Two worlds with different needs: the sealing of a pressurised flange and the strength of a structural connection. Both depend on the actual bolt load, but they govern it with distinct rules.
- ✓ ASME PCC-1: guidelines for pressure-boundary flanged joints
- ✓ EN 1090-2: execution of steel structures, connections included
- ✓ Bolt load as the quantity that decides sealing
- ✓ Prescribed preload control methods and available methods
ASME PCC-1 collects guidelines for the assembly of bolted flanged joints that form a pressure boundary, and applies to joints with ring-type gaskets entirely contained within the bolt circle. It is not a prescriptive code but a guidance document, which also addresses the training and qualification of those who physically carry out the assembly.
EN 1090-2 instead belongs to the world of construction: it specifies the requirements for the execution of steel structures and devotes a section to bolted connections, distinguishing between non-preloaded and preloaded assemblies and regulating the preparation of contact surfaces in slip-resistant connections.
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On preload control, EN 1090-2 provides four methods: the torque method, the combined method, the HRC method and the direct tension indicator method. These are methods acting on torque, rotation, shearing of the spline end or deformation of an indicating washer: ultrasonic measurement of elongation is not among these four.
The references in this section
| Reference | What it governs |
|---|---|
| ASME PCC-1 | Assembly of pressure-boundary bolted flanged joints |
| EN 1090 and structural connections | Execution of steel structures and tightening of preloaded assemblies |
Where ultrasonic measurement fits in
It is worth being explicit: where a standard prescribes a tightening method, that method must be followed. Ultrasonic measurement of elongation does not replace the procedure required by the specification or by the applicable standard.
Its ground is another: knowing the actual load of a bolt, verifying uniformity across a ring of studs, rechecking the same joint after a period of time to recognise loosening in progress. The method is described in the Ultrasonic bolt tension section.
Frequently asked questions
No. EN 1090-2 provides four methods for tightening preloaded assemblies: torque, combined, HRC and direct tension indicators. Where the standard or the specification prescribes a method, that method must be followed.
It is a guidance document for the assembly of pressure-boundary bolted flanged joints, not a prescriptive code. It becomes binding when a contract or a company procedure expressly refers to it.
Knowing the actual load of the individual bolt, verifying the uniformity of tightening across the whole joint and rechecking the same element over time, provided the reference reading on the unloaded bolt was recorded at assembly.
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