Does metal expansion joint belong to special equipment? Don't be fooled
Metal expansion joints are not necessarily special equipment. The key depends on these three parameters-nominal diameter, design pressure and medium. Take the corrugated expansion joint used in the power station industry as an example. For those with DN300 or more and a pressure of 1.6MPa and steam, nine times out of ten should be managed according to special equipment; However, those large-diameter thick-walled expansion joints in the cement industry take normal temperature flue gas, and the pressure is only 0.1MPa, so they basically don't need to enter the supervision catalogue. Don't hear "metal expansion joint" and think that you have to apply for inspection. It's all to scare you.
What do the regulations say?
The pressure pipeline components in the Special Equipment Catalogue include "compensator (expansion joint)", but there is a premise: the nominal diameter is ≥150mm, the design pressure is ≥1.6MPa, and the medium is gas or liquefied gas, or a liquid with a maximum operating temperature ≥ standard boiling point. If you compare the general corrugated expansion joint or the double hinge transverse expansion joint in your project, if you use steam, hot water and compressed air, you will most likely have to manage it by pressure pipe elements. If desulfurization flue gas and cement kiln tail waste gas are taken, the temperature is high but the pressure is low, so they are often exempted.
Don't use non-metallic expansion joints. The non-metallic expansion joint has JB/T 12235-2015 national standard, but it is not in the special equipment catalogue because the fabric fiber has limited pressure bearing capacity. However, as long as the parameters of metal rectangular expansion joints and high-temperature axial expansion joints are sufficient, the design, manufacture, installation and inspection must comply with TSG D0001, GB/T 12777 and other standards. Two days ago, a customer took our straight pipe pressure balance expansion joint and asked me why there was no TS logo on the nameplate-I said that your pipe diameter was only DN80 and the pressure was 0.6MPa, which was not within the scope of supervision at all. It was a waste of money to do TS.
How to judge whether your expansion joint should be monitored or not? Three steps.
Is the nominal diameter ≥150mm? Is the design pressure ≥1.6MPa? Is the medium a gas or a high temperature liquid? The second step is to look at the structure: such as sleeve-type pipe expansion joint and rotary compensator, although they are also compensators, they are not considered bellows, and the supervision and determination in some places are controversial. The third step is to look at the pipeline category: if the whole pipeline belongs to GC1 and GC2, the expansion joint will naturally follow. For example, the metal expansion joint connected behind the desulfurization flue gas baffle door directly skips the flue gas at normal pressure and temperature.
In case of monitoring and inspection, how to choose the type without stepping on the pit? If you clearly know that the project belongs to the category of special equipment, be sure to purchase products from manufacturers with corresponding manufacturing licenses. However, if you buy the "non-standard" one cheaply, the on-site supervision will not recognize it, and the rework loss will be ten times more expensive than the expansion joint itself. On the other hand, if your project clearly doesn't need monitoring and inspection, don't listen to people fool you and add money to do TS. The budget saved is enough to buy a few electric plug-in insulation doors.
Whether the metal expansion joint is special equipment or not depends on the three axes of "diameter, pressure and medium". Don't be intimidated by the word "expansion joint", and don't take it seriously. If you really want to judge it, look through the Pipeline Grade Table or Pressure Pipeline Summary Table given by the design institute, which will clearly write whether the pipe section is a pressure pipeline. If it doesn't work, send the parameters of your metal hose, PTFE-lined metal hose or large-diameter thick-walled expansion joint to our technology to help you close it-don't let compliance problems get stuck in your project acceptance.
So, back to that core question:Are metal expansion joints special equipment?The answer is clear – look at the parameters. The pipe diameter is less than 150, the pressure is less than 1.6MPa, and the medium is water or low-temperature liquid, so it is appropriate to leave it alone; On the other hand, no one can avoid the monitoring and inspection of DN200 and 2.5MPa bellows on steam pipelines.