Hot Pipe Material Redux

[ndutton]

Some time back we had a discussion about suitable materials for the construction of hot pipe systems. Brass, stainless, black iron and galvanized were mentioned. Stainless was the gold standard with brass a close second.

Regarding the steel/iron pipes, I recalled that in several years working at the boat plants we never used galvanized pipe for our hot sections, always black iron. I wasn't sure why but metallurgic issues were the common explanation at the time. Here on the Moyer forum it was agreed that there was no problem using galvanized pipe for the hot section and this from the most knowledgeable members.

Now, I run across this, of particular interest to our application is the last paragraph.

I am blacksmith and welder. Metal fume fever from zinc is still a hazard that can and does kill. Before I knew about it, I welded together a propane gas burner using galvanized pipe and gave myself a large dose of zinc poisoning. The "flu" lasted about a week and was similar to a recent bout of pneumonia. I have since tried all the safety precautions using venting, fans behind you, rebreathers, etc and no matter what I have tried, I always got exposed and wound up in bed and/or hospital. I won't go near the stuff anymore, no matter what I am offered to make a repair.

I use blackpipe in all my gas lines and in any application where the pipe is going to get hot. Even just oven heat is enough to gas off little bits of zinc. Since blackpipe is available in the same sizes and fittings, why take the chance?!? Steer away from the stuff!

Daniel Kretchmar
www.irontreeworks.com

Given his background, this guy's statement seems to bear some weight. Maybe there's something more to the use of black iron than just the cheapest material available.

Footnote: Brass alloys consist of 15% - 30% zinc. DYOC (draw your own conclusion).

[sastanley]

Neil,
I definitely had some off-gassing when I put my new hot pipe together with galvanized pipe...I made sure the hatches were open, and that we didn't hang out down below the first few hours/whenever it was smelling.

I think the hot pipe wrap helps a bit, but it certainly doesn't seal it.

In this particular application, I am not sure you gain anything from galvanized vs. black. It might last an extra year or two, but if it goes 20 or 30 years, what's the difference of one or two more years?

[keelcooler]

Kretchmar is right, thanks for this safety item Niel. Yes bronze and brass contain zinc however it's in the alloy, not a dipped external coating. The first 2-3 hr is a real coating burn off w/galvanizing. Black iron is much preferred.

Today's galvanized pipe is mostly Chinese with a poor longevity history. US black iron is good, used extensively in underground gas pipes, it meets stringent specs for corrosion. No proper yard or builder would use galvanized pipes or fittings in exhaust fittings. Plus the protective galvanize coatings will be burnt off in short order.

The mixer is the most important alloy to get right. SS is not recommended here because of crevice corrosion concerns. I believe MMI uses red brass pipe, although the internet photo appears yellow brass. This material will give the best service life. I think best bang for the buck, w/superior corrosion resistance is red bass pipe w/cast bronze fittings.

My 49 yr old jacketed copper/nickle exhaust was pressure tested and shows no sign of failure w/salt water use. It's why all the best large yacht builders demand this material when selecting a mixer for that 60k plus engine w/a 4k plus turbo just 4" away. Copper/nickle is close to red brass and bronze on the nobility scale.

Building a new exhaust? Do yourself and the next owner a service. Spend the extra 50 over the cost of black iron. This is a job you only want to do once.

[ndutton]

ABYC Specs

Here's more:

ABYC article P-1 discusses exhaust systems in detail. Regarding the hot portion of a wet exhaust system, Article P-1, Section 1.7.8 states:

The section of the exhaust system extending from the engine manifold to the point of water injection shall be constructed the same as a dry exhaust system.

Table 1 in the same Article specifies allowable materials for exhaust systems. The dry exhaust list specifies aluminized steel, carbon steel, nickel-iron chrome and stainless steel. No galvanized steel, no brass, no bronze.

Reference: http://www.ntsb.gov/Dockets/Marine/D...012/234864.pdf

[keelcooler]

Looks like I stand corrected in suggesting copper alloys in dry exhaust system applications based on ABYC guidelines. I wonder why Pearson did not comply when my boat was built in the 60’s. I guess that’s why many builders ignore some of ABYC’s voluntary standards. As long as they follow mandatory USCG and NFPA requirements, they have adhered to the letter of the law.

It’s interesting that NFPA pleasure and commercial motor craft regulations permit copper alloys in dry exhaust systems except when used w/diesel. If we all had copper monster exhaust systems we wouldn’t have such a lively forum topic.

ABYC permits 316 L stainless only. I don’t think they make threaded 316 L fittings,so you can’t build your own. As Niel said; “draw your own conclusions”. The cost of a custom 316 L welded setup will reinforce that “gold standard” phrase.

[ndutton]

Keel,
Copper dry exhaust? Previously I'd only seen copper in water jacketed exhaust systems.

[marthur]

316 threaded stainless fittings are readily avialalbe (try McMaster Carr if you don't have a local supplier: http://www.mcmaster.com/#)

The difference between 316 and 316L is in the amount of carbon content (the L means low carbon). This is not significant unless you are going to weld the steels. The lower carbon content in 316L prevents "sensitization", which is when chromium collects around the carbon in molten steel. The chromium concentrations are where corriosion would begin.

IF you do not weld, there is no important difference in the corrosion resistance of the two alloys. So using the 316 threaded fittings should pose no problems.

[keelcooler]

Marther, That’s good info, looks like about 400 for a 316 dry set up before a mixer.

Neil, My engine hot section is short, about 6” before the water jacket. Aft dry loop runs about 20”. No threaded connections, it’s welded/brazed to the manifold steel flange. Frankly I’ve been expecting it to fail being 49 years old so I water pressure tested when I had the motor out last year. I did not want to remove the engine again in order to cut out that beast. With CO leakage our number one safety concern I double checked to confirm gas tight. I do want to have a material plan when replacement is needed.

I suspect the material is copper/nickel alloy. Before the 70’s there were no water trap systems and few small diesels in US boats. Most sailboats had Gray’s, Palmers or a4’s. These boats had all manner of dry and jacketed copper alloy exhaust systems. Where a riser or loop was needed they were dry and required asbestos wrap. Most of the long dry loop runs were at the transom just prior to water mix. Some times three different hot sections. In the late 60’s wet stacks became popular and seem mostly a mix of metals.

[ndutton]

Keel,
Thanks for the history lesson. This predates me but only by a little and is interesting stuff. Starting from about 1971 I only saw aqualift systems in a variety of configurations for sailboat auxiliaries with one noted exception, the Newport 41 by Capital Yachts. It was water jacketed copper from the dinette seat where the engine was located to the transom, over a third the length of the boat.

[ButchPetty]

I myself welded for a living for over ten years. I welded countless amounts of galv. materials. Got galv poisoning many times. No biggie. Gone in a few hours. But that only happens when the metal is actually burnt, not when heated. It would have to get red hot to cause harmful fumes. The smell of galv not being burnt is not harmful.....unless maybe if your a hypochondriac.
So yes, the guy way over exaggerated the whole issue or has a weak immune system.
Either way, not a worry now or later.
But thanks for the info.

Some time back we had a discussion about suitable materials for the construction of hot pipe systems. Brass, stainless, black iron and galvanized were mentioned. Stainless was the gold standard with brass a close second.

Regarding the steel/iron pipes, I recalled that in several years working at the boat plants we never used galvanized pipe for our hot sections, always black iron. I wasn't sure why but metallurgic issues were the common explanation at the time. Here on the Moyer forum it was agreed that there was no problem using galvanized pipe for the hot section and this from the most knowledgeable members.

Now, I run across this, of particular interest to our application is the last paragraph.



Given his background, this guy's statement seems to bear some weight. Maybe there's something more to the use of black iron than just the cheapest material available.

Footnote: Brass alloys consist of 15% - 30% zinc. DYOC (draw your own conclusion).

[Clucas]

Brass hot section?

Given the above, what's the consensus on using brass for the hot section as an alternative to black iron? Yes, it contains zinc (15-30% per Keelcooler in the post above), but it is integral to the alloy and not a coating. Does that mean less or negligible gassing off?

[hanleyclifford]

Maybe we could turn the question around. Given what we know about the reactions of metals in salt water, why would we want to use anything but black iron?

[lat 64]

Maybe we could turn the question around. Given what we know about the reactions of metals in salt water, why would we want to use anything but black iron?

Has anyone used Schedule 80 for exhausts?

[msauntry]

Here's more:

ABYC article P-1 discusses exhaust systems in detail. Regarding the hot portion of a wet exhaust system, Article P-1, Section 1.7.8 states:


Table 1 in the same Article specifies allowable materials for exhaust systems. The dry exhaust list specifies aluminized steel, carbon steel, nickel-iron chrome and stainless steel. No galvanized steel, no brass, no bronze.

Reference: http://www.ntsb.gov/Dockets/Marine/D...012/234864.pdf

Carbon steel is the what the galvanized pipes are made out of, so it's OK.

[ndutton]

The referenced article P-1 is an interesting read. I'm relatively certain with galvanized pipe it's not the pipe material in question but the zinc coating.

Looking at table 1 on page 6 in the link, the only mention of galvanized anything being allowed is for gasoline engines, wet exhaust section. The section of the exhaust from the manifold exit to the point of water injection is discussed in section 1.7.8, page 4 of the link. It says there that the hot section shall be constructed the same as a dry exhaust system. No mention of galvanized material being allowed for dry exhausts.

For those interested, slide to the last page and have a look at the drawing in figure 5, 'Typical Waterlift Exhaust System.' You'll have to print it out and hold it in front of a mirror for the proper orientation.