As for the material compatibility, biodiesel is quite different from petro — diesel. Biodiesel is compatible with high-density polyethylene (HDPE), and it is incompatible with polyvinylchloride (PVC) and polystyrene (PS), as PS is readily soluble in biodiesel and PVC is slowly dissolved in biodiesel. Polypropylene (PP) is affected by biodiesel, showing a swell increase (by 8-15%) and reduced hardness (by about 10%). Polyurethane (PUR) is also affected showing some swell increase (by 6%). Biodiesel affects some natu­ral rubber and all nitrile rubber products, and biodiesel is compatible with commonly used viton-type synthetic rubbers in modern vehicles. Studies indicate that viton types B and F (FKM-GBL-S, and FKM-GF-S) are more resistant to acidic biodiesel [50]. Biodiesel affects, and is affected by, many metals including copper, zinc, tin, lead, cast iron, and brass, whereas biodie­sel does not affect stainless steel (304 and 316), carbon steel, and aluminum. Brass, bronze, copper, lead, tin, and zinc may accelerate, by catalytic activi­ties, the oxidation process of biodiesel creating fuel insolubles or gels and salts. As such these metals should be avoided as materials of construction for piping, regulators, and fittings in applications where biodiesel is expected to be in contact with them.

Neat biodiesel may degrade some hoses, gaskets, seals, elastomers, glues, and plastics with prolonged exposure. Acceptable storage tank materials for biodiesel include aluminum, steel, fluorinated polyethylene, fluorinated polypropylene, Teflon, and most fiber glasses [51].