Steam supply to flammable storage tanks

Can anybody tell me what codes, (NFPA or otherwise), governs the steam pressure, piping, and or safety devices required on flammable storage tanks (lube and fuel- 5,000 gallon type) that are heated with steam? I thought that such systems were limited to 15psi or less, but what scares me most is if things went bad, having a slug of lube and or waste fuel oil finding its way back in the condensate return to my huge steam boiler system. Train men please chirp-up!