Exhaust elbow.. Stainless or aluminium

[contessaman]

Some advice please...

Bowman heat exchanger comes with a cast alloy water injection elbow. However, I need to make up a different elbow to put a bit of height on my exhaust before the water gets injected. I'm good friends with a professional welder who can help me out. I will need to buy ready made bends to get the radius I require and these will be butt welded to tubing.

Question is do I do it in aluminium as per original or stainless 316? Looking at what's available off the shelf in terms of bends, the stainless mandrel bends are only 1.5mm wall thickness versus the cast aluminium bends of just over 3mm wall thickness. Not sure what works out stronger but 1.5mm seems thin for a marine exhaust....

The finished article will be like an inverted U shape just over 12" high. The exhaust goes up , does a 180 back down then gets the water injection. I need to do this to get enough height for it to be a downhill run to the water trap.

Thanks in advance as always

 

[DownWest]

316 every time over ally. Hot gases and seawater are not kind to ally. Look a bit harder for 2mm SS bends.

 

[BabaYaga]

316 every time over ally. Hot gases and seawater are not kind to ally. Look a bit harder for 2mm SS bends.

IIRC the standard elbow on the recent Beta engines is alloy, so probably much depends on the exact composition.

I have the Beta high rise elbow, which is still made from stainless steel. Recently I replaced it, after 10 years and 500 hours. Quite a bit of corrosion was found, but no holes yet.
See this thread:

http://www.ybw.com/forums/showthrea...rise-exhaust-life&highlight=high+rise+exhaust

The wall thickness on mine was 2.8mm, so in the OP's situation I would not bother with anything less than 2.5mm.

 

[Jcorstorphine]

You could try www.nero.co.uk who do a range of weld fittings of different schedules. Hope I don't offend your welder but it is very important to back purge the fittings and pipe work with inert gas so as to stop oxidation of the parent material.

 

[Hydrozoan]

IIRC the standard elbow on the recent Beta engines is alloy, so probably much depends on the exact composition.

I have the Beta high rise elbow, which is still made from stainless steel. Recently I replaced it, after 10 years and 500 hours. Quite a bit of corrosion was found, but no holes yet.
See this thread:

http://www.ybw.com/forums/showthrea...rise-exhaust-life&highlight=high+rise+exhaust

The wall thickness on mine was 2.8mm, so in the OP's situation I would not bother with anything less than 2.5mm.

Yes, my Beta replacement is alloy but very much thicker - and, they say, should last longer than the previous SS one.

 

[Heckler]

Some advice please...

Bowman heat exchanger comes with a cast alloy water injection elbow. However, I need to make up a different elbow to put a bit of height on my exhaust before the water gets injected. I'm good friends with a professional welder who can help me out. I will need to buy ready made bends to get the radius I require and these will be butt welded to tubing.

Question is do I do it in aluminium as per original or stainless 316? Looking at what's available off the shelf in terms of bends, the stainless mandrel bends are only 1.5mm wall thickness versus the cast aluminium bends of just over 3mm wall thickness. Not sure what works out stronger but 1.5mm seems thin for a marine exhaust....

The finished article will be like an inverted U shape just over 12" high. The exhaust goes up , does a 180 back down then gets the water injection. I need to do this to get enough height for it to be a downhill run to the water trap.

Thanks in advance as always

I made one from stock SS pipe fittings and an ASAP water injection SS part. It bolts on to the aluminium stock heat exchanger on my MD22
Stu

 

[contessaman]

You could try www.nero.co.uk who do a range of weld fittings of different schedules. Hope I don't offend your welder but it is very important to back purge the fittings and pipe work with inert gas so as to stop oxidation of the parent material.

Brilliant thanks I hadn't seen their website. Could somebody in the know explain what the difference between 10 or 40 schedule is? I'm sure my welder will know about that he makes aircraft parts for a living but I will check. Looks like Nero have 316 bends and pipe at 2.77 mm that should be fine yes?

 

[contessaman]

Oh wait I've sussed it the schedule is basically a certain wall thickness.
So.. Definitely 316 stainless, but do I want 2.77mm or 3.8mm wall thickness? Strength and durability vs. Weight and strain on heat exchanger..
Final thoughts? Given that the thing will be quite gangly I'm going to have a bracket on it close to the hose end that bolts to a hard point to the engine to relieve some of the strain on the heat exchanger.
Grateful for any other good advice or experiences on the subject...
Cheers gents

 

[earlybird]

Brilliant thanks I hadn't seen their website. Could somebody in the know explain what the difference between 10 or 40 schedule is? I'm sure my welder will know about that he makes aircraft parts for a living but I will check. Looks like Nero have 316 bends and pipe at 2.77 mm that should be fine yes?

I bought the bits and pieces for a high rise bend to fit my Beta 25 by visiting Nero. Very obliging, I would recommend them.
I used 1.25" sch. 10 material, wall thickness ~2,7mm IIRC. Sch.40 would be uneccessarily heavy IMO.
Cost of materials was ~£40 plus a few hours in my workshop, I cut the mounting plate, prepped the tube joints and machined the outlet OD to 40mm etc.
I got a local outfit to tig weld it, they charged me ~£100 done by a coded welder after I tacked it with mig. The geometry needed to be fairly accurate.
Seems to be lasting the course well.
Add; At the "concept" stage it seemed to be turning out fairly hefty and I was originally going to put a support bracket on, but when I got it assembled I decided it wasn't needed.

 

[DickieT]

Yes, my Beta replacement is alloy but very much thicker - and, they say, should last longer than the previous SS one.

Not perhaps relevant to the OP but my alloy Beta one is now five seasons old and shows negligible signs of corrosion - it's removed every year for checking. Previous to this the SS versions did not fair as well. But as you say very thick walled casting and not overly expensive from what I remember. Perhaps a bit of useful info for other Beta owners...

 

[contessaman]

Sweet thanks for that. I've gone ahead and ordered the bits from Nero.
I went for the 40 sch in the end I guess it'll be heaver but I'm larger bore at 2" anyway so the 3.77mm wall will be more in proportion and I'm planning an extended blue water cruise so extra lifespan will be good for me. Best bit is they even had a reducer which I can use as the other way as an expander to widen my elbow at the end so it will fit the existing 63mm rubber hose in the boat! I'm well pleased thanks for bringing their website to my attention. I will try and have a support tang from near the outlet end back to the engine block. Thanks again all , fair winds