Calculate a pressure test safe distance (exclusion zone radius) for pneumatic tests from test pressure and gas volume using the ASME PCC-2 method.

ASME PCC-2 stored-energy screening for pneumatic tests with air, nitrogen or natural gas. Not for liquid-only hydrostatic tests.

Atmosphere and scaled factor
Standard sea-level atmosphere is filled in.

PCC-2 specifies 20 m/kg⅓ or greater. Use a higher value only when the owner’s risk criteria require it.

Pressure Test Safe Distance Formula

The following formula is used to calculate the safe distance required for a pressure test.

R = 20×(E/4266920)1/3
  • Where R is the safe distance (exclusion radius, m), at least 30 m when E ≤ 135.5 MJ and 60 m when E ≤ 271 MJ
  • E is the stored gas energy (J): E = V × Pabs ÷ (k − 1) × [1 − (Patm ÷ Pabs)((k − 1) ÷ k)]
  • V is the pressurized gas volume (m³), e.g. Ï€ × D² × a ÷ 4 for internal diameter D and length a
  • Pabs is the absolute test pressure, Patm the atmospheric pressure (Pa) and k the gas heat-capacity ratio (1.40 for air or nitrogen)

What is a Pressure Test Safe Distance?

Definition:

A Pressure Test Safe Distance is a minimum distance that humans should have spaced between them and a pressure vessel undergoing a pressure test.

The formula above is provided by ASME.

How to calculate Pressure Test Safe Distance?

Example Problem:

The following example outlines how to calculate a Pressure Test Safe Distance.

First, determine the internal diameter. In this case, the internal diameter is 2 m.

Next, determine the length. For this problem, the length of the vessel is measured to be 3 m.

Next, determine the test pressure. This is predetermined to be 500 bar.

Finally, calculate the Pressure Test Safe Distance using the formula above:

V = π × 2² × 3 ÷ 4 = 9.425 m³; with air at 500 bar(g), E = 979.9 MJ (229.6 kg TNT)

R = 20 × 229.6(1/3)

R = 122.48 m

FAQ

What is the importance of calculating the Pressure Test Safe Distance?

Calculating the Pressure Test Safe Distance is crucial for ensuring the safety of personnel and equipment during pressure testing of vessels. It helps in determining a safe perimeter to prevent injuries or damage in case of a vessel failure.

Can the Pressure Test Safe Distance formula be used for any type of pressure vessel?

The formula provided is a general guideline and can be applied to various types of pressure vessels. However, specific vessel designs or testing conditions may require adjustments or the use of more specific formulas as per relevant engineering standards.

How does the test pressure affect the calculated safe distance?

The test pressure directly influences the calculated safe distance, with higher pressures resulting in a larger safe distance. This is because the potential energy released in case of a failure increases with pressure, necessitating a larger safety margin.