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| Tony's Tips |
ARTICLE DATE: 08/01/2006 |
| Aftercooler thoughts, opinions, and answers to some quires... |
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This is not in defense of CAT or anyone else
referencing your total disgust for saltwater cooled aftercoolers that may use
aluminum in part of their construction. It's just that maybe there might be
other considerations involved here than just a defective design based SOLELY
upon the use of the materials in question.
No matter how much design effort is put into a particular mechanical component,
you can not have perfection in a design that will satisfy all the desired objectives.
No choice of one design will cover "all the bases", as all designs have many
objectives, with many of them "trades offs", as to overall initial cost, choice
of materials, weight, acceptable design life, maintenance, etc. In the case
of seawater cooled aftercoolers, CAT is not the only company that employs this
system (SWAC), and is also NOT the only company that has chosen to use an aluminum
alloy for the main part of the housing and/or components that typically have
a copper alloy core inside of the housing with seawater passing thru the core.
In fact, I cannot think of one diesel engine company manufacturing marine diesels
under 12 liters of displacement developing above 50 HP per liter, that does
not employ SWAC and that does not use aluminum in part of the construction
of these seawater cooler aftercoolers.
With over 20 years of dealing with many styles of seawater cooled aftercoolers
from all of the companies discussed on these forums, my opinion is that each
company has employed "their" design that best meets their objectives and design
criteria. ALL of these designs employ some type of "seal" and "insulator" system
that keeps the seawater from bypassing the core and entering the engine. This
same seal/insulator also keeps the water from contacting the air side of the
system which is commonly made from an aluminum alloy and bridging the gap between
the core and the housing. This is the small area (boundary) where the problems
start to occur and where design and assembly make the unit more or less prone
to failure.
I have found much fault with the SERCK coolers used on Cummins engines but
can also say that with proper maintenance, these aluminum housed seawater cooled
aftercoolers, which also have a copper alloy core, can outlast the engine.
BUT, I can likewise say, without reservation, that they do have the potential
for leakage from the seawater side to the air side (aluminum) and, depending
upon all of the conditions present, engine failure can result.
In the case of the Cummins supplied seawater aftercoolers, the main fault doesn't
lie strictly because they chose to use aluminum on the air side, but rather
because of the assembly practice that is used for the component. This particular
"design" relies solely on an "O" ring for this seal that keeps the seawater
where it is supposed to be. Problem is though, the seal is only a very small
boundary, dimensionally and, because of all of the variables in operation related
to moisture on the air side (condensation) and seawater on the other side,
the potential for pitting, corrosion, and worse (leakage) is an on-going potential
problem. But, keeping this problem from happening is relatively easy. Just
disassemble the aftercooler when new, and re-assemble it with copious amounts
of the best marine grease you can get in the suspect areas*, and then do it
every 1000 hours (or less) or every two years. By doing this, the potential
for leakage and/or progressive corrosion is just about nil, and these aftercoolers
made w/ aluminum and copper alloy can give good reliable service for well over
10 years (* there is a thread on this procedure w/ pics on these forums). Also,
this particular design of aftercooler (water seals are located on the bottom
and top), aggravates the issue as condensation on the air side sits at the
bottom seal and is only separated from the seawater by about 1/16". Even though
the condensation is fresh water, it still causes pitting and corrosion to the
sealing surface on the aluminum housing. This is where "grease" really mitigates
the problem and keeps it in check. If this design were flipped 90 degrees,
much of this problem would not be there. Is any of this a "design flaw", that
should start a "class action" law suit?? No, it's just one of the trade-off's
in the overall design.
I'm not familiar w/ the CAT aftercooler, but maybe their particular "trick"
design for maintaining seawater where it is supposed to be leaves something
to be desired. But maybe they have some of the same couch engineers working
for them that Cummins has, that have no real experience with servicing aftercoolers
and understanding what really happens in their use when seawater is attempted
to be held in place w/ a dry rubber seal. Possibly, just the application of
the right grease when assembled new would solve much of the issue, but maybe
not. I don't know in this case.
I have dissembled quite a few of Yanmar aftercoolers used on their smaller
engines and one on a 4LH. They also use aluminum for the air side of the housing.
BUT, they also "epoxy" ( at least it seems like some type of epoxy) the cores
in the housings and I have yet to see one leak. Tough to service, if needed,
but their "trick" doesn't seem to leak, and, seems to have good isolation for
preventing galvanic corrosion or electrolysis. I also recently worked on a
Volvo 41 series aftercooler and this one had plastic seawater caps, an aluminum
housing and a brass/copper (?)alloy core. It was leaking, and we needed a new
core. Overall, I did not like the design (the way it was "sealed"), as it seemed
to have the potential for Murphy's Law to come into play during the assembly.
Generally, I would tend to disagree w/ you, Karl, as to the "law suit" thing,
IF your sole contention is the use of aluminum as part of the construction
in a saltwater cooled aftercooler. That doesn't mean I would not like to see
all saltwater aftercoolers made from titanium, stainless, bronze, and cu-ni,
I just think that the culprit ( if any) may be in a particular design flaw
and/or assembly/maintenance practices, and NOT just because CAT chose to use
some aluminum in the construction. Can you post some specifics as the actual
design or construction, or do you happen to have a parts/assembly breakdown
or technical drawing that can be scanned/posted??
Just my thoughts.
Tony
I did a good job passing Corrosion 101 years ago and since then have had enough
experience in this field to make some qualified judgments as to design, functionality,
and overall usefulness of marine engines and components in this field. I'd
be the last person to argue that a cast titanium housing for sea water cooler
aftercoolers would not be a superior choice of materials for this type of service.
But I also realize that design is "give and take", and this is where I think
you are missing the point. What you are really advocating, since you are adamant
on this subject, is to take on all of the companies that use aluminum in their
designs, Volvo, Cummins, Yanmar, MAN, MTU, etc.. As for the other "qualified"
individuals you mention as "people of a like mind" supporting your feelings,
well again, we all have our opinions. Mine is only based upon my own experiences
and my reasoning for this posting is to help avoid some of the issues that
come with the ownership of these types of engines. It's not to litigate my
way into an replacement engine.
Also, if a properly chosen aluminum alloy is the wrong material, then what
is the right material that would keep the costs competitive w/ what the market
will bear, along with having ALL of the mechanical properties needed for this
component? If the design life of the engine is 3000-7000 hours / 10-15 years
of marine service, and the aftercooler made with an aluminum housing outlasts
the engine in most cases w/ proper maintenance, then why go after the aftercooler
design when it was a piston or valve that let go and took out the engine.
Karl, you are a very knowledgeable guy, but you are also a Detroit guy dealing
w/ heavy iron. These engines we are talking about are in a different class,
and I personally don't think the comparison is fair. The Cat 3208 at 375 HP
built close to a 20 year track record with aluminum housed seawater cooled
aftercoolers w/ probably only a handful of failures ( not that I even know
of one). If the 425 CAT is experiencing many failures, then let's look at it
as an individual flaw and not just categorize everything else built w/ similar
material as trash. As for failures of other designs/makes of aftercoolers w/
aluminum housings, again I have not seen this issue unless it was related to
poor maintenance or a flawed design that made the aluminum parts more susceptible
to failure.
I'd also like to mention the following since you are so hung up on the galvanic
series. There are 1000's of aluminum hulled crew boats in service all over
the world and most of them have propellers, sea strainers and heat exchangers
made of materials based on copper alloys. Certainly they have zincs and/or
impressed voltage cathodic protection ( like aftercoolers) , but the fact remains
that using aluminum and copper based alloys was the best trade-off in design.
Should we start looking into premature hull failures and find a common denominator
that has deep enough pockets to sue?? Again, I'm not saying that aluminum is
the best material for making aftercooler housings - it's just the best compromise
at this point in material design for this purpose. Maybe in a few years, a
high strength / hi-temp engineering thermoset plastic will be the material
of choice for these components. In the case of CAT and their issues, I would
tend to treat that as a individual problem that needs to be dealt with. Aluminum
has its place in the marine environment, it's just that it needs a little extra
thought as to how and where it is used and how it is maintained to get the
longevity in service that it can have. Tony
I'm not arguing w/ you as to the problems associated w/ aluminum and copper
based alloys touching each other when immersed in seawater. The "copper penny"
thing (a well know analogy) is a perfect example, and, in fact, all that needs
to be part of that scenario is the right moisture and Father Time, total immersion
is not even necessary. But, now take that copper penny and lay a 1" x 1" X
1/32" thick piece of common plastic ( a piece of milk carton for instance)
between it and the aluminum hull. Problem basically gone, immersed or not.
The issue here is really whether the design of the aftercooler is such that
isolation and sealing along w/ continuing long term proper maintenance can
happen during the course of the useful life of the motor. If SERCK were to
redesign the neck portion where the aftercooler core seals in the housing by
adding a stepped plastic sleeve about 3/16" thick w/ a "O" ring groove in the
aluminum housing, and an "O" ring under the bronze cap that squashes the whole
thing together, I'd say that the useful life and possibility of failure would
be nil for 20+ years even w/o the use of grease (although it should still be
used). Plus, it would make maintenance much easier. This simple modification,
early on, would cost close to nothing, and to change now would still be in
the long term interests of all. I would call this an improved design or modification
to an already reasonable design. Don't forget one of my motto's "ALWAYS LEAVE
ROOM FOR IMPROVEMENT". In this case, SERCK has left that room and maybe CAT
left too much room.
In Cats case, maybe their issue is with the way they chose to seal and isolate
the components. Bad /defective design?? Very possible. Bad choice of materials,
maybe, if the alloy of aluminum was wrong, and /or the overall design does
allows contact between the two very opposite alloys in the presence of seawater
(or fresh water for that matter).
So Karl, go ahead and rant and rave about aluminum and its use in these applications.
Don't spend your time worrying about it, let me and the other people who are
willing to re-educate themselves to deal w/ the potential issue. It is dealable!!
Maybe Pascoe needs to look at this in a different light, instead of just condemning
it all. Why doesn't he offer a suggestion as to improvement, instead of just
complaining?? If I were you, I'd spend my energy looking at "that" engine you
came close to upgrading to and buy them so you can really enjoy your boat.
Once you experience replacing 40 year old diesel technology w/ a current a
design, you may be willing to change some of your perspectives. Actually waiting
a while was a good thing now that "common rail" is here. The experience is
unbelievable compared to regular mechanical injection. But to do this, after
you buy them, dissemble the aftercooler and use your knowledge to reassemble
/ modify it to keep it sealed and isolated for the next 10-20 years, or longer.
There are some amazing greases and assembly sealants available today that can
easily accomplish this task. After that, I think we will both do better, have
more time to go fishing, and stand a better chance of keeping the lawyers out
of our lives and our pocket books. Tony
You have worn me out and I'm sure you want to get on too. But your efforts
have paid off as you have convinced me that you will never be a candidate for
repower because no manufacturer of an marine engine today of this class (or
any class?) could offer you what you want. You need that 8 -10+++ pounds of
iron per horsepower as it probably does give you most of the features you mentioned.
So forgiving are those old Detroit's.
As for JML and his problem, hopefully he will be able to get this worked out
w/ CAT. With a service bulletin on his side, I have no idea why he is getting
the run around. But, with so many eyes watching these forums now, I suspect
he'll come out whole in the long run.....................................................Tony |
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