STEAM BLOWING SERVICES 40 BAR <
Steam lines are blown prior to starting up a new unit to remove any foreign matter that may be remaining in the equipment and steam piping after erection is completed. If such foreign matter were allowed to enter the plant steam system during operation, considerable damage could result.
Debris As mentioned, construction debris left in piping can cause severe damage to the equipment and instrumentation downstream (e.g., turbine blades, control valves, etc.). In addition to “regular” construction debris—weld slag, sand, oil, dust, and rust—steam piping also contains a layer known as mill scale. Theory During steam blowing, the piping is blown with enough velocity to ensure it will experience sufficient cleaning force for adequate removal of debris and scale. Typically, during the steam blow, the force of the steam is at least 20% higher than would be experienced for all plant operating conditions (CFR ≥ 1.2). Thus, any potentially damaging particles will be blown out of the piping prior to plant operation.
LP (COUNTINUOUS) BLOW METHOD
The low-pressure steam blow technique has become standard practice for cleaning most steam system circuits. This method requires the steam generators to be continuously fired to generate steam velocities exceeding the velocities generated during normal plant operations. To control pre-determined steam conditions at the piping inlet, an orifice plate or sacrificial valve is used.
The LP continuous blow method is used for both targeted and service steam blows. Cleanliness In order to provide a quantitative measure of system cleanliness, a technique of detecting particles in the steam exiting the blow is used. The emerging steam is monitored for particles by quantifying impacts on a polished metal plate commonly known as a target. Guidelines state the allowable quantity and size of particle impacts on the target.
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