Steel Pipe Jacking Pipe Testing

Steel pipe jacking inspection mainly conducts scientific testing and analysis on the appearance and dimension inspection, mechanical property testing, non-destructive testing, chemical composition analysis, anti-corrosion layer property testing and weld quality special testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Appearance and dimension inspection: Mainly inspects the inner and outer surface quality and geometric dimensions of the steel pipe jacking. Including checking whether there are the harmful defects such as the cracks, folds, scars and delaminations, and measuring the dimension parameters such as the outer diameters, wall thicknesses, ovality and straightness of the pipe body, ensuring that they meet the design and construction specification requirements.

Mechanical property testing: Evaluates the behaviour characteristics of the steel pipe under the loads, and is the core of ensuring the safety of the pipe jacking structures. The key items include the yield strength, tensile strength, elongation after fracture and hardness testing. These data are directly related to the ability of the pipeline to bear the jacking forces, earth pressures and ground loads during the jacking process.

Non-destructive testing: Without damaging the structure of the steel pipe itself, the internal and surface defects are detected. The main methods include the ultrasonic flaw detection (UT), used to detect the internal inclusions, delaminations and weld defects; radiographic flaw detection (RT), used to intuitively display the defect shapes; magnetic particle flaw detection (MT) or penetrant flaw detection (PT), used to detect the surface and near-surface cracks.

Chemical composition analysis: Through the means such as the spectrometry analysis, the chemical compositions of the steel pipe material, such as the contents of the carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulphur (S) and alloying elements, are determined. The composition is the basis determining the mechanical properties, welding performance and corrosion resistance of the steel, and needs to conform to the corresponding material standards (such as Q235B and Q355B).

Anti-corrosion layer property testing: For the steel pipe jacking with the external anti-corrosion layers (such as the epoxy coal tar pitch, three-layer PE and fusion bonded epoxy powder), the anti-corrosion quality needs to be detected. Including the coating thickness measurement, adhesion testing (pull-off method), holiday detection (electric spark leak detection), as well as the chemical resistance and impact resistance, to ensure the effective anti-corrosion of the pipeline during the service period.

Weld quality special testing: For the welded steel pipe jacking, the welds are the weak links of the quality control. The testing covers the weld appearance formation, reinforcement and undercut conditions, and uses the non-destructive testing methods (UT and RT) for the 100% or proportional sampling inspection of the internal weld quality, ensuring that there are no defects such as the lack of fusion, incomplete penetration, blowholes and slag inclusions.

Testing Scope

Incoming raw material inspection: The steel plates or coils intended for making the pipe jacking are re-inspected, ensuring that their quality certificate documents are complete and valid, and the sampling inspections of their mechanical properties, chemical compositions and dimension tolerances are carried out, controlling the product quality from the source and eliminating the unqualified materials from entering the production lines.

On-line inspection in the production process: The real-time monitoring and measurement are carried out at the key processes such as the steel pipe rolling, welding, straightening and sizing. The forming precision, welding process parameter stability and weld appearance and dimensions are emphatically checked, realizing the process quality control and discovering and correcting the production deviations in time.

Final inspection before the ex-factory of the finished products: After the manufacture of the steel pipe jacking is completed, the comprehensive ex-factory inspection is carried out according to the product standards (such as GB/T 50268) and purchase technical agreements. Including all the specified testing items, and issuing the complete quality certificates. Only after the qualification, can the products be allowed to leave the factory and be used in the pipe jacking projects.

Site arrival re-inspection: After the steel pipe jacking arrives at the construction site, the construction or supervision units need to carry out the arrival acceptance. The quality certificate documents are checked, and the sampling inspections of the appearance, dimensions and anti-corrosion layers are carried out. When necessary, the third-party witnessed sampling testing can be carried out, confirming that the products are not damaged during the transportation and storage.

Monitoring during the jacking process: During the pipe jacking construction, the sealing of the pipe joint interfaces and the deformation conditions of the pipe body are monitored. The changes of the pipeline axes and elevations are observed through the measuring instruments, and whether there are the leakages and misalignments at the pipe joint connections is checked, evaluating the effects of the jacking forces on the pipe body structures.

Applicability testing for the special environments and media: For the steel pipe jacking conveying the corrosive media (such as the sewage and seawater) or laid in the corrosive soils and stray current areas, the corrosion resistance evaluations need to be added, such as the intergranular corrosion testing and stress corrosion cracking testing, ensuring their long-term service safety.

Testing Methods

Dimension measurement method: The measuring tools such as the outer diameter micrometers, wall thickness gauges, π tapes, steel tape measures, rulers and feeler gauges are used for the direct measurement. For the ovality, the difference between the maximum and minimum outer diameters of the same cross-section is usually measured; the straightness is measured through the wire-pulling method or laser collimators, and the results need to conform to the provisions of the standards such as GB/T 21835.

Mechanical testing method: In accordance with the GB/T 228.1 standard, the tensile testing is carried out on a universal material testing machine, obtaining the yield strength, tensile strength and elongation. The hardness testing commonly uses the Brinell (HBW) or Rockwell (HRB/HRC) hardness testers, carried out at the specified positions of the pipe body according to the GB/T 231.1 or GB/T 230.1 standards.

Ultrasonic flaw detection method: Utilizes the principle that the high-frequency sound waves reflect when encountering the defects during the propagation in the material. During the operation, the probe moves on the steel pipe surface, and the positions and amplitudes of the reflected waves are observed on the instrument display to judge the defect sizes and depths. This method is sensitive to the planar defects (such as the cracks and delaminations), applicable to the base material and weld testing.

Radiographic testing method: The X-rays or γ-rays are used to penetrate the steel pipe. Since the defective parts and sound parts have the different absorptions of the rays, the differential images are formed on the films or digital imaging plates. This method can intuitively and permanently record the defect morphologies, especially suitable for the detection of the volumetric defects (such as the blowholes and slag inclusions) in the welds.

Coating testing method: The coating thicknesses are measured with the magnetic thickness gauges (ferrous substrates) or eddy current thickness gauges (non-ferrous substrates). The adhesion adopts the pull-off testing instruments. The dollies of the specific sizes are bonded to the coatings and pulled off perpendicularly, and the pull-off forces are recorded. The electric spark holiday detectors are used to detect the coating continuity. During the scanning at the set voltages, the electric sparks and alarms will be generated when the pinholes are found.

Chemical analysis method: The spark direct-reading spectrometers are mainly adopted for the fast and multi-element simultaneous analysis. The sampling is usually carried out at the pipe ends or on the dedicated specimens. After the excitation, the contents are determined by measuring the intensities of the characteristic spectral lines of the elements. This method has the high precision and speed, and is the common means of the composition control in the steel plants and large manufacturing plants.

Testing Standards

Domestic Standards:

1. GB/T 228.1-2021, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. GB/T 231.1, Metallic materials — Brinell hardness test — Part 1: Test method

3. GB/T 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

4. GB/T 229-2020, Metallic materials — Charpy pendulum impact test method

5. GB/T 232-2010, Metallic materials — Bend test method

6. GB/T 4340.1-2009, Metallic materials — Vickers hardness test — Part 1: Test method

7. GB/T 21835, Dimensions and masses per unit length of welded steel pipes

8. GB/T 50268, Code for construction and acceptance of water and sewerage pipeline works

International Standards:

1. ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature

2. ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Universal material testing machine: The core equipment for the mechanical property tests such as the tensile, bending and compression. The precise loading is realized through the servo control systems. The force transducers and extensometers measure the loads and deformations respectively, and finally the computer systems automatically calculate the various strength and plasticity indicators of the material, with the accurate and reliable data.

Ultrasonic flaw detector: The portable digital ultrasonic flaw detector is the main tool of the on-site testing. Its core components include the pulse generators, receiving amplifiers, probes and displays. The modern instruments have the A-scan display, automatic defect assessment, data storage and transmission functions, and are equipped with the probes of the multiple angles to adapt to the testing at the different positions.

Radiographic testing equipment: Including the X-ray machines or γ-ray sources, imaging systems (films, digital imaging plates DR or computed tomography CT) and protection facilities. The mobile X-ray machines are applicable to the construction sites, while the circumferential exposure X-ray machines can efficiently detect the girth welds. The digital imaging technologies (CR/DR) are gradually replacing the traditional film methods.

Spectrometer: The spark direct-reading spectrometer is the key equipment for the quantitative chemical composition analysis. Consisting of the excitation sources, spectroscopic systems, photometric systems and computer control systems. Before the analysis, the calibration with the standard samples is needed. During the analysis, the sample is excited as the electrode in the argon atmosphere to generate the spectra, and the instrument quickly determines the percentage contents of the various elements accordingly.

Coating testing instrument group: Including the magnetic/eddy current thickness gauges, pull-off adhesion testers, electric spark holiday detectors, as well as the cross-cut testers and impact testers. These equipment are mostly of the portable designs, suitable for the fast and effective quality evaluations of the various performance indicators of the steel pipe anti-corrosion layers in the factory workshops or field construction sites.

Precision geometric quantity measuring instruments: Covering the traditional measuring tools (such as the laser range finders, high-precision electronic digital callipers and ultrasonic thickness gauges) and advanced measuring systems (such as the laser three-dimensional scanners and total stations). The latter can quickly obtain the overall three-dimensional point cloud data of the pipe body, and obtain the comprehensive shape dimensions and geometric tolerance data through the software analysis, with the higher efficiency.