Hydrostatic Test Calculator

Input Panel

Formula Used

• Base test pressure (high point): P_test,high = F * P_design * (S_test / S_design)
• Hydrostatic head: dP_head = rho * g * dz
• Low-point pressure: P_test,low = P_test,high + dP_head
• Effective thickness: t_eff = t - CA
• Thin-wall hoop stress (approx.): sigma_h = P_test,low * D / (2 * t_eff)
• Allowable hoop stress limit: sigma_lim = k * Sy * E
• Pipe volume (optional): V = pi * ID^2 * L / 4
• Fill time (optional): t = V / Q

How to Use This Calculator

1. Select your units, then enter the design pressure and test factor.
2. Set the allowable stress ratio if temperature affects allowables.
3. Enter fluid density and elevation difference to account for head.
4. Provide OD, thickness, corrosion allowance, yield strength, and efficiency.
5. Optionally add test length and pump flow for fill-time estimates.
6. Press Calculate to view results, then download CSV or PDF.

Example Data Table

Hydrostatic Testing Guide

Hydrostatic testing is a controlled pressure test that confirms the integrity of piping, spools, and pressure boundaries before commissioning. A water-based test is preferred because liquid stores far less energy than gas, reducing consequence if a leak occurs. Even so, preparation matters: isolate the test section, verify blinds and restraints, remove or protect instruments, and confirm relief and vent paths.

A reliable plan starts with the target pressure at the highest point, then checks the maximum pressure at the lowest point after adding static head. Static head rises with elevation difference, so a long riser can push the low-point pressure above your intended limit. This calculator reports both pressures and estimates thin-wall hoop stress so you can spot potential over-stress early and adjust the gauge setpoint, test factor, or fill elevation strategy.

Use accurate material data whenever possible. Yield strength and joint efficiency affect the stress limit, while corrosion allowance reduces effective thickness. If test temperature changes allowable stress, capture that effect with the allowable stress ratio input. Document assumptions clearly because hydrotests are often reviewed by owners, inspectors, or regulators.

Example workflow: assume design pressure 10 bar, test factor 1.5, stress ratio 1.00, water density 998 kg/m3, and elevation difference dz 20 m (low minus high). The calculator returns a high-point pressure near 15.0 bar and a low-point pressure near 17.0 bar after head. With OD 219.1 mm, wall 6.0 mm, CA 1.0 mm, yield 350 MPa, and efficiency 1.00, the hoop stress result can be compared directly to your chosen yield fraction limit.

Acceptance criteria should be defined before you start. Many procedures require a minimum hold time, no visible leakage, and a stable pressure corrected for temperature effects. If pressure drops, confirm whether it is due to trapped air dissolving, hose expansion, or an actual leak. Always apply exclusion zones, communicate by radio, and never tighten bolts on a pressurized system. Treat every hydrotest as a managed energy event. Under supervision always.

During execution, fill slowly, vent high points, and hold at intermediate plateaus to check for leaks and trapped air. Stabilize pressure, record temperature, and monitor gauges at representative locations. After the hold period, depressurize in a controlled way and drain safely. If a repair is needed, re-test the affected boundary per your procedure. Solid documentation, careful venting, and proper head management are what turn a pressure number into a defensible integrity check for the site.

FAQs

Short answers for field planning and documentation.

What pressure should I enter as design pressure?

Enter the governing design pressure for the test boundary, typically the maximum allowable operating or design basis used for that system. If multiple segments exist, use the segment that will be hydrotested and documented.

Why does the low-point pressure exceed the gauge setpoint?

Static head adds pressure at lower elevations. When the low point is below the high point, the fluid column increases pressure by rho times g times dz. This is why a tall riser can create higher pressure at the bottom.

How do I choose the test factor?

Use the factor specified by the applicable code, owner specification, or project procedure. Common practice ranges around 1.25 to 1.50, but limits may change with material class, temperature, or brittle fracture concerns.

What does the allowable stress ratio mean?

It adjusts the test pressure when allowable stress at the test temperature differs from the design temperature. If allowables are lower during testing, use a ratio below 1.00. If they are higher, the ratio may be above 1.00.

Is the hoop stress equation always accurate?

It is a thin-wall approximation suitable for preliminary checks on straight pipe where diameter-to-thickness is large. For thick-wall parts, complex fittings, or vessels, use the governing code equations, detailed geometry, and certified material data.

How is volume and fill time estimated?

The calculator estimates internal volume using ID and test length, then divides by pump flow. Real fill time can be longer due to venting, hose losses, pump performance, and stop-start plateaus used for safety and inspections.

What if my stress check shows REVIEW?

Confirm units, dimensions, and corrosion allowance first. Then reduce the high-point target to keep the low point within limits, shorten the elevation column, or revise the procedure per the governing standard. Do not proceed until engineering acceptance is documented.