Rotting at the water line. New thread from Another Rotted Out Steamer Replaced.....

Dave in QCA

We are all familiar with the problems of rotting that sometimes occurs in cast iron steam boilers, right at the water line.  In articles that go into great lenght on this subject, it is concurred by all that it is a result of having high chlorides in the water combined with very high temperatures in the cast iron, which occurs in pinned cast iron boiler sections, right at or slightly above the water line.  The exact reaction is called graphitic corrosion.



Since this problem is apparently caused by the combination of factors, removing any one of the factors seems like a possible cure the problem.  That problem, premature failure, which is really unacceptable to the building owner.  You should not have to change out your steam boiler like you would a fanbelt, or a lightbulb!



Of course, the boiler companies for quite some time have said, "the problem is the chloride level.  It's not our fault."  But, the chlorides were always there, and the old boiler (without pins) lasted for 75 years.



So, it seems, that a change in the design of cast iron boilers is the solution. 

My observations of a few boilers now on the market is that change is beginning to take place.  The Burnham Megasteam, of course, is the obvious front runner.  There is no pinning at all.  The heat transfer area is expanded by the use of horizontal flue passages that route the combustion gasses horizonatlly back and forth through the boiler castings, much like the hold coal fired cast iron sectional boilers were set up.  Burnham even warrants this boiler expressly against water side corrosion.   WOW! 

Probably everyone on this site has seen images of this boiler, but if not, here is a link to some views of the castings.   <a href="http://usboiler.burnhamparts.com/oil/megasteam.php">http://usboiler.burnhamparts.com/oil/megasteam.php</a> 



As Steamhead said, we are waiting and waiting for Burnham to market a gas burner for this boiler too!  It would also be nice if they could expand the line and go up to sizes in the small commerical range too.  (important to me, becuase that is what I would need.)



I have also notice that the Smith GB-300 has an unusual design to their castings.  See Picture Attached.  The bottom of the casting has deep ribs, much like Weil-McLain used to do on the H series boilers.  When you look at the sides of Smith's casting, note that the pinning stops right below the water line, and the section widens out, making a larger steam chest.  One would think that this design would be much less prone to water line rotting.  I would love to hear from all of the pros whether they have encountered rotting at the waterline in this boiler.  The other curious thing, the GB-300 dissappeared from Smith's product list about a month ago.  Literature, brochure, and Installation manuals are still in the literature section.



Also, I have noticed that ECR, in the Dunkirk D248 as well as the identical product in the Pennco line had a pattern in the pinning, that appears to decrease the amount of pins at the middle area of the water line.  It's not real obvious, but it is there.



So, my questions to the Pros are as follows:

1.  Do my observations relate to intentional improvements in Smith and ECR castings that reduce the occurance of rotting  in these boilers in actual real world application?  

2.  Are there any rumors out there of Burnham expanding the design that it has introduced in the Megasteam to both gas and larger sizes? 

3.  Are there any rumors of any of the other boiler manufacturers working on a product to compete with the Megasteam?



I hope this proves to be a productive and helpful thread.....

Rod

Pictures

Hi Dave-  A very interesting thread! I've been saving pictures of rotted out boilers that have been posted by the pros and thought it might be of help to post them together for comparison.  The first two were contributed by Steamhead and the last one by Ron Jr.

Other than where marked as such, I don't know the type /model. Maybe one of the pros can identify them for us.

- Rod

Mike Kusiak_2

Cast iron exposed to combustion tempertures

One thing I have noticed about the Megasteam and other multipass boilers is that the area exposed to combustion temperatures is entirely below the water line. This prevents any area of the cast iron above the water line from rising to temperatures significantly above the boiling point.





Compare that to the atmospheric designs, where above the water level, the cast iron sections are heated to much higher temperatures, approaching that of the flue gas itself. This seems like a poor design, as the cast iron is exposed to thermal stress by the temperature differential between above and below water level, in addition to the much higher temperature it has to endure above the water line.



Eliminating the pinning above the water line may be helpful as it reduces the heat transfer to the area not backed by liquid water, and should result in a decrease in temperature of the cast iron in this area.

Steamhead

The left one

is a Weil-McLain EG, the middle one is a Burnham Independence. Not sure what the one on the right is, but it's definitely a light commercial one- possibly a Weil-McLain 80 series?

Steamhead

Right you are, Mike

and that is also what makes the MegaSteam as efficient as it is. Designing a boiler so all the heat-transfer surface is below the waterline not only eliminates overheating and unequal expansion, but also allows better heat absorption. 



Dave, I haven't heard anything from Burnham or anyone else. Burnham knows we want them to market a gas option for the MegaSteam as well as a small commercial 3-pass steamer, but that's all I know.



The casting variations you mention might help, but they cannot completely eliminate the problem. Three-pass is the answer.

Big Ed_4

Mega Steam

Is the Mega rated for a gas burner ?

Steamhead

Not

at the moment.