Seeking advice from experienced experts regarding pipe fittings issues
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This post was last edited by wangqiande2oo8 on 2021-12-28 at 16:34. During the on-site construction, seamless steel pipes with a DN150 size were purchased in accordance with national standards; the safety valves and matching flanges are imported products of 6 inches in size. It’s not clear whether they will be suitable for use during construction. The following sentence was found on Baidu. “The biggest difference between American standard pipe fittings and Chinese standard pipe fittings is the diameter; American standards correspond to what is commonly referred to as Series A in China, while Chinese standards correspond to Series B. For example, in the case of elbows: DN100*6 – the nominal diameter is DN100 in both standards. According to the Chinese standard, the outer diameter of DN100 is 108 MM and the thickness is 6 MM. Under the American standard, DN100 corresponds to 4’ in inches; the outer diameter is 114.3 MM with a thickness of 6 MM as well. Moreover, the length of elbows according to the American standard is slightly greater than that according to the Chinese standard. In other words, for fittings with the same nominal diameter (including elbows, tees, reducers, and pipe caps), the diameter sizes differ between American standards and Chinese standards. ” Another welder said there was undercutting and such things. I am a production worker in the manufacturing field, so I’m not very familiar with this kind of specialized knowledge. I kindly ask the experienced members in the group to provide detailed guidance. Thank you so much!
When purchasing, fittings, flanges, and valves should be bought according to the same standard! Failing to do so will lead to issues such as inconsistent outer diameters and flange holes that are too small
It is possible to weld pipes with a diameter of 159 to standard American 6-inch flanges; there is no problem with that.
It seems that DN is applicable to the nominal diameter used in calculations. The actual purchase seems to apply to φ outer diameter × wall thickness. φ108×6; there are also other wall thicknesses, I guess. Process production workers had better get a copy of \"Principles of Chemical Engineering\" to read; it’s a required course. For reference.
During welding, excessive melting near the joint between the base material and the weld seam causes a depression to form in the transition zone between the metal from the electrode and the base material metal (a pit at the edge of the base material); this is known as undercutting. See the figure below: The hazards of edge biting not only result in thinning of the base metal, but also create geometric discontinuities at the interface between the base metal and the weld, thereby leading to stress concentration and a reduction in the strength of the weld. Edge biting is often caused by excessive current during welding, along with too fast movement of the electrode (wire). If the thickness of the base material meets the strength requirements, the edge where biting occurs can be polished to create a smooth transition, thereby eliminating stress concentration. In general pressure vessel welding, welds are not allowed to have undercut defects. The welding current is too high ； The arc did not stay on either side of the weld ； DC welding machines (especially those for high-current welding ； And the welding arc is too long ； Improper ground wire location, etc.) ； All of these can cause undercut defects in the welds.