accelerated flow corrosion

[mech6tav]

our condesate minuim flow recirc piping back to the condenser is a 4 inch sch.80 carbon pipe reduced to an 2 inch sch. 80 carbon pipe then back to 4 inch to the condenser. we are having problems with re occuring accelerated flow corrosion,original installation utilized an eccentric reducer. we have tried concentric reducers,
and other remedies to no avail,the reducers are 12 inches before the first 90 should we replace the 2
inch configuration to straight 4 inch ? need some remedie that will last longer than 6 mo. to 18mo.
condesate pump pressures around 350 psi. coming off 8 inch main pipe.there is vaccum pulled on the steam turbine condenser.
any recommendations greatly appreciated

 

[stanweld]

You can change metallurgy of the pipe (to P11) in the area affected or purchase carbon steel pipe with a Cr equivalent > 0.15, somewhat harder to do but not impossible.

 

[hacksaw]

well if your 4" line is sized for 10 ft/s, and assuming that the condensate is not flashing, then the 2" reduced section is seeing 40 ft/s flows at a minimum.

are you using a recirculation valve or an restriction orifice?

 

[rmw]

In a similar application I had flashing big time (at an orifice). Where is the pressure drop taken and have you totally ruled out flashing?

rmw

 

[mech6tav]

THER IS CURRENTLY AN CONTROL VALVE IN THIS SYSTEM . I WOULD SAY THAT THE CONDENSATE IS FLASHING OFF, THE WEAR WE ARE SEEING LOOKS LIKE CAVITATIONAL WEAR

 

[MJCronin]

mech,

Cavitation....wouldn't you expect this to occur in this type of system..!!!

If you rename your pump "boiler feed pump" and GOOGLE recirc and "boiler feed pump" you can learn a lot.....

You could just buy one of these:

http://www.cuservices.net/pdf_files/Brochure_C500.pdf

or these:

http://www.cuservices.net/pdf_files/CU_Info_Sheet.pdf

or these:

http://www.ccivalve.com/pdf/205.pdf

or these:

http://www.pharmpro.com/ShowPR.aspx...YPE=WN&PRODCODE=2910&PRODLETT=A&CommonCount=0

or these:

http://www.spxprocessequipment.com/sites/dezurik/AppData_PDF/250_01_1.pdf

Where are you located and where is the plant ???

-MJC

 

[mech6tav]

yes sir i would expect to see this kind of wear at this point , what would be the better solution keep the pipe the same size all the way to the condenser ,or install a diffuser as described in the information that was recomended. i am in ms. as is the plant ,we are a combine cycle power generation plant

 

[stgrme]

There is no doubt that flashing will occur in your system. I presume that the control valve is installed between the two reducers (a 2-inch valve) and I suspect that flashing takes place downstream of the valve. If this is the case, you need to address the piping downstream of the valve to minimize the effects of flashing.

The amount of piping downstream of the valve should be minimized. Locate the valve as close to the condenser as possible.

To increase wear resistance, change the material of the downstream piping to P22. I also suggest Schedule 80 for additional wall thickness.

To reduce velocity, make the downstream piping one or two sizes larger than the 4-inch piping upstream of the valve, i.e., downstream piping should be 6-inch or 8-inch. This means that the connection at the condenser needs to be increased to the same size as the downstream piping. A long diffuser rather than a standard pipe reducer will avoid abrupt changes in velocity. Mount the diffuser directly at the discharge from the valve.

Please note that adding another pressure-reducing device downstream of the control valve may restrict the valve's capacity. I would not recommend installing such a device unless you have analyzed the entire recirc line.

Best of luck,

 

[mech6tav]

the configuration you described is correct, all of the flashing is ocurring inside the discharge of the valve, deteriating the valve body and the first half of the reducer.would increasing the valve size to 4''and eliminating the reducers all together be an fesable option?
we have not had to replace a valve yet but it is not far away.

 

[stgrme]

Even if you increase the valve to 4-inch you need to make the downstream piping larger as I noted above. The specific volume downstream of the valve will increase dramatically.

You say that the valve body is deteriorating. If the body is carbon steel, you will need to change the material of the valve body to an alloy steel (P22) like the downstream piping.

You need a "severe service" valve with a torturous flow path or with multi-stage pressure reduction like the ones shown in the links from MJCronin above. Another alternative is a "severe service" valve and separate pressure-reducing device, like those from CU Services (links also from MJCronin above), located downstream of the valve.

I suggest working with a manufacturer (Fisher, CCI, DeZurik, Copes-Vulcan, etc.) to define a replacement for the existing control valve with or without a separate pressure-reducing device downstream.

Good luck!

 

[mech6tav]

thank,s for all the help and useful information
greatly appreciated

 

[MJCronin]

mech....

Where are you located and where is the plant ???

-MJC

 

[mech6tav]

I AM LOCATED AT THE PLANT IN CALEDONIA, MISSISSIPPI
THANKS FOR THE INFORMATION YOU SUGGESTED

 

[chief]

Consider fitting a Gem type steam trap, no moving parts and high efficiency with 10 year warranty

Offshore Engineering&Design

 

[rmw]

If it is condensate recirc, can you locate the valve right up next to the condenser? That will allow the flashing to occur as it enters the condenser. And if you can, be sure to put a baffle inside the condenser where the condensate recirc return enters if there is not one (whether or not you can relocate the control valve). If there is already one, beef it up. Make it stout. Let Bubba do it.

rmw

PS: mech-are you having a little trouble with that caps key?

PPS: and mech, remember one more thing. A young engineer at a combined cycle not far from you over in Arkansas once reminded me that I had to keep in mind that those plants (your generation of combined cycle plant) were the best plant low bid could buy. Plan to spend some money implementing the type fixes recommended above (better metallurgy control valves and piping) in your plant to bring it up to the standards to which it should have been built in the first place. I never did visit your plant, but I did get to Southhaven and Sterlington, so I am familiar with what you have to start with. Sad in some cases.

 

[mech6tav]

what you saw at southhaven & sterlington is exactly what we have ,other than minor difference,s.
we have decided to try something very similiar to what you suggested.we are going to replace the 4''- 2''reducers and 2''valve to 4inch .put 1 4''- 2'' reducer close to the condenser as possible and run 2'' pipe inside the condenser with a baffle plate welded to the condenser wall or floor.hopefully this will help put an end to welding in new reducers every 6-8 months.


not very computer savy sorry about the caps lock deal


just a mech. trying to make it

appreciate the reply,s and information it has been very helpful in making a decision as what to do with this problem.

 

[stgrme]

I respectfully submit that a 4-inch by 2-inch reducer downstream of the control valve is not the way to go.

As I noted above, increase the size of the pipe downstream of the control valve to 6-inch or 8-inch, and use a diffuser between the control valve and the downstream piping. This also means increasing the size of the connection on the condenser to 6-inch or 8-inch.

Installing a 4-inch by 2-inch reducer downstream of the control valve increases the velocity in the pipe and may restrict the control valve's capacity. Also, there should not be a run of piping inside the condenser. The baffle should be located at the inside of the nozzle on the wall of the condenser. See HEI Standards for Steam Surface Condensers for guidelines on connections and baffle specing (escape area).