During hydrostatic testing of welded pipe for strength and tightness, the minimum test pressure is typically what multiple of the internal design pressure?

Introduction / Context:
Hydrostatic tests are proof tests applied to piping to demonstrate structural integrity and leak tightness. Industry practice sets the test pressure as a multiple of the design pressure to provide safety margin.

Given Data / Assumptions:

• Standard welded pipe designed for internal pressure.
• Ambient temperature, incompressible test fluid (water) used.

Concept / Approach:
Common standards specify a hydrostatic test pressure of about 1.5 times the internal design pressure for proof testing. This level reveals gross defects without approaching yield for properly designed systems.

Step-by-Step Solution:
1) Identify the reference: internal design pressure.2) Apply rule of thumb: P_test ≈ 1.5 * P_design.3) Select the matching option.

Verification / Alternative check:
Many piping codes and manufacturer hydrotest recommendations fall in the 1.3–1.5 range; 1.5 is a widely taught value.

Why Other Options Are Wrong:
0.5 is below operating proof; 2.5 and 3.5 are excessive and risk plastic deformation.

Common Pitfalls:
Confusing design pressure with maximum allowable working pressure; ignoring temperature-dependent allowable stresses.

Final Answer:
1.5 times the design pressure