Welding Electrode Testing

Welding electrode inspection mainly conducts scientific testing and analysis on the chemical composition analysis, deposited metal mechanical property testing, covering quality and operational property testing, weld metal diffusible hydrogen content determination, metallographic structure analysis and weld radiographic 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

Chemical composition analysis: Through the methods such as the spectroscopic analysis and chemical titration, the chemical compositions of the core wires and coverings of the welding electrodes are precisely determined, such as the contents of the elements such as the carbon, manganese, silicon, sulfur and phosphorus. This is the fundamental basis of ensuring that the metallurgical properties of the electrodes, weld metal strengths and crack resistance meet the requirements.

Deposited metal mechanical property testing: After the welding, the tensile, impact, bending and other testing are carried out on the weld metals, to determine their tensile strengths, yield strengths, elongations, impact toughness and bending properties. These data directly reflect the load-bearing capabilities and safety of the electrodes in the welded structures.

Covering quality and operational property testing: Evaluating the covering uniformity, moisture absorption, eccentricity and the operational properties during the welding processes, such as the arc stability, slag detachability, spatter amounts and weld formation. The good operational properties are the premise of ensuring the welding efficiency and weld qualities.

Weld metal diffusible hydrogen content determination: The glycerin method, gas chromatography method or mercury method is used to determine the diffusible hydrogen contents in the deposited metals. The hydrogen is the main factor causing the welding cold cracks. The strict control of its content is crucial for the welding of the high-strength steels, large thicknesses and rigid structures.

Metallographic structure analysis: The micro-structures of the welds, heat-affected zones and base metals are observed and analysed, checking whether the harmful structures such as the coarse grains, Widmanstatten structures and hardened martensite exist, and evaluating their effects on the joint mechanical properties and crack resistance.

Weld radiographic testing (RT) or ultrasonic testing (UT): The non-destructive testing technologies are used to check whether the welds have the internal defects such as the blowholes, slag inclusions, lack of fusion, lack of penetration and cracks. This is the core means of evaluating the internal quality grades of the welded joints.

Deposited metal corrosion resistance testing: For the special electrodes such as the stainless steel and heat-resistant steel, the intergranular corrosion testing, salt spray testing or electrochemical testing need to be carried out, to verify the durability and stability of their welds in the specific corrosive environments.

Testing Scope

Carbon steel and low alloy steel electrodes: Widely applied to the fields such as the construction, bridges, ships and pressure vessels. The testing emphases are the mechanical properties (especially the low-temperature impact toughness), diffusible hydrogen contents and crack resistance, ensuring the safety and reliability of the structures.

Stainless steel electrodes: Used for the corrosion-resistant occasions such as the chemical, food and pharmaceutical equipment. The testing core is the chemical compositions (especially the chromium, nickel and molybdenum contents), intergranular corrosion resistance and the ferrite content control of the welds, to meet the corrosion resistance and hot crack resistance requirements.

Hardfacing electrodes: Used to repair the worn parts or endow the surfaces with the special properties (such as the wear resistance, heat resistance and corrosion resistance). The testing focuses on the hardnesses of the hardfacing layers, wear resistance (such as the wear testing), impact wear resistance and the bonding strengths with the base metals.

Cast iron electrodes: Used for the welding repair and restoration of the cast iron parts. The testing needs to pay attention to the hardnesses, color matching with the base metals, crack resistance (through the thermal stress simulation testing) and processing properties of the weld metals.

Non-ferrous metal electrodes: Such as the nickel-based, copper-based and aluminum-based electrodes. The testing emphases are the chemical composition control, mechanical properties of the welds, electrical/thermal conductivity, as well as the corrosion resistance in the specific media (such as the alkaline and reducing atmospheres).

Special purpose electrodes: Such as the underwater electrodes and vertical-down electrodes. The testing needs to simulate the special working conditions, evaluating their arc stability, slag detachability, weld formation and mechanical property maintenance capabilities under the specific environments (such as the water pressures and specific positions).

Covering type identification: The testing scope covers the various covering types such as the rutile type, cellulose type, low-hydrogen type and iron oxide type, evaluating their applicable power sources (AC/DC), welding positions and the generated slag characteristics.

Testing Methods

Spectroscopic analysis method (OES): The arc or spark is used to excite the samples, and the quantitative analysis of the core wires and deposited metals is carried out by analysing the characteristic spectral lines. This method is fast and accurate, is the mainstream method of the chemical composition testing, and can simultaneously determine the multiple elements.

Deposited metal mechanical property testing method: The tensile, impact and bending specimens are strictly prepared according to the standards such as GB/T 2650~2654 or ISO 15792. The testing is carried out on the equipment such as the universal testing machines and impact testing machines, obtaining the accurate strength, plasticity and toughness data, and determining the electrode grades.

Glycerin method/gas chromatography method for the hydrogen determination: The glycerin method is to introduce the gases collected from the welding specimens into the measuring tubes filled with the glycerin, measuring their volumes to calculate the hydrogen contents. The gas chromatography method is more precise, and can separate and quantify the hydrogen of the different forms. Both need to strictly follow the standards such as GB/T 3965.

Metallographic specimen preparation and observation method: The weld cross-sections are cut, mounted, ground, polished and etched (such as with the nital solutions) to make the metallographic specimens. Under the optical microscopes or scanning electron microscopes, the structure morphologies, grain sizes and defect distributions are observed, and the quantitative analysis is carried out.

Non-destructive testing (NDT) methods: The radiographic testing (RT) uses the X or γ-rays to penetrate the welds, displaying the internal defects through the films or digital imaging. The ultrasonic testing (UT) uses the reflection characteristics of the high-frequency sound waves at the defects for the positioning and quantification. The two complement each other, jointly guaranteeing the internal quality of the welds.

Corrosion testing methods: Such as the sulfuric acid-copper sulfate corrosion testing of the stainless steel electrodes (GB/T 4334). The specimens are boiled in the specific corrosion solutions for a certain time and then bent, checking whether the cracks appear on the surfaces to determine the intergranular corrosion tendency. The salt spray testing simulates the marine atmospheric environments to evaluate the corrosion resistance.

Operational property comparative testing method: The welding is carried out under the standard conditions (the same currents, voltages and welding positions). The arc stability, spatter rates, slag detachability rates and weld appearance formation qualities are objectively evaluated by the experienced welders or through the dedicated equipment (such as the arc analysers).

Testing Standards

Domestic Standards:

1. GB/T 5117, Non alloy and fine grain steels covered electrodes

2. GB/T 983, Stainless steel covered electrodes

3. GB/T 3965, Determination of diffusible hydrogen in deposited metal

4. GB/T 4334, Corrosion of metals and alloys — Corrosion test method for austenitic stainless steels

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

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

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

8. GB/T 10125-2021, Corrosion tests in artificial atmospheres — Salt spray tests

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

3. ISO 15792, Welding consumables — Test methods

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

Direct-reading spectrometer: Used for the fast and precise analysis of the chemical compositions of the welding electrodes. The equipment contains the built-in standard curves, and can complete the quantitative determination of dozens of elements in the samples within one minute. It is the key equipment of the quality control on the electrode production lines.

Universal material testing machine: Used for the tensile and bending testing of the deposited metals. Through the precise loading by the servo control systems, the load-displacement curves are recorded in real time, thereby calculating the key mechanical parameters such as the tensile strengths, yield strengths and bending angles.

Pendulum impact testing machine: Used to determine the impact absorption energies of the deposited metals at the room temperatures or low temperatures (Charpy V-notch or U-notch). The equipment has the high-precision pendulums and low-temperature chambers, and can evaluate the toughness of the material under the dynamic loads. It is particularly important for the electrodes for the low-temperature steels.

Diffusible hydrogen determination instrument: Including the glycerin method hydrogen determination devices (constant temperature collectors and gas measuring tubes) or the more advanced gas chromatographs. The latter is equipped with the thermal conductivity detectors (TCD), which can separate and measure the gas contents such as the hydrogen, oxygen and nitrogen with the high sensitivity and precision.

Metallographic microscope and image analysis system: Consisting of the optical microscopes, digital cameras and professional image analysis software. Used to observe the weld micro-structures, measure the grain sizes, second phase ratios and crack lengths, and carry out the inclusion ratings, realizing the correlation analysis of the structures and properties.

X-ray flaw detector and digital imaging system: Generating the high-energy X-rays to penetrate the welds, received by the flat panel detectors or imaging plates and converted into the digital images. The system software has the functions such as the automatic defect recognition, measurement and film reading, greatly improving the testing efficiency and the objectivity of the results.

Salt spray corrosion test chamber: Simulating the marine or industrial atmospheric environments. Through the atomization of the sodium chloride solutions, the continuous spray corrosion is carried out on the welding specimens under the constant temperature and humidity conditions. Used to accelerate the evaluation of the long-term corrosion resistance of the electrode deposited metals and welded joints.