Nonmetallic compensators out of spec? Don't panic, understand these questions first
Two days ago, I met a customer who said that the non-metallic expansion joint on their flue had been used for more than a year, and recently began to leak. The inspection found that the displacement was twice as large as the design value. He came up and asked, "The non-metallic compensator exceeds the specification, is it waste?"-This kind of problem is actually quite common, but many people panic when they hear "exceeding the standard". Don't worry, let's make it clear: What exactly does the "norm" here mean? Is it the displacement compensation amount, temperature range or pressure level specified in JB/T 12235-2015? Or have the on-site working conditions thrown away the design drawings? Only by figuring out the source can we prescribe the right medicine.
Why is it beyond the norm? Three of the most common conditions
There are three of the most I've seen. The first is that the actual operating temperature is more than 50℃ higher than the design. This situation is particularly common behind the desulfurization flue gas baffle door-the design temperature is 150℃, and the actual operation occasionally jumps to 200℃ or even higher. The aging rate of the fabric fiber layer directly doubles, and it is only a matter of time before the skin becomes brittle and cracked. In the second case, the pipeline system is added with supports and hangers or the foundation settles, causing the compensator to be forced to absorb additional axial or lateral displacement. And guess what? No one at many sites checked the total displacement of the pipeline at all, thinking that everything would be fine if it was installed. The third is to be greedy for cheap when selecting the model, and take the general-purpose corrugated expansion joint to top the high-temperature corrosion condition. As a result, the rubber or PTFE layer can't bear it. To put it bluntly, it's not that the compensator can't work, but that the original parameters don't match the reality.
What are the consequences of exceeding the norm? From air leakage to shutdown
The sealing layer is cracked, air leaks and ash leaks, and the site environment is a mess. In the severe case, the structural layer is fatigued and fractured, and the whole flue stops. Take the non-metallic expansion joint (fabric fiber expansion joint) in our station as an example. If the lateral displacement exceeds 20% of the design value, the skin life will basically be discounted in half. What's more hidden is that exceeding the specification will lead to loose bolts and deformed frames. These hidden dangers are often not discovered until shutdown for maintenance-then the loss will be great. There was a case in a cement plant before. Because of the settlement of the foundation, the rectangular non-metallic expansion joint was pulled by 30mm. As a result, the fillet weld of the frame cracked after half a year's operation, and the production stopped for three days before it was repaired. The loss of production stoppage alone was enough to buy several new compensators.
How to judge if it's really over? Don't just feel
The first step is to turn out the national standard JB/T 12235-2015, and check the displacement compensation amount, working pressure and upper limit of temperature during design. Note that this standard specifies various technical specifications of non-metallic compensators, including displacement, temperature level, pressure level, etc. The second step is on-site measurement: use a dial indicator to hit the relative displacement of both ends of the compensator, scan the surface temperature of the skin with an infrared thermometer gun, and then compare the design values. If the temperature exceeds but the displacement does not, the problem may be in the insulation layer-such as the deflector tube falling off or the insulation cotton failing. If the displacement exceeds the standard, it depends on whether it is axial or lateral-different exceeds the standard, and the treatment methods are very different. If the axial direction exceeds the standard, you can try to adjust the tie rod nut (how to adjust it specifically, refer to the adjustment method of the tie rod nut of the expansion joint we wrote earlier), and if the horizontal direction exceeds the standard, you should consider whether the pipeline support and hanger are displaced.
What if it exceeds? Handle in two situations
If the excess is not much (for example, the displacement exceeds within 10%), and the equipment is still under warranty, you can contact the manufacturer to adjust the tie rod or add the guide tube to share the stress. The function of the tie rod is to limit the excessive displacement, properly adjust the nut stroke, and sometimes it can be rescued. But if it is outrageous, for example, the temperature directly explodes, or the displacement exceeds 30%, it can only be changed-don't think about making do. Once the non-metallic compensator runs beyond the specification, the growth rate of fatigue cracks is exponential. No leakage today does not mean no leakage tomorrow. Remember to communicate with us when changing and provide on-site measured data. We can customize non-metallic expansion joints (fabric fiber expansion joints) or rubber compensators to leave the safety factor sufficient. When selecting, we usually suggest that the upper temperature limit should be left with a margin of 15% ~20%, and the displacement amount should be left at least 10% more, so that even the fluctuation of working conditions can be withstood.
How to fundamentally avoid exceeding again? In the design stage, you have to think about the margin clearly
The working condition parameters given by many customers are "design values", but the actual operation will fluctuate-for example, the temperature behind the baffle door of desulfurization flue gas may instantly jump by dozens of degrees, or the impact load generated when the pipeline starts and stops is much greater than that in the steady state. When selecting a model, I would rather go a higher gear than stuck with the upper limit. For example, if the highest temperature on your site is 180℃, don't choose the general-purpose type with a temperature resistance of 200℃, simply put on a high-temperature axial expansion joint, or use a non-metallic expansion joint with multi-layer insulation. In addition, pay attention to the pre-stretching amount during installation, and let the manufacturer's technicians cooperate during the debugging stage. These details can save a lot of trouble later. Finally, make regular inspections, and don't wait for a leak to remember to check the specifications. After maintenance, a non-metallic compensator will last for five or six years. Think about it, it's better to spend half a day doing an inspection than to stop production for three days, right?