Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article deals with the ageing of polyethylene coatings used to protect, combined with cathodic protection, buried steel pipelines from corrosion. The main aim is to propose a predictive model to estimate the coating’s average specific electrical resistance at any service time. This model is based on data obtained with line current attenuation (LCA) tests. The article is well written but several points of concern have to be carefully addressed before the article can be accepted:

1. Table 2 is confusing because the initial coating electrical resistance measurements, which were carried out using drainage tests (DT) in any case, are presented the same way as those carried out after 8-11 years, which were obtained using DT or LCA tests. Thus, the initial values given in column 3 do not relate to the measurement method given in column 2. I suggest to list the initial coating electrical resistance values in column 2 and give the type of test used for other measurements in column 3.
2. Lines 501-502 (page 13): this sentence is incomprehensible: I think something is missing.
3. In the discussion of the results obtained with both methods (pages 13-14), the authors observe a significant difference between the results of the two techniques. They conclude that the LCA method is more reliable and then discard the data obtained with the DT method. However, the initial values were measured with the DT method and are then included in the model together with the results obtained at 8-11 years with the LCA method. This must be carefully justified, because if the DT method is inadequate, then the results this method gave at t = 0 should be discarded too.
4. The authors state that the aging model is based on the exponential Arrhenius model (page 15, line 537). I do not see the link between the aging exponential model and Arrhenius law, which describes the role of temperature. The aging exponential model rather looks like an exponential decay, which would mean that the average coating electrical resistance R decreases at a rate proportional to its current value, that is dR/dt = -λR. The authors must comment on this and discuss on the scientific meaning of this result.

Author Response

Please see the response attached.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors presented an interesting manuscript investigating the ageing of polyethylene-coated underground steel pipelines. The value of the work lies in its practical nature with regard to the anti-corrosion protection of gas pipelines and waterworks using a 3LPE coating. The authors examined the ageing of such a coating on real underground steel pipelines. Field measurements were performed after 9, 10 and 11 years of underground exposure. Based on these results, the authors developed a predictive model for coating ageing, which can be used to estimate the average specific electrical resistance of the coating over its entire service life.

The research methodology is sound. In the field study, the authors employed two methods: line current attenuation and drainage testing. They employed the Arrhenius-based model to predict polymer lifetime. The research results are clearly discussed. The tables and graphs accurately present the data. The conclusions are supported by the results obtained and are valid.

This work can be used by design engineers, maintenance planners, quality control teams and researchers to help ensure the long-term integrity and sustainability of underground polyethylene-coated steel pipelines. Given its merits, I believe the work is worthy of publication.

However, the manuscript needs a few improvements.

1. line 284
"In both cases, the current is zero."
It needs to be clarified which current we are talking about.

2. equation (22)
Δ𝜑𝐴+ Δ𝜑𝐵
There is no explanation that these are changes in the pipeline potential at measurement points A and B.

3. equation (24)
Δ𝜑 - Should be in the index: 'average'.

4. line 398
"The obtained results have been normalized for a specific soil resistivity of 10 Ωm."
How are the calculated values of the average specific electrical resistance of the coating (R_coat) normalised in this work for a soil resistivity of 10 Ωm?

5. line 647
ACVG / DCVG
While these acronyms are familiar to cathodic protection personnel, they may not be understandable to other readers of this publication. Therefore, it is advisable to include information on what these acronyms refer to: Alternating Current Voltage Gradient and Direct Current Voltage Gradient.

 

Author Response

Please see the response attached.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors carefully took into account all the comments of the reviewer and improved significantly the article. The manuscript can then be accepted for publication.