Covering of thermodynamic steam trap when it rains

[1906]

Recently, our refinery have experienced higher steam consuming when it rains and ,we think, one possible reason will be performance loss of steam trap by higher heat loss on the surface(most of our traps are thermodynamic type). In other words, vapor pressure on top of the trap disk will be condensed by cold rain and it will not trap condensate properly. Finally steam loss. Above is the logic we thought, so now we are considering covering of steam trap. Re this matter please comment on following question if you have good explanation.

a) Does the covering of steam trap(esp. thermodynamic
type) is common practice ?
b) If it is common pactice, how do you usually covering
steam trap ?
c) If you cover steam trap, how do you usually evaluate
the performance of steam trap cover ?
d) Any other method, improve steam trap performance loss
when it rain ?
your comment would be highly appreciated.

 

[quark]

Spirax has insulated TD traps, i.e the disc cover is insulated. I once used these kind of traps for open area condensate lines. The rough method is to collect condensate and check the performance before and after insulation.

Also check for correct insulation thickness of steam piping. There may be more condensate formation. Also check the possibility of gaps between two insulation lengths.

 

[quark]

For example see item no. 14 in the exploded view on page no.2 of the document below.

http://www.spiraxsarco.com/assets/uploads/PDFS/TI/P614_03.PDF

 

[learner08]

TD traps are usually not recommended for outdoor application. However, if for one reason or another a TD trap needs to be installed in an outdoor application, the control chamber needs to be protected/insulated.

TLV manufacturers TD traps which comes readily with insulated control chamber.

 

[25362]

On the other hand if the non-insulated traps are then thermally insulated, it may result in a situation, especially in summertime, of not allowing the flash steam to condense more readily, holding down the disc, not allowing sufficient condensate to pass.

Provided the heat transfer is caused by ambient temperatures, such as at night, or in winter, the cycles may become more frequent owing to the additional heat loss. However, this may actually compensate for the added heat load that the trapped unit would realize.

I fully adhere to quark's recommendations on measuring the amount of condensate before and after insulation.

 

[Joesteam]

The TD trap has a vapor pressure on top of the disc that keeps it in the closed position. When this vapor condenses or leaks under the seat the pressure drops and the trap opens. The trap will remain open untill all of the condensate drains, more vapor will delvelop on top of the disc, and the trap will close again.

When it rains, sure enought, the trap cycles much quicker because the rain is condensing the vapor on top of the disc. This will not only use a bit of steam but also shorten the life of the TD trap.

Most manufacturers of TD's know this. They make newer pre-insulated caps on the TD's, and they control the cyclcing not by a loss of heat from the top but rather the finish on the disc itself to allow a small leakage and the trap will cycle.

For older traps, they make these little metal covers - a 'rain hat' that will prevent this short cycling. In my experience, these do work, however they do NOT last long - either getting blown away or not replaced during a repair or trap checking cycle.

As for the trap operation, they will make the trap cycle less frequently, but once the trap does cycle open, it will drain all the condensate present. TD traps are always beholden to this on/off cycle, in which the opening of the trap is not tied to the amount of condensate that may be present.

For this reason, I have always preferred thermostatic traps on drip and tracer lines installed outside....