Seawater Piping Materials Evaluation 3

[ATSMech]

I am working on a materials evaluation and life cycle cost analysis for a project. I have read a fair amount of the threads on the subject, and I have done enough research to thoroughly think myself in circles. I would like to get some opinions regarding my current options.

Conditions:
Dry Dock Dewatering / Drainage Systems - potential for long periods of stagnation (ex. dewatering system runs roughly once a year depending on ship maintenance timeline)
Located on a historically polluted river (lots of shipyard & industrial work).
Water Quality: no tests on file, but extrapolating from average salinity maps I am looking at a chloride concentration of roughly 12,000 ppm.
Water temp: max summer surface temp is 86F(30C).
Max flow through the system will be around 12 fps.
Life Span: 50 years (span of the LCCA not necessarily of the systems)
Pipe sizes: 6", 8", 14", 20", 24", 54"

Materials Considered:
Cement Lined Ductile Iron (w/ or w/o cathodic protection (CP))
316L SS (w/ or w/o CP)
2205 Duplex
2507 or Zeron100 SDSS

Questions:
1.) Has anyone crunched the numbers between materials like these to get a gut feel for the best choice? I am currently leaning towards Duplex or Super Duplex for the 24" and under and going concrete lined DI for the 54".
2.) I have read about PREN values and the issues with crevice / pitting corrosion, but is there anyway to extrapolate that resistance to an expected service life? I am a design engineer now but was an API certified inspector in my last career, and I know that just because you have initiated corrosion doesn't mean that the material is at the end of life. It seams like most articles talk purely about resistance to the initiation of corrosion.
3.) In general, is going down the road of cathodic protection worth it compared to alloy selection? In other words, is it worth while for me consider given the conditions of the project? I am leary of complicating the system and adding required maintenance tasks that may or may not get performed.

Materials like HPDE and GRP are in the back of my mind as well, but I am not as familiar with the joining and installation methods.

Thank you in advance.

 

[EdStainless]

I am a stainless guy, but GRP sounds like a better bet to me for the smaller lines.
Lined DI for larger ones is also a good call.
With stainless once pitting initiates it will continue, there is no stopping it.
>99% of your surface may be fine, but the pits will continue until they are through the wall.
I also have to presume that over the next 40 years the salinity of the water will increase.
The only alloys that will handle this are super duplex and superaustenitic grades.
The problem with SS is that there will be no biological control. The effects of biofouling and stagnant brackish water bode poorly for SS.

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P.E. Metallurgy, Plymouth Tube

 

[SJones]

The aversion to CP is correct - it will add a whole suite of design, monitoring and maintenance activities. Apart from that, it's not of the highest reliability for internal surfaces of piping systems. There are in depth standards for GRP and HDPE piping systems that will address joining: ISO 14692 for GRP; AWWA M55 for PE. The key will be finding designers and installers who know what they are doing with the materials.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[ATSMech]

Thank you both for your responses. This has helped validate the conclusions I was starting to come to.

On another note, I have read a number of your other posts on similar topics, and I wanted to thank you both for your commitment to a forum like this. It is a great resource.

-Aaron

 

[LittleInch]

Those posts echo my thoughts.

At that low a pressure and temperature a metallic solution will either be prone to potential pitting or attack or super expensive and difficult to weld in that sort of location.

Go for something inert and simple.

HDPE or UHMWPE or GRE.

Beware GREs tendency to get damaged very easily in construction and not show it for a few years or become abraded.

PE is the easiest material to joint and install but can be temperature and pressure limited and can creep.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[blacksmith37]

GRP and other polymers where service conditions will permit I can't be specific but Amoco got DNV to accept GRP for fire water lines for platforms .

 

[LittleInch]

Aluminium Bronze is also used for seawater if you need a metallic option, but again isn't cheap, but I think cheaper than super duplex

http://copperalliance.org.uk/docs/l...aluminium-bronze-corrosion-resistance-pdf.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ATSMech]

Thank you for the replies.

The more I look into it, the more I am leaning towards GRP. I like the idea of being able to spec different resin systems, as my pump suction diameter will be limited and may run around 15 fps. Given its a dry dock application we are designing around the expectation of sandblast material in the drainage water and being able to spec a more abrasion resistant resin system is a plus.

Regarding Aluminum Bronze, NAB is on the short list for our valve and pump case materials; however, I am concerned about the water quality (hydrogen sulfide pollution), sandblast grit, and the stagnant periods.

As a side note, the owner's design criteria for the dry dock is written around gate valves, and in my research so far for 54" valves, it appears that I am stuck with an AWWA type gate valve with a fusion bonded epoxy coating and coated DI wedge. We are working on putting together a case for butterfly valves (resilient seat and/or double offset), and in my mind, the biggest selling point for a BFV is the broader range of available materials.

Thanks,
Aaron

 

[Chumpes]

little remark : copper-nickel are better than naval brass versus generalized corrosion in wet sulfiding environments

regards

 

[LittleInch]

Be very very careful with GRE if you got particulates running at any sort of decent velocity.

GRE abrades remarkably easily and even with abrasion "resistant" resin, it may not last.

If you're only operating a few days of the year then maybe OK, but PE is much more resistant to damage from particles and a whole load easier to install and construct.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Problems during installation at a supermajor oil/gas company many years ago resulted in abandoning the previous practice of using GRE for low frequency use firewater lines (oxygenated seawater), and move out to 90:10 Cu - Ni. Cement lined pipes were once the practice before it got replaced with GRE.

 

[EdStainless]

Really George, 90/10 is a lousy choice for intermittent service.
Contaminated water, or high organic loads, or sever bio-fouling and all can lead to H2S being generated, and that leads to serious failure of 90/10.
Considering that this application is in an industrial area, and will see long periods idle they need to be more conservative.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

@Ed,
Dont know reasons for this selection, but I have seen PIDs'of two or more of the newer installations with Cu / Ni piping in this service. There may be some operating procedures to go with this selection, which I guess would be to reduce biofouling with a final rinse with hypochlorite dosed water before draining / drying out prior to idling? This may have been be a compromise selection for non production critical services like this, assuming superduplex would be difficult to justify.

 

[EdStainless]

The last 90/10 failure that I worked on was caused by starting the system with dirty water, it was what was available on site. The tubing never developed the correct surface chemistry and it was then corroding from day one. After chasing issues for about 2 years they finally gave up and replaced it all.
Yes, with tight operational controls it would work fine, but just as with stainless if you mess up once you can destroy the system.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

@Ed,
What would your recommendation then be for passivating this Cu-Ni piping option prior to introduction of this polluted seawater?

Are there sulphides in this polluted seawater? Not mentioned in @ATSMech's first post. If so, would 70:30 Cu-Ni be somewhat better than 90:10 Cu-Ni for this service? And how does this modify the passivation step?

Presume @ATSMech excludes titanium from this list for the same reason as for superduplex - high first cost and probably long lead times also.

 

[Chumpes]

@george : H2S may come from biological activities in seawater

 

[ATSMech]

All,

Thank you for the continued discussion.

After reading about the procedural requirements to ensure the protective layer is properly established in copper nickel, I abandoned the thought of using it. We will not have the option of running clean water through the system at start up, and when you factor in the abrasives and the relatively high flow rates we will have, it made the decision easier.

@George: Thank you for the cautionary example regarding GRE installation. Since posting this thread, I have talked with a few vendors about GRE systems, and I have a good sense of what will be required to ensure a solid installation. (ASME B31.3 qualified bonders, vendor QC, etc.) I came from the piping inspection world, and I plan to treat the specs for the installation as I would any welded system. (WPS review, QA/QC hold points, joint maps w/ welder names, etc.)

-Aaron

 

[ATSMech]

Given the reasons for excluding Cu-Ni, what would be the expected impact on NAB valve bodies and pump cases? I was planning on NAB as we could spec duplex trim and take advantage of the galvanic relationship and area ratios to mitigate corrosion of the trim.

Thanks,
Aaron

 

[EdStainless]

Will the pumps be set up to drain when not in use?

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P.E. Metallurgy, Plymouth Tube

 

[ATSMech]

@EdStainless

Worst case answer...no

The pumps are about 50 ft below grade with discharge check valves. Pump cases and suction side may drain slightly, but all of the piping and valving on the discharge side will remain flooded.

-Aaron