Polyethylene chemical storage tanks require the correct installation for two essential reasons. First, venting ensures the safe operation of the tank and the chemicals stored under pressure within the tank. Secondly, proper installation is vital to maximize the life of the chemical storage tank.
A crucial factor impacting the safe operation of the poly chemical storage tank and maximizing the useful life of the tank is proper and safe venting of the tank. This article will examine proper installation to ensure safe chemical storage tank venting.
Mechanical Vs. Pneumatic Tank Fill Determines Venting Requirements
Poly Processing commissioned an engineering consulting firm to determine the proper venting requirements necessary for polyethylene storage tanks. Two methods of filling were considered, 1) mechanical pumping and 2) compressed air (pneumatic) from tanker trucks.
As a result, the proper and safe venting requirements are specified in the Poly Processing Technical Bulletin, "Venting: Design for ACFM." One item of warning from this technical bulletin regarding venting:
Venting capacity must equal or exceed Air Cubic Feet per Minute (ACFM) coming from tanker truck for adequate margin of safety and increased tank life.
Poly Processing has two innovative solutions for the safe venting of chemical storage tanks. The SAFE-Surge® Emergency Air Surge Protection is used in applications where venting is piped outside the building. It functions by relieving pressure when it exceeds .25 PSI which is allowable pressure for a polyethylene tank designed to the ASTM D-1998 standard.
The second venting lid, the FS 2650, combines a manway and U-vent. It’s perfect for tanks that vent directly to the atmosphere. This lid is capable of relieving a volume flow rate of up to 2650 ACFM. The FS 2650 guarantees that the tank cannot become over pressurized, regardless of the size of the fill line.
Proper installation of the SAFE-Surge® Emergency Air Surge Protection vent is essential.
- SAFE-Surge® lids are heavy. Do not use a ladder and attempt to carry the lid to the top of the tank for installation. Use proper lifting equipment- a hoist or scaffold- to place the SAFE-Surge® lid over the tank manway.
- Rotate the lid until the warning label is next to the edge of the tank.
- Secure the lid with the polyethylene bolts provided.
- Make certain the movement of the center cap of the lid is unrestricted and able to open to relieve pressure build-up in the tank.
To install an FS 2650 venting lid, use the same work instructions as an 8 bolt manway (SAFE-Surge lid.)
Proper Venting Extends Chemical Storage Tanks Life
Often times, the importance of venting is overlooked as a very important step that promotes tank longevity. Please refer to the PE Life Expectancy PDF on our Technical Bulletins page for more information.
Polyethylene tanks are rated at atmospheric pressure/vacuum. Adequate vent size is always based on flow and delivery rates so it is important to gather the following information to adequately determine the proper venting requirements:
- Is the tank to be filled pneumatically?
- Is the tank to be vented into the atmosphere?
- Does the length of the vent exceed 3 feet (piped to a central vent system)
- Is a fume scrubbing system to be used?
- Are vent screens to be used (restricts flow)?
- Does the tank manufacturer offer a method of “emergency venting” to prevent overpressurization?
Finally, a qualified Poly Processing representative will inspect your chemical storage tank installation to verify proper venting installation. A safe, long-lasting storage tank is the result.