Temperature (Exposed Surface or Sheath) of Insulated Heat Traced Pipe In Cl I Div. 2 Area

[raytisch]

Hello All,

Our project involves installing new electric heat trace on an existing outdoor pipeline that will be insulated with Rockwool and covered with metal covering and sealed to keep water out. This heated pipeline will occasionally pass through Class I Div. 2 areas.

Seeking confirmation regarding the temperature location needing to be evaluated that shall not exceed 80 percent of the autoignition temperature of the gas or vapor in the Class I Div. 2 Area.

I am attempting to resolve what appears to me to be a conflict between the NEC and ANSI/IEEE 515-2002. ANSI/IEEE 515-2002 is referenced in Article 427.1 Scope - Informational Note.

Is the temperature requiring evaluation taken from the exposed surface (outer surface of the insulated pipe covering) or from the sheath temperature on the pipe (under the covered insulation) of the pipe?

The sheath temperature is the temperature of the heating cables installed directly on the pipe and will be greater than the exposed surface temperature.

Per NEC:

Chapter 5 Special Occupancies - 501.135 Utilization Equipment.

(B) Class I, Division 2. In Class I, Division 2 locations, all utilization equipment shall comply with 501.135(B)(1) through (B)(3).

(1) Heaters. Electrically heated utilization equipment shall conform with either item (1) or item (2):

(1) The heater shall not exceed 80 percent of the autoignition temperature in degrees Celsius of the gas or vapor involved on any surface that is exposed to the gas or vapor when continuously energized at the maximum rated ambient temperature. If a temperature controller is not provided, these conditions shall apply when the heater is operated at 120 percent of rated voltage.

Per ANSI/IEEE 515-2002:

6.4.5 Hazardous (classified) locations

The resultant sheath temperature, Tsh, shall be less than the ignition temperature (°C) of the specific gas/vapor/dust involved,

Thank you in advance for any feedback you can provide to help clarify this issue.

 

[retirede]

We a,ways used the surface temp of the heating cable because you can’t guarantee that the insulation or other covering can keep the gas away from the heater.

 

[raytisch]

Thank you for your reply, retirede. You make a valid point. The heat trace vendor had also commented in a similar way. My reply to the vendor was an assumption has to be made that the insulation is in place, installed, and maintained properly. Unfortunately, anyone who has been at a facility using insulation over piping probably will recall seeing damaged insulation coverings somewhere on the site.

 

[rbalex]

We a,ways used the surface temp of the heating cable because you can’t guarantee that the insulation or other covering can keep the gas away from the heater.

Actually, in Division 2, you can just about ignore it. There aren’t supposed to be any ignitable materials in the first place. if you believe, there really might be some, you have a Division 1.

The actual ignition factor is Joules/sec energy transfer. That's why NFPA 497, Table 4.4.2 lists the Mimimum Ignition Energy (MIE) for many of the materials. Temperature is most relevant in static airflow cases.

When I was on the API Subcommittee on Electrical Equipment (SOEE), we did some tests on motors and discovered we could achieve at least an additional 100C above their “perceived” temperature rating to avoid autoignition as long as the motor’s fan was running. I say “perceived” because the effective motor temperature rating is based on its temperature rise at standard operating conditions; i.e., Starting a motor is not “normal” per the NEC. See Section 500.8(B)(2(5)[2023NEC]

It only takes air movement of about three mph across a surface to cover the 25% AIC temperature reduction used. At the time, several SOEE members were also CMP14 members. However, the NEC is not intended to be a design document and is rather conservative for the benefit of those who still use it as such.

 

[retirede]

Actually, in Division 2, you can just about ignore it. There aren’t supposed to be any ignitable materials in the first place. if you believe, there really might be some, you have a Division 1.

The actual ignition factor is Joules/sec energy transfer. That's why NFPA 497, Table 4.4.2 lists the Mimimum Ignition Energy (MIE) for many of the materials. Temperature is most relevant in static airflow cases.

When I was on the API Subcommittee on Electrical Equipment (SOEE), we did some tests on motors and discovered we could achieve at least an additional 100C above their “perceived” temperature rating to avoid autoignition as long as the motor’s fan was running. I say “perceived” because the effective motor temperature rating is based on its temperature rise at standard operating conditions; i.e., Starting a motor is not “normal” per the NEC. See Section 500.8(B)(2(5)[2023NEC]

It only takes air movement of about three mph across a surface to cover the 25% AIC temperature reduction used. At the time, several SOEE members were also CMP14 members. However, the NEC is not intended to be a design document and is rather conservative for the benefit of those who still use it as such.

You are correct - those were D1 applications. Sorry if I confused things.

 

[raytisch]

Actually, in Division 2, you can just about ignore it. There aren’t supposed to be any ignitable materials in the first place. if you believe, there really might be some, you have a Division 1.

The actual ignition factor is Joules/sec energy transfer. That's why NFPA 497, Table 4.4.2 lists the Mimimum Ignition Energy (MIE) for many of the materials. Temperature is most relevant in static airflow cases.

When I was on the API Subcommittee on Electrical Equipment (SOEE), we did some tests on motors and discovered we could achieve at least an additional 100C above their “perceived” temperature rating to avoid autoignition as long as the motor’s fan was running. I say “perceived” because the effective motor temperature rating is based on its temperature rise at standard operating conditions; i.e., Starting a motor is not “normal” per the NEC. See Section 500.8(B)(2(5)[2023NEC]

It only takes air movement of about three mph across a surface to cover the 25% AIC temperature reduction used. At the time, several SOEE members were also CMP14 members. However, the NEC is not intended to be a design document and is rather conservative for the benefit of those who still use it as such.

Bob, Thank you for your reply to my question. I appreciate the feedback as I work with the client and vendor to propose a solution that meets the applicable codes.

The ignitable material in question is jet fuel (kerosene). I'm not clear what you meant by 'Actually, in Division 2, you can just about ignore it.' The pipeline being insulated and heated is an asphalt line running alongside a jet fuel line. The run from land to the dock is about 600'. The jet fuel line has a flanged cover in one location and a screwed valve fitting at another. Per API RP 500, Figure 96, there is a Cl.1 Div.2 3' radius around both these possible leak points. This would be an abnormal situation. This makes a couple of very small portions (<3' in length) of the asphalt pipe run go through a Cl.1 Div.2 area. The rest of the run is general and would not have a temperature restriction.

Taking the feedback provided here, it appears I may be able to have the heat trace vendor make provisions that ensure the classified areas have limited cable sheath temperatures. This would incur additional costs for the extra HT passes required, thermal paste needed, and metal channels installed over the MIQ cables for these areas. These additional provisions would not be required for the remaining portions of the run.