Analysis on the Leakage of the Flange Connection of the Water-Containing Hydrofluoric Acid Pipeline
Round 1
Reviewer 1 Report
This paper cannot be accepted for the following reasons:This paper predicts leakage by calculating the moment applied to a flange in the pipe. However, leakage should consider bolt pretension and gasket type in bolted flanges.
That is, there is no prediction for leakage.
Author Response
Thank you for the comments. Although Leakage rate prediction should cover many factors such as bolt pretention, internal pressure, pipe loads, compression and resilience ability of the gasket, and even the sealant properties, it is practical to give fast leakage scanning by the equivalent pressure method, which requires internal pressure and pipe loads. In this paper, the discussed pipe is under low pressure and mild temperature, which often escapes from detail pipe analysis and results in leakage. The motivation of the paper is to ring a bell for such kind of pipe which conveys hazardous chemical product. Leakage analysis is necessary for hazardous chemical product even the pipe works under low pressure and mild temperature.
Reviewer 2 Report
The manuscript lacks detail. It is not clear the type of analyses that were conducted, what are the characteristics of the elements used, how is nonlinearity considered, how is the temperature factored in the analyses, etc.
The static analysed are too simplified and the conclusions seem to be based on the results of a regular linear elastic analysis.
The figures are low quality and some of them are even photographs taken from a computer screen.
Author Response
Thank you for the comments. All the analyses are linear elastostatic analysis. The elastic modulus, Poisson's ratio and linear expansion coefficient have been given in this paper. The PIPE16 and PIPE18 units of ANSYS can apply internal pressure and temperature load to realize the pipeline stress analysis under the corresponding load. Gravity loads are applied as vertical inertial forces. The pipeline stress is very low under the low internal pressure and mild temperature, but the analysis shows that the pipeline stress under the action of gravity can not be ignored。The leakage of flange is mainly caused by the bending moment dued to gravity.
We provide a clearer picture of Figure 2, Figure 8, and Figure 11.Please find attached file.
Author Response File: 
Author Response.docx
Reviewer 3 Report
See attached file
Comments for author File: Comments.docx
Author Response
Thank you for the comments. Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
I consider the presented material as a practical application of one of the main problems of the university course in strength of materials.
In the article, the authors should indicate the novelty of the research method or in the problem statement, or the features of investigation, that are valueable for further researchers. In the presented manuscript in the conclusions one can find some well known ideas.
In fact, the paper reproduces the procedure for calculating load, pressure etc., which must be performed at the stage of pipeline design. Various causes of leakages are mentioned, but research focuses on only one of them. An interesting problem can be optimal placement of supports depending on the length of pipes and calculated bending moments.
The study of a particular case of the consequences of improper pipeline design without any development is unlikely to be of interest for a scientific publication, but may be useful as a motivating example for students.
Comments for author File: Comments.docx
Author Response
Thank you for the comments.Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The criteria for leakage is still not provided in this study.
Author Response
Thank you for the comments. The criteria for leakage is provided in this paper."
Equivalent stress method, NC3658.3 method and ASME B&PVC specification VIII-I (appendix 2 method) are three mature flange leakage analysis methods which are widely used at present. The first two methods are mainly used for flange under general working condition without high temperature , high pressure or low temperature. In this study, equivalent stress method will be adopt to analyze the leakage of the flange connection of the water-containing hydrofluoric acid pipeline.
Equivalent pressure method converts external loads such as axial force and bending moment at the flange into equivalent pressure, then add the equivalent pressure and the design pressure to get the total pressure. Finally, the total pressure is compared with allowable pressure in the temperature and pressure table related to flange material in ASME B16.5. It is theoretically considered that when the total pressure is less than the allowable pressure given in the standard, the flange will not leak;Otherwise, it will leak.
"
Reviewer 2 Report
This manuscript shows the application of well known elastic structural analysis to a case of a segment of pipeline under distributed loads representing gravitational loads and temperature effects. There is no significant novelty in the material presented.
Author Response
Thank you for the comments. The piping lines convening highly hazardous medium under low pressure and mild temperature are often escaped from strict scrutiny of piping stress analysis by experience. But once this kind of pipeline leakage, it will cause great harm to people. In this paper, the stress analysis of water-containing hydrofluoric acid pipeline is carried out. It is found that the self-weight of t pipeline will produce a large bending moment, so that the equivalent pressure of flange is too high and leakage may occurs. In order to ensure the sealing performance of the flange, the flange should be put as far as possible at the position with zero bending moment. This idea is not mentioned in the literature. For multi-support pipeline, it belongs to the statically indeterminate beam. Using the deformation coordination condition that the rotation angle is zero on the symmetric boundary of the beam, we derive the position of zero bending moment of the equal-span braced and non-equal-span braced pipeline under the gravity load.The derivation and conclusion have not been seen in other literature.
Reviewer 3 Report
Including the conclusions from answers 1 and 2 in the introduction may increase the quality of the article.
Author Response
Thank you for the comments. Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
The presentation of the results has been improved.
One more question is in the applied file. The model is not general. It is nessesary to mention about the limitations of the proposed equations.
Comments for author File: Comments.docx
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 3
Reviewer 2 Report
I suspect the reason the authors do not find this approach in the literature is related to my reason to recommend not to publish the article. From the point of view of structural mechanics, this is a very standard analysis that I would assume professionals in charge of designing pipelines use frequently when looking at their structural design. In my opinion there is no novelty or advancement of knowledge here, at least from the standpoint of structural engineering.
Other papers on the topic, including one in this same journal, investigate the issue of corrosion, which would occur even if the pipeline is properly supported and sized.
Author Response
Many thanks for comments!
Finding zero bending moment location to position flange connection may be a occasional problem for many pipe-line designer. The main task of a pipe-line designer is to qualify the strength of the pipe, the sealling performance of the flange connection and so on. They do often adjust the supporting postion and add flexible components to reduce the bending moment. They seldom find zero bending moment location to position flange connection, because there is no such instruction in any design code. However, for gravity bending dominated pipe-line, postion flange connection near zero bending moment location may be the optimal design for the liner pipe with too many flange connetction.
Although the method to obtain the zero bending moment location is traditional and easy, I believe it does add some thing to the pipe-line design to aviod leakage under such simliar conditons.
