64.What is steam blowing? Why it is necessary? How many type of steam blowing are in the practice? What is deciding factor for the completion of steam blowing and who shall decide the completion?

A process undertaken during initial plant installation, to remove any mill scale in SH tubes and pipes by blowing steam and venting out the same is known as steam blowing. Continuous and Puff Steam blow methods are used. In continuous method the boiler shall be prepared for full load and the steam at full load flow, pressure and temperature shall be blown for some hours. In Puffing method, pressure in the boiler will be raised to 250 Deg.C, at around 40 bar, and the stop valve in the temporary pipe is opened quickly. This will create a sudden change in velocity in the pipe. It is claimed that this the best economical method. A target steel plate is put at the end of the pipeline sections and the same is observed for the indentations after the steam blow to establish the cleanliness of the steam pipes. Since the steam admitted to turbine should not contain any contaminant (damages the turbine internals), the Turbine commissioning in-charge will give clearance for the completion of satisfactory steam blowing operation.