Condensate Line Erosion

[Pulpboy]

I'm trying to prevent erosion in an elbow in our condensate line. I read an article of the National Board of Boiler and Pressure Vessel Inspectors about increasing plain carbon steel to a low chromium alloy.

Has anyone had any experience with erosion in the elbows of condensate lines and did they ever change to a different material other than carbon steel.

 

[Weldmedic]

Although Im not sure of the system designation, I was involved with a project in the turbine area at a nuclear plant where we replaced a large number of fittings (Over 100)with P5A (2.25%) CrMo.
Sizes included 6" and up to 18" I believe. This was in 1988.

 

[Metalguy]

IF your condensate line carries 2-phase (water & steam), then very small amounts of Cr will make a big difference.

First I'd remove a sliver of the elbow and find out how much Cr it has. There is a big diff. between erosion-corrosion (now simply called wear) rates for a Cr level of .02 and .10%.

Once you know what level of Cr you have, together with your wear rates, you can attempt to determine how much Cr you'll need.

You might get by with 1 1/4Cr (P11), or even a selected carbon steel that contains close to the max. allowable Cr.

 

[samuelliu]

The most erosion in condensate is caused by steam flashing out, and it maight be more importment that you try improve the process and/or system rather than upgrading the material, as many flashings could be avoidable or can be pushed to downstream of the elbow.

Regards,

 

[Pulpboy]

Thanks for the info everyone.

FYI my plan goes something like this:

I examined all the variables including Dissolved Oxygen,pH, temperature, pressure and flow and have conclude that I can't really change any of them so I'm looking into the velocity, geometry and materials.

The velocity could be changed by increasing the pipe size or the pipe geometry (elbow close to control valves) could be changed but for the space available it looks like a material change is probably my best bet.

Thanks.

 

[PVRV]

Where is the elbow located at ?
Condensate (LPG ?)

thanx

 

[MJCronin]

dosen,

I have piping replacement experience at a nuclear power plant with "flashing heater drains".The situation is similar to your elbow problem

This plant had problems over a number of years (17 total)with the feedwater heater drain piping going to the plant's main condenser. The 3 and 4" NPS piping was eroding away at the extrados of the downstream elbows.

After evaluating several possible soultions that involved material substitution, piping reconfiguration etc. The piping consultant recommended replacement of the Schedule 40 carbon steel system (ASTM A106 GradeB) with one of 2-1/4 Chrome- 1 Moly (ASTM A335-P22). This material substitution was recommended by several other power plants. For good measure, schedule 80 material was used.....

The consultant also evaluated and recommended 304L/316L piping as it also offered erosion resistance. In what are called "boiler blowdown" tanks at fossil fired plants, a 304SS insert is used to protect the tank interior from flashing flow.

The SS material was not selected for the piping system based on the additional cost over the P22...........

I recommend that you evaluate using threaded P22 or SS elbows.....in sched 80 if you can afford them. Periodically replace the elbows as they wear..

My opinions only

MJC