Sea Water Pumps Discharge Manifold-Materials and Coating

Glass-reinforced polyester, or naval brass/bronze, are immediately suitable materials. Many other plastics will be suitable, including uPVC.

Others may be investigated here.

There are several different coating methods and cathodic strategies available, you need to study what's available and make a decision based on your budget and resources....

http://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2011-05/RP-F102.pdf

Good day sir, the cause of your problem is now apparent: internal corrocoat coating may not have been correctly installed (if there were issues with the cleaning of the mild steel prior to coating, for example.)

Next question: are you sure the failure mode is pinholes from the inside out, or could be it be the reverse? Sea air is wicked corrosive also, as you know better than I.

Any of the two-part epoxy coatings might do for a re-coating job during plant outage, assuming that localized areas can be identified, cleaned to the metal, and evenly coated, so that the pits are filled with epoxy.

I provided below link for pin hole photo. I hope it can give an idea about nature of corrosion.

https://photos.app.goo.gl/QNMZiX6rTuDfjxvg1

It looks inside out to me, as most of the surface exterior of the pipe appears A-OK.

This is something hard to avoid on seawater cooling system, when using mild steel, as no corrosion inhibitor is being applied to the water, typically.

Your coating on the inside of the pipe took a "vacation", and when the cat is away, the rats come to play.

Anodic pits travel through the metal quickly with such a corrosive water (with added corrosive bleach) as yours. It may have failed even quicker due to sulfate reducing bacterial pits if not treated with bleach, however.

I recommend moving away from metal piping system for this, since reinforced fiber glass pipe will clearly perform the same job without corrosion issues.

As far as SS is concerned, superduplex SS offers the best combination of properties for these applications.

But Titanuim is even better.

I have a problem slightly similar to Jilal. I am in a steel mill and have a damper plate to isolate air flow from basic oxygen process. When closed it dips in water to seal. Originally it was made of mild steel but bottom edge (portion dipping into water) failed (seemed to corrode away). At someone's suggestion we put an overlay of 1/4" (plate is 1") inconel625. It worked well and we are about to make another but I question if Inconel was best choice. Temperature stays below 200 degree F(95C) and there is not much abrasion (When open out of flow and when closed in water) but the water is exposed to gases from process. Gasses are mostly air, water(from quenching the hot gases), excess oxygen, carbon dioxide (from removing carbon from cast iron), sulfur dioxide (always some sulfur in the ore), and anything else blown out of heat. I looked at your graff but could resolve little. Where could I find clear (and un biased) comparison of Inconel 625, 317SS, 316SS, 304SS, and/or others for corrosion resistance in this (not at all like sea water) application?

Your problem is older piping and a combination of electrolysis & the Sodium Hypochlorite Concentration your using for marine growth.

The electrolysis is attacking the steel Under the Coating.

It is attacking the steel and the weld joints. It really does a number on bronze, even naval bronze as well. I bet, if you actually check the injection rates, you will see it's not what you think it is.

Check your chemical compatibility charts at that concentration and check for proper grounding of electrical equipment.

Your options are: A) Change the piping to FRP, Fiberglass Reinforced Polymer MARINE GRADE piping. B) Or the much more expansive Super Duplex Stainless Steel A-5 Piping. C) Do away with the Sodium Hypochlorite Generators Injection System and replace it with an impressed current copper and aluminum marine growth protection system At your source water point, the Seawater lift pumps. D) Clear up the electrolysis issues either with a catholic protection system or Zinc Anodes where applicable. E) If you replace the piping with Steel, use a good grade of Ceramic Epoxy with the proper perpetrations and bonding primers for the ID Lining. And a good poly epoxy O.D. coating system. Check with your company's engineering group. I'm sure they have the coating specs they used that was approved by ABS And NSTI when the rig was built.

Internal lining of the existing piping will not work at those pressures and on older piping. It will just flake off and clog up smaller piping such as the engine radiator coolers tubes and such.

How old is the rig and piping?

Is it a platform, Jack Up or Semisubmersible?

I think you may confuse the OP with terms like catholic protection (mental image of a priest exorcising the pipe), or proper perpetrations (I would even dare present any mental image for this one, unless it would be a masked bandit delivering stolen replacement pipe and ceramic epoxy.

Other than that, I pretty much agree with you, and happy to jokingly point out your typos for general humor (at your expense), welcome.

Sorry, but these are the best images of the scene I could get.

.......electrolysis.......

Please do not use the term electrolysis when discussing marine corrosion........ because there is no such animal.........you probably will not even find the word in any reputable paper/publication on marine corrosion. The corrosion to which you refer may be either galvanic action or stray electric current corrosion or could be even caused by MIC (Microbiologically Induced Corrosion), or differential aeration.......definite NOT electrolysis, whilst the word does exist it is relative to lead/acid batteries and definitely not marine corrosion.

If corrosion becomes a serious problem it is always good to get the services of a qualified metallurgist to determine the cause of the corrosion......they can detect the exact type of corrosion, its cause, and the best methods of reducing the problem. If you take incorrect steps to avoid a type of corrosion, that you think it may be, you can actually aggravate the corrosion problem that you have.

"wOw" ... I haven't the time right now to even list all the appropriate questions to ask.

"Flow: up to 60,000 m3/hr" ... that alone (^{_{without even attempting the calculations}}) probably confirms (or at least strongly suggests) that FAC (flow accelerated corrosion) is part of the equation here.

"GA" to lyn , as titanium certainly HAS proven to be uniquely superior in applications such as this... especially AT high velocities with seawater (its passive film, like that on SS, will heal itself readily, e.g., from damage by sand, in the presence of the slightest bit of dissolved O₂).

Unfortunately, that {titanium} is probably "not-in-the-budget" for THIS application.

Coating (internal, most likely the culprit here) is going to be a specialty that will necessitate somebody having TRUE EXPERIENCE in this particular application.

AGAIN , I would refer THIS sort of question to those REAL experts:

See my post HERE.

[ Obviously, YOU would want to ask the "Coatings / Linings" groups this question.

It is unlikely that a CP/ICCP system will do much here... though I might be corrected on that...]

It sounds like the cooling water line on a coastal sited power generation plant that is drawing and expelling seawater. A rather substantial plant I might add.

That flow is equivalent to a bit more than 264,000 gpm. This can only happen in really large diameter pipes, probably with diameter over 3 m.

Cast your housing utilizing Naval bronze #464....

Sea water and other caustic fluids EAT CARBON. Steel castings. Yes, this material is expensive....so are repairs and downtime......

Too true.........almost everything with "marine" in front of it expensive........2 main reasons are:

1. Materials and equipment used in marine applications are specialised

2. There are not large amounts of these materials and equipment manufactured compared to other types of engineering, they are therefore expensive

316 stainless steel is an even better choice of material to be utilized as a casting material for your pump housing. Most likely more expensive than the Naval bronze..... Aluminium Nickle Bronze is also an other choice...... Again Expense of materials vs repair and downtime is something to consider.

Marine grade stainless steels are probably one of the cheapest and worst options when trying to overcome marine corrosion. SS is okay if there is a plentiful supply of oxygen in the water and all surfaces are in contact with it........no oxygen.......corrosion takes place, because once the protective coating is scratched/damaged in any way, if there is no oxygen.....the protective coating cannot be replaced.....corrosion occurs. Marine growth on ss surfaces will cause corrosion to occur.

Hi Hilal,

It would appear that the material the manifold is made from is not suitable for purpose & I'm of the opinion that any attempt to cut corners, ie coat with polymers or the like is a false economy, I suggest you have the manifold remanufactured in a salt water proof stainless steel, I think from memory EN43 but I may be wrong, anyway It's what we used to make parts for diving valves, you could have one made whilst keeping the old one working then do a quick change. not the cheapest fix but permanent.

Bazzer

Good evening.

I have been working on a similar problem on a Seawater Plant in Qatar.

There are too many issues that are both related and not related on your equipment.

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