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What is the hydrotest pressure formula per ASME B31.3?

ASME B31.3 Paragraph 345.4.2 specifies P_T = 1.5 × P × (S_T / S), where P is the design pressure, S is the allowable stress at design temperature, and S_T is the allowable stress at test temperature. The minimum test pressure is 1.5 times the design pressure adjusted for the stress ratio.

How long should a hydrotest be held for a piping system?

ASME B31.3 requires a minimum hold time of 10 minutes for piping systems. For pressure vessels, the hold time may be longer per the applicable code. The test pressure must be maintained without visible leakage for the entire hold duration.

What is the allowable stress for A106 Grade B carbon steel at 400°F?

For A106 Gr.B carbon steel pipe at 400°F (204°C), the allowable stress (S) is approximately 16.7 ksi per ASME B31.3 Table A-1. At ambient test temperature (70°F), S_T is approximately 20.0 ksi.

Can the hydrotest pressure exceed the yield strength of the pipe?

No. ASME B31.3 limits the test stress to no more than the yield strength at test temperature. If the calculated P_T would exceed 90% of the specified minimum yield strength (SMYS), the test pressure must be reduced to stay within the code limit.

hydrotest · Engineering Calculator

Hydrotest Pressure Calculator for 6-Inch Schedule 40 Carbon Steel Pipe

Formula

P_T = 1.5 × P × (S_T / S)

Governing Standard

ASME B31.3 Process Piping — Paragraph 345.4.2

Required Inputs

Design Pressure (P) in psig
Allowable Stress at Design Temperature (S) in ksi
Allowable Stress at Test Temperature (S_T) in ksi

Output

Minimum Hydrostatic Test Pressure (P_T) in psig

Notes

The test pressure shall not exceed the maximum allowable stress at test temperature. For 6-inch Schedule 40 carbon steel pipe (A106 Gr.B), typical design pressure is 1480 psig with S=16.7 ksi and S_T=20.0 ksi, yielding P_T = 2,646 psig. Hold time: minimum 10 minutes for piping systems.

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