Materials

• BS 3059 Grade 440 seamless carbon steel tubes.
• Welding Processes / Procedures
• STT II – Surface Tension Transfer (STT) Process with certified & tested weld procedures.
• TIG welding process.
• Fabrication Standards / National Codes
• AS1228 – Power Boilers
• AS4458 – Pressure Equipment Manufacture
• AS4041 – Pressure Piping
• AS4037 – Pressure Equipment – examination & testing
• Quality Assurance Requirements
• Material certification for all materials
• Inspection and Test Plan (ITP)
• 100% radiography on butt weld joints

1.The function of the superheater in the thermal power plant is to remove the last traces of moisture ( 1 to 2%) from the saturated steam coming out of boiler and to increase its temperature sufficiently above saturation temperature.
2.The super-heating heating raises overall overall cycle efficiency efficiency as well as avoids too much condensation in the last stages of the turbine which avoids the blade erosion.
3.The heat of combustion gases from furnace is utilized for the removal of moisture from steam and to superheat the steam.
4.Super-heaters usually have several tube circuits in parallel with one or more return bends, connected between headers.

The panels are joined in two ways:
By means of welding 4mm – 8mm thick flat bar to the the tube surfaces;
Welding Extruded longitudinally finned tubes.

Application
 

Boiler water walls are membrane walls that are made of tubes welded together with or without a strip of metal in between. These walls form the enclosure of the coal combustion chamber. Water wall tubes are also referred to as the evaporator section; they contain water mostly in liquid form which gradually evaporates as it rises in the boiler.

Challenges

As the water wall tubes form a lining along the whole boiler, they are submitted to a temperature gradient of 300 °C to 500 °C between the bottom section of the boiler and its top. To facilitate fitting, the panels in the boiler should preferably be made of steel grades that do not require any post-weld heat treatment. Vallourec supplies tubes for water walls in all grades, from carbon steel to advanced low-alloy steel, with outside diameters ranging from 31.8 mm to 63.5 mm.