Pipeline bolt issues
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Why do bolts of type M36 in the Pipedata Pro 9.1 software correspond to different screw diameters? Also, how can one determine the M size of a bolt on-site based on its diameter? What is the relationship between the measured diameter and the nominal diameter of the bolt? It seems there’s no such corresponding relationship in the standards either; any advice would be appreciated? @Thank goodness you're here
Pipedata is a tool for reference only; standards should be followed.
Why can’t I find any standard that specifies the relationship between the nominal diameter and the actual measured diameter?
For M36, the diameter of the bolt is basically 36, which can be measured on site. Since the bolt sizes for American standards are in imperial units, on your drawings the bolt hole sizes for those two flanges are 1 3/8 and 1 1/2 respectively; however, when converted to metric units, they are both indicated as M36, and obviously these sizes are not the same. In fact, when using bolts in accordance with ASME B16.5, it is still best to use inches as the unit, as issues can easily arise regarding the compatibility of bolts, gaskets, and flanges
For plug specifications in American standards, one should generally refer to ASME B18.2.1. The diameter of the bolts has some variation, but it is basically the same as the M value. Check the national standard: GB901
Well, but national standards generally use nominal sizes; for bolts, we have M36, M39, and M33 – the differences between them are only a few millimeters, making it difficult to distinguish them on site
:Handshake, thank you; this skill level is truly exceptional
The storage on site must be quite chaotic – there are no markings on the bolts, so one has to measure them. It should be possible to do that; our colleagues have measured them on site
Mm-hmm, so the nominal size of this bolt can only be estimated: Q
The difference between the bolt hole and the bolt is usually 3 mm. M39 bolts are generally inserted into holes of size 42; try inserting them there. If the bolt is too large, it won’t fit in, while if it’s too small, there will be too much space left.
I sometimes can’t tell either. Should we measure the nut again? Nuts are different after all.