Question: Why do Exhaust Silencers fail?
Answer: Exhaust panels fail from movement, whether physical movement from flow, or
thermal movement from temperature over time.
Question: How does Schock design silencer to extend life and combat these failure modes?
Answer: Schock designs silencer panels with the aid of an FEA Analysis, as well as applying industry experience. There are no one-size fits all. We analyze our silencer panel frames and designs by using your plant GT start up and shut down information. We are interested in how your GT starts up and shuts down (time vs. temperature curves).
It is through these conditions from ambient temperature to run temperature, and conversely that all silencer frame materials are going through the thermal growth cycles. These cycles are where fatigue cracks will begin forming over time.
The design truly boils down to designing so the cross-section frame & outer Perforated materials act and thermally move as one unit. In other words, we do not want the weld filler (or lack of in skip welds) to move any differently than the base materials. Failure to follow this rule causes thermal cracks to form pre-maturely.
Figure 1: indicates thermal cracking at each skip weld, and differential thermal movement between welded and un-welded material connections.
These thermal movement variants are enhanced by improper material type and thickness selections. Therefore, the FEA analysis predicts the amount of lifetime thermal cycles the design can support BEFORE cracks begin. As we run these different designs, Schock Engineering adjusts the parameters of the model and re-runs until we get the maximum desired Cycles based on the site GT data.
The physical movement failures are caused by the Exhaust Panels having too much thermal growth room during startup/shut down conditions. All silencers require some sort of panel guide to keep them in position, and some sort of support to carry the load to the stack base. Our proven Stack Support brackets and guides are over-designed to thermal move, carry minimum heat to the casing plate, and keep the silencer panels in position for decades. Additionally, Schock ties silencer panels together in groups of 2-3 to further limit the movement from high velocities during running conditions.