Stress monitoring

Any resultant stresses on the boiler’s thick-walled pressure components are mainly from the internal pressure. The difference between the permissible thermal stress value and the actual value is defined as the thermal stress margin. For safety reasons, this margin is monitored continuously.

 

This module performs the following basic functions:

 

• It determines the thermal stress margins in the main pressure components of the boiler in the online mode
• It determines the safety margin for heated surfaces by monitoring the heat load of its heating components - mainly the superheater components

 

 

The components that restrict the boiler start-up speed are its thick-walled pressure components. The basic function of the boiler start-up program module is to systematically identify thermal stresses and then determine the margins of stress that may occur as a result of the start-up. Mechanical stresses are calculated within appropriate standards.

 

Boiler thermal stress interface

 

 

Calculations in the program are performed online. The program systematically monitors the operating status of power equipment, looking for characteristic stages of the start-up cycle (shut-down, standstill, start-up). The completion of each start-up is followed by calculations related to this start-up, along with an update of the forecast start-up loss template. To determine the specific state of the beginning and the end of any given unit start-up, the application performs detailed calculations for every start-up stage of the unit.

 

Thermal stresses in the thick-walled components are calculated online; the calculation method depends on the complexity of the thick-walled component shape, along with the applied method to measure the metal temperature.

 

The calculation result is then processed into information, which has two applications:

 

• The information is displayed on the screen monitor of the unit operator
• The information for the control system represents the boiler thermal restrictions.

 

 

In the first application, the operator uses the information obtained for manual start-up. The method of thermal stress margin visualisation is shown in the picture.

 

The thermal stress module complements the power plant diagnostic system. Periodic tests of the unit’s thick-walled component material with non-destructive (NDE) methods enable the degree of degradation of each component to be assessed. However, the correctness of equipment operation in the period between the subsequent NDE tests is monitored by the presented thermal stress program module.

 

download brochure "Stress Monitoring" (0,2 MB)