Hydrostatic strength test

Hydrostatic Strength Testing Service – Comprehensive Structural Integrity and Leakage Assessment for Pressure Vessels, Piping, Valves and Enclosures

As an ISO/IEC 17025 accredited independent testing laboratory, we provide comprehensive hydrostatic strength testing services to manufacturers, engineering contractors, asset owners, and regulatory authorities across the oil and gas, petrochemical, power generation, aerospace, marine, pharmaceutical, and municipal infrastructure sectors. Hydrostatic strength testing – also known as hydrostatic pressure testing or hydrotesting – involves pressurising a pressure‑containing component with water (or a compatible liquid) to a pressure exceeding its maximum allowable working pressure (MAWP), in order to verify its structural integrity, leak‑tightness, and safety margin. This fundamental test method is capable of detecting material defects, weld imperfections, seal failures, and structural weaknesses that could compromise safe operation under service conditions. Our test protocols are executed in accordance with ASME Boiler and Pressure Vessel Code (BPVC) Section VIII, API 510 (Pressure Vessel Inspection), API 570 (Piping Inspection), ISO 9809, EN 13445, GB/T 150 (Pressure Vessels – Chinese National Standard), and GB/T 20801 (Pressure Piping Code). Our inspection and test reports are recognised by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Ecology and Environment (MEE), and international certification bodies for equipment registration, plant safety compliance, and quality assurance.

Test Articles and Equipment Types We Assess

Our hydrostatic test facilities accommodate a wide range of pressure‑containing components, systems, and custom fabrications. Typical test articles include:

Pressure vessels – cylindrical and spherical vessels, autoclaves, reactors, separators, accumulators, and custom fabricated pressure chambers
Piping systems and components – pipelines, pipe spools, flanges, fittings, expansion joints, and complete piping assemblies
Valves and actuators – gate, globe, ball, butterfly, check, and control valves with pressure‑containing shells
Industrial enclosures and housings – electrical enclosures, battery housings, explosion‑proof boxes, and sealed instrument housings
Marine and subsea equipment – pressure hulls, subsea control modules, riser components, and underwater connectors
Pneumatic and hydraulic components – cylinders, accumulators, reservoirs, and valve blocks
Gas cylinders and portable pressure containers – compressed gas cylinders, fire extinguishers, and refrigerant containers
Field‑erected tanks and large‑diameter pipelines – for on‑site hydrostatic testing of fixed equipment and long‑distance transmission lines

Hydrostatic Test Procedure – Pressurisation, Hold and Leak Detection

Preparation and filling – ensuring complete filling and air removal – We fill the test article with clean water (or a specified compatible test fluid) and remove all trapped air through vent ports, ensuring that the internal volume is completely filled with liquid. For large vessels and long pipelines, we use staged filling and circulation to ensure complete fill and to avoid air pockets that could cause pressure instability or false readings.
Controlled pressure ramp‑up – gradual pressurisation to the test pressure – Using a calibrated hydraulic pump system (pressure range 0.1‑200 MPa, accuracy ±0.1 % full scale), we increase the internal pressure at a controlled rate (typically 0.5‑1 MPa/min, or as specified by the applicable code) to the target test pressure. The target test pressure is typically 1.3‑1.5× the MAWP (or design pressure), as defined by the relevant design code and the client’s specification.
Hold period and pressure monitoring – verifying pressure retention and stability – Upon reaching the target pressure, we maintain the pressure for a specified hold period (typically 15‑60 minutes, depending on the component volume and code requirements). During the hold period, we continuously record the pressure‑time profile using a calibrated pressure transducer (accuracy ±0.1 % full scale) and monitor for any pressure decay. The allowable pressure drop is typically ≤ 2 % of the test pressure (or as defined by the applicable code). Any pressure drop exceeding the allowable limit is investigated as a potential leak or deformation event.
Leak detection – visual inspection and supplementary methods – During the hold period, we conduct a thorough visual inspection of all welded joints, flanged connections, threaded fittings, seal areas, and the shell surface for any signs of leakage (weeping, dripping, or streaming). For hard‑to‑observe areas, we use white absorbent paper, dye‑enhanced test fluid (with UV light detection), or a soap‑solution bubble test (for small localised areas). For critical applications, we employ acoustic emission monitoring or pressure‑decay rate analysis to quantitatively assess the leak rate.
Post‑test depressurisation and drainage – preventing residual stress and corrosion – After the hold period, we slowly and controllably depressurise the test article to avoid hydraulic shock. The test fluid is drained, and the interior is dried using hot air or nitrogen purging. For carbon steel and low‑alloy steel components, we apply a temporary corrosion inhibitor or maintain a dry inert gas blanket to prevent internal corrosion.
Safety precautions and risk control – ensuring personnel and equipment safety – Although hydrostatic testing stores significantly less energy than pneumatic testing, we still implement strict safety measures: a pressure relief valve set at 110 % of the test pressure, protective barriers around the test article, remote pressure control, and a clearly defined exclusion zone with no non‑essential personnel during the pressurised phase.

Deformation Measurement and Structural Integrity Assessment

Dimensional verification – pre‑test and post‑test measurements – We measure critical dimensions (overall length, diameter, flange face flatness, wall thickness at selected points) before and after the test using calibrated callipers, micrometers, and laser‑based measurement systems. Any permanent deformation (e.g., bulging, ovality, or length change) exceeding the code‑allowable limit (typically ≤ 0.2 % of the dimension) is reported as a failure.
Strain monitoring – using strain gauges for real‑time stress analysis – For high‑stress regions (weld zones, openings, geometric discontinuities), we apply electrical resistance strain gauges to monitor the strain during pressurisation. The strain data is used to verify finite element analysis results and to detect any local yielding.
Wall thickness measurement – ultrasonic thickness gauging – ASTM E797 / GB/T 11344 – Using a high‑frequency ultrasonic thickness gauge (accuracy ±0.01 mm), we measure the wall thickness at predetermined points before and after the test to detect any thinning or local bulging caused by the pressure.
Non‑destructive testing (NDT) – for defect confirmation after the test – If any leakage or permanent deformation is observed, we perform supplementary NDT (dye penetrant – PT, magnetic particle – MT, or ultrasonic – UT) on the affected areas to identify the location and nature of the defect.

Temperature and Medium Conditions – Simulating Service Environments

Ambient‑temperature hydrostatic testing – the standard baseline test – Most hydrostatic tests are performed at room temperature (approximately 20 °C), which is the reference condition for most design codes and provides a reliable verification of shell strength.
Elevated‑temperature hydrostatic testing – for high‑temperature service equipment – For equipment that operates at elevated temperatures (e.g., boilers, heat exchangers, steam piping), we use a heated pressurisation system to raise the test fluid temperature to the specified value (e.g., 100 °C, 200 °C, or 300 °C). The test is performed at the elevated temperature, and the pressure is corrected for thermal expansion of the fluid and the test article.
Low‑temperature hydrostatic testing – for cryogenic and sub‑zero applications – For cryogenic storage tanks, LNG carriers, and deep‑sea equipment, we perform hydrostatic testing at low temperatures (e.g., -40 °C, -196 °C) using special low‑temperature compatible test fluids. The test ensures that the material retains adequate toughness and ductility under cold‑service conditions.
Special test fluids – for food, pharmaceutical, and clean‑room applications – For equipment intended for food, pharmaceutical, or electronics applications, we use deionised water, distilled water, or other specified non‑contaminating fluids to prevent internal surface contamination.

Hydrostatic Burst Testing – Determining Ultimate Strength and Safety Margin

Hydrostatic burst test – progressive pressurisation to failure – API 1104 / ASME B31.3 – For high‑reliability verification or for code‑required burst testing of certain components (e.g., pressure relief devices, rupture discs), we continue to increase the internal pressure (using a high‑capacity hydraulic pump) until the test article ruptures or reaches the maximum pressure of the test system. The burst pressure (the peak pressure before failure) is recorded, and the burst ratio (burst pressure / MAWP) is calculated. A burst ratio of ≥ 4 for carbon steel vessels and ≥ 3 for stainless steel vessels is typically required by design codes.
Failure mode analysis and classification – ductile, brittle, or leakage‑type failure – After the burst test, we examine the failure location and the nature of the failure (e.g., ductile tearing, brittle fracture, weld separation, or gasket extrusion). The failure mode is classified and compared to the expected failure mode for the material and design. Any unexpected failure mode is investigated and reported.
Safety precautions for burst testing – enhanced protection and procedural safeguarding – Because burst testing involves higher pressures and the potential for explosive release, we implement enhanced safety measures: a test shield (metal cage) around the test article, a qualified pressure relief valve, remote pressurisation controls, and a cleared exclusion zone.

In‑Service and Field Hydrostatic Testing – On‑Site Verification

Field hydrostatic testing – using portable pumps and temporary piping – For in‑service equipment that cannot be transported to the laboratory (e.g., large storage tanks, field‑erected vessels, long‑distance pipelines), we perform field hydrostatic testing using portable high‑pressure pumps, temporary piping, and calibrated instrumentation. The test is conducted in accordance with the same code requirements and includes a full visual inspection and pressure decay monitoring.
Sectional hydrostatic testing – for long pipelines and complex systems – For long pipelines, we divide the pipeline into manageable sections and perform hydrostatic testing on each section separately, followed by a full‑system test to verify the integrity of the entire assembly.
Hydrostatic testing of in‑service equipment – for periodic inspection and re‑certification – We perform hydrostatic testing on in‑service equipment as part of periodic inspection programmes (e.g., API 510, API 570), verifying that the equipment remains safe for continued operation.

Test Standards and Specification Compliance – Supporting Regulatory and Contractual Requirements

Our hydrostatic strength testing is performed in accordance with a wide range of national and international standards. The most commonly requested include:

ASME BPVC Section VIII – Boiler and Pressure Vessel Code – the primary code for pressure vessel design and testing in North America and internationally
API 510 – Pressure Vessel Inspection – for in‑service inspection of pressure vessels
API 570 – Piping Inspection – for in‑service inspection of piping systems
ISO 9809 – Gas cylinders – Test methods – for the testing of gas cylinders
EN 13445 – Unfired pressure vessels – the European standard for pressure vessel design and testing
GB/T 150 – Pressure Vessels – the Chinese national standard for pressure vessel design and testing
GB/T 20801 – Pressure Piping Code – the Chinese national standard for pressure piping design and testing
PED 2014/68/EU – Pressure Equipment Directive – for European market access and regulatory compliance

Report Acceptance and Regulatory Recognition

All hydrostatic strength tests are performed under our ISO/IEC 17025 accreditation and in accordance with the applicable design and inspection codes. Our final test reports include: a complete description of the test article (manufacturer, model, serial number, material, design pressure), the test method and conditions (test pressure, hold time, temperature, test fluid), the test equipment and instrumentation (with calibration records), the pressure‑time records, the leak test results (location and description of any leaks, or a statement of no leakage), the dimensional verification records, a clear pass/fail verdict against the code requirements and the client’s acceptance criteria, and a summary of any observations or recommendations. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Ecology and Environment (MEE), and international certification bodies for equipment registration, plant safety certification, and quality assurance. Bilingual (Chinese/English) versions are available to facilitate submissions to domestic and international regulatory authorities.