Corrugated Steel Pipe Testing

Corrugated steel pipe inspection mainly conducts scientific testing and analysis on the appearance quality inspection, geometric dimension testing, mechanical property testing, coating quality and thickness testing, sealing performance testing and corrosion resistance evaluation, 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 quality inspection: Checks whether there are the defects such as the cracks, holes, pits, folds, delaminations and severe rust on the corrugated steel pipe surfaces. It is observed whether the corrugation shapes (waveforms) are regular and continuous, and whether the welds are smooth and free of the welding defects such as the cracks, blowholes and undercuts, ensuring that the product appearance meets the design drawings and relevant standard requirements.

Geometric dimension testing: The tools such as the callipers, tape measures, thickness gauges and depth gauges are used to precisely measure the key dimensions of the corrugated steel pipe such as the pipe diameters (inner and outer diameters), wave heights, wave pitches, wall thicknesses (including the thicknesses at the wave crests, wave troughs and flat parts), pipe section lengths and ovality. These dimension parameters directly affect the structural load-bearing capacity and connection sealing of the pipeline.

Mechanical property testing: Through the sampling to make the specimens, the tests such as the tensile, compression and bending are carried out on a universal material testing machine, determining the mechanical indicators such as the yield strength, tensile strength and elongation of the corrugated steel pipe. For the large-diameter or special structures, the ring stiffness, ring flexibility and flattening tests also need to be carried out, to evaluate its ability to resist the external pressure deformation and spring-back.

Coating quality and thickness testing: For the corrugated steel pipes with the anti-corrosion coatings such as the galvanized or aluminium-zinc coated, the coating thicknesses, uniformity and adhesion need to be tested. The magnetic thickness gauges or eddy current thickness gauges are usually adopted to measure the thicknesses, and the bonding firmness between the coating and the substrate is evaluated through the hammer testing, bending testing or cross-cut testing, ensuring the long-term anti-corrosion effects.

Sealing performance testing: Evaluates the sealing of the connection parts between the corrugated steel pipe sections, especially for the pipes connected with the bell-and-spigot, flange or split clamp types. Through the water filling pressure testing or air tightness testing, the specified pressures are maintained for a certain time, checking whether there are the leakages at the interfaces, verifying the effectiveness of the sealing materials and connection processes.

Corrosion resistance evaluation: According to the use environments, the accelerated corrosion tests are carried out on the corrugated steel pipes or their coatings, such as the neutral salt spray testing and cyclic corrosion testing, simulating their durability in the corrosive media such as the acids, alkalis and salts. At the same time, the corrosiveness of the site soils or environmental media can be tested, providing the basis for the material selection and protection designs.

Raw material chemical composition analysis: The samples are taken from the steel plate raw materials used to make the corrugated steel pipes, and the contents of the main elements such as the carbon (C), silicon (Si), manganese (Mn), phosphorus (P) and sulphur (S) are determined with the spectrometers or chemical titration methods, ensuring that the raw materials meet the steel grade standards and guaranteeing the product properties from the source.

Testing Scope

Highway and railway culverts and passages: As the main application field, the corrugated steel pipes used for the drainage culverts, pedestrian passages or small bridges under the highways and railways are tested. The ring stiffness, corrosion resistance and long-term structural integrity under the backfill earth pressures and vehicle dynamic loads are emphatically tested, ensuring the traffic safety.

Municipal drainage and sewage pipelines: The corrugated steel pipes used for the urban rainwater discharge, sewage conveying and utility tunnels are tested. In addition to the routine items, the inner wall smoothness (hydraulic characteristics), chemical corrosion resistance (especially in the sewage environments) and long-term sealing reliability of the interfaces need to be particularly focused on.

Farmland water conservancy and flood control works: The corrugated steel pipes used for the irrigation canals, inverted siphons, reservoir spillways and dam drainage pipes are tested. The testing emphasis is on their external pressure stability, water scouring resistance and corrosion resistance under the high groundwater levels or immersion environments.

Industrial plant and storage structures: The corrugated steel pipes used for the industrial building ventilation ducts, material conveying pipes, underground utility tunnels and storage structures are tested. According to the specific conveyed media (such as the dust and gases), their wear resistance, temperature resistance and durability under the special environments need to be evaluated.

Temporary works and emergency rescue: The rapidly assembled corrugated steel pipes used for the construction access road culverts, temporary drainage and disaster emergency rescue are tested. The testing focuses on the portability, fast connection reliability and mechanical properties meeting the short-term high-intensity use of the products.

Product ex-factory and arrival acceptance: The ex-factory inspection carried out after the completion of the corrugated steel pipe production, and the arrival re-inspection after the products arrive at the construction sites. The testing items usually cover the appearance, dimensions, material certificate document checking and the necessary sampling property tests. It is the key link of the quality control.

In-service pipeline safety evaluation: The periodic testing or safety evaluation is carried out on the corrugated steel pipes that have been in operation for many years, including the wall thickness measurement (corrosion thinning), appearance defect survey (such as the rust and deformation) and structural deformation monitoring, providing the technical basis for the maintenance, reinforcement or replacement decisions.

Testing Methods

Visual inspection and touch method: The most basic method. The inspectors carry out the systematic inspection of the inner and outer surfaces of the corrugated steel pipe through the naked eye observation and hand touch, with the aid of the auxiliary tools such as the endoscopes, identifying the obvious defects, damages and abnormal conditions. This method is simple and fast, but has the high requirements for the personnel experience.

Dimension measurement method: The general measuring tools meeting the precision requirements (such as the steel tape measures, vernier callipers and outer diameter micrometers) and dedicated gauges (such as the waveform templates and depth gauges) are used, and the various geometric dimensions of the pipe materials are directly measured and recorded according to the measurement positions and procedures specified in the standards.

Non-destructive testing technology: Under the premise of not damaging the components, the physical methods are used to detect the internal and surface defects. The common methods include: ultrasonic testing (UT) for the thickness measurement and the detection of the internal defects; magnetic particle testing (MT) or penetrant testing (PT) for the detection of the surface and near-surface cracks; radiographic testing (RT) for the internal quality inspection of the important welds.

Laboratory physical and chemical testing method: The representative specimens are cut from the products or the same batch of raw materials and sent to the laboratories for the testing according to the standard methods. Including the mechanical property testing with the universal testing machines, composition analysis with the chemical analysis equipment, and corrosion resistance accelerated testing in the equipment such as the salt spray test chambers.

On-site performance testing method: The overall performance tests carried out at the construction sites or under the simulated conditions. For example, the water filling sealing tests are carried out on the installed pipe sections; the settlement observations are carried out on the backfilled culverts to indirectly evaluate the structural stability; the falling weight impact tests are used to evaluate the impact resistance of the pipe crowns.

Coating testing method: For the anti-corrosion coatings, the magnetic method (galvanized layers) or eddy current method (non-magnetic coatings) is adopted to measure the thicknesses; the coating adhesion is tested with the cross-cut method, bending method or tensile method (pull-off method); the coating uniformity is quickly inspected with the copper sulfate solution testing method, etc.

Digital testing technology: The three-dimensional laser scanners are applied to obtain the precise three-dimensional point cloud models of the pipes, used to analyse the overall deformations and ovality; the pipeline crawling robots (CCTV) equipped with the high-definition cameras and sensors are used to carry out the video testing and defect positioning of the interiors of the long-distance and large-diameter pipes.

Testing Standards

Domestic Standards:

1. GB/T 34567, Cold-formed corrugated steel pipe

2. GB/T 13912, Metallic coatings — Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods

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

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

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

6. 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

General measuring tools and gauges: Including the steel tape measures (for the lengths and circumferences), vernier callipers and micrometers (for the precise dimensions such as the wall thicknesses, wave heights and wave pitches), radius gauges and depth gauges, ultrasonic thickness gauges (for measuring the wall thicknesses with the coatings or accessible from only one side) and ovality gauges. They are the basic tools of the dimension testing.

Mechanical property testing equipment: The core equipment is the microcomputer-controlled electronic universal testing machine, equipped with the corresponding tensile, compression and bending fixtures, used to precisely determine the strength and elongation of the material. In addition, the ring stiffness testing machine is the dedicated equipment specially used to determine the ring stiffness of the plastic or metal corrugated pipes.

Non-destructive testing instruments: Including the ultrasonic flaw detectors and thickness measuring probes, magnetic particle flaw detectors (used with the magnetic suspension liquids and ultraviolet lamps), colour penetrant flaw detection reagent kits, and X-ray or γ-ray flaw detectors (for the internal quality inspection of the important welds). These equipment are crucial for finding the hidden defects.

Coating testing instruments: The magnetic/eddy current thickness gauges are the common instruments for measuring the non-magnetic or magnetic coating thicknesses on the metal substrates. The adhesion testers (such as the cross-cut testers and pull-off adhesion testers) are used to quantitatively evaluate the coating bonding strengths. The salt spray test chambers are used to simulate the marine or industrial atmospheric environments and accelerate the corrosion resistance evaluation.

Chemical composition analysis equipment: The direct-reading spectrometers can quickly and accurately analyse the contents of the multiple elements in the metal materials. In addition, the carbon-sulphur analysers and infrared carbon-sulphur analysers are also the common equipment of the raw material chemical composition verification in the laboratories, ensuring that the material designations meet the standards.

On-site testing and monitoring equipment: Including the pipeline closed-circuit television testing systems (CCTV crawlers) and pipeline periscopes (QV) for the internal visual inspection; total stations and spirit levels for the installation positioning and deformation monitoring; earth pressure cells, strain gauges and data acquisition systems for the long-term structural health monitoring.

Sealing and pressure testing equipment: Mainly consisting of the pressure testing pumps (manual or electric), pressure gauges, pressure transducers, plugging heads, connecting pipelines and data recorders, used for the hydrostatic testing or pneumatic testing of the pipes or pipe fittings, verifying their pressure-bearing capacities and sealing performances.