MD2020 Stainless steel exhaust elbow

[MikeBz]

6 years ago I replaced the cracked, original, cast iron exhaust elbow on our MD2020 with a welded stainless steel aftermarket version. This summer I noticed the occasional drip of salt water under the engine which it turns out is coming from the weld between the flange and the tubular elbow. If I don’t wish to have it rewelded (yet to explore the possibilities with that) then the question is what to replace it with this time? Options appear to be:

1. Aftermarket cast iron (UK retailer) £174
2. Volvo cast iron (UK retailer) £280
3. Unbranded welded stainless steel (UK retailer) £250
4. Orbitrade welded stainless steel (ASAP) £390
5. Unbranded cast stainless steel (Chinese, EBay) £196
6. Cast stainless steel (Parts4Engines) £220

I’m not favouring another welded stainless version - I don’t see the point in spending more than the cost of a genuine cast iron item given that I will probably have changed boats long before one of those rusts through, and I wouldn’t buy one the same as has failed. I’m leaning towards the S/S cast version from Parts4Engines but I wonder whether there are unknown (to me) pitfalls with these.

 

[jamie N]

Can't imagine why you'd not get it rewelded, but by someone who'd do a proper weld?
Can't help with your other options though.

 

[earlybird]

+1; those pics appear to show that the original weld had little or no penetration into the flange. Any competent welder would avoid that fault.
If you do go for a re-weld, all the dirt and carbon needs to be ground out of the faulty section.

 

[penfold]

It's the Heat Affected Zone that has failed and cracked, not the weld. May be a lack of penetration or may be poor material choices. Whether it's worth bothering with rewelding depends on what it's like inside.

 

[vyv_cox]

It's the Heat Affected Zone that has failed and cracked, not the weld. May be a lack of penetration or may be poor material choices. Whether it's worth bothering with rewelding depends on what it's like inside.

Cracking like this appears to be thermal fatigue, caused by repetitive heating and cooling of a possibly poorly made weld. There is an example of a similar Yanmar one on this page Fatigue

 

[ean_p]

Cracking like this appears to be thermal fatigue, caused by repetitive heating and cooling of a possibly poorly made weld. There is an example of a similar Yanmar one on this page Fatigue

As an aside Vyv what materials would have an improved (over Cast Iron or SS)performance in such a duty? Would cast / fabricated bronze be better or would cost exclude this?

 

[Neeves]

Parts4 engines seem to buy their offering directly or indirectly from the same source I bought from in China. I bought through Aliexpress who offer items from Chinese retail outlets and there are many such outlets all dealing with the same item(s) at different prices. My unit came with the gasket.

This is one source at random

115.37￡ |Ap03 861906 21190094 Stainless Steel 304 Exhaust Elbow For Volvo Penta Md2010 Md2020 Md2030 - Exhaust Headers - AliExpress

You may be offered different sources and different prices. Prices vary from the different outlets and freight can also vary - so shop around (if you want to follow this route)

I say Parts4engines offer from the same source - because the images used in advertising are identical. Parts4engine may buy from the original manufacturer, rather than a retail outlet. Buying from the original manufacturer can be much cheaper but they are geared up too sell in bulk and a one off shipment can be expensive as they don't sell one, but 100, units and simply cannot be bothered shipping one unit as cheaply as possible.

My elbow has only been in use for a few months, I was perfectly happy with the price I paid, delivery and quality and have no reason not to buy my next one the same way.

Jonathan

 

[garymalmgren]

A simple question that is not really related to the crack.

That is the exhast manifold that is fiited to the head, right?

The cooling water should be injected after the"U" bend.
Why is there (leaking) water that has flowed in the opposite direction of the exhaust gases?

gary

 

[Tranona]

If you look at the link in post#7 you will see the injection point is immediately after where the tube is welded to the flange.

 

[peteK]

A simple question that is not really related to the crack.

That is the exhast manifold that is fiited to the head, right?

The cooling water should be injected after the"U" bend.
Why is there (leaking) water that has flowed in the opposite direction of the exhaust gases?

gary

Maybe the inner pipe is ieaking were it been welded.

 

[Daydream believer]

I would get my welder out of the shed & weld it. I have rods for SS. However, I know a coded welder at our club who would do a "proper job" for a pint of beer & a thankyou. I think that would be the better option.
Considering you have managed 6 years out of the old one, then same again should give you another 6 . Which is not so bad in the scheme of things. Just hang on to this one in the event of a major failure somewhere along the line. It will get you out of trouble if not already blocked with deposits.

 

[Beneteau381]

A simple question that is not really related to the crack.

That is the exhast manifold that is fiited to the head, right?

The cooling water should be injected after the"U" bend.
Why is there (leaking) water that has flowed in the opposite direction of the exhaust gases?

gary

The water is injected in to an "annular" space, ie a tube within a tube, both are welded to the flange? and goes downwards. However I suspect that the amount of water being injected could be pushing some backwards, indeed I would be having a look to see if there is any carbon/salts blockage helping to create a slight pressure in the space pushing the water back to the flange. Also I would caution about the welding, I made an elbow for my MD22, its worked flawlessly for 12 years, however the flange warped horribly when the welder in Holyhead welded the tube to the flange.

 

[Daydream believer]

. Also I would caution about the welding, I made an elbow for my MD22, its worked flawlessy for 20 years, however the flange warped horribly when the welder in Holyhead welded the tube to the flange.

I would just run it under my milling machine & true it up .Only a few minutes in a machine shop Once cramped up.

 

[Boater Sam]

That weld could have been made with a dis-similar rod material from the base elbow metal, I have seen cracking in this situation.

 

[Beneteau381]

I would just run it under my milling machine & true it up .Only a few minutes in a machine shop Once cramped up.

The welder passed a disk over it, I filed it, the only option on the boat in HH, it worked ?

 

[Daydream believer]

The welder passed a disk over it, I filed it, the only option on the boat in HH, it worked ?

P B O

 

[vyv_cox]

That weld could have been made with a dis-similar rod material from the base elbow metal, I have seen cracking in this situation.

In seawater yes, it's known as knife-line cracking due to sensitisation. It is a corrosion mechanism so probably not in this case.

 

[vyv_cox]

As an aside Vyv what materials would have an improved (over Cast Iron or SS)performance in such a duty? Would cast / fabricated bronze be better or would cost exclude this?

Oddly enough it seems to be engine dependent. Volvos seem to fail predominantly by corrosion, in which case the stainless ones as currently fitted by Neeves would seem to be the better material.
The small Yanmar elbows mostly fail in fatigue, as in my link posted earlier, although I have read of some that seemed to have corroded. It's more of a design issue than materials, making the tubes in thicker section would help a lot. Stainless is probably as good as anything although interesting that Beta are now supplying cast aluminium ones with much thicker walls.

 

[MikeBz]

Lots of useful replies, thanks. I need to clean up the inside and have a better look.

I would be reluctant to assume that because a picture on e.g. Aliexpress looks identical to one on a UK supplier’s they are both sourcing/selling the same product.

I did send the pics to the supplier for comment but haven’t had a response - not entirely unexpected given that it’s 6 years old, and the purpose of this thread isn’t to beat up the supplier.

 

[Neeves]

If you use the search function I had a thread on stainless exhaust elbows. Someone bought one, like mine, a bit earlier than I did and may have further comment.

I find it sufficiently intriguing that a supplier in the UK has an identical, not similar. but identical in every facet, including the orientation of the device to be fairly confident that the UK supplied device and the Aliexpress device come from the same casting.

Jonathan