home decoration and bought PE pipe, I plan to spread it in the yard in the open air, but my friend said that "PE pipe will shrink when exposed to the sun", which made many people mutter - will PE pipe really be "sunburned small" by the sun? In fact, this problem has to start from the material characteristics of PE pipe and the influence of sunlight.

First, the core material of PE pipe is polyethylene (PE), which is a thermoplastic resin with a molecular structure like a string of soft chains. Like all materials, PE pipe also has the characteristics of thermal expansion and contraction: when the temperature rises, the molecular movement becomes intense, the chain segment expands, and the pipe will expand slightly; when the temperature decreases, the molecules shrink and the pipe will shorten slightly. But the linear expansion coefficient of PE pipe is about 0.15mm/(m · ℃) (about 10 times that of steel pipe), that is to say, a 1-meter-long PE pipe will shrink by 0.15mm for every 1 ° C drop in temperature. If it is summer sunlight, the surface temperature of the pipe may rise from 25 ° C to 45 ° C, expanding by 0.3 mm; when it cools down to 20 ° C at night, it will shrink by 0.75mm - such a change is actually very small, almost invisible to the naked eye, and will not "shrink" to affect the use.

So why do some people think that PE pipe "shrinks"? In fact, the more common is the "invisible damage" of ultraviolet rays. The ultraviolet rays (UV) in the sun will penetrate the surface of the PE pipe and destroy the molecular chain of polyethylene: the originally tight long chain is broken and becomes a short URL, the pipe will gradually become brittle, lose elasticity, and crack on the surface - at this time the pipe looks "smaller", but it is actually the structural damage caused by aging, not the real volume shrinkage. For example, the PE pipe that has been stacked in the open air for several years feels hard and will break with force, but the length is not much shorter.

Let's talk about the actual use scenario: if it is a buried PE pipe (such as municipal water supply and drainage, gas pipes), the soil will play the role of a "thermal insulation layer", the temperature change is small, and the impact of thermal expansion and contraction can be ignored; if it is installed in the open air (such as agricultural irrigation pipes, balcony rain pipes), as long as you choose a UV-resistant PE pipe (such as a PE100-grade pipe with carbon black or UV stabilizer added), or wrap it with thermal insulation cotton and sunscreen film, you can delay aging, and the shrinkage is almost negligible.

To sum up: PE pipes will not shrink significantly in the sun, and the so-called "shrinkage" is mostly a misunderstanding of aging; what really needs to be worried about is the aging caused by ultraviolet rays - as long as you choose the right pipe and do a good job of protection, PE pipes are fully capable of outdoor work. Next time you encounter the saying "PE pipe sun shrinking", you might as well take a ruler to measure and touch the elasticity of the pipe to distinguish whether it is thermal expansion and contraction or aging!