Engineering guide
The 159N module belongs to the module family for flange calculation according to DIN EN 1591-1. This standard treats gasketed flange connections as a complete system: flanges, bolts, and gasket are considered together with their stiffnesses and deformations, so that in addition to the strength verification, the leak tightness verification can be carried out across all load conditions.
Anyone who wants to calculate a flange connection to EN 1591 works through several coupled conditions – the assembly condition with the bolt assembly force, the test condition, and the operating conditions with internal pressure, temperature, and additional external loads. The modules of the 159 series cover the main calculation and supplementary subtasks; 159N is one of these supplementary building blocks within the calculation chain.
Typical applications are critical flange connections in apparatus engineering and piping where the classical design to AD 2000 B 7/B 8 or EN 13445 is not sufficient because a verified leakage rate is required – for example for media subject to the German TA Luft clean air regulations.
Typical workflow
Define the connection
The geometry of both flanges, the bolting (number, thread, material), and the gasket with its characteristic values to EN 13555 are specified. The gasket parameters largely determine the required surface pressures.
Set up the load conditions
For the assembly, test, and operating conditions, pressure, temperature, and additional loads (axial force, bending moment from the piping) are compiled. Each condition enters the calculation with its own material properties and gasket requirements.
Calculate compliances and load redistribution
From the elastic compliances of flanges, bolts, and gasket, the method determines how the assembly bolt force redistributes in the subsequent conditions – including the creep and settlement behavior of the gasket and differential thermal expansion.
Determine the required bolt force
The minimum assembly force is found iteratively so that in all subsequent conditions the gasket surface pressure needed for the required tightness class is maintained without exceeding the allowable stresses.
Perform the strength and tightness verifications
Finally, the load ratios of flanges, bolts, and gasket are checked in every load condition, and the assembly instructions (tightening torque, scatter of the tightening method) are derived.
Frequently asked questions
How does the calculation to EN 1591-1 differ from the classical flange calculation?
Classical methods such as AD 2000 B 7/B 8 or the Taylor-Forge method essentially perform a strength verification with generic gasket factors. EN 1591-1, by contrast, analyses the elastic interaction of flange, bolt, and gasket across all load conditions and additionally verifies leak tightness for a defined leakage rate. For this it requires tested gasket characteristics to EN 13555.
Why is the procedure iterative?
The required assembly bolt force depends on the load redistribution in the subsequent conditions, which in turn depends on the gasket surface pressure in the assembly condition – and the gasket stiffness is itself load-dependent. The standard resolves this coupling by iteration until the minimum required bolt force covers all subsequent conditions.
What role does the scatter of the tightening method play?
Depending on the assembly method (torque wrench, hydraulic tensioning, angle-controlled tightening), the actually applied bolt force scatters considerably. EN 1591-1 accounts for this through scatter factors: the lower bound must ensure tightness, while the upper bound must not overload flanges, bolts, or gasket. A more accurate tightening method therefore often leads to a more economical joint.
Technical content source: LV-Solved-Problems-Content 628d313247e7