Welding quality directly affects the performance and safety of the boiler structures, boiler welding quality is not good, it may leak or explosion, causing heavy losses to life and property of the people, therefore, to explore the causes of boiler welding defects, improve welding quality of the boiler, ensure the safe operation of the boiler it has a very important significance.

1 Causes and Preventive Measures of incomplete penetration

Mainly due to lack of penetration of 1.1 Cause analysis yielded incomplete penetration defects in the following aspects: ① Membrane Water pipes at the site were pipe butt installation, since the gap is narrow, obstacle operation, very prone to lack of penetration. ② Group gap inconsistent performed on site film and sheet assembly, it is necessary to simultaneously set a plurality of weld, but so very difficult group for the same space. In addition, a plurality of weld can not simultaneously welding, weld when welding finished part, yet remaining gap welding weld will shrink, or even zero. These weld in the welding is very prone to incomplete penetration defects. Obstacles that both sides of the tube when ③ welding and powerful groups that appear wrong port causing incomplete penetration and so on.

 Measures 1.2 lack of penetration preventive measures to prevent lack of penetration are: control joint groove dimensions, such as forming side welding joints, its assembly clearance should be electrode diameter, the blunt edge should be about half the diameter of the electrode; carefully clean root; welding should choose the right welding speed and welding current; short arc welding and the like. From the most difficult parts of the arc, where the smallest obstacles crater sealing, so as not to affect the operation and welders welding line of sight, reduced quality of welded joints; welded joints to avoid the temperature is too low, the best way to use the two butt welding; There are obstacles in the site, it is difficult angle done nozzle, wire and weld retaining provisions, can be adjusted according to the actual situation until after the difficult position that the normal angle welding. For example, for Membrane Water: ① Group should carefully check weld flush former case, for relatively minor modification can be corrected or mechanical flame after orthopedic Group; deformed too much, the overall orthopedic difficulties can be large Quick weld between the first fins cut its slotted length according to the degree of deformation and stress on the size, generally no more than 1500mm, and then a single root canal orthotics. Wall welding until after the entire piece, and then cut back fin seam welding method segmented re-weld. Minimum clearance and maximum clearance ② strict control multiple weld group to make the most of the space to meet the group weld quality requirements; the largest group of the gap of no more than 5mm. When welding, take the first small gap welding weld, the weld after welding large gap. This will help to avoid incomplete penetration, but also helps to reduce welding stress and deformation, while reducing waste weld. ③ When fins welded to the site, so that tube spacing restrictions at best end use relatively sharp grinding tungsten welding, torch increasing accessibility, and should be appropriately reduced welding speed, increase the arc in here residence time, to be equal to the pool size and other parts, and then forward the molten metal to "penetrate" state. ④ For each piece last welding weld gap is too small and difficult to guarantee the quality of welding, you can use the ends of the grinding sharper tungsten welding to make concentrated arc, easy to weld root penetration.

2 unfused causes and preventive measures

2.1 Analysis of the Causes unfused welding current is too small or welding speed too fast, because the heat is not enough, the base material or the first welding groove weld metal is not fully melted; selection of the current is too large, so after half a rod made Red and cause melting too fast, when the base material has not yet reached the edge of the molten metal melt electrodes have been covered up; weldment cooling too fast, or from welding at low temperature, so that the starting end of the base metal is not melted, resulting in incomplete fusion ; welding rod, wire or torch flame biased towards the side of the groove, or eccentric because welding arc biased towards one side, the base material or the previous weld metal was not fully melted filler metal cover caused; when the base material or the previous one groove weld metal surface rust or dirt, because the temperature is not enough, but failed to cover the molten filler metal during welding thereof, will form a layer between the edge and unfused. In the power station boiler heating surface pipe installation, due to the same stop arc weld process, resulting in a "cold joint" In particular, large diameter pipe "cold joints" more often, also contributed to the cause of lack of fusion between layers.

2.2 Preventive Measures rod and welding torch angle unfused be reasonable, shipped strip swing should be appropriate to observe the groove on both sides of the melting conditions; use larger welding current and flame can rate, welding speed not too fast, so that the energy increase enough to melt the base metal or weld metal front layer; welding electrodes found during the eccentric, should adjust the angle of the arc in the right direction; carefully clean the dirt and weld groove on; using hydrogen arc bottoming root After the layer of weld inspection, should be timely sub-layer welding seam; in order to avoid "cold joints", the wire length should be planned, so as not to replace the wire during the welding process. To avoid jitter wire grip wire from the wire at the end should not be too long, we recommend using stop Arc "hot connection" method. This approach is when you need to change the grip position when the wire connector, the first contact with the wire end and the pool, while the arc slightly after the shift, or toward the side of the groove, to be solidified and the wire ends of the pool stick together After a moment how quickly transform wire grip position to complete this action, the arc back into place immediately and continue welding. The use of "hot connection" method, both to ensure the welding quality, but also improve efficiency.

Causes and Prevention Measures 3 stomata

3.1 Causes of factors stomatal pores generated is multifaceted. When the pre-construction site preparation work quite well qualified welding has strictly to do: ① strict compliance with welding parameters and stable; little polarity and the type of impact ② current; ③ weldment groove comply with the requirements and clean, use low hydrogen type electrode strict baking, and placed insulation barrel, used with the check; ④ welder strong sense of quality; ⑤ with strict measures to wind and rain; ⑥X ray inspection results are non-hydrogen welding porosity caused when pores generation is often due to arc and arc caused by improper closing.

Preventive Measures 3.2 stomatal control measures are: ① carefully clean the inner and outer sides of the range of 15 ~ 20mm groove surface and oil, rust, paint and other contaminants wire surface, until all the exposed metallic luster. When welding, wipe it with acetone; ② strict accordance with the provisions of the electrode drying, after incubation put in special electrode insulation tube, used with the check; ③ large drafts, not welded; ④ appropriate to increase the arc current, the base material heat input increases, the cooling rate slows bath; ⑤ When starting, along the joint a little distance from the arc, and then back to the joints, the gas escape time becomes longer; ⑥ welding time, once due for some reason honeycomb pores, the need to immediately stop welding, and grinding with a grinding machine. Prohibit the use of arc remelting method to eliminate pores. Because of the emergence of honeycomb pores, often due to some reason such as argon gas plenum temporary fault) protection failure, then the pore surface oxide films are used not only to make the weld arc remelting brittle, but can not eliminate porosity ; ⑦ TIG welding specifications when larger pipeline, used to pay attention to the water cold welding moment is reliable, because water cold welding Moment failure prone pores; ⑧ high purity (greater than 99.99%) of argon flow To moderate the nozzle inner wall must be clean.

Cause 4 Crack and Preventive Measures

4.1 Cause analysis of welding cracks may crack in the welding process to produce, can be generated in the post-weld in place even after a certain time. The main reason for the formation of welding cracks are the following: when the carbon content or parathion ① base metal content is too high, their weldability, easy to crack. When higher ② welding, flux and other soldering materials and parathion content of alloying elements, the greater the tendency to crack. ③ low temperature or under windy conditions welding, weld cooling too fast too easy to crack. ④ welding thick plate because of its rigid structure is also easy to crack.

4.2 Countermeasures crack crack is welded structure of the most dangerous defect is not allowed, you can control which emerge from the following aspects: ① tack welds should be thick enough long enough; ② must not strong group with; ③ Do not force beat weld ; ④ dissimilar steel welding process is to be determined according to the physical properties of the two materials, chemical properties and weldability when welding. For example: When the heat resistant steel and stainless steel, due to the different thermal expansion coefficients between the two, one side of the arc heat faster time to stay longer appropriate; ⑤ welding as far as possible when there is ignition device steel welding equipment, on the one hand reduce hardened, you can also reduce the possibility of tungsten folder appears.