thePetroStreet

Dear sirs,

We have a 36" dia CS piping with insulation + steam tracing. The piping is internally aluminized. Following is the details:

MoC: A672 C60 Cl 12, internally aluminized

Size: 36" x 7.92 mm thk

Service: Acid gases (sulfur rich)

Operating Conditions: Pressure- 0.6 kg/cm2, Temp- cyclic - 130 to 343 deg C.

Insulatuion: Yes - 115 mm thk

Steam Tracing: Yes LP steam - through 4 nos of 0.5" dia SS tubing at 90 degrees apart.

Minimum temp to be maintained: 120 deg C.

Now, because of severe blistering in aluminized coating due to cyclic temp and acid gases, it has been proposed to change this piping from CS to SS304L.

It has been decided to use the same steam tracing tubings for new SS lines.

My question is:

since heat conductivity of SS is almost half than that of CS,

(1) can the same nos (04) of steam tracing lines will be enough? or
(2) no of steam tracing lines have to be increased?

I have read somewhere that the steam tracings are provided just to compensate for any heat loss occurs because of any damage in insulation. Hence, as far as insulation is wrapped and mounted properly and there is no damage, then there is no need to redesign the steam tracing system while we are upgrading MoC of parent pipe with same size.

Request to do the needful,

Thanks and Regards,

Steam tracing requirement does not really depend upon the material of construction and its thermal conductivity. It depends mainly on the process temperature to be maintained, the piping diameter, ambient temperature and the insulation.
As soon as all the above factors stays the same, there would not be any need of re-designing the system.
You can proceed with the material change of service piping without making any modification in steam tracers. If they were working well with CS they would do equally good with SS.

Thanks for quick response....

Steam tracing desinging depends upon the temperature you want to maintain in working fluid. This can be jusitified by considering the factors involved in the heat conduction. By the simple formula, These are thermal conductivity, Area of contact, Temperature gradient, and wall thsickness of piping and tubing. Now in this case, thermal conductivity of CS is 47 k - (W/mK) in contrast to SS 19 k - (W/mK). Wall thickness is same. Area is same. Temperature gradient is same. I agree with arcpro that thermal conductivity wont bother you and keeping all the factors your system would go fine.

Trace tubing is already SS so no chance of dissimilar metal contact i mean corrosion. Further, SS is the recommended material for steam tracing in all the cases so it will serve its purpose independent of pipe material. But please consider these

Stainless steel tubing tracers should be type 316 seamless cold drawn and fully annealed with a maximum Rockwell hardness of RB80 and meet or exceed ASTM Standard A269. Minimum wall thickness shall be as follows:
3/8" O.D. x .032" wall (10 mm O.D. x 1 mm wall)
1/2" O.D. x .035" wall (12 mm O.D. x 1 mm wall)
3/4" O.D. x .049" wall (20 mm O.D. x 1.2 mm wall)

Stainless steel tubing should be used if the saturated steam pressure or the item being traced has a maximum temperature above 400°F (204°C) and there is no corrosion or other deterrent for using stainless steel.


Basis for a Good Design . . . Thermon Guide Book on Steam Tracing

Every steam tracing design will involve six design factors of
which three are given (fixed) and three are variable. The given
factors are: nominal pipe size, desired maintain temperature
and low ambient temperature. The variable factors are: tracer
type, size and number; steam pressure (temperature); and insulation
type and thickness. Establishing a balance amongst the
variable factors will provide maintain temperatures within the
desired range. Conversely, should any of the variable factors
deviate, the balance will be upset and the temperature could be
outside of the desired range.

Just to be consider with my previous reply

Nice explanation Usman.

Excellent presentation, dear Usman sir. Great...