Zong Zhaofeng Hou Yaping Song Qingjie Yan Jinyong (Zhongyuan Oilfield Construction Group Co., Ltd., Fuyang 457001, China) Zhu Jiling (Chlorin Rubber Factory of Zhongyuan Petroleum Exploration Bureau, Fuyang 457001, Henan Province) Welding is an important process in pipeline construction, and the quality of welding will be good or bad. It directly affects the construction speed of the pipeline and whether it can operate safely and reliably after the pipeline is put into production, which will directly affect the survival of the construction enterprise. At present, in addition to continuously improving the welder's technical level, strict requirements, and strict control, the key means of ensuring the quality of welding is to conduct quality inspection afterwards, which plays a role in monitoring and guaranteeing the quality of welding.
The most used method for internal quality inspection of pipelines is ultrasonic flaw detection. In order to accurately judge welding defects, in addition to long-term and rich experience in flaw detection, it is necessary to have a comprehensive understanding of the distribution law of pipeline welding defects.
1. Distribution of defects along the weld section For the annular weld of pipeline welding, the cross section or longitudinal section can be divided into three parts: the weld surface, the weld interior and the weld root. The welding defects are different according to the three parts. Nature and morphology (see Table 1). For surface defects, it can be directly observed with the naked eye or low magnification magnifying glass. It is intuitive, image and accurate, and the nature of the defects is well recognized. For root defects, if it is a large-diameter pipe, it can be drilled into the pipe and observed with the naked eye, and the nature of the root defect determined after the flaw has been verified. After repeated several times, the experience of determining the nature of the root defect can be gradually accumulated. If the flaw has been determined as an internal defect and the defect is found when the root is verified, it should be considered as a root defect or a joint effect of the two factors, but not simply because the root has found the defect. Internal defects are root defects. For small-diameter pipes or inability to enter the pipe to check for root defects, it is necessary to consider the nature of the root defects to consider whether the pulse waveform is continuous, the spatial position of the defects on the pipe, and the formation of the surface weld.
2 The distribution of the defect along the fixed pipe space position The fixed pipe annular weld position is divided into the entire weld as a fixed circumference, with a positive inscribed quadrilateral horizontally placed in the annular weld, dividing the overhead weld and the half pitch Welding (upward slope welding), vertical welding, flat climbing, flat welding and other parts.
Table i defects in three parts of the position of different properties and morphological defects, location defects, defects, defects, surface defects, weld size, non-conformity, weld height, width, narrowness, undercut, continuous undercut, partial undercut, parent metal, weld edge The surface of the weld bead on the weld surface of the lack of meat is welded by the slag. The pores are dense. The pores are spherical. The surface of the weld is small. The root defect is not welded. The continuous weld is not penetrated. Incompletely welded through the root of the weld, continuous or intermittent, no welding, collapse, continuous collapse, intermittent collapse, partial collapse, vertical collapse along the weld root, continuous or intermittent weld, depressed weld, continuous weld, local weld, intermittent weld along the root of the weld or Local weldment highlights internal defects, stomata, spherical stomata, stomata, stomata, dense stomata, gas residue, small slag inclusions in the weld, single slag, slag inclusions, residual impurities, weld defects, welds, weld metal The local unbonded welds between the welds or the local unfused weld defects between the base metal and the weld have different shapes at different positions, and the molten metal has a falling tendency when the position is raised at the position of the weld. The surface of the weld is prone to welds and the roots are prone to collapse. In the vertical welding position, the liquid droplets drop vertically downward along the direction of the weld, and the root of the weld is likely to be incompletely welded, and the surface is prone to defects such as undercut and irregular weld bead. When the vertical welding transitions to the flat welding position, the droplets have a tendency to drip into the inside of the tube. The root of the weld is prone to be welded, and the surface is prone to too low a weld bead. The internal pores of the weld are mostly distributed in the upright and vertical welds. Because of these parts, the arc is generally pulled longer and the air is easy to invade. Clips (down 90 pages) Except for closed gas water heaters, other gas water heaters should not be installed in toilets and other parts without natural ventilation. In-line and semi-closed forced exhaust gas water heaters should be installed in mechanical exhaust devices. In the kitchen, semi-closed natural vented gas water heaters should not be installed in rooms with mechanical exhaust.
For the installation of a closed water heater, the room or space should be reserved for the installation location and the holes for effective ventilation. The room with non-closed water heaters should have reliable ventilation and conditions, and the installation location and ventilation conditions should be consistent. Relevant provisions of the current industry standard "Standards for Installation and Acceptance of Household Gas Burning Appliances" (JJ 12-1999).
4 Establishing a water heater installation condition review system According to the introduction of the gas station of a city construction bureau, the previous housing design of the city did not consider the installation and use of gas water heaters. Most of the doors and windows were not designed according to the requirements of gas water heaters. The installation location of the gas water heater is not designed. In the past few years, attention has been paid to the installation problem. Most of the housing design is only considering the installation of the closed gas water heater. The semi-closed gas water heater that needs to be installed outdoors is still not considered in the design. Now the difference between the semi-closed gas water heater and the closed gas water heater is very large. The semi-closed type of strong water heater can be bought around 700 yuan, while the closed gas water heater is also the cheapest (15) yuan, the average consumer. In terms of price, most of them buy semi-closed gas water heaters. Therefore, in three months, seven people in the city died of oxygen deficiency due to the use of gas water heaters.
The safety problem of gas water heaters has caused harm to many people. The number of people who die indoors due to indoor oxygen deficiency or carbon monoxide poisoning caused by the use of gas water heaters in the country is as many as hundreds, which is much more serious than the casualties caused by fire. However, the former is more scattered and concealed, and the latter is more concentrated. For the fire protection problems of buildings, the state pays more attention to it, and has developed a special fire protection system for engineering design and construction drawings, so that many innate problems of fire protection design can be avoided. For residential buildings that are related to the health and safety of residents, the author recommends adopting a special review system for the installation conditions of gas water heaters in the design and construction drawings to avoid the congenital problems of architectural design and ensure the safety of residents.
(2(1)1-09 Editor Wang Dexiang) (Continued from page 84) The slag is mostly distributed in the elevation and flat welding parts, because the molten iron and slag in these parts are easily confused, especially the interlayer slag in the overhead welding position is not easy to clean.
3. From the shape of the surface weld, the normal surface weld of the fixed pipe should be welded and the corrugation is almost uniform and uniform, and the seam width is uniform. However, sometimes the defects in the root or interior of the weld are not reflected in the weld, and sometimes there is an abnormality in the surface weld. For example, if the gap of the flat welding is too large, it will easily lead to the formation of welds in the root welds, and sometimes it may not be welded. The internal defects are mostly vents, which is caused by anti-burn through arc and elongated arc. Finally, the surface weld will be wide and low, and sometimes the surface weld will not fill the groove on both sides to ensure the same weld width as other parts. If the gap of the countersink is too large, it may cause continuous collapse at the root of the upset weld, and a large number of pores will appear inside, and the surface weld will be high and wide. If the counter gap of the overhead welding is too small, there will be continuous incomplete penetration of the positive pressure welding, and defects such as incomplete penetration, unfusion, and slag inclusion will occur at the positive pressure welding head, and the surface weld will be narrow and high. Phenomenon, the weld at the joint appears higher.
4 The difference in the nature of the defects caused by the electrode is due to the large difference in the composition of the coating, which leads to a large difference in welding metallurgy, specification selection, and transportation methods, so it appears in the nature of defects. Certain differences. When an acid electrode is used, the flat and upright welds are easy to advance due to slag, often forming sand holes and slag inclusions, and the surface welds of the vertical welding are easy to be rough and difficult to tidy. Defects in weld size are characterized by thinner welds. The internal pores are often carbon monoxide pores, which are generally small in size. The possibility of slag inclusion in the weld is greater than that of the alkaline electrode, and the reflection of the ultrasonic pulse waveform is often low and messy. When using an alkaline electrode, the surface weld size often has a thicker weld, and the vertical weld is easy to bite and a weld is present. The anvil weld of the root is prone to collapse, and the weld is prone to weld, and the weld is often covered with pores. The pores in the weld are often hydrogen pores, and the size thereof is generally large, and the possibility of slag inclusion in normal conditions is small. Sometimes there are hot cracks in the arc pit and dense pores at the joint. Ultrasonic wound pulse waveform reflections are often high and single.
(2(1)1-02-09Editor Yang Jun)
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