Fig. 2. Stress concentration resulting from overload and underload of boiler screen suspensions.
The strain gauge correction of the hydraulic force gauges must be taken into account in non-free systems and allows to maintain the accuracy of the DM3 method adjustment with a significant reduction in the time of work. This modification is especially useful on old units with corroded threads and difficult access to them. We know from the present experience that the value of this correction ranges from 0 to even 30% of the measured value of the ‘hydraulic’ force. The size of the correction depends on the diameter of the rods and the method of their installation (if the the rods are rigid or with more or less flexible springs), the type of suspended load (header or hanger pipe, airtight waterwall, steel coils). The measurements carried out in this way allow to determine the actual forces acting in the rods along with their mutual interactions taking into account changes in the stiffness of the supporting structure of the object and the object itself. This procedure leads to the definition of the influencing numbers kni and the actual correction factor k which is the quotient of the sum of the measured loads and the sum of the designed loads important in further numerical calculations.
kni = Pni/Pnn
kni – influencing number for the i-rod determined by the load change in the n-rod,
Pni – load change in the i-rod caused by the change in load on the n-rod,
Pnn – force value in a loosened rod.