Welding is mainly used for surfacing welding of valve sealing surface, repair welding of casting defects and welding required by product structure. The selection of welding materials is related to its process methods. The materials used in electrode arc welding, plasma arc welding, submerged arc welding and carbon dioxide gas shielded welding are different. The most common and commonly used welding method is various materials used in electrode arc welding.
01 Requirements for valve welders
The valve is a pressure pipeline element. The skill level and welding process of the welder directly affect the product character and safety production, so it is urgent to strictly require the welder. Welding is a special process in the valve production enterprise, and there must be special means for the special process, including the management and control of personnel, equipment, process and materials. The welder shall pass the basic knowledge and actual control examination of correct examination for boiler and pressure vessel welders, hold the certificate (certificate), and can engage in welding operation within the period of validity.
02 Storage requirements for valve electrodes
1) Pay attention to the ambient humidity to prevent the welding rod from being damp. The relative humidity in the air is required to be less than 60% and a certain distance from the ground or wall.
2) Distinguish the model of welding rod and the specification shall not be confused.
3) During transportation and stacking, pay attention not to damage the coating, especially stainless steel electrode, surfacing electrode and cast iron electrode.
03 Welding repair of valve castings
1) Welding repair is allowed for valve castings with sand inclusion, crack, air hole, sand hole, looseness and other defects, but oil stain, rust, moisture and defects must be removed before welding repair. After removing the defects, polish the metal luster with sandpaper. Its shape should be smooth, with a certain slope and no sharp edges. If necessary, non-destructive control shall be carried out by powder or liquid penetration, and repair welding can be carried out only when there are no defects.
2) Repair welding is not allowed if there are serious penetrating cracks, cold shuts, honeycomb pores, large areas of porosity on the pressure bearing steel castings, and there are no defects to be removed or the parts that cannot be repaired and polished after repair welding.
3) The number of repeated welding repair after leakage test of pressure bearing steel casting shell shall not exceed twice.
4) The casting must be polished flat and smooth after welding repair, and no obvious welding repair trace shall be left.
5) The NDT requirements of castings after welding repair shall be implemented in accordance with relevant standards.
04 Stress relief treatment of valve after welding
1) For important weldments, such as the weld of thermal insulation jacket, the weld of valve seat embedded on the valve body, the surfacing sealing surface requiring post welding treatment, and the welding repair of pressure bearing castings exceeding the specified range, the welding stress shall be eliminated after welding. If it is impossible to enter the furnace, the method of local stress elimination can also be adopted. The process of eliminating welding stress can refer to the welding rod manual.
2) The welding stress shall be eliminated after welding if the welding repair depth exceeds 20% of the wall thickness or 25mm or the area is greater than 65C 3¡ and the shell test leakage.
05 Valve welding procedure qualification
The correct selection of welding rod is only an important link in the special process of welding. It is only the correct selection of welding rod. Without the guarantee of the previous articles, it is impossible to obtain good welding quality.
Since the welding quality of electrode arc welding is different from the important parameters specified by the quality of electrode itself, diameter of electrode, base metal, thickness of base metal, weld position, preheating temperature and adopted current, pay attention to the changes of these important parameters.
In the valve products, the welding process qualification includes surfacing of sealing surface, inlay welding of valve seat and valve body and welding repair of pressure parts.
For specific process qualification methods, please refer to ASME section IX welding and brazing qualification standard and China’s machinery industry standard JB / T 6963 fusion welding process qualification of steel parts.
Post time: Sep-24-2021
