Don't hurry to dismantle it first: three signals to judge whether to repair or replace it
On-site inspection shows that there are cracks and bulges on the surface of the rubber expansion joint, and the first reaction is often "it's over, you have to replace it with a new one". Wait a minute. Whether the repair method of flue rubber expansion joint can be used depends on the degree of damage. Give you three self-test signals:
- Signal 1: The crack depth does not exceed 1/3 of the thickness of the rubber layer.Take a caliper to measure it. If it is just a surface crack and the fiber skeleton layer in the middle is not hurt, cold adhesion reinforcement can be completely done. Once it is more than half deep, or the skeleton layer is bare and fluffy, then don't bother – just change it.
- Signal 2: The aperture of the leakage point is less than 5mm.Small pinholes or trachoma that can be plugged with a quick-cure rubber repair. However, if the crack length exceeds 100mm, or there is a large area of delamination (such as rubber and fabric delamination), the repair strength is not enough, and there is a high probability of secondary leakage in the later period, so it is better to replace it as a whole.
- Signal 3: The corrosive medium did not penetrate the flange surface.In many working conditions, the flue gas contains sulfur, and the rubber becomes hard and brittle after being corroded. Break the damaged edge with your hand. If it breaks and has no elasticity, it means that the rubber has aged and denatured, and it is white to repair it. On the contrary, if the rubber still has toughness, but only local mechanical damage, the repair effect is guaranteed.
These three signals are not hard standards, but they can save you at least half of the overhaul time and cost. By the way, if you use this site on siteNon-metallic expansion joint (fabric fiber expansion joint)Orrubber compensatorYou can turn through the warranty book. Many manufacturers with minor damage during the warranty period will directly repair it for free. Don't mess around with it yourself.
Three Things You Must Do Before Patching: Shutdown, Dust Cleaning, Material Preparation
Mending is not a job you can do with your sleeves rolled up. Do three things first, and one less is equal to doing it for nothing.
First, shut down completely and isolate.The flue system must be stopped, powered off, and upstream and downstreamFlue gas baffle doorOrDesulfurization flue gas baffle door, hang the "No Start" sign. Some masters try to save trouble, only turn off the fan but not the baffle. As a result, negative pressure leads to backward flow of residual smoke, and hydrogen sulfide is poisoned during the repair process-this is no joke.
Second, the dust should be clean enough to lick it.Dust, oil and scale on the inner wall of the flue must be removed. Wipe with a wire brush and alcohol, dry and wipe with a clean white cloth. There should be no dust on the cloth. Why? The bonding between repairing agent and rubber belongs to chemical crosslinking, and the ash layer will form an isolation film, and the bonding strength will decrease by more than 70%. You don't want to work hard to fix it and leak again when you start it up, do you?
Third, the material preparation should be "in the right seat".Select materials according to the type of damage: two-component polyurethane repair agent for cold adhesion method, unvulcanized film and vulcanizer for hot vulcanization, glass fiber cloth or carbon fiber cloth plus epoxy resin for patch reinforcement. Note that if you are patchingRubber PTFE compensatorWith PTFE layer attached to the surface, ordinary adhesive can't stick, so it must be activated with nano-corrosive solution first. This is easy to ignore in many scenes, so remember.
Three mainstream ways of on-site repair: cold bonding, hot vulcanization and patch reinforcement
If you choose the right method, the patch will last. Each of the three methods has its own applicable scenarios:
Cold sticking method:The fastest and most convenient. Applicable torubber compensator、Rectangular non-metallic expansion jointSmall localized cracks or perforations. Operation process: Polish the wound surface until fresh rubber is exposed → Apply primer → Apply repair glue → Apply patch cloth → Pressure and cure. When the temperature is lower than 5℃, the adhesive will cure slowly, so heat gun must be used to assist in heating. The cure time is usually 24 hours, but it can withstand slight pressure after 12 hours. An empirical data: the tensile strength after cold adhesion repair can reach 60% ~80% of the original rubber, which is more than enough to cope with the negative pressure of conventional flue gas.
Thermal vulcanization method:It has the highest strength and can restore more than 90% of the performance of the original gum. For areas with extensive damage or heavy stress, such asRound Flap Door (Double Seal)The reinforcing edge at the junction with the expansion joint. It is necessary to cut the unvulcanized raw rubber sheet appropriately, spread it on the ground base surface, heat it to 140 DEG C to 160 DEG C with a portable vulcanizer, and maintain the pressure for 30 minutes. The disadvantage is that special equipment and power supply are required, and it is difficult to operate when the site conditions are limited. But once done, the lifespan is almost the same as the original parts.
Patch reinforcement method:Somewhere in between the first two. Epoxy resin was impregnated with fiberglass cloth or carbon fiber cloth, and multilayer lamination was adhered to the outside of the damaged area. Commonly used inNon-metallic expansion joint (fabric fiber expansion joint)Because the matrix of the fabric expansion joint itself is multi-layered fibers, patch reinforcement is equivalent to "weaving another layer". Note that each layer must wait for the top layer to dry (not sticky) before continuing, otherwise it will be easy to delaminate. The advantage of patch reinforcement is that no heat source is needed, and the curing strength at room temperature is enough. The disadvantage is that the requirements for operation techniques are high, and the bubbles will bulge later if they are not cleaned up.
And guess what? Many old masters mix three methods: small holes are cold-glued, large holes are hot-vulcanized, and corners are reinforced with patches. Flexible matching is king.
How to check and accept after repair? Air tightness test and thermal cycle verification are indispensable
Step 1: Airtight testing.Apply soapy water or special leak detection solution to the repair area and the surrounding 50mm range, and then introduce compressed air of 0.05~0.1MPa into the flue (the specific pressure refers to the design pressure of the system, do not overpressure) for 10 minutes. Observe if there are continuous bubbles emerging. Note that the small bubbles may be the internal pores generated during the curing process of the repair glue, and it is fine if the bubbles disappear after standing for 5 minutes; If bubbles continue to occur, it means that there are through holes and rework is necessary.
Step 2: Thermal cycle verification.This is a link that many people ignore. Rubber and adhesive seal well at room temperature, but when they encounter the actual temperature of flue (often 80℃ ~200℃), the thermal expansion coefficient is different, and debonding may occur. How to test? Low temperature flue gas is passed through first (150°C) for 2 hours and cooled again for inspection. If it's okay both times, you can basically put it into long-term use with confidence.
By the way, the acceptance record should be kept: repair time, operator, material batch number, photos, and airtight data. Convenient for later tracing. Many factories lack this link in their equipment ledger, and when it leaks, they remember "Who repaired it? What glue was used?"-then it's too late.
Four daily habits to extend your life and save more money than tinkering
No matter how awesome the repair is, it is better to maintain it in place. Four habits with almost zero cost and doubling the effect:
1. Discharge condensed water regularly.After the flue system is shut down, acidic water will condense inside, accumulate at the bottom of the expansion joint, and corrode the rubber layer. Drain manually at least once a week, or install automatic traps. This is in theCorrugated expansion joint for power plant industryAndDesulfurization flue gas baffle doorIt's especially important in the maintenance of.
2. Avoid hot and cold.Rubber is afraid of sudden cold and heat. Start the preheating when the machine is turned on, and control the heating rate within 20 DEG C/min; Cool naturally when shut down, do not spray with cold water. Many tearing accidents of rectangular non-metallic expansion joints are caused by the stress concentration caused by the sharp change of temperature difference.
3. Check flange bolt torque.The bolts at the flange of the rubber expansion joint can loosen due to vibration, and leaks often start at the flange face. Check with torque wrench once a month, pre-tighten in diagonal order, torque value refer to factory manual. Don't tighten it blindly, too tight will crack the rubber gasket.
4. Do visual + wall thickness inspection once a year.The data were recorded at the thinnest point of the expansion joint (usually the crest and trough) by ultrasonic thickness gauge, and the trend curve was established. When the wall thickness is reduced by more than 30%, even if there is no leak, it is time to include it in the replacement plan-this is called preventive repair, which is much cheaper than waiting for a big hole to be broken before emergency repair.
In the final analysis, the repair method of flue rubber expansion joint is only an emergency measure. If it is managed daily, it is not necessary to go to this step at all. If it really comes to the day to repair, don't panic. Follow the above process. If you need to replace it, repair it if you need to repair it. Just know what you know.