Recently, an OEM (original equipment manufacturer) that makes large filter units for food-grade services was reporting leaks on the cover gasket that they were using. The gasket in service was a 22” OD (outer diameter), 1/8” thick EPDM (ethylene propylene diene monomer) rubber full-face gasket with eight ¾” studs (as shown below). 

For a great marksman, hitting the center of a target is not a problem. You set up a target, and he can hit it. In fact, he can hit it all day long; because this is what he does. However, all his skill and confidence won’t help him a bit if he’s presented with two targets and not told which one he is to hit. Which one should he focus on and which one should he ignore?

Hazardous Nature of Hydrogen Fluoride    

Anhydrous Hydrogen Fluoride (AHF) is used as a catalyst in the reaction that combines C3 and C4 olefins and isobutane to produce alkylates, an important component of gasoline. AHF readily reacts with any available moisture to create the corrosive and toxic Hydrofluoric Acid.

So hazardous is this material to humans that OSHA lists the Permissible Exposure Limit (PEL) to 3-ppm averaged over an 8-hour shift, while the National Institute for Occupational Safety and Health (NIOSH) lists the IDLH (Immediately Dangerous to Life or Health) concentration at 30-ppm. In and of itself, this hazard level arguably makes HF Acid Alkylation Units the single most dangerous sealing application in modern refining.