wet steam destroys 'impingement' plate 1

[rsauk]

Several exchangers are having tube failures due to 'wet steam'eroding impingement plates and consequently tube failure follows.

The steam inlet nozzle is 4"nb and is therefore very difficult to repair impingement plate.

Is it possible to fit a 'diffuser' within the nozzle.
If so,does a design exist.

 

[TBP]

I would focus more on addressing the root cause of why this is happening, rather than designing something to deal with the symptoms. There should NOT be "wet steam" in your system.

I'm assuming that there's a temperature control valve on the steam supply to each heat exchanger. Is there a trap on the steam line just ahead of this control valve? If there isn't then any time the control valve is closed, condensate will collect ahead of it. When the HX goes into service, the first thing that happens is that all of this water gets shot into it as the valve opens. I've seen HX bundles that look like they've been beaten with a hammer, right under the steam inlet because of no trap ahead of the control valve.

 

[davefitz]

I don't think a diffuser in the nozzle will have any effect on the flow distribution within the vessel. It is probably a good idea to take fiedl data and determine if there are operating conditions that are way outside of teh original design rating of the device. Operaing at a higher duyt or lower shell pressure will cause much higer velocities than full load design case. Also, the steam inlet enthalpy may be lower than design, so the erosion baffle was not correctly designed for the actual flow.

 

[steam4]

I agree with TBP. And to go one step further, we usually recommend to put that steam trap on the blowdown connection of the strainer before the control valve. This will keep the strainer belly dry and prevent this water from blasting thru the control valve.

 

[abcmex]

I agree with TBP too. I would like to add some comments:
The steam trap should be before the isolation valve to keep the steam line hot and dry. The control valve should be protected with a strainer as STEAM4 mentioned and the strainer should be installed horizontally to avoid that condensate can be collected. The isolation valve should be located before the strainer and the control valve to allow maintenance.
Review additionally if you have enough traps and if they are big enough on the steam line going to this equipment to remove the condensate of the system.
If you suspect that even after doing all possible steps (treating the root of the problem first) you still have condensate, then use a steam separator. with this you will be able to change the eroded impingment plates (last ditch effort).
I would recommend you to consult technical information of Spirax Sarco (

http://www.spiraxsarco.com).

 

[jmw]

If you want to know what wet steam can do, ask Solartron Mobrey to show you their picture of a power station where the turbine was destroyed by a water drop in the steam... and not just the turbine, the whole plant was totally destroyed. Why Solartron? they have a device called Hydrastep which detects water in steam and is a vital protective device for power stations. You may find it useful too.

http://www.solartronmobrey.com