Expansion Joint Challenges
Design factors to consider when selecting your next GTX expansion joint.
In Gas Turbine Exhaust Applications
Designing an effective custom expansion joint for a GTX (Gas Turbine Exhaust) application requires
strict attention to a number of unique engineering problems. Typically installed in the vital space
between the turbine and exhaust duct, a GTX expansion joint represents a single point of failure - if
the joint fails, the plant ceases to operate as the turbine must be shut down. Therefore, when
FlexCom engineers are tasked to design a custom expansion joint for a gas
turbine exhaust system,
we expect to face certain challenges common to most gas turbine applications, but unique compared
to other industrial facilities.
Heat stress poses an intense issue to gas turbines, since the thermal state of a GTX system
fluctuates severely during the course of turbine operation - particularly as the turbine starts.
A gas turbine initiates from a cold state to extreme heat very quickly, subjecting an expansion
joint installed on the exhaust outlet flanges to thermal shock. If the joint is not adequately
protected against these rapid shifts in thermal stress, the heat will damage the joint and
ultimately cause it to fail.
In addition to heat, vibrations and mechanical movement add significant stresses to an operating
GTX expansion joint. As turbines and connected ductwork assemblies increase in size, power and
temperature output, so too do they produce greater levels of duct movement and overall metallic
vibrations. The turbulent flow of exhaust gas through the joint additionally increases vibration
- as well as “flutter”, rapid shifts in gas pressure that can damage an unprotected fabric joint.
These mechanical stresses can cause significant damage to an inadequately designed joint in a
relatively short amount of time.
For gas turbine exhaust applications, we at FlexCom recommend using a flat belt composite
expansion joint designed with highly
temperature resistant fabrics. The fabric and stainless
steel construction of FlexCom flat belts provide highly efficient movement compensation and
vibration isolation, while our PTFE/fiberglass laminate fabrics reliably insulate the joint
against the unique thermal stresses found in the exhaust duct of a gas turbine.
For hot-to-hot configurations (one in which both flanges must operate at the exhaust gas
temperature), we also recommend including an accumulation pillow in the custom joint design.
A pillow will reduce the overall temperature of the joint, as well as limit vibration
transmission to the turbine outlet flange and help absorb ductwork movement stresses in these
very high temperature environments.
Custom design of a gas turbine exhaust expansion joint
requires a special level of
engineering precision, as well as specialized expertise in compensating for the extreme stresses
present in this type of exhaust ductwork. Don't risk your gas turbine operation on a lesser
quality product - contact FlexCom offices today and let us show you how our custom designs deliver