When it comes to Linear Polyethylene, Cross-Linked Polyethylene and FRP tanks, none of these materials is better than the others but each material has its proper application.
Whether it be Linear (LLDPE or HDPE) or Cross-Linked (XLHDPE) Polyethylene is a very abrasion and chemically resistant material. The shortcoming is that Polyethylene, in general, is not a strong material by comparison to FRP or various metals. Polyethylene also has a lower maximum temperature threshold, compared to FRP or metal tanks. But, Polyethylene is generally less expensive. In smaller size tanks, the cost savings can be substantial while still realizing the same, or better service life. Linear Polyethylene has a 120F maximum temperature limit and 150F degree maximum for XLPE. Typical lead time is 4 – 6 weeks after drawing approval.
FRP (Fiber Reinforced Plastic) Tanks are typically used for larger vessels, taller and narrower vessels, and for elevated temperature applications. Where Polyethylene (not being as strong as FRP) is limited to roughly a 2.5:1 height to width ratio, FRP can be as much as a 5:1 height to width ratio, or more. A parallel that I like to use is Boats. You don’t see many Polyethylene boats, but you see a lot of FRP boats. FRP is just stronger. FRP Tanks with certain Durakane resins can handle up to 250 degrees F for short periods of time without softening. One important caveat; FRP tanks do not do well with Sulfuric Acid. FRP is limited to 67% max, at 70 degrees F. We usually use, ASSMANN 2.2 SG Linear Low-Density Polyethylene for the best results. I also sometimes move to Viton lined or Coated Steel Tanks; especially if the temperature is elevated. Typical FRP Tank lead time is 9-12 weeks after drawing approval.