Steam Pressure for Tracing

[owg]

For a South Ontario, Canada location, is there an advantage using say 150 psig steam versus 50 psig steam? 150 psig costs more but may be less likely to freeze. What is the role of the quality of the steam?

HAZOP at

http://www.curryhydrocarbons.ca

 

[NiravK]

In addition to cost of 150 Psig Steam, you also need to consider the cost of piping for 150 Psig Steam. The higher pound rating of materials.
Also, it will be difficult to execute steam tracing with IBR rating pipe for 150 Psig steam.
I mean to say the bends you need to provide for tracing around valves, elbows will be difficult for execution.
Generally, it is easier for lower rating pipes to heat and bend according to the requirement around valves and bends.

How much the advantage would be as far as heat is concerned? Saturation temp for 50 psig & 150 psig steam would be around 145 deg C and 180 deg c respectively. I don't find much difference.

regards,

 

[owg]

Thanks nirav2909 these are good points. Is it your position that there would be negligible additional resistance to freeze-up due to plugging, trap malfunctions, missing insulation, dead points, short term header outages, and the like?

HAZOP at

http://www.curryhydrocarbons.ca

 

[NiravK]

I do not have experience of working in the cold conditions what you are referring to.
However,if insulatinos are proper, why would the steam or condensate freeze which is above 140 deg C? is it too much of heat loss due to cold climate?
regards,
nirav

 

[kmpillai]

In addition to the above points, in the low pressure steam latent heat is more. So I prefer the low pressure steam.

 

[owg]

nirav2909 - If insulation is OK, then there is no problem. However insulation is removed for maintenance and sometimes not immediately replaced or replaced improperly.

kmpillai - This is one of the points we are wondering about. Inspite of the lower latent heat for higher pressure steam, would the total heat loss be the important issue. Starting from say 150 psig sat steam, don't you have to lose more heat to get to 32 deg F liquid than with 50 psig sat steam?

HAZOP at

http://www.curryhydrocarbons.ca

 

[Arcticdesert]

OWG,

What sort of temperatures is your plant opperating in? Do you have much wind when the temperatures are cold?

We use 150# steam for just utility and stripping. We see temperatures as low as -65ºF. All heat tracing is Propylene Glycol.

The our plant was originaly steam traced, but some of that froze resulting in a broken pipe and the plant burned down the first year winter. (bad times)

If your temperatures and wind are not to cold, steam works fine. Steam traps and insulation are someting the opperators will need to watch closely on their rounds.

Keep your stick on the Ice!
ArcticDesert

 

[owg]

We don't see much below -10 deg F, and we would not expect much wind at that low temperature.

HAZOP at

http://www.curryhydrocarbons.ca

 

[TD2K]

Freezing problems with your steam tracing are going to be related either to insulation problems (missing, wet or poorly installed sections) or most likely, traps that aren't working.

I've seen steam tracing specifications allow for both 50 and 200 psig steam tracing in the same plant and they had temperatures as low as or lower than what you are looking at. The choice between the two levels was based on what was available in the area and what temperatures you needed to maintain. In many cases, either will give you the same temperature though you may need larger/more tracers with 50 psig steam. 150 psig steam will also allow you to run longer lengths of tracers as well as have more vertical lift(s) allowed depending what pressure your collection system(s) run at.

I wouldn't automatically go with 150 psig steam just to avoid freezing concerns although the cost premium for 150 psig versus 50 psig may be fairly small. Piping and tubing are likely to be the same (if you use copper tubing, you might need higher wall thicknesses). Small welded or threaded valves are likely to be class 800 so that's not a change. Even flanged valves for 150 psig steam are likely still class 150 depending on your design conditions and/or piping specifications.

If 50 psig steam is in excess (and is more likely IMO to be in excess than 150 psig steam), that may be a major reason to use it for tracing purposes.

 

[RogerH]

Owg and others
I would state that the pressure range chosen for steam tracing is normally governed by the temperature needed, i.e. is more applicable for process required steam tracing and not really for winterisation steam tracing, i.e. to avoid freezing.
But in older plants some critical (winterisation) tracing is sometimes changed to a higher pressure due to problems getting the tracing to work. E.g. in offsites installations with long distances there might be a sound justification for using a higher pressure.
In cases where the condensate backpressure gives problems this is (higher pressuer) unfortenately a solution that is commonly used. It will solve the problem for the problematic part but can/will give a site wide problem with other parts of the steam tracing network.
Roger

 

[Keithbowers]

Return of condensate is much more difficult with low pressure steam. Freeze ups are much more likely with 50# steam for this reason.

 

[MikeONeill]

I'd advocate 75-100psi pressure if substantial backpressures are not an issue. The abilty to use as much latent heat as possible, without freezing, is desireable. If your traps are working properly, freezing won't be an issue at 75#.