1. B1, B2 Where does the code name come from? — — Find out first that these two are not made up by the manufacturer
"What is the difference between your B1 and B2? Is it the number that the manufacturer slapped his head?" Well, it's really not. Although in our industry, there is no mandatory national standard to specify specific definitions of B1 and B2, most established manufacturers (including us) have used themWave number or stiffness classBy convention. Simply put, B1 typically representsSingle wave structure(or basic type), B2 representsDouble wave structure(Reinforced). This code name can be found in the General Technical Specifications of Metal Corrugated Expansion Joints and the procurement specifications of many engineering companies. You can understand it as "basic model" and "strengthened model", but don't think that it's just an extra wave-behind it is the change of the whole mechanical model.
2. Hard difference in structure: the difference of one wave, the compensation amount and stiffness all change
Take the one we know bestUniversal corrugated expansion jointAndHigh temperature axial expansion jointSpeaking, the most intuitive difference between B1 and B2 is the wavenumber. B1 is usually designed as 1 complete waveform (containing two half waves), while B2 is two waveforms (four half waves). And guess what? Just this wave of difference,The difference of axial compensation amount is more than one time。 For example, the single-wave compensation amount of the B1 type of a certain DN200 may only be ±15mm; Type B2 of the same size, the double wave compensation can reach ±30mm. But here's the trade-off – the stiffness will drop. The softer the bellows, the more difficult it is to resist the blind plate force generated by pressure thrust and internal pressure. Therefore, the wall thickness, the number of layers or the design of reinforcing ring of B2 often have to be overweight. Two days ago, I met a customer who made steam pipelines, and insisted on replacing B2 with B1. As a result, the axial thrust pushed the bracket crooked. Tsk, that's the price of not understanding structural relationships.
3. Pressure, temperature, displacement-what work can B1 and B2 each do?
Let's start with stress. B1 has an advantage in high-pressure scenarios because of its single wave and relatively high stiffness (note that it is "relative"). For example, in the working condition of 2.5MPa in chemical pipelines, B1 type is often more stable. What about B2? Double wave leads to the reduction of overall stiffness, and the end corrugation is easy to become unstable when subjected to internal pressure, so it is more suitable for the occasion of medium and low pressure (≤1.6MPa). Let's talk about the temperature. At high temperature, the material of corrugated pipe will creep, and B2 has a higher creep risk because of its large wave number and large deformation. OurHigh temperature axial expansion jointIt is clearly stated in the product information: If it exceeds 400℃, it is recommended to preferentially choose B1 or install a guide tube. What about displacement? The B2 is inherently designed for large displacements-you let it absorb ±50mm of axial displacement, and it can dry beautifully; But if you want it to withstand lateral displacement, don't count on it, it doesn't have the capability. At this time, we have to consider the double hinge type or the universal type (such as oursCompound hinge transverse expansion joint）。
4. Installation and maintenance: Is B2 more delicate than B1? Speak with cases
To be honest, B2 is indeed a little more "delicate" than B1. It's not metaphysics. Because B2 has a large wave number and a longer overall length, it is easier to be bumped and deformed during transportation and hoisting. There was a cement factory project last year, and the customer ordered a batch of B2 typeMetal Corrugated Expansion Joints in Cement IndustryAs a result, two bellows were found to have slight depressions during on-site installation-later, it was found that it was caused by the brutal loading and unloading of the logistics company. If it is type B1, the single wave is short and the stiffness is high, so it is not so easy to be injured. There is another detail when installing: B2 must be strictly centered, otherwise the double waves will be unevenly stressed, resulting in overstretching on one side and squeezing into "wrinkles" on the other side. In terms of maintenance, the inspection cycle of B2 is recommended to be 30% shorter than that of B1. For example, in chemical pipelines, B1 can be inspected once a year, and B2 is best taken a look at half a year, paying special attention to whether there is corrosion or fatigue crack at the trough.
5. Guide to selection and pit avoidance: Don't just look at the code, working condition parameters are king
Finally, let's talk about something that digs out my heart. The code names B1 and B2 are just an entry label in our industry, just like "general-purpose" and "enhanced". What really decides which one you should use, isPressure, temperature, displacement, medium corrosivity, cycle lifeThese five parameters. As a counter-example: a customer saw that the next factory used B2 and bought it. As a result, his pipeline was high-temperature and high-pressure steam (540℃, 10MPa), and B2 leaked after less than 3,000 cycles. Why? Because the instability pressure of double wave bellows at high temperature is much lower than that of single wave. On the contrary, if you have a large displacement of the pipe but a low pressure (such as flue gas pipe), hard on B1 will waste materials and not compensate enough. So, uh,What is the difference between metal corrugated expansion joints B1 and B2Just knowing the name is useless, you have to know how to count. You can look through our websiteStiffness and Calculation Formula of BellowsAndModel and size of expansion jointThose two questions and answers contained specific calculation steps. If you are really unsure, throw the working parameters to the manufacturer and let the technology produce a type selection calculation book-it is ten times more reliable than your blind guess.