Many customers always feel that the compensator is installed once and for all. Especially the non-metallic compensator (also called fabric fiber expansion joint), because it doesn't look "tough" like the metal corrugated expansion joint, it feels delicate and easy to break. In fact, on the contrary, the maintenance difficulty of non-metallic compensators is not technical, but that you don't use the right method.
"How to maintain non-metallic compensator?" This question, our after-sales engineers have to be asked hundreds of times a year. Today, I disassembled it and crumpled it to make it clear. Each one is the experience hammered out in the actual project.
Find out the structure of non-metallic compensator first, then talk about maintenance
If you don't even know what layers it consists of, maintenance is busy. The non-metallic compensator is not a whole cloth sleeve, it is a flexible joint made of multiple layers of different materials, and mainly depends on the skin to absorb thermal displacement and vibration. Common structures include:
- Skin (non-metallic band)— — The outermost sealing layer, usually glass fiber cloth coated with fluororubber, silicone rubber or polytetrafluoroethylene, depends on it for temperature resistance and corrosion resistance.
- Thermal insulation-The interior is filled with ceramic fiber blanket or glass wool, which is used to block high temperature and protect the skin.
- guide tube— — Install inside the pipeline to guide the flow of media and avoid high-temperature airflow directly washing the skin. This is the same as the guide tube of the metal expansion joint.
- Flange plates and bolts— — Metal parts that press the skin against the pipe flange, by which standard non-metallic expansion joints are installed.
So what is the nature of maintenance? Is to protect the skin, keep the seal, and prevent the bolts from loosening. You remember the structure in your mind, and you will naturally understand it later.
Where to look for daily inspections? Focus on checking these parts
Inspection is really not difficult, just see with your eyes. It is suggested that in the order of "from the outside to the inside", more than a dozen compensators on a pipeline can be checked once in half an hour.
First Lookskin surface。 Any bulging, delamination, cracking, scratching? The most common injury is abrasion-dust particles, driven by airflow, sand the skin like sandpaper. If the outer fiberglass cloth is found to have broken yarns or exposed yarns, it means that the skin has begun to deteriorate.
Second Lookflange bolt。 This one is the easiest to overlook, but goes wrong the most. Under the temperature change of non-metallic compensator, the thermal expansion and contraction of bolts produce stress relaxation, which has to be tightened once in one or two months. You try the wrench one by one. If you can twist it half a turn, even if the torque is insufficient.
Third Lookguide tube。 Extend a flashlight from the entrance of the compensator and shine it in to see if the guide tube is curled and fallen off. Just two days ago, a cement factory customer reported that the compensator was hot. When he disassembled it, he saw that half of the guide tube was burned through, and the flue gas was sprayed directly on the skin from the gap. It was found that the insulation layer of the whole pipeline would have to be scrapped a few days later.
Remember, the skin is a consumable and can be replaced if it is broken. However, if the deflector and the insulation layer are broken, it is a systemic problem, and the maintenance cost is completely different.
The timing of cleaning and replacing non-metallic compensator
The topic of cleaning is quite controversial in the industry. Here is my view:If you can not wash it, don't wash it. Don't clean the dust.
Why? Once the surface coating of non-metallic skin is corroded by chemical cleaning agent, the sealing performance is degraded directly. Are the solvents you use to remove oil or rust? How much acidity and alkalinity? Don't be smart until the manufacturer gives advice.
If the dust accumulation is too thick and affects the heat dissipation, just purge it with dry compressed air, control the pressure within 0.2MPa, and keep a distance of more than 30cm from the skin. If there is really oily stain, brush lightly with a soft bristle brush dipped in neutral soap, then quickly rinse with clean water and air dry, and the process is controlled within 10 minutes.
So when should I change it?Penetrating cracks or air leakage in skinSwitch it directly without discussion. If only the surface coating is powdered, it can last another month or two, but there must be a replacement plan. There is a rough empirical figure for reference: the skin life of non-metallic compensator is about 3~5 years under normal temperature flue gas conditions; Under the high temperature above 300℃ or the working condition containing sulfur and alkali, the service life is shortened to 1~2 years. This is not said by patting the head, but summarized with reference to JB/T 12235-2015 standard and a large number of engineering cases.
Maintenance Myth: These Actions Can Instead Damage the Compensator
The following operations are the "negative teaching materials" seen repeatedly at the after-sales site.
Myth#1: The tighter the bolts are tightened, the better.The skin is sealed by the uniform pressure of the pressure plate. If you tighten the bolts on one side, the pressure plate is warped, and the other side leaks. The correct method is to pre-tighten diagonally several times, and finally tighten it uniformly with a torque wrench. The torque value refers to the requirements of the installation drawings.
Myth 2: If you find small cracks, use glue to mend them.Not only does this fail to restore the mechanical properties of the structure, but the solvent in the glue will further damage the skin coating. Many customers take structural glue on them by themselves, and as a result, the cracks get bigger and bigger.
Myth 3: Ignore maintenance during system downtime.When the machine is shut down, the residual medium in the pipeline (especially sintering flue gas and desulfurization slurry) will crystallize or corrode the skin inside the compensator. If the machine is shut down for more than one week, it is recommended to open the drain outlet to drain the accumulated liquid, and purge it with low-pressure steam if necessary.
To add, a non-metallic compensator cannot be used as a pipe support point. In some sites, in order to save supports, the weight of the pipeline is pressed on the compensator, and the skin is overloaded every day, and its life is more than halved.
Maintenance cycle and record management under different working conditions
There is no uniform standard for maintenance cycle, it depends on your operating environment. We usually divide our customers into three categories:
- Normal operating conditions(The temperature is lower than 200℃, the medium is non-corrosive and dust-free): Inspect once a quarter, and tighten the bolts once every six months.
- bad working conditions(High temperature and high dust, or containing acid, alkali and sulfur components): Inspect once a month, and tighten the bolts every quarter. Under this working condition, the surface temperature of the skin is measured with an infrared thermometer, which is much more reliable than hand touch.
- Extreme operating conditions(For example, near the desulfurization flue gas baffle door and the smoke exhaust system of the power station): See it once a week, focusing on observing whether there are any traces of acid dew point corrosion. By the way, the skin material of the non-metallic compensator in the desulfurization system must be acid-resistant fluororubber coating, otherwise it will be useless no matter how diligent the maintenance is.
Records management, don't bother. Each compensator establishes an independent ledger, which contains three lines: installation date, problems found in previous inspections, and details of replacement parts. With two or three years of data, you can find out the loss law of the compensator on your pipeline and prepare the wearable parts in advance.
To put it bluntly, the answer to the question "how to maintain non-metallic compensators" is twelve words:Understand structure, check frequently, do not move, keep records。
Although this article is about maintenance, if you encounter problems at the selection or installation level, don't shoulder it yourself. Whether the compensator can live long or not is decided from the day of selection and installation. If you are unsure of the specific working conditions, talk to the manufacturer's technical support directly, which is much more efficient than thinking about it on the spot.