If by your phrase "hazardous area device" you mean are they considered "safe" for installation in areas where explosive and/or combustible vapors may be present, we have found that they are not. We install them in enclosures with continuously supplied purge air on our platforms.
Rosalyn,
I have had the experience of build ups of Aspahltenes and combinations of asphaltenes with scale/sand/silt in vessels and lines. Sometimes the use of xylene will dissolve some or all of the deposits. If your oil stream is more of the paraffinic variety then diesel may work as well...