Saltwater piping material

[Mako]

What would be the preferred material for a saltwater piping network? This will be the emergency bilge, washdown and fire fighting network. One shipyard had recommended 304 stainless while the other uses galvanized Sch40 in all their commercial boats.

There will always be standing water in the network and it's not practical to flush/pickle it except perhaps during long term layup.

My experience is that anything galvanized could have some minor corrosion from nicks during install, and stainless corrodes when underwater. Plastic is not an option per ABS and BV class rules.

Which is the best, or least worst, solution?

 

[CPseudonym]

Least worst is galvanized sch 40 for my money. Problem with SS is it's just as good as the welder joining it.

 

[Mako]

Good point as there would be too many welds to make and even a pressure test could pass even with deficient welds.

Another thing I was thinking about is that although stainless piping looks pretty in all those yachts, I still prefer color coded piping networks. These are from a tug they recently completed:

 

[FF]

Schedule 80 plastic pipe can be threaded like steel pipe and is very robust.

To thread a solid plug is slipped in so the plastic does not distort , and removed once the threads are made.

Our 90/90 has 4 compartment subdivision so the bilge pumping is complex.

The Hayward true unions make assembly a snap.

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(PVC) Plastic Pipe Fittings, Schedule 80. This specification covers the requirements for materials, workmanship, dimensions and burst pressure of poly (vinyl ...

 

[Obx]

I agree with FF I have used PVC for many jobs, 15 yrs ago I built a garage at my previous house and piped the air system I wanted with nothing but pvc. I know the owner and he said it's still in place working fine.
My present place I did the same and it works like a charm I intend to do the same on my GB for air (in the engine room) and water (fire).

 

[Capt.Bill11]

Schedule 80 is great, I use it a lot.

But I'm not sure if I'd want it for my fire water lines.

 

[sunchaser]

Mild steel pipe has been used for sea water piping for a very long time. Think navy and big ship maritime use. In industrial applications the same. Just be careful with grounding and electrical system conditions. Care should be taken in design so piping runs can be serviced and replaced as needed.

For fire piping system design, if done right, procedures should be implemented to allow for backfilling with fresh water when system "stagnant."

 

[Capt.Bill11]

What would be the preferred material for a saltwater piping network? This will be the emergency bilge, washdown and fire fighting network. One shipyard had recommended 304 stainless while the other uses galvanized Sch40 in all their commercial boats.

There will always be standing water in the network and it's not practical to flush/pickle it except perhaps during long term layup.

My experience is that anything galvanized could have some minor corrosion from nicks during install, and stainless corrodes when underwater. Plastic is not an option per ABS and BV class rules.

Which is the best, or least worst, solution?

Are you building to class?

If so, you are wasting your time here. You need to be asking those kinds of question of the class society you are building to based on what level of class your are building to.

 

[Mako]

Has to be metal. I'm thinking of a sea chest with access plate above waterline. Seems easy enough to install a hose thread to facilitating fresh water flushing, perhaps with a rust inhibitor. Good idea Obx!

 

[Nightsky]

I am surprised by both of the yards options. 304 ss is not as corrosion resistant as is 316ss especially for seawater. All the bilge plumbing in my previous boat (93 ' steel hull) was in black steel no galvanized at all. In fact my insurance provider required the removal of any galvanized bilge plumbing added or mixed in.

 

[Mako]

I've been reading through BV Yacht class rules which state: "Materials readily rendered ineffective by heat should not be used for fire mains. Where steel pipes are used, they should be galvanized internally and externally. Cast iron pipes are not acceptable."

I've been thinking of taking advantage of the allowance that vessels under 24m can use a single pump for bilge and fire systems (and hence a washdown pump as well). Perhaps it is better to regularly use a pump than to let it sit for years rotting.

So the key is keeping the galvanized piping from corroding, which means freshwater flushing regularly, perhaps with a rust inhibitor that is not harmful to the environment (we use these in our district cooling systems).

 

[FF]

"galvanized internally and externally."

Internally ???

 

[Mako]

Yes, GI pipe is always galvanized in the inside. Check it out the next time you stop off at Home Depot.

 

[Pieyed47]

Has to be metal. I'm thinking of a sea chest with access plate above waterline. Seems easy enough to install a hose thread to facilitating fresh water flushing, perhaps with a rust inhibitor. Good idea Obx!

How large are your lines? and what is the longest runs?

 

[psneeld]

From a marine engineer friend and very familiar with large to mega yacht design and construction......

"If it is a boat large enough (and worth) to be classed then the naval architect has all the information needed. A knowledgeable yard would not have told him that plastic piping was prohibited by class as that is not the case at all.

Look up BV Rules for Yachts 2012, page 256 Table 7 - Limits of use for plastic piping.

http://www.veristar.com/portal/veri.../documents/NR500_consolidated_january2016.pdf

A great deal depends on the size of the boat. Someone is misleading this guy .......

Lightweight stainless tubing is not the piping to use, particularly 304, it is a waste of money but sched 40 316L is preferred if there is some great desire to see shiny piping. Common old galvanized schedule 40 steel pipe in the engine room space will probably last longer than the boat itself and is easily and cheaply repaired or replaced if necessary."

 

[Mako]

I have been reading the IACS regs about plastic piping. We even use CPVC in residential fire fighting systems. However the plastic piping rated L1 for marine use is very expensive and probably not readily available in my part of the world. I will chat with the shipyard however. Not too interested in needlessly wasting money however

 

[psneeld]

Then this is also recommended for saving money...

"I can't think of a bigger waste of money than putting an under 24m boat in class. The initial cost of design, construction, and annual survey costs will quickly equal the cost of building ........ he is getting some of the worst advice possible from someone

If he wants to be able to say the boat is built to some standard then he should look at the European "Recreational Craft Directive" for advice.

Here is a link to a dummies guide to the RCD. http://www.boatdataservices.com/uploads/3/4/8/8/3488223/rcdeuguide_pdf_version.pdf"