Gas Turbine Power Plant Expansion Joints Gas Turbine … · Gas turbine power stations subject the exhaust duct and HRSG casing to extreme stress and fatigue, with the expansion joint

Gas Turbine & Combined Cycle Plants

Gas Turbine Power Plant Expansion Joints

Gas Turbine Power Plant Expansion Joints

Gas turbine power stations subject the exhaust duct and HRSG casing to extreme stress and fatigue, with the expansion joint being the focus point of the systemic issues. Both fabric and metal expansion joints are used in many positions around the plant.

Base Load Operational Plants

Base load stations can obtain acceptable performance from a basic design, due to the reduced stresses and fatigue caused by fewer start-ups and shutdowns. Good construction techniques and fabrication quality are essential to bring simpler solutions to the required reliability. Stations originally designed for base load are now being asked to run cyclically.

Cycling Operational Plants

Conversely, cycling plants are subject to increased maintenance when using basic duct and joint constructions that were not designed for the increased stresses and fatigue. DEKOMTE’s designs and constructions offer technically based guarantees and

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a lifespan of up to 25 years, depending on the site‘s operating conditions.

The biggest challenges occur in high-cycling plants. Steel frame designs should minimize the temperature gradient across frame to minimize stress and fatigue. Design of the flow plate is made in such a way that the axial, lateral and possible angular movements are considered to make sure that no points are fixed and stressed during the movements.

DEKOMTE has proven designs for cycling operational plants with installations in a vast number of power stations around the world, as OEM equipment and as retrofitted systems. DEKOMTE offers improvements in the construction of the fabric joint and insulating bolster to allow use of the latest materials and production processes. The tailored joints are built on custom molds giving higher joint flexibility and greater plant availability. The clamping area and the bolts are designed in such a way that there is no overheating, allowing the application of constant pressure during operation.

Introduction

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With a worldwide reputation for excellence, DEKOMTE de Temple manufactures fabric and stainless steel expansion joints for all applications within a gas turbine power station, and offers varying technical standards to suit the technical requirements, maintenance cycles, and budgets for each joint.

GT Exhaust / HRSG Inlet (Hot Casing)

4 GT Exhaust / HRSG Inlet (Cold Casing)

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Penetration Seals 10 Pumpable Insulation and Casing Repairs

12 Inspection, Monitoring, and Installation

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DEKOMTE is accredited to RAL GZ 719, the world-class quality standard for fabric expansion joints, ensuring that a detailed and thorough technical approach is maintained in all products offered, and the highest quality is ensured in the delivered solutions.

Base load stations can obtain acceptable performance from a basic design, due to the reduced stresses and fatigue caused by fewer start-ups and shutdowns. Conversely, cycling plants are subject to increased maintenance when using basic duct and joint constructions that were not designed for the increased stresses and fatigue.

The use of a competent third-party design authority (such as DEKOMTE), to verify and compare each of the solutions offered can establish a consistent basis for the comparison of possible design solutions.

The design is broken into key elements to establish independent technical criteria for each one. The expansion joint also represents a system that requires a complete analysis of the total scope using the latest technology. In DEKOMTE’s experience, the only reliable way to carry out a technical analysis is using FEA (Finite Element Analysis) and CFD (Computational Fluid Dynamics) programs, taking extreme care to ensure the correct boundary conditions and calculation parameters are used in these processes.

GT Exhaust / HRSG Inlet (Hot Casing)

Gas turbine power stations subject the exhaust duct and HRSG casing to extreme stress and fatigue, with the expansion joint being the focus point and relief. Many problems with the complete design become evident in this area.

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Key elements of the design are:

Steel Frame DesignThis is the most critical aspect of hot casing solutions. The temperature gradient created on the frame during transient operating conditions of the gas turbine creates high fatigue stresses that may result in cracking and gas leakage with cycling.

Flow PlateSmooth cross section changes in the duct are important to reduce turbulence and insulation degradation.

Internal BolsterFully encapsulated and formed insulating bolsters (or pillows) protect the joints from the inside, and segmented sections can reduce compression and damage caused by the movements.

FabricFormed fabrics that prevent creasing, crumpling and folding through all movement are important for cycling and longer life. Durable multi-layer compositions with high temperature membranes and outer protection protect the gas-tight seal from stress and damage.

Bolting / Clamping DetailA gas-tight seal is achieved with proper design of the bolting and clamping to meet the required site pressure.

Duct ConnectionBoth welded and bolted flange systems are available with consideration given to thermal fatigue, distortion and remaining gas-tight.

Adjacent Insulation and CladdingThe expansion joint system is further protected from excess external radiated temperatures by tightly integrating adjacent insulation and cladding insulation.

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Other details to consider when looking at the joint design are the duct condition, stiffeners, supports, and moving points, ensuring that they work as a system with the correct movements.

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DEKOMTE recommends a review of the connection and internal lining of the joints to ensure that no heat path becomes a weak element of the design.

The design is broken into key elements to establish independent technical criteria for each one. The expansion joint also represents a system that requires

a complete analysis of the total scope using the latest technology. In DEKOMTE’s experience, the only reliable way to carry out a technical analysis is using FEA (Finite Element Analysis) and CFD (Computational Fluid Dynamics) programs, taking extreme care to ensure the correct boundary conditions and calculation parameters are used in these processes.

GT Exhaust / HRSG Inlet (Cold Casing)

Expansion joints that are installed within a section of duct with internal lining, known as cold casing duct arrangements, experience lower stresses than hot casing arrangements. Protecting the expansion joint frame and bolster from the highest gas temperatures will increase the joint‘s life and reliability.

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Steel Frame DesignAs a cold casing system, the steel frame design is not subjected to the thermal stresses, as long as the frame can remain cold.

Flow PlateSmooth cross section changes in the duct are important to reduce turbulence and insulation degradation. The liner plate should cover over the complete expansion joint space, allowing flexibility by floating/sliding sections. A liner that is seamless over the adjacent flanged connections protects the casing and interface to the expansion joint frame.



Bolting / Clamping DetailA gas-tight seal is achieved with proper design of the bolting and clamping to meet the required site pressure.

Duct ConnectionBoth welded and bolted flange systems are available with consideration given to thermal fatigue, distortion and remaining gas-tight.

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The movements are also not significant due to the low temperature, and the main function is isolating the structure of the duct, HRSG, and stack to allow civil structural tolerances, vibration elimination, and flexibility from dynamic weather loading.

DEKOMTE recommends the use of a ¼” reinforced rubber expansion joint or a multi-layer PTFE expansion joint with rubber sealing area as the best solutions, as these address the main issues:

• Weather tightness• Water sealing• Environmental degradation

The effect of these aspects include heavy corrosion on the roof section caused by weather ingress into the duct through the joint flanges, and also on the bottom, caused by water leakage out through the flange from inside the unit.

DEKOMTE recommends the retrofit addition of water barriers, drains, and flow plate systems. These give the security of a cleaner, longer functioning expansion joint by eliminating the build-up of water, deposits, and debris from the inner joint space.

Careful consideration of the material selection will help a joint at the stack connection reach an expected life of 20 years. Short-term cost savings can result in high maintenance costs on an expansion joint where the cost of access is prohibitive.

HRSG Outlet

The HRSG outlet is a cool condition operating expansion joint, where the temperature conditions are typically a maximum temperature of 302oF, which are favorable to a simple material and thin layered expansion joint.

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Steel Frame DesignThe use of the correct material, coating, and drain design reduces corrosion and extends the life.

Flow PlateA protective flow plate and water barrier prevents condensation, water and debris from pooling in the expansion joint space.

FabricMaterials that are stable for the environmental and plant conditions will maximize the maintenance life cycle. Fabric compositions that include water sealing materials along with gas-tightness will extend the life of the joint.

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Leaking packing glands and mechanical seals have a detrimental impact on casings and adjacent equipment – not only do they require more regular maintenance, but they can necessitate additional maintenance and repairs to the surrounding area, that in the longer term make them an expensive and unreliable solution.

DEKOMTE solutions are gas-tight and ensure no loss of flue gas or heat to the environment.

DEKOMTE offers both metallic bellows and fabric expansion joints for this application, and the choice is normally established by the HRSG OEM. Metallic bellows offer the lowest initial cost and are therefore favored for the first installation. In high movement areas and for retrofit, fabric joints offer the best solutions and flexibility in the most compact design.

Retrofitting metallic bellows is uncommon due to the necessity to either:

• Deliver the bellows in split halves resulting in:- welding the bellow on site, which is notoriously

difficult and leaves areas prone to corrosion and failure

- limiting construction to a single layer bellow, which is stiffer than multi-layer solutions

• Deliver the completed bellows resulting in: - A bellow more flexible than a split halve bellow

- Cutting the steam nozzle to slide over the completed bellow

- Complete NDT on the nozzle- Coded welding to re-attach the nozzle- Complete the pre-weld and post-weld heat

treatment

In almost every case, the bellow failed due to movement-induced issues, therefore installing the same or less flexible solution is not going to deliver reliability.

DEKOMTE has developed the most reliable fabric solutions for penetration seals, both as an OEM installation with cost optimization being a key function of design, through to retrofit where longevity, durability and reliability are the keys to the design.

Penetration Seals

Penetration seals are the most challenging expansion joints in a combined cycle power plant. The high levels of movement of these small joints in this environment demand the best technical solutions and highest quality of products to survive.

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Steel Frame DesignCasing collars can align the joints by resetting the pipe concentricity to the casing position. Pipe collars can manage temperatures in the seals and offer space for integration of piping insulation to protect the seal from the inside.



Bolting / Clamping DetailA gas-tight seal is achieved with proper design of the bolting and clamping to meet the required site pressure. When possible to attach to the pipes, bolted flanges can eliminate the maintenance required of a circumferential clamp.

Casing Insulation and Nozzle LinerThe insulation around a nozzle in the casing is subject to highly turbulent gas flow, which invariably pits and pulls the insulation into the gas stream. DEKOMTE can avoid this by installing encapsulated casing bolsters and redesigned nozzle liner plate sections.Ensuring casing temperature is maintained will ensure the further reliability of the penetration seal.

Pipe Insulation Tight integration of the insulation to the expansion joint pipe collar prevents damage from excess external radiated temperature.

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If the liner plate system and attachments are in sound mechanical condition, then repairing the insulation can be intrusive and expensive.

DEKOMTE can repair missing insulation pockets and hot areas of casing by injecting liquid insulation from the outside, while the unit is running.

Causes of insulation loss:

• No liner• Liner plate damage• Gas flow under liner (by distortion / gap in liners)• Compacting of insulation• Degradation of insulation (by vibration / moisture)

Effects of insulation loss:

• Casing cracks leading to gas leakage• Temperature-induced material fatigue• All effects cause adjacent safety and environmental

concerns

Pumpable Internal Insulation

The pumpable soluble fiber insulation is a mix of short fibers dispersed in high temperature binders that, upon drying, produces a strong insulation structure with low thermal conductivity.

Applications:

• GT Casings• GT Exhaust Diffuser• Penetration Seals• HRSG Casings

Pumpable Insulation and Casing Repairs

In cold casing duct systems with liner plates securing the insulation in place, the condition of the insulation is paramount to ensure that the casing stays in good condition. The cold casing must stay cold and well-insulated.

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Insulation Technical Details

Pumpable Material

• Low thermal conductivity (1100°F - 0.05 btu)

• Use limit 2300°F

• Melting point >2730°F

• Wet density 70 lb/cu.ft

• Dry density 17 lb/cu.ft

• Low shrinkage

• Good adhesion

• Resistant to flue gas velocities up to 65 ft/s

Typical Casing Insulation

• Low thermal conductivity (1100°F - 0.05 btu)

• Use limit 2300°F

• Melting point >2730°F

• Dry density 6 lb/cu.ft

• No adhesion

• Resistant to flue gas velocities up to 16 ft/s

Casing Repairs

DEKOMTE also offers casing repairs, liner modifications, and new attachment solutions. These are aimed at maintaining casing temperatures for a longer life.

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Inspection, Monitoring, and Installation

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The integration of duct supports, stiffeners, and bracing sections into the expansion joint solution can result in a complete problem solving package, rather than contractually interfaced scopes. DEKOMTE manages the technical and commercial aspects of the various on-site disciplines and trades.

DEKOMTE also supports and advises its customers on supply and installation appropriate to their requirements. The design of the expansion joint uses the latest materials and composition to optimize cost and technical function.

We provide a quality package comprising creativity, design, practical experience and technical expertise to be able to offer the optimum selection of components and fully developed solutions.

It is our primary objective to guarantee plant availability, even under the harshest conditions over many years.

Following installation, the DEKOMTE Customer Service team is available at all times to answer your questions.

Design Studies and Technical Support

Design comparison, investigation, and modelling can be achieved using DEKOMTE’s extensive database of empirical knowledge.

DEKOMTE offers objective technical support at short notice for critical problems.

Engineering support in the form of annual inspections or lifetime assessments can form a critical part of the maintenance planning of a power plant or industrial manufacturing process.

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a plant and produce a technical report for maintenance planning and plant improvement, establishing a baseline of the site’s expansion joints and helping to build a plan to reduce total costs.

Turnkey Installation

The use of skilled design engineers, technicians, and service engineers, together with qualified on-site skilled labor means DEKOMTE offers a complete turnkey contracting solution for duct problems.

Please contact us for further information and to discuss your specific requirements.

Engineering Services

DEKOMTE pushes the boundaries of product development with the latest computer and industry best practice tools and procedures. The discerning use of FEA (Finite Element Analysis) and CFD (Computational Fluid Dynamics), together with 2D and 3D design, allows a correlation of on-site empirical experience and theoretical models. Formulation of specifications, tenders and design critique are also offered as an independent technical service.

Plant Survey

DEKOMTE has experienced site engineers and designers who are able to review all expansion joints in

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Documents

Gas Turbine Power Plant Expansion Joints Gas Turbine … · Gas turbine power stations subject the exhaust duct and HRSG casing to extreme stress and fatigue, with the expansion joint