1. Consider the physical properties, mechanical properties and chemical composition of weldment materials:
(1) For welding of structural steel, generally consider the principle of equal strength, and select welding consumables that meet the requirements of mechanical properties of the joint.
(2) For dissimilar steel welded joints between low carbon steel and low alloy steel, welding consumables corresponding to steels with lower strength grades are generally selected.
(3) For the welding of heat-resistant steel and stainless steel, in addition to considering the strength, the main chemical composition of the weld metal should be considered close to the chemical composition of the base metal.
(4) When the chemical composition of the base metal contains high levels of harmful impurities such as carbon, sulfur, and phosphorus, the welding consumables with stronger crack resistance should be selected. Such as low-hydrogen welding consumables.
2. Consider the working conditions and performance of the weldment:
(1) Under the condition of dynamic load and impact load, the weldment has higher requirements for impact toughness and plasticity in addition to ensuring tensile strength and yield strength. At this time, low-hydrogen welding consumables should be used.
(2) When the weldment is working in corrosive media, it is necessary to distinguish the type, concentration, working temperature and corrosion type (general corrosion, intergranular corrosion, stress corrosion, etc.) of the medium, so as to select the appropriate stainless steel welding consumables.
(3) When the weldment is working under wear conditions, it is necessary to distinguish whether it is general wear or impact wear, intermetallic wear or abrasive wear, wear at normal temperature or at high temperature. Should also consider whether to work in a corrosive medium to select suitable surfacing welding consumables.
(4) For weldments that work at low or high temperatures, welding consumables that can guarantee mechanical properties at low or high temperatures should be selected.
3. Consider the complexity and structural characteristics of the weldment, welding joint type, etc.:
(1) Weldments with complex shapes or large thicknesses are prone to cracks due to the large internal stress generated by the weld metal during cooling and shrinkage. Therefore, welding materials with good crack resistance must be used, such as low-hydrogen type electrodes and high-toughness electrodes.
(2) For some joints with small grooves or joints with strict root penetration control, welding consumables with greater penetration depth or penetration capacity should be selected.
(3) When some welding parts are difficult to clean due to conditions, consider choosing welding consumables that are not sensitive to rust, oxide scale and oil, such as acid welding rods, to avoid defects such as pores.
4. Consider the spatial position of the weld:
Some welding consumables are only suitable for welding at a certain position, and the welding effect in other positions is poor. Some welding consumables can be welded in various positions. When selecting, consider the characteristics of the welding position:
5. Consider welding working conditions and operating environment:
(1) Where there is no DC welding machine, use AC and DC welding consumables.
(2) Certain steel materials (such as pearlitic heat-resistant steel) need to undergo post-weld stress relief heat treatment, but when they cannot be carried out due to equipment conditions or their own structure restrictions, welding consumables with a chemical composition different from the base metal should be selected (such as Austenitic stainless steel welding consumables) can be exempted from post-weld heat treatment.
(3) Welding consumables should be selected reasonably according to the conditions of the construction site, such as field operation and welding working environment.
(4) Where both the acid electrode and the alkaline electrode can meet the requirements, in view of the high requirements for the operation technology and construction preparation of the alkaline electrode, the acid electrode should be used as much as possible.
6. Consider the economics of welding:
(1) Under the premise of ensuring the performance, try to choose the most cost-effective welding consumables.
(2) For primary and secondary welds with different performance requirements, different welding consumables can be used instead of one-sided pursuit of the overall performance of the welding consumables.
7. Consider welding efficiency:
For structures with heavy welding workload, high-efficiency welding consumables, such as welding wire, iron powder electrode, and high-efficiency stainless steel electrode, should be used as far as possible when possible.