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. http://usboiler.burnhamparts.com/oil/megasteam.php
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.....
Dave in Quad Cities, America
Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.http://grandviewdavenport.com