Riser condition inspection

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P-Dogg
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Riser condition inspection

Post by P-Dogg »

So everyone "knows" to periodically replace risers because you cannot predict their (expensive) failure. 5 years is an oft-quoted number. Here is my story.

BLUF: Crusader 270s with 7-year old Barr risers. 5 years in substantially fresh water, then 2 years in salty water. In the water all year, nothing done to the engines after running. External riser/elbow joints show rust, one set even had evidence of a visible drip. Removed risers to at least replace the gaskets, and ended-up doing a borescope inspection, the results of which were frightening. Staring riser replacement in the face, I decided to glean what info I could from the corpse of one riser.

The outside:
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The inside. Exhaust enters from the right, cooling water enters through pipe nipple:
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You can see a lot just by looking. As far as rot-through goes, not even close. But what is intriguing is what happens after shutdown. The cooling passages are blocked by a stainless plate on the lower right-hand side, as my engine has closed cooling. Thus, water drains out on the left side cooling passages, which are connected to the exhaust elbow, and thence the sea. Note the markedly different levels of corrosion between the upper and lower cooling water passages. Water drains out of the top portion after shutdown, but remains trapped in the lower portion. It shows. There is practically no deep corrosion or blockage in the upper passage. The lower passage is rusty as all get out, and water flow is nearly blocked. Just squint and look at the color difference between the two. If you look carefully, you can see increased corrosion in the upper passage on the far right-hand side, where it is below the siphon break on the left-hand side.

Two things come to mind from the cut-away picture: Fresh water rinse, and post-run drain-down of the cooling passages. I will be replacing the lower drain plug with a valve, plumbed for easy reach, and connecting fresh water to the T-fitting that already exists in my engine raw-water intake, to facilitate after-run freshwater rinse of the entire cooling system.
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BobCT
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Re: Riser condition inspection

Post by BobCT »

wow, that's awesome work.... I've never seen a cutaway like that. I've been doing a fresh water flush for a long time, over ten years across two sets of risers/elbows. If I'm boating back to back days, I might not do it but longer than that I will every time. On the last set at five years, they looked like new (but your pic makes me think about how little you can actually see) and I could have easily gone a few more years but replaced them anyway. Now that I have my 8.1's, I'm not giving them a thought until at least year six. I want to take it up a notch and start doing the rinse with salt away at least for end of the weekend flushes.

I can live with a gradual temp climb which will at least give some warning vs. a catastrophic failure. I'm glad to see your pic supports that theory.

The other motivation is that these exhaust components are getting harder to find and there are plenty of stories on cheaper ones failing.


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WayWeGo
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Re: Riser condition inspection

Post by WayWeGo »

I am curious if you ever did a flush with Barnacle Buster or some other acid based flush of the raw water side. I have been doing that every year or two to avoid the corrosion build up that reduces water flow.
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P-Dogg
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Re: Riser condition inspection

Post by P-Dogg »

Nothing whatsoever.
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prowlersfish
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Re: Riser condition inspection

Post by prowlersfish »

Should be noted the salt level is lower where you are and where you where it was even lower.
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