Condensate looks unremarkable, but running through the pipes can make normal expansion joints quite choky. Low temperature, low pH value, frequent start-and-stop-these three conditions are put together, and the metal bellows is prone to pitting and stress corrosion cracking, and the rubber compensator may be damaged by oil or high-temperature steam recoil. Therefore, don't take the general-purpose corrugated expansion joint directly, but first understand the characteristics of the medium: the condensed water is usually distilled water or weakly acidic water, and the temperature is below 60℃, but occasionally there will be steam flushback, and the instantaneous temperature can soar above 150℃.
To put it bluntly, selection is a "gambling game". If you bet wrong, you can leak or stop. Then how do you choose?
There are only a few types of products on the market that can carry condensate water
rubber compensator— — Cheap, large displacement, good vibration absorption, but afraid of high temperature and oil. If the steam system in your factory has an oil stream, or the occasional hot steam rushes in, it is only a matter of time before the rubber ages and cracks.
Universal corrugated expansion joint(For example, SUS304 material) -Temperature and pressure resistance, but weak resistance to chloride ion corrosion. If you use softened water, or if the steam system is mixed with acid gas, the 304 perforates quickly. Why? Chloride pitting. When the condensate pH is below 5, 304 is a sieve.
Metal hose-Flexible installation, suitable for small diameter, short distance takeover, but the compensation amount is limited. Large displacement scenarios don't count on it.
PTFE-lined hose-First-class corrosion resistance, but double the price. Unless the medium pH is below 4, it is not cost effective. Two days ago, a customer said, "Our condensate is clean water, just use 304". As a result, three months later, the root of the bellows was full of pinholes-this is the typical "I thought".
Knock three numbers when selecting a model
Axial displacement due to design temperature, design pressure, condensate volume. If one of these three numbers is less, the selection is blind.
- Temperature over 100°C-Don't consider the rubber compensator, put on the universal corrugated expansion joint orExternal pressure single axial expansion joint。 The external pressure structure can separate the bellows from the medium, avoid direct washing, and is suitable for high-temperature steam backflushing scenarios.
- The displacement exceeds 30% of the product rating-preferably structures with tie rods or hinges, such asCompound hinge transverse expansion jointOrStraight pipe pressure balanced expansion joint。 Why? Because the common axial expansion joint is easily unstable under large displacement, the pipeline is deformed under force, and finally leaks. The structure with the tie rod can hold the blind plate force, so that the expansion joint only compensates for displacement and does not bear pressure thrust.
- The guide tube must be equipped with— — The condensed water washes the corrugated root, and the fatigue life is directly halved. Don't look at the inconspicuous guide tube, it can guide the medium to walk in a straight line and avoid the bellows. Many on-site workers installed the deflector backwards, and as a result, the water hammer directly deflated the bellows. The direction of the arrow is the direction of the medium flow, so don't reverse it.
Installation location is particular
The condensate pipeline is mostly laid horizontally, and the expansion joint must be installed on the side near the fixed bracket. Why? Because the fixed bracket limits the displacement of the pipe, the expansion joint can effectively absorb thermal expansion and contraction on that side. If it is installed backwards, the pipe displacement is fully pressed on the expansion joint, and it will deform quickly.
In addition, after the condensate system is shut down, it is easy to retain accumulated water. If the expansion joint is made of rubber, long-term soaking in water will accelerate aging-rubber hydrolysis, swelling, and the surface will be sticky and blistered. Recommended quarterly inspectionrubber compensatorSurface, see for cracks or softening. Metal bellows should pay attention to welds and troughs, and replace them in time if rust spots are found. Don't wait until a leak is repaired, then the pipes may be corroded through.
Real Case: Condensate Return Pipeline in Chemical Plant
Common corrugated expansion joint is used for the condensate return pipeline of a chemical plant. After 3 months of operation, there was a pinhole leak at the root of the bellows. When removed, the corrosion product is typical chloride pitting. For what? Replace withPTFE-lined hose, cooperate withDirect buried (fully buried) type expansion jointDo underground section compensation. Why use direct burial type? Because that section of pipeline is buried underground, it has to bear the pressure of covering soil and groundwater corrosion. The directly buried expansion joint has a reinforced shell and anti-corrosion coating, which has a much longer life. Running for 2 years without any more problems.
Do you think that's the truth? Don't just look at the price when selecting a model, the matching of working conditions is more important than anything else. To put it bluntly, using expansion joints for condensate water is a job of "prescribing the right medicine"-if the medium is corrosive, it is lined with PTFE, if the temperature is high, it is external pressure type, and if the displacement is large, it is hinge or pressure balance type.