Carbon Steel Pressure Barrel Testing

Carbon steel pressure drum inspection mainly conducts scientific testing and analysis on the macroscopic morphology and dimension inspection, material composition and mechanical property analysis, welding quality non-destructive testing, pressure resistance testing and leakage testing, and coating and anti-corrosion layer 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

Macroscopic morphology and dimension inspection: The inner and outer surfaces of the carbon steel pressure drum are inspected through the visual inspection and general measuring tools, checking whether there are the macroscopic defects such as the cracks, scratches, dents and deformations. At the same time, the key geometric parameters such as the total height, diameter, wall thickness, opening positions and dimensions of the drum body are precisely measured, ensuring that they are consistent with the design drawings and process requirements, providing the basic data for the subsequent pressure-bearing capacity evaluation.

Material composition and mechanical property analysis: In accordance with the relevant standards, the carbon steel material used for manufacturing the pressure drum is sampled and tested, and the contents of the main elements such as the carbon, manganese, silicon, sulphur and phosphorus are analysed, to verify whether the material designation is correct. Through the tensile testing, bending testing and impact testing (such as the Charpy V-notch impact testing), the core mechanical property indicators such as the tensile strength, yield strength, elongation and impact toughness of the material are determined.

Welding quality non-destructive testing: This is the key link of the pressure drum inspection. The radiographic testing (RT) or ultrasonic testing (UT) is mainly adopted to detect the internal defects of the welds (such as the blowholes, slag inclusions, lack of fusion and cracks). At the same time, the magnetic particle testing (MT) or penetrant testing (PT) is used to detect the defects such as the cracks and undercuts on the surface and near-surface of the welds, ensuring the integrity and reliability of the welded joints.

Pressure resistance testing and leakage testing: The pressure resistance testing (usually the hydrostatic testing) is the core item for verifying the structural integrity of the pressure drum under the pressure exceeding the design pressure. The pressure drum is filled with the liquid, slowly pressurized to the specified test pressure and the pressure is maintained, observing whether there are the abnormal deformations or leakages. The leakage testing (usually the air tightness testing) is carried out at the design pressure or a lower pressure, checking whether there are the trace gas leakages through the immersion method, soap bubble method or with a leak detector.

Coating and anti-corrosion layer testing: Detects the integrity, thickness and adhesion of the inner and outer anti-corrosion coatings (such as the paints and epoxy coatings) of the pressure drum. A coating thickness gauge is used to measure whether the dry film thickness meets the design requirements. The coating adhesion is tested through the cross-cut method or pull-off method, and it is checked whether there are the defects such as the bubbles, peeling and pinholes in the coating, evaluating the effectiveness of its long-term anti-corrosion protection.

Testing Scope

Ex-factory inspection of the newly manufactured pressure drums: Covering all the ex-factory pressure vessel products, ensuring that they meet the technical requirements of the design, manufacturing standards and procurement contracts. The testing scope includes the whole process from the incoming raw materials to the ex-factory finished products, and is the mandatory quality gate before the products enter the market.

Periodic inspection of the in-service pressure drums: In accordance with the requirements of the regulations such as the "Supervision Regulation on Safety Technology for Stationary Pressure Vessels", the periodic inspection of the carbon steel pressure drums in service is carried out. The inspection scope includes the first periodic inspection, the subsequent full inspections and annual inspections, emphatically evaluating the safety condition of the equipment after the long-term service.

Supervision inspection after the installation/maintenance/alteration: When the pressure drum undergoes the major installation, major maintenance (such as the replacement and repair welding of the main pressure-bearing components) or alteration, the supervision inspection must be carried out. The testing scope focuses on the changed parts, verifying whether the construction quality restores or improves the original safety performance of the equipment.

Special testing under the specific working conditions: For the pressure drums operating under the harsh environments such as the corrosive media, fatigue loads, high temperatures or low temperatures, the special testing needs to be carried out. The scope may include the fixed-point thickness measurement of the corrosion thinning, metallographic analysis to check the material deterioration, and hardness testing to evaluate the stress condition.

Safety evaluation after the accidents or abnormal conditions: After the accidents such as the overpressure, fire and collision of the pressure drum or the situations such as the leakage and abnormal deformation, the comprehensive safety evaluation testing needs to be carried out. The testing scope is wide, aiming to find out the damage causes, evaluate the damage degrees, and provide the basis for judging whether the equipment can be safely repaired and used or must be scrapped.

Testing Methods

Visual testing (VT): The most basic and direct testing method. The inspectors systematically observe the inner and outer surfaces, structures, welds and corrosion conditions of the pressure drum with the aid of the lighting tools, magnifying glasses, endoscopes and other auxiliary equipment, to find the obvious macroscopic defects, deformations, leakage traces and corrosion products. This method has the high dependence on the personnel experience.

Ultrasonic testing (UT): Uses the characteristics of the propagation of the high-frequency sound waves in the material for the detection. It is mainly used to measure the wall thickness (particularly suitable for monitoring the corrosion thinning), detect the planar defects (such as the cracks and lack of fusion) inside the welds and base material, and the material delaminations. It has the advantages of the high sensitivity, thickness measurement capability and no harm to the human body, but has the high requirements for the surface finish of the detection areas and the operator skills.

Radiographic testing (RT): Uses the X-rays or γ-rays to penetrate the workpiece, and the internal structure images are recorded through the films or digital imaging plates. This method has the intuitive display of the volumetric defects (such as the blowholes and slag inclusions), and the test results can be permanently saved. It is suitable for the internal quality inspection of the butt welds. However, attention needs to be paid to the radiation protection, and the detection rate of the planar defects such as the cracks is affected by the angle.

Magnetic particle testing (MT): Applicable to the detection of the surface and near-surface defects of the ferromagnetic materials (such as the carbon steel). By magnetizing the workpiece and sprinkling the magnetic particles on the surface, the leakage magnetic field at the defects will attract the magnetic particles to form the magnetic indications. This method is extremely sensitive to the linear defects such as the cracks and folds, with the simple and fast operation, but is only applicable to the ferromagnetic materials and has certain requirements for the surface condition of the workpiece.

Penetrant testing (PT): Used to detect the open defects on the surfaces of the non-porous metal or non-metal materials. The penetrant containing the dye is applied to the workpiece surface to make it penetrate into the open defects, and after cleaning, the developer is applied to absorb the penetrant in the defects, forming the visible indications. This method has the simple equipment and can detect the workpieces of the complex shapes, but can only detect the surface open defects.

Testing Standards

Domestic Standards:

1. TSG 21, Supervision regulation on safety technology for stationary pressure vessels

2. GB 150, Pressure vessels

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

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 230.1-2018, Metallic materials — Rockwell hardness test — Part 1: Test method

7. 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

Ultrasonic thickness gauge and ultrasonic flaw detector: The ultrasonic thickness gauge is used to quickly and precisely measure the remaining wall thickness of the various parts of the pressure drum, and is the main tool of the corrosion monitoring. The ultrasonic flaw detector has the more comprehensive functions, and is equipped with the probes of the different frequencies and angles, which can be used for the positioning, quantification and qualitative analysis of the weld defects. It is the core equipment for the internal defect detection.

Radiographic testing system: Including the X-ray machines or γ-ray sources, radiographic films, automatic film processors or digital imaging plates (DR/CR systems), as well as the film viewers or digital film evaluation workstations. The modern digital radiographic testing systems can improve the detection efficiency and realize the digital storage, transmission and analysis of the images.

Magnetic particle flaw detector and penetrant testing kit: The magnetic particle flaw detector includes the magnetization power sources, yokes or contact heads, as well as the fluorescent or non-fluorescent magnetic particles. The penetrant testing kit usually includes the consumables such as the cleaners, penetrants and developers. These equipment are portable, and are commonly used for the rapid detection of the weld surfaces, bevels and fillet welds on site.

Material testing machine and hardness tester: The universal material testing machine is used to carry out the mechanical property tests such as the tensile and bending. The impact testing machine is used to determine the impact toughness of the material. The Leeb hardness tester or Brinell-Rockwell-Vickers hardness tester is used for the rapid on-site testing of the hardness value of the material, indirectly evaluating the strength and heat treatment state of the material, or detecting the local work-hardened and softened areas.

Macroscopic inspection and measuring tools: Including the high-intensity endoscopes and industrial video endoscopes for checking the internal conditions that cannot be directly observed by the human eyes; weld inspection gauges, ultrasonic thickness gauges, laser range finders, callipers and micrometers for the precise dimension measurement; as well as the auxiliary equipment such as the magnifying glasses, lighting lamps and rust removal tools, which together constitute the basic tool set of the macroscopic inspection.