Non-destructive testing requirements for vacuum-insulated pressure pipelines
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Dear students: Are there any non-destructive testing requirements for the outer pipe butt welds of vacuum-insulated pressure pipelines used for transporting LNG? If so, what types of testing should be carried out, and what are the relevant reference standards? The inner tube is pressurized, the jacket is under vacuum, and the outer tube wall thickness is 3-4 mm. Thank you.
There’s no clear specification for this; it only states that the inner tube must be 100%, usually via radiography. However, the standards and specifications regarding non-destructive testing allow for deviations based on the design documents; that is, the requirements set out in the design documents specific to a particular application can be higher than those specified by the standards. Given that the medium in question is LNG, imagine if there are issues with the welds of the outer tube, which could lead to a decrease in vacuum level and an increase in temperature… The risks involved would be significant. In my opinion, at least 20% radiographic testing should be carried out for non-destructive testing purposes.
This post was last edited by mofei521 on 2015-9-11 12:44. Hello: If helium mass spectrometry testing is conducted on the external pipe welds while evacuating the interlayer, is it then unnecessary to carry out non-destructive testing? Thank you.
Do anyone else have any comments? Thank you
100% non-destructive testing is required for the inside of the casing
No reports indicating the need for flaw detection on the outer tube were seen; it is presumed that such testing is not necessary
For the inner tube, 100% radiographic inspection is required for the butt welds, as the inner tube constitutes the main part of the pressure pipeline. For the outer tube, only penetrant testing is necessary for the welds, since helium mass spectrometry testing for leaks is also performed; it is sufficient to ensure that no vacuum leaks occur. If you want to learn more, you can refer to TSG D2001, the Rules for Licensing the Manufacturing of Pressure Pipeline Components. All vacuum tube manufacturing before 2015 had to comply with the requirements outlined in this document
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