PP – Pipe Preheater Enclosure The Pipe Preheater Enclosure is designed to heat gas upstream of valves, chokes, orifice fittings and regulators. Commonly installed in locations where the valves, chokes, orifice fittings and regulators are not easily accessible. PP- Pipe Preheater Enclosure Brochure PP- Pipe Preheater Enclosure Catalog