Expansion joints boilers

The duct between the boiler outlet and the chimney connection should be designed to have a gas velocity no greater than the chimney flue, be complete with insulation, and cladding, access openings and expansion joints. It should have the least number of bends and changes of section possible and should preferably not fall between the boiler outlet and the chimney connection. 

Thickness of shell should not be less than 12 mm. Boiler quality steel should be used since these units run at high internal temperature for long time continuously. Internal lining details (e.g. type of insulating and refractory bricks used, their alumina percentage, thickness of layer, castable refractory, expansion joints provided. (Vendor to submit copies of their test certificates giving chemical analysis, refractory properties, thermal conductivities if asked for by the purchaser. The expected maximum temperature at outer surface of the shell should not normally exceed 60—65 °C.)... 

Type 321 is similar to 304 but with titanium addition five times the carbon content that reduces carbide precipitation during welding and in 425-815 C service. It has excellent corrosion resistance toward most chemicals and oxidation resistance up to SIS C. Aircraft exhaust manifolds, boiler shells, process equipment, expansion joints, cabin heaters, fire walls, flexible couplings, pressure vessels. 

Typically at the HRSG inlet the expansion joint sees the vertical growth of the boiler, which can be as much as 150 to 200 mm. Inexperienced suppliers wotdd try to use one single expansion joint for this application but in fact no individual flexible element should be asked at these elevated temperatures to absorb more than 60-75-mm lateral movement. The materials of the expansion joint start to crease or fold in the vertical side walls as the joint absorbs the lateral movement. As the folds become more and more pronounced the external materials of the joint are prevented from being cooled by the ambient air, heat builds up, and the joint fails prematurely. 

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