What is the formula for sizing blowdown piping?

The formula for sizing blowdown piping is based on ensuring that the piping system can handle the maximum flow rate while minimizing pressure drop and ensuring safety during blowdown operations. The correct answer, which involves taking double the inlet size and adding the pipe size, ensures that the system is adequately sized to handle not only the expected flow but also any potential surges that could occur during the blowdown process.

Using double the inlet size allows for sufficient capacity to manage the energy that is released during the blowdown, which naturally requires more space for the fluid to flow without causing excessive pressure drops or potential blockages. The addition of the pipe size accommodates for any friction loss or potential restrictions that might occur due to fittings or obstructions in the piping system.

The other options do not provide the necessary considerations needed for an effective blowdown system. For instance, simply using the inlet or subtracting the pipe size doesn't take into account the increase in flow rates and pressures that a proper blowdown system must be prepared for.