chinese pex ?? We have 1000' +/- of pex in use here,mostly under ground,none that color,we have had no problems in 7+ yrs.of use .Our OWB is not a "boiler", its an open system,is set up to shut off at 180*,but we have seen 200* a few times. CCW,did you not read the earlier post with pex info ?? DRASTIC weakening above 195* ?? where did you read that ?? 160psi@ 73.4*,100psi@ 180*,80psi@ 200*, boilers generally run 80# + ?????? I never heard so much negativity about pex as i do on this forum,& its biased & uninformed info about how poorly pex performs or holds up.Just read the posted report & become informed .No i'm not mad at you,just totally blown away with your post following the very informative pex info posted by kstills.
Maybe i misread the info ?? waldo, sounds like you hit the nail on the head !!
Fair questions. I'll take you at your word that you are simply trying to understand the different information being posted and not take offense. None is intended in return, either.
I'll explain it like this.
Those who read about PEX get one impression about its capabilities. Those who use it understand the realities of PEX use are a bit more complicated than simply "This pressure at This temperature"
Have you ever seen a boiler plumbed with CPVC water pipe? Why not? It is actually rated HIGHER than PEX (100psi @ 180F)- according to the stamping. But anyone familiar with it knows how easy it is to bend and deform at those temps. (FYI, I am intentionally ignoring the 'glued fittings' discussion as it isn't pertinent to the temp/pressure comparison
Even PEX's stamped rating drops 20% (!) from 180F to 200F and that is the burst/failure rating.
Take a look at a PEX hydronic installation that has the supports too far apart on a horizontal run and you'll see sagging between just about every support. It was surely fine when installed and even once filled with water. Why then? Heat and softening.
Then you have the issues concerning the fittings. PEX softens easily on the ends. *Many* fittings depend upon a tight fit or even the elasticity of the PEX to maintain a connection (BTW, I do NOT trust the latter, I use copper crimp rings on water and prefer something like ProPex fitting for HVAC). As the pipe softens the connection can weaken and even fail. A brass fitting in contact with a major heat source (think boiler) can work like a heat gun or a soldering iron against the PEX tubing.
Standard, non-oxygen barrier tubing (think drinking water) PEX is often much thinner/weaker than PEX designed for hydronic heating.
Ever need to bend or straighten PEX? Heat it. When it cools, it keeps the shape. That's a good example of how the softening and deformation works.
Now don't get me wrong. I really like PEX and would prefer to use it any time it is appropriate. I like the way it cuts and installs. I do not like the way it deforms due to weight or heat, and I do not like how it tends to kink when cold. It is easily damaged from UV exposure, too. Most of these are easily overcome by following proper installation guidelines and selecting alternative materials in combination or when necessary as appropriate.
Back to the OP's situation....
While we are all still collecting info before making a rush diagnosis, I'll throw out my speculation from the pics and info so far.
I think that
1. Hydronic (O2 barrier) PEX tubing was not used, rather the tubing looks like standard water tubing and would weaken quite quickly.
2. Although no measurements are shown, the tubing looks like maybe 1/2"? Even at 3/4", it is very possible the system couldn't carry enough BTUs from the boiler into the building, resulting in an overheating boiler.
3. Why didn't the boiler overheat/overpressure halt the failure? As others mentioned, the lack of a heat dump- combined with the inability to carry away enough BTUs- and (speculation) the transition to PEX being too close to boiler (hot fittings) led to failure.
4. To speculate even more, it is possible the PEX wasn't properly supported and when it softened it deformed, possibly even kinked, leading to flow and pressure problems, making the situation even worse.
5. I am guessing the OP does not have an auto-fill valve attached to the boiler from the fresh water supply. If not, in addition to the inability to cool the boiler properly, the sudden outrush of water could lead to a sudden drop in system pressure, allowing the water to flash to steam (literally boiling within the system). Lots of bad things can happen in those situations, probably good the pipe actually failed, boilers are pretty tough.
Hope this answers some questions about PEX, my comments, and possibly even the OP's situation