NEC Temperature Class

[Mechanical Farmer]

If I have a process that requires heat tracing I need to consider the T-rating of the heat trace elements.
Is there a provision to the NEC code that allows my to neglect the T-rating/classification if process temperature exceeds Auto Ignition Temperature. Taking the heart of the rule into consideration, the element's temperature is irrelevant. If vapor were to escape the process piping it would ignite as soon as it came into contact with oxygen.

 

[cherryg]

There is an assumption that when liquid escapes, it passes on to vapor phase. What is the flash point of this liquid? Will it remain in liquid phase or transition to vapor phase?

 

[Gr8blu]

The issue is igniting the combustible/flammable material. The normal concern is that having the material come in contact with a surface that has enough heat to ignite the material (since there is almost guaranteed to be oxygen present as well). Then the matter becomes whether 1) the material is in constant contact with the surface, or 2) only comes in contact if the process "fails" somehow, or 3) never comes in contact.

The T-classification portion of the Code basically stipulates that the surface to be contacted WILL NOT exceed 80 percent of the auto-ignition temperature of the combustible/flammable material.

If the surface is always or sometimes in contact, the T-code requirement stands. If it never contacts, it is irrelevant.
If the area has a hazardous classification of some sort, chances are better than even that the local authority would require that the surface meet the T-code criteria.