Hydrostatic test of seamless steel pipes

Seamless steel pipes (SMLS pipe) are a common pipe material, widely used in the petroleum, chemical, natural gas and other industries. When using seamless steel pipes in pipeline systems, hydrostatic tests are required to ensure their safety and reliability. Hydrostatic testing is an effective method to detect the reliability and safety of pipelines, and it is also one of the necessary conditions to ensure the normal operation of pipelines.

Purpose of hydrostatic test:

Hydrostatic test is a key method to detect the pressure bearing capacity, sealing and structural integrity of seamless steel pipes. It is suitable for high-pressure pipelines in the fields of petroleum, chemical, boiler, machinery manufacturing, etc. Hydrostatic testing can ensure that seamless pipes maintain stable performance, prevent corrosion and increase their service life in actual use.

Process of hydrostatic test:

The process of hydrostatic test of seamless steel pipes generally includes preparation, pre-test inspection, test operation, and result determination. The specific process is as follows:

1. Preparation
Prepare the equipment and test materials required for hydrostatic test, such as water pumps, pressure gauges, water pipes, valves, etc.

Steel pipe inspection: Ensure that there are no defects such as cracks and heavy skin on the surface (UT/RT inspection must be passed first).
Sealing installation: Both ends are sealed with hydraulic heads, and water injection and exhaust ports are reserved.

2. Inspection before testing
Check whether the test equipment and test materials are intact, and perform necessary cleaning and disinfection.

3. Test operation:

a. Filling water
Install the seamless steel pipe on the test bench, use a water pump to inject clean water into the pipe, let the water fully fill the pipe and exhaust the air.

b. Apply pressure
Gradually increase the pressure in the pipe (avoid pressure fluctuations) until the required test pressure is reached. The maximum pressure is usually required to be 1.5 times the working pressure. After maintaining the test pressure for a period of time (10~30 minutes), release the internal pressure.

Pressure holding time:
Conventional high-pressure pipe: 5~30 seconds, focusing on short-term high-pressure testing (such as API 5L Pipe).
Chemical pipe: more than 30 minutes, long-term pressure holding is required (such as ASME B31.3).
Alternative: Large-diameter pipes can be combined with UT+RT to ensure quality.

c. Leakage detection
Observe whether the seamless steel pipe leaks. If leaks occur, find out the cause of the leak and repair it.

4. Result determination
Based on the test results, determine whether the seamless steel pipe is qualified and whether it needs to be repaired or replaced.

Method of water pressure test:

The method of water pressure test can be divided into two types: static water pressure test and dynamic water pressure test. The static water pressure test is to press the static water in the water cylinder or pool into the pipeline for testing, and the dynamic water pressure test is to use a water pump to inject water into the pipeline for testing.

Common problems and solutions:

1. Pressure drop
Possible cause: Head leakage or steel pipe defect
Solution: Reseal or replace steel pipe

2. Pipe bulge
Possible cause: Insufficient local wall thickness
Solution: Scrap and check rolling process

3. Weld leakage
Possible cause: Unqualified welding quality
Solution: Repair welding or cut off defective section

Precautions for water pressure test:

When conducting water pressure test on seamless steel pipe, pay attention to the following points:

1. When filling water, ensure that all air in the pipe is discharged to avoid bubbles that affect the test results.
2. When applying pressure, keep the pressure stable and do not allow fluctuations. Do not apply too much pressure at one time to avoid damage to the pipe.
3. During the pressure maintenance period, the pipe should be fully inspected and pay attention to deformation, cracks and other phenomena of the pipe.
4. The water pressure test should be carried out in accordance with standard procedures and specifications, and should not be modified at will.
5. After the test, the test equipment and test materials should be cleaned and disinfected to ensure that they are clean and hygienic.

FAQ:

1. Why do we need to conduct a water pressure test?
A: The water pressure test is one of the necessary conditions to ensure the safety and reliability of the pipeline. Through the water pressure test, we can detect whether there are leaks, deformations and other problems in the pipeline to ensure the normal operation of the pipeline.

2. How to judge whether the pipeline is leaking?
A: Usually, we can judge whether the pipeline is leaking by observing whether there are water marks on the surface of the pipeline, or we can use a leak detection instrument for detection.

3. Does the water pressure test need to follow the standard procedure?
A: Yes, the water pressure test should be carried out according to the standard procedure, follow the specifications, and shall not be modified at will.

Conclusion:

The hydrostatic test of seamless steel pipes is one of the necessary conditions to ensure the safety and reliability of the pipeline. The correct water pressure test methods and techniques can effectively ensure the safety and reliability of the pipeline operation. When conducting a water pressure test, it is necessary to follow the standard procedures, pay attention to details and strictly follow the process to obtain accurate and reliable test results.

Read more: Non-destructive Testing of Seamless Pipes