A) SALIENT TECHNICAL FEATURES
The design/specifications/sizing of various systems/equipment offered for Non-metallic Expansion joints for three (03) Steam Generator(s) of 660MW unit size shall comply with the requirements detailed hereinafter:
a) Reinforced fabric-type expansion joints suitable for the service conditions shall be provided. Fabric compensator shall be suitable for most adverse operating conditions of the ductwork. The expansion joint shall conform to the requirements of FSA/EJMA standards or any other equivalent National / International standards which shall be clearly specified in the offer
b) NMEJs shall generally be multi-layer construction designed to accommodate the thermal movements complete with additional internal insulation and / or insulation bolster and flow liners as required to suit the service conditions.
c) Expansion joints shall not support the ductwork.
d) There shall be no leakage through the joint into or from the atmosphere.
e) Expansion joints shall have adequate mating surfaces for attachment to the duct work.
f) Cold preset in connecting duct system is not envisaged. Hence bidder to design the NMEJ for the design movement without cold preset.
g) Expansion joint shall be shipped as complete fabricated one piece until unless, such shipping is impossible due to major transportation limitation. Further, the complete installation of expansion joint shall be under supervision of the expansion joint manufacturer.
h) The fabrics shall be tested as per suitable, IS/ASTM/DIN or other International standards. Composite fabrics shall be tested for "temperature withstandability & permeability".
i) Dust barrier is to be provided for all gas duct expansion joints at boiler to ESP inlet
j) The corrosion resistant barrier shall be free from pinholes. Needle glass mats of 9 mm thickness (min.) with mechanical bonding shall be used for temperature below 60 degree Celsius.
k) Ash load is to be considered for the design of some of the expansion joints. The liner plates are to be suitably stiffened to take care of the ash load.
l) For the flue gas ducts or for air ducts where ingress of ash/dust particles from atmosphere or air preheaters etc. is expected, the expansion joints shall be designed with suitable insulation pillow/bolsters to take care and avoid dust accumulation.
m) The minimum trouble free operational life of expansion joint shall not be less than 20000 hrs of operation from the date of commissioning.
n) Special design requirement may be necessary for expansion joints in certain locations which are subjected to high lateral movement and in cases, if two expansion joints in series are used, the space in between them may be subjected to higher ash load. Proper support / load transfer arrangements shall be provided to take care of this additional load.
B) OTHER TECHNICAL FEATURES:
In addition to the salient features stipulated above, the bidder should also meet the following requirements for different components of the NMEJs mentioned below:
1) Fabric :
a) Different layers of coated, insulating, sealing, supporting, fabric/other materials. Following are general requirements layer wise which may be considered for different locations. However, other proven standard material of Bidder is also acceptable, provided, Bidder has proven experience of material selected in similar applications. In such a case, Bidder in his offer shall furnish necessary data/information in support of proven ness of the material offered. Bidder to furnish the basis for selection of basic type of expansion joints and thickness of each layer.
Cold air:
1) Inner Layer: Texturized glass cloth (min. thickness 0.8 mm).
2) Outer Layer: EPDM / Flouro elastomer / Flouro plastic coated on
texturized glass fabric (min. thickness 2.5 mm).
Hot air / flue gas:
1) Inner/support layer: Two (2) layers of Texturized glass cloth suitably
treated to prevent dust accumulation (min. thickness 1.4 mm for each layer).
2) Insulating layer: Insulation mattress to provide thermal barrier (min.
thickness 9 mm and density 150 kg/m3).
3) Gas seal membrane: PTFE Film (min. thickness 0.2 mm).
4) Outer layer : Flouro elastomer/ Flouro plastic coated & laminated
(both sides) on texturized glass
b) A layer of 30 x 30 wire mesh of SS 304 (or equivalent) material shall be provided on the outside for protection against mechanical damages to the NMEJ
c) Edge reinforcement / flange gasket is to be used on the multi layered flexible element to protect it from thermal degradation by the hot metal flanges and backup bars.
d) All glass fabric are to be of texturized and graphite treated.
e) All the fabric / bolster components other than insulating / glass felt mattress and wire mesh shall be sourced from original fabric/bolster component manufacturer.
f) Temperature gradients shall be calculated using the maximum ambient value. Max outside temperature of the outermost layer is to be limited to 60 deg C.
g) The fabric shall be made of asbestos free materials.
h) The fabric material used in the flue gas system from air heater outlet shall be suitably selected to resist low temp corrosion.
2) Fasteners:
All fasteners shall be cadmium coated
3) Back up bars:
a) The back-up bar of adequate width and thickness shall be provided
b) The back-up bar and flange are to be match drilled.
c) Slotted holes are not permitted in the back up bar
4) Cavity pillow /bolster:
a) Cavity pillow / Bolster is to be provided to fill the cavity between flexible elements and metal liner or baffle to prevent accumulation of particulate matter. Design guidelines for arriving bolster depth and width has to be provided.
b) Expansion joints shall be designed with suitable cavity PILLOW/BOLSTER to avoid ash /dust accumulation in both hot air (including Expansion Joints in Penthouse Ventilation Ducts) and flue gas ducts.
c) They are to be fabricated from suitable insulation mattress of density 64kg/m3 (min.) and wrapped in glass fabric (min. 0.7 mm thick) and S.S fine wire mesh (30x30 mesh) of 0.5 mm thick and shall be provided with ears or tabs that fasten under the belt to hold the pillow in place. The above specifications for bolster are minimum specifications .However, higher density of insulation mattress and better fabric and mesh than the minimum requirements specified can be considered acceptable, based on bidder’s proven experience of material selected in similar applications. In such a case, Bidder in his offer shall furnish necessary data/information in support of proven ness of the material offered.
5) Steel Parts:
a) All steel parts from inlet flange to outlet flange, with internal supports
b) Liner plates are to be provided for all hot air and flue gas expansion joints.
c) The liner plates of Expansion joints coming in interconnection ducts and vertical upward flow ducts (for hot air and flue gas ducts) shall be of floating sleeve type to take care of flow from both sides
d) Some of the NMEJs may be located in the region of water washing. Hence the liner plates are to be designed to take care of water flow from top to bottom in addition to airflow from bottom to top.
e) All fasteners, back-up bars etc. for connecting the fabric with steel parts.
f) All necessary transport clamps / frames lifting lugs for shipment.