Page 53 - banneredThermosealCatalog2010

PAGE 1 of 2 Bolting Guidelines 061107
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Bolting Guidelines
To achieve a trouble free joint, one of the most important aspects to consider is the bolts or
studs. Reliability depends on achieving and maintaining an acceptable level of tension in each
bolt. The target tension level for most applications can be calculated using Klinger's gasket
design system.
However, the method employed to tighten the bolts is very important and can result in
significant variations from those anticipated. As a guide the following table shows the variation
of bolt tension with the tightening method.
Method Used Tools Required Variation of tension
from mean value
Wrench (No Torque Control) Spanner or Wrench ±50%
Wrench (With Torque Control) Calibrated Torque Wrench ±30%
Hydraulic Tensioner Multiple Stud Tensioners ±10% to ±30%
Direct Strain Measurement Rotabolt pre-set Studs ±5%
If the initial bolt stress is too low the total amount of strain (stretch in the bolt) is low and under
these circumstances any subsequent reduction in thickness of the gasket due to creep will
quickly result in loss of bolt strain and subsequent leakage.
Within reason, it is better to approach the maximum bolt stress recommended by the
manufacturer. This is often 80% of the yield strength at the operating temperature.
Other points to consider are:
§ The crushing strength of the gasket.
§ That the hydrostatic end thrust will increase the bolt tension at the operating internal
pressure.
§ Using a bolt stress which represents less than 50% of the yield strength will cause
problems and should only be considered under certain circumstances.