High Temperature High Velocity Exhaust Liner System Schock Liner
Question: Why is the internal liner system necessary?
Answer: The internal liner system is a layer of metal (typically 409SS) to protect the porous high temperature insulation from high exhaust velocities, which in turn protects the casing plate and keeps the external duct skin temperatures at an acceptable temperature during operation.
Question: What is the common make-up of an Internal Exhaust Liner System?
Answer: The liner system consists of some types of internal support, liner pin, and liner sheets. The supports hold the liner system up to cover the insulation, and the liner pin allows the liner sheet to thermally move as the system heats up and cools down. The liner sheets typically have an oversized hole or slot to allow for thermal expansion.
Question: What is the best practice, a Scallop bar or direct pin system?
Answer: When designed properly, both systems can survive for decades. However, the Scallop bar system utilizes a 304SS stud welded directly to a 409SS scallop bar. This dissimilar metal has different thermal coefficients. Over time, these areas will crack, and the connection will fail. The Liner pin is also a dissimilar metal weld, but is located at the casing plate, therefore the temperature and the thermal coefficient is Minute.
Question: Should the same liner design be used in any Exhaust System?
Answer: No, Schock has (3) Exhaust liner designs. All of which vary stud diameter, stud grid spacing, insulation protection, under liner support, and above liner clamping, as well as additional subtle design features.
Question: What additionally does Schock do to ensure the extended life of the liner system?
Answer: Each liner system is custom designed based on the Gas Turbine run conditions, and position in overall system. This considers velocities, temperature, and start up rate. Schock designs liner sheets no larger than 4ft x 4ft to limit the overall thermal movement by piece. Additionally, Schock takes precautions to eliminate flow induction into and under the liner system. These include lapping liner sheet laps with flow and protecting the insulation cavities where exposure can not be avoided with matting or cloth.