticed carefully and addressed point-to-point. 

There are errors in the article "Error! Reference source not 80 found" with respect to the cited literature.
Line 147 (Error! Reference source not found.).
Line 168 (Error! Reference source not found.).
Line 169 (Error! Reference source not found.).
Line 214 (Error! Reference source not found.).
Line 228/229 (Error! Reference source not found.).
Line 230 (Error! Reference source not found.).
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Line 273/274 (Error! Reference source not found.).
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Line 326 (Error! Reference source not found.).
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Line 361 (Error! Reference source not found.).
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Line 528 (Error! Reference source not found.).
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Response: Thanks for noting us about this error. Actually, as the authors doubled checked, the original document has no such errors. Having said that, this happened during the submission and conversion steps. To resolve this issue, we have made the whole document plain text and removed all links and cross references.

I propose to label Figure 2 and Table 5 and Table 6 in more detail. I believe that it is not fully understood by the reader.

Response: Thanks for your comment. We changed the captions per your recommendation. Please see below:

We changed the caption of Figure 2 to this: “Figure 1. Configuration of the defects created inside the tank wall (a) defects on the internal east side of the tank  (b) defects on the internal west side of the tank”

We changed the caption of Table 5 to “ Table 1. Characteristics of the defects shown in Figure 2 created on the internal east side of the tank (wall thickness, t = 12.7 mm = 0.5 in)”

We changed the caption of Table 6 to “Table 2. Characteristics of the defects shown in Figure 2 created on the internal west side of the tank (wall thickness, t = 19.1 mm = 0.75 in)”

Figure 3 I propose to mark in detail on the drawing possible defects in the tank.

Response: Thanks for your great recommendation. We applied the changes in Figure 3.

Author Response File: Author Response.pdf