Condensate Piping Corrosion
Condensate Piping Corrosion
(OP)
We use process steam that cannot have chemicals in it because it humidifies medical products, but condense about 80% of our steam. The black iron condensate lines either get eaten from the inside or plug up with rust. We've replaced short runs with stainless steel with some success, but I understand boiler inspectors (Michigan) frown on the use of stainless. Does anyone know specifically why? Any suggestions or background on the use of stainless or other corrosion abating schemes would be appreciated.





RE: Condensate Piping Corrosion
RE: Condensate Piping Corrosion
Regarding the use of stainless steel, talk to the inspector yourself about what's permitted, and what is not. The amount of mis-information floating around general industrial operations regarding piping codes is huge, bordering on total.
RE: Condensate Piping Corrosion
a) Oxigen is available. Check the deareator and the oxygen scavenger added (this may be used as non-volatile product). Check for leaks in your system specially in areas like HVAC's where the temperature setpoint is below 100 deg C. You may use pumping traps (spirax sarco) or ogden pumps. If you keep the system hot (under pressure) there were no vacuum.
b) CO2 is available. Check the makeup water quality. Perhaps is better to use demineralized water.
c) assure that the condensate is returned. if you control the conductivity and pH.
d) proper vents are needed in such a system
Eliminate the source of the problem rather than giving aspirin (stainless pipe) for a heart problem (corrosion).
MFG
RE: Condensate Piping Corrosion
Comments regarding deaerator, oxygen scavenger and make-up water quality may not directly apply to this system’s problem. No mention of boiler problems. Corrosion occurs in the condensate system, downstream of heated devices and upstream of deaerator. The system may contain chambers and devices which undergo frequent heatups and cooldowns; necessitating vacuum breakers which let in air. The steam traps would discharge slugs of both air and relatively cool condensate during initial heating. Further, the condensate drainage design may be a semi-open, gravity type. In this case, an SS condensate system is altogether appropriate for avoiding corrosion.
tcampbe1,
What are the operating steam and condensate line pressures?
Are there cyclic heating cycles?
What are the flow characteristics of the condensate system (open, semi-open, closed, gravity drain to receiver, vacuum pumped)?
Does “humidifies medical products” mean addition of moisture into absorbent materials or perhaps sterilization?
Finally, is there any way chloride could attack either the inside (enter the condensate from the medical operations) or the outside of piping (e.g., soggy insulation)?
Ken
RE: Condensate Piping Corrosion
can you describe the condensate and Boiler water conditions (pH, conductivity, iron content,oxygen content)?
kenvlach,
I think that a condensate system without vapor conditioning (volatile treatment) may be better when is closed, if technically possible. Due to the lack of detailed information, is very difficult to give a definitive answer. Only Tcampbe1 can evaluate this.
RGS
RE: Condensate Piping Corrosion
I can suggest some options as we have supplied in the pass "clean steam generators" for the industry.
Most of the clean steamers/boilers use DI water and it is corrosive and in some cases you are allowed stainless piping, or you must use stainless piping.
Please post the info and I will find out for you.,
if you need info, I can also send it to your email box.
ER
RE: Condensate Piping Corrosion
Mike
RE: Condensate Piping Corrosion
I'm aware that in theory, galvanic corrosion should be an issue when mixing stainless and carbon steel pipe. In practice, I've never actually encountered a problem with it in this type of system. However, copper return lines can be a HUGE problem. Not always, but sometimes. The copper, in and of itself won't cause problems. However, if some other factor (like some serious carry-over from the boiler) is added to the mix, copper can be pulled-off the pipe walls, and carried back to the boiler by the condensate. There, it will plate out and set up a cell. The resulting corrosion damage can look very much like oxygen pitting.
RE: Condensate Piping Corrosion
Then the generator has to run on DI water to avoid pitting and
cracking of the stainless.
If clean steam is needed, you can not use c/s.
ER
RE: Condensate Piping Corrosion
I can suggest some options as we have supplied in the pass "clean steam generators" for the industry.
Most of the clean steamers/boilers use DI water and it is corrosive and in some cases you are allowed stainless piping, or you must use stainless piping.
Please post the info and I will find out for you.
ER
RE: Condensate Piping Corrosion
One other area we use S/S condensate lines form a 300# steam system that flashes to a 60# steam system to ensure steam purity due to process considerations. In conjunction with S/S condensate lines we use S/S Steam Purifiers to do a final polish on the 60# steam (S/S) prior to use at 15# through S/S lines.
We have never had a internal problem with SCC from the steam side. The few problems with SCC have come from wet insulation (older) and this was on lines that cycle which tend to concentrate the chlorides on the hot surface.
We also tend to use S/S sections at branch connections in C/S condensate lines where the condensate comes from a large HEs’. There have been no galvanic problems in such a system.
The biggest problem we had was CO2 in a large 300# saturated steam distribution system. This did a number on the header and condensate lines as the corrosion product was a mill type scale at 98% density of iron. We knew we had gotten a lot of CO2 into the system but RT didn’t show any damage, we didn’t find it until the header blew.
If you need clean steam 100% of the time S/S is the only way to go. I have never seen a code or specification that prohibits S/S in steam if you want to pay the freight.
RE: Condensate Piping Corrosion
Regards to Piping Classification Specification for condensate using S/S.
What material table group in ASME B16.5-2003 will you be using.
Leonard@thill.biz
www.thill.biz
RE: Condensate Piping Corrosion
I don't have the new ASME 16.5-2003. I will check around next week and see if anyone has the new 16.5 that I can get to and see what you are inferring.
I'm retired and prior to retirement I gave all my newer codes and specifications to some up and coming engineers so all my references are somewhat aged.
RE: Condensate Piping Corrosion
Thanks for all the helpful advice.
We have 2 Burnham E-50 1347 MBH steam boilers on alternate cycle. Steam pressure is 10 - 12 psi.
The galvanic aspect of stainless steel pipe might be superfluous since the steam is used on stainless steel chambers, four of them, about the size of a shipping container. Would dielectric couplers be a possibility?
The boilers are treated and monitored but I'll need to wait a few days to get the analysis. There are no volitiles in the treatment as I mentioned earlier.
The system is vented to atmosphere after the steam traps. There is a pumped condensate return tank by the chambers and a feedwater tank and pump in the boiler room.
Steam used for humidification is not returned to the system.
RE: Condensate Piping Corrosion
Here is a very interesting site. It's a little hard to navigate and a lot is still in German but the pictures are outstanding.
http://www.metallograf.de/start-eng.htm