I've got a question that may have been answered in previous threads but didnt quickly find.
I just started a new thermal imaging survey of steam traps on our Site heating distribution system.
The traps are Yarway thermodynamic disc type. Many are located up above (~20') in the distributin header. ALL of the traps were replaced during the summer so I will assume for a moment they are working properly.
Post review shows ~ 50% of the traps to have a large delta T (>30 deg F) across trap. ~20% had smaller delta T (~15 deg F) and the remaining had delta T's of a few degrees or so.
This got me thinking that since the trap is designed to occassionally pass hot condensate, then unless the thermographer is viewing it realtime for several minutes, it may be difficult assess trap condition on a single point-in-time image.
Is my thinking wrong? Would it be better to view live image for a period of time?

Thanks
Jim P

There was a discussion here:

Steam Trap Discussion

I would say that steam traps are fairly simple to assess condition... live analysis is not necessary. You just need to understand the system parameters and the temperature measurement method.

Jamie
Thanks, but I did follow that topic before I posted and still not sure it answers the question.
Suppose I take an IR just prior to hot condensate being processed and then just following the event. Would I not see two very different delta temps across the valve body?? If so, how do the charts take that into account?

Jim P.

For the applications that I am familiar with, the steam traps operate on a fairly consistent basis - passing condensate every ~ 10 seconds or so...

This leads to relatively consistent inlet and outlet temperatures, based on the system pressures and ambient losses - unless there is some increased demand on the trap (startup, other transient).

Variances in temperature that I am familiar with are typically associated with clogged strainers, trap blowing by, or plant transients - also early on in our monitoring program, we found many 'mud legs' completely filled with corrosion products, thus blocking the inlet to the trap.

There should be an expected temperature range, based on the system operating pressure, fairly close to saturation temperature for the trap inlet pressure, and an outlet temperature range that should be a little below the saturation temperature of the trap outlet pressure. The temperature range should be revised as normal ranges are derived over several inspection intervals.

quote:

thermodynamic disc type

Hello,
I figure some possible explanations to the different behaviour of your steam traps:
- Does your steam traps all work with the same inlet steam conditions (pressure)?
- Some off the traps could receive more condensate than others. Normally because of main piping heat loose, but also due to heat loose in the pipe which goes to the steam trap (are these small pipes insulated? How long do they are?). So condensate flow can be different in the different traps.
- Although thermodynamic traps works discontinuously, the metal thermal inertia uses to be big, so temperature differences in the outer part of the trap could not reflects the discontinuity in condensate flow.
We have some of these (Gestra) for low pressure (6 bar) steam pipes, without condensate recovery. Condensate is expelled with frequencies of 1 pulse every 3...10 seconds, I believe that is difficult to see the condensate flow though the pipe temperature changes.
Hope this can help you.

PD: Why did you change them?

Thanks guys for the information.

I discussed with the engineer who simply stated they wanted to take the opportunity in the summer months to replace them all at once...to start fresh with new. Apparantly, there has been problems with leak by and corrosion but couldnt get any more infomration than that. This was the first time I was asked to thermally image the traps - for baseline.

At the time I took baseline images, the lines were not yet fully lagged so thought it was good time to perform. But this was only a few weeks ago and obviously there was little steam load so maybe I need to re-perform during colder weather.
If I find significantly different results, I will report back

Again, thanks for the input

Jim P

Jorge is correct with his points. I have found many disc traps that show no or very little delta-t from the condensate to discharge side and yet found them to be operating normal. Basically the entire thing looks hot. This was due to the high-pressure steam resulting in very little condensate build up. This meant that the trap took a very long time to discharge as it took a long time to build condensate.

Steam traps, even disc traps should be inspected with both IR and Ultrasound. Using a thermal imager is nice and helps, but you can also perform a good survey with a point radiometer (IR Gun). But listening to the trap is important to verify it is operating properly. With UT you will be able to tell if the hot traps with no Delta-T are not failed in the open position.

Also since the hot traps can take very long to discharge (I have found myself waiting sometimes 5 or even 10 minutes just because the HP steam trap has not built up enough condensate to discharge) a nice trick to speed up this process so that you can hear the discharge with UT is pour some water over the trap. This will cause condensate to build up quickly and you will be able to verify if the trap discharges and closes back.

I do have some nice video of thermography and ultrasound on disc traps on my web site:

http://www.tdlir.com/show005.html

Hope this helps.

Sonny James
NDE Institute of Trinidad Ltd.
www.learnndt.com