Seawater application
Seawater application
(OP)
Hi,
One of our contractors stated that for a Fire Water (seawater) system Stainless Steel may be specified (316L).
So far, I have never seen Fire Water systems specified in Stainless Steel.
Although the system temperature will not be that high (aprrox. 30 degr.C max), we believe that st.st. is not suitable. The system is filled but normally no flow.
Thanks in advance for any reply.
Regards.
One of our contractors stated that for a Fire Water (seawater) system Stainless Steel may be specified (316L).
So far, I have never seen Fire Water systems specified in Stainless Steel.
Although the system temperature will not be that high (aprrox. 30 degr.C max), we believe that st.st. is not suitable. The system is filled but normally no flow.
Thanks in advance for any reply.
Regards.





RE: Seawater application
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http://www.corrosionsource.com/handbook/CPS/
RE: Seawater application
When I left they were trying to get a ruling on using a Polyliner to rehabilitate some cement lined DI pipe.
RE: Seawater application
RE: Seawater application
Stagnant seawater water isn't good on low alloy SS. The O2 depletion and sediemnt combine to kill you. There are stainless grades that would work (AL-6XN), but at a price.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Seawater application
RE: Seawater application
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Seawater application
Dry system or wet?
Standby pressure (if a wet system)?
Operating pressure?
If dry, how often is the system wetted for testing, and with what?
Land based, ocean structure, or ocean vessel?
As a general recommendation, use a copper alloy such as 90-10 or 70-30 CuNi (these are the standard alloys for US Navy ships).
RE: Seawater application
GRP or GRE is a good solution, depending upon the media temperature ofcourse, if its buried line GRP?GRE is even better as it doesnt need protection from outside. Normal carbon steel piping with come internal coating such as glass flake etc. is a very good, proven and economical solution.
RE: Seawater application
Thank you all for your input sofar! The original spec is indeed based on GRE/GRP. But now 316(L) stainless steel seems to be the selected material despite the fact that we already advised not to do so.
The system is wet and operating on a pressure of 16 barg at temperature of approx. 25 degr.C, and is circulating to avoid algal growth. But the system do have death ends.
All recommendations based on industrial practice or common sence makes sence, CuNi 90/10, GRE etc..
I'm just a piping engineer,so do anybody having ideas how to convince client based on corrosion (scientific) explanations?
Thanks again in advance.
Regards.
RE: Seawater application
RE: Seawater application
CuNi tends to corrode uniformly at a very low rate, forming a weak passive film. Crevice corrosion, should it occur, will manifest itself on the OUTSIDE of the crevice as opposed to inside the crevice.
Stainless steel for a stronger passive film, but are prone to pitting and crevice corrosion. Pitting and crevice corrosion or localized corrosion, and will lead to failure much, much quicker than the corrosion you'll likely see on CuNi alloys.
RE: Seawater application
RE: Seawater application
As much as I love SS (it pays my bills) 90/10 is a much better option in stagnant seawater than 316.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Seawater application
Cu Ni 90/10 is good option for low velocities as the protective layer it forms is not so strong as in case of SS, in addition fabrication and maintenance is not so easy due to its poor weldeability, Cu-Ni fittings might be expensive for that working pressure.
On the other hand, GRP/GRE piping system has higher initial cost but very low operating cost due to minimum maintenance and longer life compared all other options.
RE: Seawater application
Again thank you all for your responses.
I have checked the site of Outokumpu, www.outokumpu.com, and found a corrosion handbook free of charge. It's an interesting site anyhow. I have received a copy and it provides a lot of usefull info, also related to this thread.
Thanks!
Regards.