Rust Never Sleeps.

Nov 24, 2014
159
Catalina 310 Staten Island
Back in 2019 I had extensive work done on my 2003 Catalina 310, including replacing the exhaust elbow, as the weld connecting the stainless steel cooling water pipe to the cast iron elbow had cracked. I had a new elbow/pipe assembly made up entirely of stainless steel. Now the weld at its lower portion is starting to deteriorate. What should I do. Have it made over again? Cover it with high temperature expoxy putty? Remove the elbow when the boat is hauled and have a muffler shop re-weld it. Awaiting all suggestions
 

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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Let me preface with I know nothing about welding. This little bit of information below might mean the elbow wasn't welded together correctly in the first place. I defer to the experts

Does welded stainless steel rust?
Under normal conditions, stainless steel withstands corrosions of all kinds. However, in extreme circumstances, stainless steel can rust. This occurs when the chromium oxide layer – the very element that protects stainless from rusting – is destroyed or removed. Sometimes this can happen during welding, either during heating or cooling process.
Even with TIG welding, rust can be one of the biggest challenges of welding with stainless steel. That’s why cleaning and prepping your stainless before you start is so important. With a properly cleaned and prepped piece of stainless steel, the chromium oxide inside acts as a protective seal against rust during the welding process. It can help the stainless heal itself from discoloration and permanent marks
 
Nov 24, 2014
159
Catalina 310 Staten Island
Let me preface with I know nothing about welding. This little bit of information below might mean the elbow wasn't welded together correctly in the first place. I defer to the experts

Does welded stainless steel rust?
Under normal conditions, stainless steel withstands corrosions of all kinds. However, in extreme circumstances, stainless steel can rust. This occurs when the chromium oxide layer – the very element that protects stainless from rusting – is destroyed or removed. Sometimes this can happen during welding, either during heating or cooling process.
Even with TIG welding, rust can be one of the biggest challenges of welding with stainless steel. That’s why cleaning and prepping your stainless before you start is so important. With a properly cleaned and prepped piece of stainless steel, the chromium oxide inside acts as a protective seal against rust during the welding process. It can help the stainless heal itself from discoloration and permanent marks
Another thing to consider is the location of the weld. The elbow is subject to considerable heat from the exhaust. The pipe, on the other hand is cooled by the seawater. This means that the two pieces will expand and contract to different degrees, resulting in further stress on the weld. This is a potential problem spot no matter how carefully the weld is done, and should be inspected regularly by the owner, as well as the yard. The original equipment involved welding stainless steel to cast iron; two metals that expand at different rates, resulting in further stress on a weld that is weaker to begin with. The whole assembly was covered with insulation, making inspection difficult. I remember seeing rust spots on the insulation, as well as on nearby screws and fittings, progressing over 2 years until the weld just broke apart. It must have deteriorated progressively over time until said failure
 
Oct 10, 2019
114
Signet 20 0 Ithaca
Remember, it is stainLESS steel, not stainPROOF steel. It will still rust, especially the lower grades, like 304/18-8.

316 would undoubtedly last longer, and you can get 316 pipe and fittings pretty easily. Heavier schedule pipe would help, too.

Cost of materials is only part of the cost of your project.
 
Oct 26, 2010
1,881
Hunter 40.5 Beaufort, SC
Well, to start off, that weld would never pass a QC inspection when new! There appears to be incomplete fusion in the area of the heavy rust and significant undercut there too. I probably wouldn't have accepted that weld on my anything I paid someone to weld. The pooling of the weld deposited material is not "wavy" like a good weld would be and looks more like "dabs" of weld material applied.
 
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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Well, to start off, that weld would never pass a QC inspection when new! There appears to be incomplete fusion in the area of the heavy rust and significant undercut there too. I probably wouldn't have accepted that weld on my anything I paid someone to weld. The pooling of the weld deposited material is not "wavy" like a good weld would be and looks more like "dabs" of weld material applied.
Good call. Looks like it was done by an amateur. Probably not cleaned and prepped properly either, which takes me back to that article I posted.
 
Oct 29, 2005
2,355
Hunter Marine 326 303 Singapore
Recently I came across, on YouTube a passivation process called Bluing. Wonder if we could use it on the exhaust elbows to retard or prevent rusting?

Ken Y
 
Nov 24, 2014
159
Catalina 310 Staten Island
Well thank you everyone. I am posting another photo of the same fitting. At the lower right you can see salt deposits left over from water that was seeping out from the rusted part of the weld, and then boiled off by the heat.
IMG_6949.JPG
 
Oct 26, 2010
1,881
Hunter 40.5 Beaufort, SC
Weld filler material flow is a little better on the middle of the weld on that side but still overall a Butt-Ugly weld that looks like it was done by a shop student still learning to weld. :poop:
 
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Nov 24, 2014
159
Catalina 310 Staten Island
Remember, it is stainLESS steel, not stainPROOF steel. It will still rust, especially the lower grades, like 304/18-8.

316 would undoubtedly last longer, and you can get 316 pipe and fittings pretty easily. Heavier schedule pipe would help, too.

Cost of materials is only part of the cost of your project.
Saying stainless steel won't rust is like saying a Jeep Wrangler will NEVER get stuck in the snow or mud
 
Nov 24, 2014
159
Catalina 310 Staten Island
Weld filler material flow is a little better on the middle of the weld on that side but still overall a Butt-Ugly weld that looks like it was done by a shop student still learning to weld. :poop:
When I looked at the bill for the work, I felt like I was getting charged $100.00 for a haircut at the local beauty school
 
Oct 22, 2014
20,989
CAL 35 Cruiser #21 moored EVERETT WA
that weld would never pass a QC inspection when new!
:plus:
Welding stainless is not as bad as aluminum. It takes a bit of skill.
Projects that I have had welding done included cleaning up the weld by grinding the excess weld to smooth, and then passivation, as mentioned by @Ken13559. It is not really bluing, it is a process of removing the free iron particles from the surface of the work. (" In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer that is less likely to chemically react with air and cause corrosion.")

It will still rust, especially the lower grades, like 304/18-8.
The fact is stainless is just that Less rust staining. As Dave states the lower grades are more likely to rust.
Looking at the picture it appears the part is made of 304 stainless not 316.
7AB100C8-D4D0-4ADD-9AF2-B58C3232578D.jpeg
Both types have their uses. 304 will show rust quicker. 316 may be too brittle for the job of the exhaust elbow. I am not sure. Perhaps one of our metallurgist here can give us the answer.

As Smokey identifies the weld technique is questionable. If done at a muffler shop they likely did not finish the piece to get the iron dust in the shop off the piece before you put it into the boat.

Sometimes I wonder why maintaining a boat can be so difficult.
 
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Nov 24, 2014
159
Catalina 310 Staten Island
:plus:
Welding stainless is not as bad as aluminum. It takes a bit of skill.
Projects that I have had welding done included cleaning up the weld by grinding the excess weld to smooth, and then passivation, as mentioned by @Ken13559. It is not really bluing, it is a process of removing the free iron particles from the surface of the work. (" In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer that is less likely to chemically react with air and cause corrosion.")


The fact is stainless is just that Less rust staining. As Dave states the lower grades are more likely to rust.
Looking at the picture it appears the part is made of 304 stainless not 316.
View attachment 185030
Both types have their uses. 304 will show rust quicker. 316 may be too brittle for the job of the exhaust elbow. I am not sure. Perhaps one of our metallurgist here can give us the answer.

As Smokey identifies the weld technique is questionable. If done at a muffler shop they likely did not finish the piece to get the iron dust in the shop off the piece before you put it into the boat.

Sometimes I wonder why maintaining a boat can be so difficult.
I do know someone who fabricates custom motorcycle frames that will redo the piece for less than what a boatyard might charge
 
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Oct 29, 2005
2,355
Hunter Marine 326 303 Singapore
:plus:
Welding stainless is not as bad as aluminum. It takes a bit of skill.
Projects that I have had welding done included cleaning up the weld by grinding the excess weld to smooth, and then passivation, as mentioned by @Ken13559. It is not really bluing, it is a process of removing the free iron particles from the surface of the work. (" In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer that is less likely to chemically react with air and cause corrosion.").......
Just nice. I've got my SS U-Mixing elbow welded with SS plate over the pittings. Now soaking it in citric acid to clear off any rust. So in effect I'm passivating the SS U-Mixing elbow and not realising. :D That's good.
Thanks for info :)

Ken Y
 
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Jun 25, 2004
475
Hunter 306 Pasadena MD
Question for y'all about the stainless steel mixing elbows. Most postings about them say that they're better than the cast iron. A while back, I was talking to our local diesel mechanic, who has worked in our marina for going on 15 years. He said that he didn't care for the stainless elbows because it was harder to get them screwed down properly so that they wouldn't leak. Presumably because they're made from harder steel. Any opinions on this?
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
What does he base that on? Poor machining is all can think. Mine installed perfectly and no leaks. Buy one from a reputable shop. There is one with a storefront on Ebay. I don't have his name but several members have used him.
 
Oct 10, 2019
114
Signet 20 0 Ithaca
Unclear if y'all are talking about a threaded fitting or a flanged fitting, but any threaded joint is going to leak without some kind of additional sealant added, that's why they make plumber's tape and pipe dope. Any flanged fitting requires a gasket or it will leak. If your parts are sound and use the right stuff and apply the right torque, material shouldn't matter.
 
Nov 24, 2014
159
Catalina 310 Staten Island
:plus:
Welding stainless is not as bad as aluminum. It takes a bit of skill.
Projects that I have had welding done included cleaning up the weld by grinding the excess weld to smooth, and then passivation, as mentioned by @Ken13559. It is not really bluing, it is a process of removing the free iron particles from the surface of the work. (" In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer that is less likely to chemically react with air and cause corrosion.")


The fact is stainless is just that Less rust staining. As Dave states the lower grades are more likely to rust.
Looking at the picture it appears the part is made of 304 stainless not 316.
View attachment 185030
Both types have their uses. 304 will show rust quicker. 316 may be too brittle for the job of the exhaust elbow. I am not sure. Perhaps one of our metallurgist here can give us the answer.

As Smokey identifies the weld technique is questionable. If done at a muffler shop they likely did not finish the piece to get the iron dust in the shop off the piece before you put it into the boat.

Sometimes I wonder why maintaining a boat can be so difficult.
Having had a Cannondale Mountain bike frame crack at the weld some 25 years ago and falling one my face, I can vouch for that. Failures of those early welded aluminum frames were so common that Cannondale was Called Cracknfail on various cycling forums
 
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Jan 27, 2008
3,045
ODay 35 Beaufort, NC
While you may be noticing some salt water leaking as cause for concern you should be much more concerned about Carbon Monoxide in the exhaust leaking into your boat! Get a CO alarm and seal that leak immediately. This can be deadly.
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
He said that he didn't care for the stainless elbows because it was harder to get them screwed down properly
I think he's referring to the hand made SS tube mixing elbows rather that the HDI Marine cast 316 SS mixing elbows. The HDI cast SS elbows are identical to the Yanmar CI elbows except for the metal. Oh yes, and the price ...... less than 1/2 the price of a CI elbow.

SS Mixing Elbow.jpg