## thermal relief flowrate of steam traced pipe blocked in

## thermal relief flowrate of steam traced pipe blocked in

(OP)

Hi

I'm going to define an overpressure protection device for a steam traced & insulated pipe-line.

How can calculate or estimate the heat-trasfer coefficient U or the max thermal flux to the fluid?

There is a short-cut method?

Tx very much

Main data:

fluid heavy oil

normal temperature of fluid 70°C

steam satur. temperature 150°C

case: pipeline blocked in

I'm going to define an overpressure protection device for a steam traced & insulated pipe-line.

How can calculate or estimate the heat-trasfer coefficient U or the max thermal flux to the fluid?

There is a short-cut method?

Tx very much

Main data:

fluid heavy oil

normal temperature of fluid 70°C

steam satur. temperature 150°C

case: pipeline blocked in

## RE: thermal relief flowrate of steam traced pipe blocked in

This is the maximum steam flow so heat gain cannot be higher than that. It can only diminish as the blocked-in fluid temperature increases by time.

Pressure rise due to heat gain in liquid-full systems occurs much faster than in gas-filled or gas-liquid systems. So the TRV will open much before the maximum fluid temperature is reached (150 degC in this case). There is no reason to consider the maximum steam temperature as relieving temperature of the fluid.

Dejan IVANOVIC

Process Engineer, MSChE

## RE: thermal relief flowrate of steam traced pipe blocked in

You can calculate how much a D orifice (or whatever orifice size you are using) PSV flows for your fluid and set pressure. Then go back and compare this to the calculated flow you need for the heat input following the method suggested by Dejan. My experience is that typically the capacity of the PSV is orders of magnitude greater than the calculated flow rate. Granted, there are exceptions but you need a lot of heat input to exceed the nominal capacity of a D orifice PSV set at even 100 psig. For most cases, I don't even bother calculating a flow rate, I just use a nominal capacity of 0.5 gpm and fill in the data sheet. Now, for those systems where there is a significant heat input and a significant flow rate of fluid has to be relieved, that calls for a deeper evaluation to ensure my PSV is large enough.

## RE: thermal relief flowrate of steam traced pipe blocked in

TRV exit backpressure should be taken into account when selecting the type of TRV. TRV inlet and exit lines should also be insulated where required.

## RE: thermal relief flowrate of steam traced pipe blocked in

It is a very easy method even if not rigorous.

Below my calc

300 mm pipe od

100 mm insulation tk

min ambient T -7°C

DT (product - ambient) 70+7 = 77 ~100°C, max heat loss from pag 5 table 1: 75 W/m

DT (product - ambient) 100+7 = 107 ~125°C, max heat loss from pag 5 table 1: 94 W/m (to take in account a middle temperature

heat transfered to fluid =~ max heat loss

## RE: thermal relief flowrate of steam traced pipe blocked in

If you like to play with steam tracing calculations, attached is a free spreadsheet from ChE Resources (make sure you have the Solver add-in installed in Excel). Below is the link to Thermon software (free).

http://thermon.com/software/computracest.aspx

Dejan IVANOVIC

Process Engineer, MSChE