In ASME B31 piping, the discharge pipe sectional area shall not be what relative to the full area of the valve outlets?

In ASME B31 piping, the discharge pipe sectional area shall not be what relative to the full area of the valve outlets?

• A. Greater than the full area of the valve outlets discharging there into
• B. Equal to the full area of the valve outlets discharging there into
• C. Less than the full area of the valve outlets discharging there into
• D. The discharge pipe should be as long as possible

Answer: (C)

The key idea is that after a valve, the discharge path must not constrain the flow. The cross-sectional area of the discharge pipe should not be smaller than the full area of the valve outlets—meaning it must be at least as large as the valve outlet area (and can be larger). If the discharge path were smaller, it would choke the flow, causing higher velocity, greater pressure drop, potential erosion, and adverse effects on valve performance. So the forbidden condition is the discharge pipe being smaller than the valve outlet area. Being equal to or larger than the valve outlet area is acceptable, while making the discharge path excessively long isn’t a specified sizing criterion.

The key idea is that after a valve, the discharge path must not constrain the flow. The cross-sectional area of the discharge pipe should not be smaller than the full area of the valve outlets—meaning it must be at least as large as the valve outlet area (and can be larger). If the discharge path were smaller, it would choke the flow, causing higher velocity, greater pressure drop, potential erosion, and adverse effects on valve performance. So the forbidden condition is the discharge pipe being smaller than the valve outlet area. Being equal to or larger than the valve outlet area is acceptable, while making the discharge path excessively long isn’t a specified sizing criterion.