Rectangular Steel Tube Testing

Rectangular steel tube inspection mainly conducts scientific testing and analysis on the dimension and shape inspection, surface quality inspection, chemical composition analysis, mechanical property testing, process property testing and 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 inspection: Detects the side lengths, wall thicknesses, diagonal differences, straightness and cross-section shapes of the rectangular steel tube. The precise dimensions are the basis for meeting the structural assembly, interchangeability and mechanical property calculations, and are also the important basis for the subsequent processing (such as the cutting and welding).

Surface quality inspection: Through the visual inspection or using the tools such as the magnifying glasses and surface roughness testers, it is checked whether there are the defects such as the cracks, scars, folds, scratches, pits and rust on the steel tube surface. The surface defects will affect the aesthetics of the product, and may become the stress concentration points, reducing its fatigue strength and corrosion resistance.

Chemical composition analysis: Through the methods such as the spectrometry analysis and chemical titration, the contents of the carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulphur (S) and alloying elements (such as the chromium, nickel and molybdenum) in the rectangular steel tube are determined. The chemical composition is the fundamental factor determining the strength, toughness, weldability and corrosion resistance of the steel.

Mechanical property testing: This is the key to evaluating the load-bearing capacity of the rectangular steel tube, mainly including the tensile testing (determining the tensile strength, yield strength and elongation after fracture), hardness testing (Brinell, Rockwell or Vickers hardness) and the possible impact toughness testing. These data are directly related to the safety of the structures.

Process property testing: Including the flattening testing, bending testing and flaring testing. These tests simulate the deformations that the steel tube may bear in the processing or use, used to evaluate its plasticity and the ability to bear the cold working deformations. It is the important link of inspecting its process quality.

Non-destructive testing: Without damaging the material, the technologies such as the ultrasonic flaw detection, eddy current flaw detection, magnetic particle flaw detection or penetrant flaw detection are used to detect the hidden defects such as the cracks, inclusions, blowholes and delaminations inside and near the surfaces of the steel tube, ensuring its reliability in the key applications.

Testing Scope

Building structure field: The rectangular steel tubes used in the main and auxiliary structures such as the high-rise buildings, industrial plants, stadiums and bridges. The testing emphasis is on the dimension precision, mechanical properties (especially the yield strength and impact toughness) and the integrity of the welded parts.

Machinery manufacturing field: Used for the machine equipment frames, guide rails, supports and conveying manipulator arms. The testing focuses on the dimension stability, surface hardness, straightness and fatigue resistance, to ensure the precision and life of the equipment operation.

Automobile and rail transit: Applied to the automobile chassis components, bus body frames and rail transit vehicle bodies. The testing requirements are extremely strict. In addition to the routine properties, the impact resistance, fatigue strength and lightweight indicators of the material need to be emphatically focused on.

Energy and power industry: Used for the power towers, internal structures of the wind power tower drums, solar supports and boiler steel structures. The testing needs to consider the durability, corrosion resistance and low-temperature toughness of the material under the long-term loads and harsh environments.

Furniture and decoration engineering: Used to make the metal furniture, display racks, guardrails and curtain wall keels. The testing pays more attention to the appearance quality (such as the surface finish and coating adhesion), dimension precision and environmental indicators (such as the harmful substance contents in the coatings).

Special application fields: Such as the offshore platforms, pressure vessel components and lifting equipment. This type of applications has the highest testing requirements for the rectangular steel tubes, and the comprehensive chemical composition, mechanical properties, non-destructive flaw detection and corrosion testing under the specific environments need to be carried out.

Testing Methods

Dimension measurement method: The tools such as the high-precision callipers, micrometers, π tapes, laser range finders and coordinate measuring machines are used for the direct measurement. For the batch testing, the dedicated gauges such as the go/no-go gauges and templates are commonly used for the fast judgement.

Physical and chemical analysis method: The chemical composition analysis mainly adopts the spark direct-reading spectrometry (OES) or inductively coupled plasma atomic emission spectrometry (ICP-OES), which is fast and accurate. The mechanical property testing is carried out according to the standard specimens, and the tests such as the tensile and bending are carried out on the universal material testing machines.

Macro and micro examination method: The macro examination observes the surfaces and fractures with the low-power magnifying glasses; the micro examination (metallographic analysis) needs to observe the structure morphologies (such as the grain sizes and non-metallic inclusion grades) under a metallographic microscope after the sampling, grinding, polishing and etching, evaluating the internal quality of the material.

Non-destructive testing (NDT) method: The ultrasonic flaw detection (UT) uses the high-frequency sound waves to detect the internal defects; the eddy current flaw detection (ET) is applicable to the fast detection of the surface and near-surface defects of the conductive materials; the magnetic particle flaw detection (MT) and penetrant flaw detection (PT) are mainly used to detect the surface open defects.

Corrosion testing method: The common methods of evaluating the corrosion resistance of the rectangular steel tube include the neutral salt spray testing (NSS), copper-accelerated acetic acid salt spray testing (CASS) and the copper sulfate testing applicable to the galvanized layers. These methods simulate the harsh environments and accelerate the corrosion processes for the evaluation.

Coating property testing method: For the rectangular steel tubes with the coatings, the coating thicknesses (magnetic thickness gauges), adhesion (cross-cut method and pull-off method), hardness, impact resistance and weather resistance (such as the UV aging testing) need to be detected.

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 229-2020, Metallic materials — Charpy pendulum impact test method

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

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

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

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

Dimension measuring equipment: Including the vernier callipers, outer diameter micrometers, wall thickness micrometers, laser length measuring instruments, coordinate measuring machines (CMM), as well as the spirit levels and collimators for detecting the straightness and flatness. The high-precision equipment is the key to ensuring the interchangeability and assembly of the product.

Chemical composition analyser: The direct-reading spectrometer is the most commonly used fast analysis equipment in the iron and steel industry, and can analyse the contents of the multiple elements within dozens of seconds. For the precise quantitative analysis in the laboratories, the carbon-sulphur analysers, inductively coupled plasma mass spectrometers (ICP-MS), etc. may be used.

Mechanical property testing machine: The electronic universal material testing machine is the core equipment for the tensile, compression and bending testing, and can precisely record the load-displacement curves. The supporting equipment includes the impact testing machines (Charpy pendulum) and Brinell/Rockwell/Vickers hardness testers.

Metallographic sample preparation and analysis system: This system includes the cutting machines, mounting machines, grinding and polishing machines, metallographic microscopes and image analysis software. Used to prepare the standard metallographic specimens, observe and quantitatively analyse the microstructures of the material. It is an important means of evaluating the heat treatment process effects.

Non-destructive testing equipment: The ultrasonic flaw detectors (with the probes), eddy current flaw detectors, magnetic particle flaw detectors (with the magnetic suspension liquids) and penetrant testing reagent kits. The selection of these equipment depends on the types, positions and detection efficiency requirements of the inspected defects.

Environmental and coating testing equipment: The salt spray test chambers are used to simulate the marine or industrial atmospheric corrosion environments; the coating thickness gauges (magnetic/eddy current types), adhesion testers, gloss meters and colour difference meters are used for the comprehensive evaluation of the surface coating quality.