Plumbing For Volvo Penta

Mr. CDK, You're preaching from a position on the high alter of a Cres trailor park .....

If readers wish to observe your gospel and construct a boat out of recycled egg cartons , that's a personal choice.

To interested Boatdesign net readers....Do not Use Stainless steel plumbing in a submerged seawater environment or your boat building endeavours will be relegated to CDK trailer park status. .

 

I'm not quite sure what you mean by submerged seawater environment, I thought the subject was raw water and engine cooling pipework. The raw water should not be de-oxygenated so near the surface, but I would be careful about any coolant mixtures being left permanently inside stainless pipes. It will all depend on the chemistry, but it is a fact that Stainless needs oxygen to maintain its anti-corrosive "skin".

I was doing contract work in a distillery almost 40 years ago. It was at the time of one of the many African wars and copper was at an extortionate price. As extra work, they asked us to replace some corroding copper waste pipes with stainless steel from the still house to a collection pond. This fluid was the left overs after the whisky had been steamed off, Spent Lees, I think they called it.
We installed the first line, 6" diameter and probably 3mm thick, then went back to do our main task. Six weeks later we went down to install the second line and found that holes had already appeared in the first one. They had no option but to order some very expensive copper.

 

When seawater stagnates in a cooling system, it becomes anaerobic. SS will not tolerate anaerobic conditions. If the fluid is in constant circulation, it will not become anaerobic. Do not use SS with stagnant water.

 

Once it starts it won't stop,

http://www.edstrom.com/Resources.cfm?doc_id=148

 

Like you wrote, it all depends on the chemistry.
Stainless needs some oxygen to build the protective layer, not to maintain it. In a closed cooling system - with or without anti freeze - there is no free oxygen, so there is also no corrosion. That is why engines with an alloy head on a gray cast block have a long service life.

Stainless pipes in a closed cooling system are not prone to bacterial corrosion because the environment is sterile.
The only (rare) case of corrosion is when the fluid contains reducing agents like acids; that probably was the case in the distillery. The industry offers stainless products for these conditions as well, but they are extremely expensive and very difficult to machine.

 

The hallucinations will subside if you take your medication Michael!

 

I'm not sure that there is universal agreement with your first statement, see also what it says here about heated seawater.

http://www.bssa.org.uk/topics.php?article=100

In a closed cooling system the coolant will most likely include a corrosion inhibitor for about 5% of its volume. That's what causes the nasty smell.

From what I've read so far, I should not use stainless on the seawater side, but it should be fine in the closed system especially if a coolant is used.

Having said all that, on my own boat I removed a stainless steel exhaust water trap that had seen 27 years service and had never been drained in the 15 years that I owned it, nor probably in the preceding years. It is still in my shed and shows no signs of corrosion.

 

PPR plastic is cost effective. If you feel you must use metal ,for instance heat exposure, Ask around your local commercial shipyard for Cupro Nickel tube offcuts . Many times short pieces of Marine grade offcut stock can be collected for small installations or manifolds.

This yachts MTU engine installation used several short lengths in its cooling system . My local marine engineering shop has a barrel full of offcuts.


http://www.copper-pipe-fittings.com/cupro-nickle-tubes.html

 

Now you're talking. Problem is that it requires a lot of skill to weld properly. In the early days we used to silver solder the smaller fittings(2" and under), but that was even more demanding and nowadays it tends to be socket-welded for the smaller bores. For larger butt-welded joints, cleanliness, Hi-purity argon and skillfull purging is a must for quality finishes.

 

Yes indeed...I joined section of Cupro Nickel in the vessels pressure fresh water system two years ago and it has wept green tears ever since !!!!!!!!! Perhaps a project for next week and more patience.


Another reason for PPR ...even a amateur fitter like me can place a pipe in the heat weld die and press the trigger.

 

Sadly, many welding career odysseys have foundered on the Cunifer rock.

 

I rest my case!

This is a very convincing observation. The stainless (304) parts I built, like protruding stern tubes, coolant plumbing and injection nozzles in the turbo chargers enter their 4th year of service, unscathed. I won't be around anymore to check for corrosion 23 years from now.

 

I checked up this morning with a plumber friend of mine regarding the ppr. He says the larger dia that Im looking at (50mm) are not used here, PPR is not allowed in commercial construction. His says its easy to find pipe and fittings but because nobody uses it finding a welder is the trick. I will inquire at the plumbing supplies tomorrow.
His advice was 16ga 316 stainless with mandrel bends, all tig welded together, can be bought locally from Alstrut and very cost effective, He made the point with copper after braising the bends on, the copper becomes anneald and too soft to hold the clamps tightly and tends to warp. I can see that.

 

Had a chance quickly this afternoon and went past the plumbing supply shop, First question "I" was asked is what is PPR? they have PE but never heard of PPR! After some searching we found it under a certain brand name. They rang the Distributors and here is were its gets interesting, Minimum quantity 5 lengths that's 20m, minimum quantity bends per angle 5, the welder can be hired, booking 3 months in advanced, minimum hire $500Au.
All I can say is welcome to OZ. no bloody wizard here mate!
I went past Alstrut 316 stainless Mandrel bends from 90 to 15deg in 38mm OD $24 each no min quantity length of 4m long 316 tube $80, pretty easy to see which way I'm going.
The only factor in using stainless is forming a bead at the pipe end to stop the hose rolling off, I'm thinking a touch larger pipe say a 2mm peice and braised on with silver solder. Any suggestions for that one?
Katoh

 

Why do you not use Marine Water Hose, see Vetus page 122? You can get bronze or plastic connections, (see aquafax.co.uk for ideas), skin fittings etc and use heavy duty Stainless hose clips, see Vetus.

Welding 16G 316 with all these bends requires a degree of skill and would need a TIG welding set and purging. Any internal blemishes would be prone to corrosion. You would still need to make hose tails, unless you are fortunate enough to find some ready made that you could adapt.

I have been fabricating and installing piping systems in the marine and offshore environment since 1964 and I have never seen 16G stainless employed for any service, let alone seawater. I would advise you against this route. If you want to use stainless, use sch 40s as a minimum for the seawater side.