If you don’t learn nickel pipe welding, you’ll be Out

Why is nickel alloy more and more widely used Nickel has good mechanical, physical and chemical properties. Adding suitable elements can improve its oxidation resistance, corrosion resistance, high temperature strength and some physical properties. Welding characteristics and requirements for nickel and nickel-based alloys Cleaning before welding The surface cleanness of welds is an important requirement for successful welding of ni-base corrosion resistant alloys. The pollutants on the surface of welded parts are mainly the surface oxide scale and the elements that cause embrittlement. S, P, Pb, Sn, Zn, Bi, Sb, As and other elements that can form eutectic with Ni at low melting point are harmful elements. These harmful elements increase the tendency of thermal cracking of nickel-based corrosion resistant alloys. These impurities must be completely removed before welding preheating or welding. 1. Workshop dirt and grease can be degreased by steam or removed with acetone and other solutions. 2. Paint and other sundries insoluble in degreasing agent can be cleaned with chloromethane, alkali and other cleaning agents or special synthetic agent. Marking inks are generally cleaned with methanol. 3. Impurities that are pressed into the surface of welding parts can be cleaned by grinding, shot peening or hydrochloric acid solution (10% volume ratio) and washed with clean water. Restricted heat input It may be disadvantageous to weld nickel-based corrosion resistant alloys with high heat input method. A certain degree of annealing and grain growth occurs in the heat affected zone (HAZ). High heat input may result in excessive segregation, carbide deposition, or other harmful metallurgical phenomena. This may cause thermal cracking or reduce corrosion resistance. The grain size of the base material must also be considered when selecting the welding method and welding process. Due to the presence of more carbides and intermetallic compounds in the grain boundary of coarse grains, the tendency of thermal cracking is increased. Process characteristics 1) liquid weld metal has poor fluidity Weld metal fluidity is poor, not easy to flow to both sides of the weld. Therefore, in order to obtain good weld formation, sometimes using the swing process. But this wobble is a small wobble, not more than three times the diameter of the electrode or wire. The groove Angle of the joint is larger. 2) depth of weld metal melting This is also an inherent characteristic of ni-base corrosion resistant alloys. It is also impossible to increase the weld depth by increasing the welding current. As mentioned above, if the current is too large, it is harmful to the welding, causing cracks and pores. 3) preheat and post weld heat treatment Nickel base corrosion resistant alloys generally do not require preheating before welding. However, when the base material temperature is below 15°C, the area 250-300mm wide on both sides of the joint should be heated to 15-20°C to avoid condensation of moisture. Post-weld heat treatment is generally not recommended. Nickel and nickel alloy pipeline specific construction Groove machining 1) mechanical method should be adopted for groove processing. If plasma cutting is adopted, the processed surface should be cleaned; 2) groove processing should be in the form of large Angle and small blunt edge, and should meet the requirements of the design and operating instructions; 3) appearance inspection shall be carried out after groove processing, and the groove surface shall not have cracks, delamination and other defects; 4) if the design requirements of the groove surface for nondestructive testing, should according to the regulations of design, without design rules, casting tube, used for the degree of toxicity to extreme harm medium of pipe and pipe fittings and to design pressure is equal to or greater than 10 mpa pipe or tube, penetrant examined in response to the groove, such as defective should keep clear of in time. Groove cleaning and group matching Before group alignment, grease and rust shall be polished on the groove and within the range of 20mm on both sides until the metallic luster is exposed. The surface of the corresponding polishing range shall be cleaned with organic solvent before welding. After the solvent volatilization in the groove on both sides of the 100mm range should also be painted anti-splash coating. The welding point 1) small current, small swing and small line energy are adopted in welding; 2) in the case of argon arc welding, the inside of the pipe should be protected by argon filling. The purity of argon should be no less than 99.99%. When making the bottom, the front edge of the weld pool should keep a small hole with a diameter of 2mm-3mm, and the welding wire should be transferred to the weld pool in a drop shape. 3) when filling and covering surface by manual arc welding, chalk shall be applied to the base material within the range of no less than 100mm on both sides of the groove to prevent spatter damage to the base material; 4) clean the interlayer and surface thoroughly with Angle grinder or stainless steel wire brush. White corundum grinding wheel must be used for grinding and cutting, and it shall not be mixed with carbon steel. 5) pipe and fittings shall be cushioned with rubber or asbestos cloth, and shall not be mixed with carbon steel; 6) if there is cross-work during site installation, the pipe should be covered with asbestos cloth for the possible contaminated parts; 7) when the wall thickness is large, symmetrical welding should be selected for filler welding to prevent welding deformation; 8) socket welding must be formed twice; 9) after the completion of welding, clean the surface of the weld in time, check the appearance of the weld, and write the welder code on the 20mm-50mm from the weld with the coating without zinc, sulfur and other elements. Electrode arc welding of nickel-based corrosion resistant alloys Electrode classification: The electrode of ni-base corrosion resistant alloy is divided into five categories, namely, industrial pure nickel, ni-cu, ni-cr-fe, ni-mo and ni-cr-mo. Welding process 1) due to the shallow melting depth of nickel base corrosion resistant alloy and the poor fluidity of liquid weld metal, the change of welding parameters must be strictly controlled in the welding process. Ni – based corrosion resistant alloy welding rod generally used dc, electrode connection positive. 2) electrode of each type and specification shall have an optimum current range. For the specific joint welding current setting should consider the thickness of the base material, welding position, joint form and clamping rigidity and other factors. 3) the fluidity of liquid nickel-based corrosion resistant alloy is poor, in order to prevent the occurrence of incomplete fusion, porosity, etc., general requirements in the welding process to appropriate oscillation electrode. 4) when the arc is broken, the arc height should be lowered slightly and the welding speed should be increased to reduce the size of the weld pool. This will reduce the crater crack. The reverse arc ignition technology should be used in the rearcing of the welded joint so as to adjust the weld seam smoothness and inhibit the occurrence of porosity. Tungsten gas arc welding of nickel-based corrosion resistant alloys Tungsten gas shielded arc welding has been widely used in the welding of nickel base corrosion resistant alloys, especially for thin plates, small sections, joints can not be used for backing welding and welding residual slag is not allowed. Tungsten gas arc welding can be used not only to weld solid solution strengthened nickel-based alloys, but also to weld precipitated hardened nickel-based alloys. Tungsten gas shielded arc welding is the most common method for welding precipitated hardening nickel-based alloys. Welding wire Nickel-based alloy welding wire is not only used for tungsten electrode gas arc welding, but also for melting electrode gas arc welding, plasma arc welding and submerged arc welding. In order to control pores and thermal cracks, Ti, Mn, Nb and other alloy elements are often added in the welding wire. Welding process 1) direct current positive connection and negative electrode are adopted for manual welding and automatic welding. Welders are usually equipped with high frequency arc initiation and current attenuation devices. 2) since the welding wire needs to be added with elements to improve crack resistance and control porosity, the welding seam should contain at least 50% filler metal, so that these elements can play an effective role. The welding pool should be kept calm to avoid arc stirring the pool. 3) during the welding process, the heating end of the wire must be in protective gas to avoid the hot end oxidation and the resulting pollution of the weld metal. The welding wire shall enter the weld pool at the front end to avoid contact with tungsten electrode. conclusion The precondition of successful welding of nickel and nickel-based alloy is to clean up before welding. The welding of nickel and nickel-based alloy should use smaller welding line energy and control the temperature between layers strictly.铜焊丝,Copper Welding Rods,铝焊丝,aluminium welding wire,镍焊条,Nickel electrode,药皮焊条,Flux Coated Brazing Welding Rods