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Hydrostatic Testing of ERW Steel Pipes is a method used to assess the strength and leak prevention capability of ERW steel pipes. It is one of the simplest ways to detect leaks in pressure vessels and is considered one of the most reliable and safe methods for verifying the integrity of newly manufactured ERW steel pipes, as well as during repairs, modifications, and commissioning phases. This hydraulic pressure test utilizes water as the medium, pressurizing the pipes after they are filled with water. It checks for structural damage at a specified pressure and ensures compliance with allowable water seepage (or pressure drop) standards.
1. Pre-test
Gradually increase the water pressure in the ERW steel pipe to the specified test pressure, stabilizing it for 30 minutes. If the pressure drops during this time, water can be added to maintain pressure, but it must not exceed the test pressure. Inspect for leaks at the ERW steel pipe interface and accessories. If a leak is detected, stop the test, identify the cause, and take corrective measures before retesting.
2. Main Test Phase
Cease water injection to stabilize the pressure for 15 minutes. If the pressure drop does not exceed the allowable value after this period, reduce the test pressure to the working pressure and maintain it for 30 minutes. Conduct a visual inspection of the ERW steel pipe. If there are no leaks, the water pressure test is considered passed.
3. Precautions for ERW Steel Pipe Hydraulic Testing
The criteria for passing the test include allowable pressure drop and allowable water seepage values, determined by design requirements. If none are specified, select values based on actual conditions. Only after meeting these requirements can the ERW steel pipe be put into service with water.
Use the water injection method to measure actual water seepage during the hydraulic pressure test.
When multiple pipe materials are involved, tests should be conducted separately for each material. If separate testing isn't feasible, combined tests must be done, adhering to the most stringent standard among the materials used.
Unless otherwise specified in the design, the length of the ERW steel pipe for hydraulic pressure testing should not exceed 1 km. For pipes that cannot be tested in sections, the relevant engineering parties should determine the length based on specific project conditions.
The water supply pipeline must pass the hydraulic pressure test, be flushed, and disinfected before being connected to the grid. It can only be put into operation after the water quality meets the required standards.
In ERW steel pipe hydraulic testing, ruptures are often found at the weld line, indicating that the strength of the welded joint is lower than that of the base metal. Experimental analysis shows that if an internal scratching groove is formed on the inner surface of the steel pipe during burr removal in the weld, the thickness of the sample at the weld may be compromised. In tensile tests, these samples are prone to breaking at this weak point.
The water pressure test of the water supply pipeline serves as a means to evaluate the final quality of the laid steel pipe. Two main requirements for the static hydraulic pressure test are: it must accurately reflect any leaks in the pipeline, and the test must be conducted without causing damage to the interfaces, which could compromise project quality and lead to costly rework or even safety hazards.
Additionally, when conducting tensile tests of the weld per API SPEC 5L, whether to remove or retain the residual height of the weld can affect outcomes. Frequent weld failures indicate that the strength of the ERW steel pipe weld is inferior to that of the base metal. This can arise from either the lower strength of the welded joint or the scraping of the inner surface during burr removal. Poor transition between the weld and base material can lead to stress concentration, reducing the overall structural strength of the weld compared to the base material. Therefore, optimizing the transition shape between the welded areas and the base metal is crucial for ensuring the overall quality of the steel pipe.
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