Requirements for welding materials in steel structure welding
The mechanical properties of deposited metal in welding data shall not be lower than the lower limit value of corresponding base metal standards or meet the requirements of design documents.
[clarify] welding data has a serious impact on the safety of welded structure, and its composition, physical properties and process performance should conform to the rules of corresponding national standards, and the construction enterprises should adopt the sampling method for verification.
1. Welding data shall be stored in a dry and well ventilated place, and shall be kept, dried, distributed and recovered by special personnel with specific records.
[clarify] the storage requirements of welding data are to avoid corrosion, damp, deterioration and even drop of welding data, which will affect the normal operation.
The drying of low hydrogen type electrode shall meet the following requirements:
1. The welding rod shall be dried at 300-430 ° C for 1.0 ~ 2 h before use, or according to the welding rod application instruction provided by the manufacturer. When the welding rod is put into the oven, the temperature should not exceed half of the final drying temperature. The drying time should be calculated after the oven reaches the final drying temperature;
2. The dried low hydrogen welding rod shall be placed in the heat preservation box with the temperature not lower than 120 ° C for storage and ready for use; the low hydrogen welding rod shall be placed in the heat preservation cylinder and taken as soon as it is used;
3. The electrode should not be placed for more than 4h after drying, and the electrode used for class III and IV structural steel should not be placed for more than 2h after drying. Re drying should not exceed 2 times.
[clarify] low hydrogen type electrode is mainly used in important welding structure, and the requirements for low hydrogen electrode are more stringent. Before packaging, the low hydrogen electrode is generally baked at the required temperature of diffusing hydrogen and packaged in sealed containers. If the sealed package is in good condition, it can be used immediately after opening the package without baking; however, if the package is damaged or it is used more than 4 hours after opening the package, it should be baked according to the rules of this standard.
In order to remove the crystal water and adsorbed water in the coating of low hydrogen type electrode before welding, the main purpose is to avoid introducing hydrogen into the weld metal due to the thermal differentiation of the arc during the welding process, and hydrogen is one of the primary factors for delayed cracking.
Hydrogen induced delayed cracking is more sensitive in welded joints of quenched and tempered steel, high strength steel and bridge structure.
The flux shall meet the following requirements:
1. Baking should be carried out according to the temperature recommended by the manufacturer before use; wet or caked flux is prohibited to be used;
2. The flux used for class III and IV structural steel shall not be placed in the atmosphere for more than 4 hours after baking.
The flux of submerged arc welding has the function of maintaining and participating in alloying of weld metal. The flux polluted by oil, oxide scale and other substances will form pores and affect the process performance. The moisture-proof treatment and baking treatment of flux is to reduce the crystallization water and adsorption water in the flux, and avoid the moisture in the flux from introducing hydrogen into the weld metal through arc thermal differentiation in the welding process, and hydrogen is one of the primary factors to delay the occurrence of welding cracks. If the flux is subjected to severe moisture-proof treatment and baking treatment, the test proves that the hydrogen content in the deposited weld metal of submerged arc welding is less than 8ml / 100g, so submerged arc welding can be regarded as a low hydrogen welding method in practice.
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