Steel Pipe Support Testing

Steel pipe support inspection mainly conducts scientific testing and analysis on the dimension and shape testing, mechanical property testing, load-bearing capacity and stability testing, connector property testing, surface quality and anti-corrosion testing and weld quality non-destructive 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

Dimension and shape testing: This is the basic item of the steel pipe support inspection, mainly measuring the actual outer diameters, wall thicknesses, lengths and straightness of the steel pipes. Through the tools such as the vernier callipers, wall thickness micrometers, steel tapes and feeler gauges, whether they meet the tolerance requirements of the design drawings or the relevant standards (such as GB/T 3091) is inspected. The pipe diameter and wall thickness deviations directly affect their load-bearing capacities, and the excessive straightness deviations will affect the installation stability and the stress properties of the overall structures.

Mechanical property testing: Used to evaluate the ability of the steel pipe materials to resist the external forces, and is the core of ensuring the support safety. The key indicators include the yield strength, tensile strength and elongation after fracture. Usually according to the GB/T 228.1 standard, the tensile testing is carried out on the universal material testing machines. The yield strength determines under how much load the support begins to have the permanent deformation, the tensile strength characterizes its maximum load-bearing limits, and the elongation reflects the plastic deformation ability of the material.

Load-bearing capacity and stability testing: This is a comprehensive testing, simulating the stressed states of the supports under the actual working conditions. Mainly including the axial compression bearing capacity testing of the upright posts, bending property testing of the horizontal bars, as well as the overall stability testing of the frame bodies. Through the hydraulic loading systems, the incremental loads are applied to the test pieces until the failure or the specified maximum test loads are reached, to verify whether their design bearing capacities and ultimate bearing capacities meet the requirements of the scaffolding safety technical specifications such as JGJ 166.

Connector property testing: The special testing is carried out on the connecting parts such as the couplers, connection discs and pins. The main items include the anti-slip properties, anti-destruction properties and torsional stiffness property testing of the couplers. For example, according to the GB 15831 standard, the anti-slip testing is carried out on the right-angle couplers, ensuring that under the specified torques, the nodes will not slip when subjected to the transverse forces. This is the key to guaranteeing the overall structural stability of the scaffolding.

Surface quality and anti-corrosion testing: Whether the internal and external surfaces of the steel pipes have the defects such as the cracks, scars, folds and delamination is checked. These defects will become the stress concentration points, inducing the structural failures. For the galvanized or painted supports, the anti-corrosion layer thicknesses (using the coating thickness gauges), adhesion and uniformity need to be tested, to evaluate their corrosion resistance and ensure the service lives under the specific environments.

Weld quality non-destructive testing: For the steel pipe supports or connectors manufactured with the welding processes, the non-destructive testing must be carried out on their welds. The common methods include the visual testing (VT), ultrasonic testing (UT) and radiographic testing (RT). The testing purpose is to find the internal defects of the welds such as the blowholes, slag inclusions, lack of fusion and cracks, and judge their quality grades according to the relevant welding standards, ensuring that the weld strengths are not lower than the base materials.

Testing Scope

Steel pipes for scaffolding: This is the most common testing object, including the upright posts, horizontal bars and diagonal brace bars used for the coupler-type, bowl-type and disc-type scaffolding in the building and bridge construction. The testing needs to strictly follow the industry standards such as the Safety technical code for steel tube scaffold in building construction (JGJ 130), emphatically focusing on the dimensions, mechanical properties and corrosion conditions of the pipes.

Steel pipes for the formwork support systems: Applied to the formwork support systems of the cast-in-place concrete structures, bearing the newly poured concrete and construction loads. This type of support has the extremely high requirements for the verticality, load-bearing capacities and stability. During the testing, according to the Technical code for safety of forms in building construction (JGJ 162), in addition to the routine items, the axial compression stability of the upright posts and the compression strengths of the adjustable jacks particularly need to be emphasized.

Temporary supports and jigs for the steel structures: The temporary support steel pipe frames (jigs) used in the large steel structure installation and bridge closure projects. The testing scope not only includes the steel pipes themselves, but also focuses more on the stability verification of the overall structures, node connection reliability and foundation settlement monitoring. Usually, the customized testing and monitoring need to be carried out according to the special construction schemes.

Municipal and pipeline engineering supports: The support systems used to support the municipal pipe galleries, water supply and drainage pipelines and cable trays. The testing needs to consider the environmental corrosion factors, emphatically checking the anti-corrosion coating qualities of the steel pipes, seismic properties of the supports (such as the lateral force resistance) and creep characteristics under the long-term loads.

Pipes for the temporary facilities such as the stages and exhibition frames: The steel pipe supports used to build the temporary stages, exhibition stands and lighting frames. The testing emphases are the performance degradation evaluation after the repeated use, including the connector wear, local deformations of the pipe bodies (dents and bends) and fatigue properties, ensuring the safety under the dynamic loads.

Old steel pipes and turnover materials: The pre-entry testing is carried out on the old steel pipes about to be put into the new projects or currently in the turnover use. The testing scope needs to be expanded. In addition to the basic items, the corrosion depth measurement (especially the inner walls), end face cut flatness inspection, as well as the local hardening and micro crack screening caused by the collisions must be added, to accurately evaluate their remaining load-bearing capacities.

Testing Methods

Dimension measurement method: The standard measuring tools are used for the direct measurement. The outer diameters and wall thicknesses are measured at least at three cross-sections at the two ends and middle of the steel pipes, and the minimum values are taken as the judgment basis. The straightness testing usually places the steel pipes flat on the platforms, uses the feeler gauges to measure the clearances between the maximum bending points and the platforms, or uses the wire-pulling method with the steel rulers for the measurement. All the measurement results need to be compared with the allowable deviations specified in the product standards.

Destructive testing method: Mainly used for the final judgment of the material mechanical properties. The specimens are cut from the steel pipes, and the tensile testing is carried out on the universal testing machines, obtaining the stress-strain curves, thereby calculating the yield strengths, tensile strengths and elongations after fracture. For the connectors such as the couplers, the anti-destruction testing is carried out, loading until the test pieces fracture or severely deform, recording their destruction loads.

Non-destructive testing method (NDT): The testing is carried out under the premise of not damaging the service properties of the inspected objects. The ultrasonic testing (UT) uses the high-frequency sound waves to detect the internal defects of the material; the magnetic particle testing (MT) is suitable for the surface and near-surface crack detection of the ferromagnetic materials; the eddy current testing (ET) is often used for the fast screening of the surface cracks and measuring the plating thicknesses. These methods are crucial for finding the potential safety hazards.

Load testing method: Simulating the actual stressed states for the performance verification. For example, the axial compression testing is carried out on a single upright post, measuring its deformations (compression amounts) under the different loads until the instability failure. The stability testing is carried out on the whole frame bodies or typical units, through the lateral loading or eccentric loading, evaluating their overall anti-overturning abilities and deformation coordination.

Chemical analysis and metallographic inspection method: Through the spectroscopic analysis or chemical titration methods, the chemical compositions of the steel pipes (such as the C, Mn, Si, S and P contents) are determined, confirming whether their materials meet the designation requirements such as Q235 or Q345. The metallographic inspection observes their micro-structures (such as the ferrite and pearlite) under the microscopes after the specimen preparation, etching and polishing, judging whether the material heat treatment processes are normal and whether the structure defects exist.

Torque testing and fastener inspection method: Targeting the connection systems. The torque wrenches are used for the tightening torque testing of the coupler bolts, ensuring that they reach the specification requirements (such as 40-65 N·m). At the same time, whether the threads of the bolts and nuts are intact and whether the thread stripping occurs are checked, as well as the adjustment flexibility and self-locking properties of the adjustable base jacks and head jacks.

Testing Standards

Domestic Standards:

1. GB/T 3091, Welded steel pipes for low pressure liquid delivery

2. GB/T 13793, Straight seam electric resistance welded steel pipes

3. GB 15831, Steel tube scaffold couplers

4. JGJ 130, Safety technical code for steel tube scaffold in building construction

5. JGJ 162, Technical code for safety of forms in building construction

6. JGJ 166, Safety technical specification for disc scaffolding in building construction

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

International Standards:

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

2. EN 12811-1, Temporary works equipment — Part 1: Scaffolds — Performance requirements and general design

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: It is the core equipment of carrying out the mechanical property testing, which can carry out the multiple tests such as the tensile, compression and bending. It applies the precisely controllable loads through the hydraulic or electric servo systems, and is equipped with the high-precision force transducers and displacement transducers, collecting the load-displacement data in real time and automatically generating the test reports, used to determine the key indicators such as the yield strengths and tensile strengths of the steel pipes.

Dimension measurement tool group: Including the electronic digital vernier callipers (measuring the outer diameters and inner diameters), wall thickness micrometers (precisely measuring the wall thicknesses), large vernier callipers or pi tapes (measuring the pipe end circumferences to convert the diameters), steel tapes (measuring the lengths), as well as the straightedges and feeler gauge combinations (measuring the straightness). The high-precision instruments need to be regularly sent to the metrology institutions for the calibration, ensuring the accuracy of the measurement results.

Non-destructive testing equipment: The ultrasonic flaw detectors transmit the ultrasonic waves to the steel pipes through the probes, and judge the internal defect positions and sizes according to the reflected waves. The coating thickness gauges use the magnetic induction or eddy current principles to quickly and non-destructively measure the thicknesses of the galvanized layers or paint layers on the steel pipe surfaces. The magnetic particle flaw detection machines are used to detect the crack defects on the surfaces and near the surfaces of the steel pipes.

Load-bearing and stability testing system: Usually composed of the large reaction frames or loading platforms, large-tonnage hydraulic cylinders, high-precision load transducers, displacement gauges (such as the LVDT displacement transducers) and data acquisition and analysis systems. It can carry out the static load, dynamic load or stability testing on the whole frame bodies or full-scale models, monitoring the stress, strain and deformation data in real time.

Chemical composition analyser: Such as the direct-reading spectrometers, which can excite the steel pipe samples within seconds and quickly and accurately determine the contents of the multiple elements by analysing the characteristic spectra generated. In addition, the carbon-sulfur analysers can be specially used for the precise determination of the carbon and sulfur element contents in the steel, which have the decisive effects on the material properties.

Environmental and auxiliary equipment: Including the Leeb hardness testers, used to quickly detect the surface hardnesses of the steel pipes and indirectly evaluate their strengths; metallographic microscopes and the matching cutting machines, mounting machines, polishing machines and etchants, used for the micro-structure analysis of the material; high-precision electronic balances, used for weighing the specimen masses to calculate the theoretical weights, etc. These equipment jointly constitute the complete steel pipe support testing capability system.