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can stainless steel de-alloy? Perry

G.Kaske_2 Member Posts: 30
In the right enviroment can be suseptable to pitting corrosion, and stress corrosion. Here is a link to a NASA web site on some studies, and tests done to certain metals good primer. HTTP://corrosion.ksc.nasa.gov/corr_control_matsel.htm#stainless%20steels

I think you will find a similar enviroment in a MOD/CON boiler HX.


  • hr
    hr Member Posts: 6,106
    spent several hours on the phone

    last night with my friend comparing notes on his leaking mod con HXers. They had to go back to the man, by the way, sorry :(

    Seems they present with a 3/4" deep layer of white sludge, almost like a stalagmite.

    After cleaning the HX they just start to sweat, not a leak via a pin hole, or even a fine mist, the HX just gets moist, even afer drying it off a dozen times. Similar to those press fitting seeps we saw recently.

    I know brass can de-zincify under certain water conditions and this is common in many western states. The CDA has plenty of studies and case history on that.

    I wonder that stainless could see the same breakdown. Does the alloy process of ss form a chemical bond, or is it like mixing various colors of playdo by hand, a streaked product so to speak :)

    Just as O2, but not water, can pass through a non barrier plastic tube wall, it seem small molecules of water pass through these failed HXers.

    I believe the failure, in these cases, is from the inside out, not an issue with gas quality, or inhaled toxic products thinning the ss from the fire side.

    If so, seems to me a proper cleaning and treatment with a product that coats the would be the answers.

    OR!! what about an anode solution? Perhaps even an external vessel, like a pot feeder with the anode material.

    Is this the case in large, critical duty HXers in your industry. Seems water chemistry and metallurgy are the skills to marry for that job?

    He had some interesting stories to share regarding aluminum HX breakdowns also. Enough gunk to plug the 1" condensate drain found on some brands.

    hot rod

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  • G.Kaske_2
    G.Kaske_2 Member Posts: 30
    300 series stainless

    I know you oriented question to Perry. But here is a little NASA metallurgy tid bit. 300 series stainless not as immune as one may think. Can be prone to pitting and stress corrosion cracking under certain conditions.

  • G.Kaske_2
    G.Kaske_2 Member Posts: 30
    300 series stainless

    I know you oriented question to Perry. But here is a little NASA metallurgy tid bit. 300 series stainless not as immune as one may think. Can be prone to pitting and stress corrosion cracking under certain conditions.

  • Perry_3
    Perry_3 Member Posts: 498
    Failures of SS - and other things...

    All metals have their failure mechanisms.

    Yes, brass can dezincify as you have mentioned. Dealloying is particaluarly common to copper based alloys under certain parameters; and is not limited to just copper alloys.

    But, dealloying is not the most common cause of failures in most metals and it is very rare for it to happen in the class of alloys we call Stainless Steel.

    I have my suspicions here - and have been thinking on it since last night once Hot Rod mentioned it.

    I sure wish I could have seen that boiler HX in person - and then sent it to one of the metalurgical labs I use if it was not one of the obvious failures of the 300 series of SS.

    My background here is that I have spent several decades as some kind of "plant" engineer; where my key job is figuring out why something has failed or wore out early - and how to upgrade either the part, the equipment, or the system so that it is more reliable and works better. A lot of that gets into the degradation and wear of metals (and plastics, etc). I have attended numerous classes on the failures of metals. I have 3 different metalurgical labs that I currently use now based on what evaluation needs to be done if it is not something obvious from my previous training (or if I need to formally document the cause of the problem).

    So we have presumably a 300 seriess SS alloy that has microleaks so that it "weeps." This alloy is in a service where it sees modest temperature, with heating system water inside of it - and cumbustion gasses and condensation on the other side.

    Based on what I know about 300 series SS my first guess would be chloride contaimination of the HX. Under modest to high temperature conditions free chlorides causes several forms of degradation: Pitting or cracking. The pitting and cracking may be very fine - and you may not be able to see it without a microscope. I have attached a photo of chloride induced stress corrosion cracking of 304 SS.

    Fine cracks or very small pits (mircro pitting) would appear as the metal weaping...

    This could originate from either the ID or the OD of the boiler tubing.

    For the ID of the boiler tubing: I wonder if chlorinated city water can be high enough in chlorine to cause a problem from the inside? I do know that a lot of commercial systems dechlorinate city water before putting it into 300 series SS pipes if the pipes are expected to get hot...

    Alternately was the heating water circuit contaminated by another source of chlorides. If that is the case I'm not sure how you adequately clean up the circuit.

    What strikes me as a very plasuable scenerio... is that the contamination occured from the OD of the tubing.

    And specifically during boiler cleaning.

    How many people clean the burner chamber with a commercial detergent or other type of non pure solvent based cleaner. The vast majority of off the shelf home and industrial cleaners have a fairly high chloride content (cleaning residue, and electrical or duct tape residue, has been a huge problem in the industry). Then once warmed by firing the burner the chloride residue would start to go to work on the 300 series SS - and there is almost nothing you can do to stop it once it starts. The only question is how long will it takes before the cracks or pits get through the tube wall.

    Chloride free cleaners are available - but are not the common ones available in most stores. Whatever, one thing that we should probably let people know is to not use ordinary cleaners when cleaning out boilers (and Aluminum alloys and copper alloys are also affected by certain cleaners as well). I note that tape residue is also a big problem as well.

    I have sent a message to my work email to check with what products we use at the plant for cleaning 300 series SS in areas where it can get warm or hot.

    What is interesting is that when I have been mentally desingning my personal idea of a better boiler - I'd been debating a completely different alloys that were what I figured to be better to build a boiler coil out of: Of the two under consideration one 439 SS has better heat transfer (but the same resistance to common chemical attacks as 304 SS), and another one (a real specialty alloy) was specifically designed to be resistant to various chemical residues - and has better heat transfer.

    I note that the posting the other day about sea-salt spray is really the same issue. Chloride contamination of the metal in the firing box where there is enough heat to affect at least 300 series SS and perhaps Aluminum (I do not have near the working knowlede of Aluminum failures as I do for 300 series SS because I have seen a lot of 300 series failures - and Aluminum is rarely used in power plants).

    I would like to point out that there are other things that can cause failures in 300 series of SS (and in other metals). Chloride problems is just what I consider the most likely.

    I'd really like to see one of these failures myself. Unfortunatly, Manuafacutures may not tell you what the real cause was - and may not even do the right analysis to find out either.

    So I hope that helps...

    For now I would advise not using any standard commercial cleaning products to clean SS boiler coils - unless they are certified to be chloride free (you might want to check with your industrial supply house for a chloride free cleaner product).

    Alcohol, or Acetone would be OK in a pinch - just ensure everything is well ventilated while in use and well dry before the boiler is reassembled. I also not that those may affect gaskets, seals, and certain plastics as well so that they must be handled carefully. Pure bottled water is OK too (although I might just be tempted to use distilled water).

    The Viessmanns 316T (in the Vitodens and Vitocells) should be more resistant than ordinary 304 SS (normal 316 is about 5 times as resistant as 304 to chloride issues).

    Hot Rod; is there any possibility that you could have the your freind contact the Mfr involved and get me into the loop on the failure anlaysis?

  • psd_3
    psd_3 Member Posts: 86
    It depends on the alloy

    Some grades of SS will pit due to corrosion, others are pretty much bullet proof.

    When the going gets tough, look for an all fuel grade SS like AL29-4C. 313L isn't too bad too bad either. The key is the low carbon content with added alloys like Chromium and Molybdenum.


    http://www.protechinfo.com/pdf/1016 (10-00).pdf
  • Steve Ebels_3
    Steve Ebels_3 Member Posts: 1,291
    What's going on?

    How old are these units and what type of construction are they. Do you have any idea what the grade of alloy is? 300 series? 400?
  • Perry_3
    Perry_3 Member Posts: 498
    313L not great; AL29-4C would be


    You posted while I was writing my big post above.

    AL29-4C would stand up to a lot of stuff; 313 SS would not, although it would be modestly more resistant to chloride than 304.

    If the problem is not chlorides.... Then who knows for sure without an analysis.

  • Perry_3
    Perry_3 Member Posts: 498
    300 - 400 SS Chemical Resistances

    Unfortunately; 400 series of SS has essentially the same chemical resistances as the 300 series of SS.

    If this is chloride issues... then 439 SS is equal to 304 SS.

    400 series of stainlesses do have better heat transfer.

    I do note that there is a class called "superferritics" that are highly resistant. AL29-4C is in this class of materials.

  • bob_50
    bob_50 Member Posts: 306

    I don't know much about metalurgy but I do have some experiance. Had a job where they buried five 3/4" 316 lines that were engineered to carry oil. They backfilled the trench with an insulating material called Gilsotherm. It was about a year after installation before they went to use them. They pumped abunch of oil in but nothing came out the other end. By the way the piping was bonded and hooked up to some kind of cathodic protection. This is when i got involved. we dug it up and the 316 pipe looked like it was made out of compressed steel wool. An engineer told me that the gilsotherm contained chlorine and had leached one of the alloys out of the ss. We replaced it with some pipe and fittings we had custom made by Babcock&Wilcox out of 500ss. The welder had to take a special test and the pipe had to be absolutely dry when we welded it. It was really something to see ss pipe that you could pull apart with your fingers.
  • Perry_3
    Perry_3 Member Posts: 498
    Something I should have mentioned

    While 316 SS is more resistant to chlorides than 304 SS; that only buys a little more protection. Is it enough for normal levels of chlorination of water. It may well be (and this might be the reason that Viessmann uses it instead of 304). Would it be enough to handle cleaning or tape residues inside the firbox. Probably not.

    In the end; 316 SS is fairly succesptable to chlorine attack in comparison to some other alloys

  • Leo G_99
    Leo G_99 Member Posts: 223

    diluted to about 50/50 seems to work very well if the build up is not huge.

    Leo G
  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
    Kitchens filled with austenitic pots and martensitic knives

    But I kick my stainless steel frying pans - what you want most is tinned copper

    Stainless proofing of otherwise rust prone steel works by mixing more than 11.5% of Chromium into an iron base. What happens next is that the Chromium, upon contact with the elements, forms an invisible layer on the surface of the metal and this invisible layer does not corrode further. Plus, it is self healing, ooh Chromium makes nice hubcaps. (This is exactly the same idea behind the steel bridges that were popular at one time and that require no painting - they just rust once on the surface and stop. In these rusty magic iron alloys it is copper that takes on the role of the defender of the stain, just like Chromium does in stainless steel, minus the shine)


    Superheroes all meet their kryptonite. Chloride viciously savages the rust protecting invisible Chromium rich layer. Even minute amounts of Chloride ions. Ever saw Superman? he falls apart at even the idea of the presence of kryptonite.

    And so, we need an antidote... which there is...

    Molybdenum keeps chloride at bay. So does Titanium, the T in the 316T or 316Ti of Viessman - otherwise, the ordinary 316 and its mate, the ubiquitous 304 (and that's the pots and pans 18-8 you'll find in kitchens) are highly weak-kneed when made to work in the presence of Chloride. Stress corrosion is what gets them, more than the Chloride itself. No stress, no sweat.

    Is a boiler stressed? Valium in the make-up water does the trick.

    Welded plate exchangers are very much stressed, daily heat in heat out, they grow, expand and contract and they are not well built for releasing these stresses. Bam, in any area where the movement induced stress concentrates and with the minute presence of savage Chloride - you get a crack, a hole and a leak.

    I don't know that the particular plate exchanger we're talking about is made of these austenitic stainless steels (the 2xx and 3xx series) These alloys are mostly non magnetic, that's one way to guess at the mixture. Their main beef is that they contain expensively beautiful Nickel (I've always been partial to Nickel plated stuff, it glows with the same luster silver does, but without the tarnish. Solid Nickel tea service sets are quite the thing, so are the Nickel plated S&W - I have my superheroes)

    Beyond the usefulness of a tea set, Nickel adds ductility and formability to the otherwise brittle Chromium rich stainless alloys. Pots and pans with 18% Chromium and 8% Nickel fall into the category of metals you can bang into shape, like Viessman's highly twisted and stressed coiled exchanger. Cool.

    The reason we should all kick our stainless cookware, as you probably all know, is because it is impossible to fry delicate items such as perch filets and bacon strips. Austenitic stainless steel does not transfer heat, not even a third as good as plain steel. I have my doubts about even boiling a pot of water. This is not cool.

    With this added thermal transfer resistance, it is no surprise to see austenitic stainless steel suffer greatly from heat stress (with the ever so popular 304 and 316 topping the patient list) . There is nothing gracious about the way they twist. Added stress along with the faint presence of chloride ions we shouldn't have forgotten about and... crack. Note though, that kitchen pots unlike welded boiler parts live relaxed stress free lives and all the Chloride soups we cook in them do not matter much.

    What else

    There are the 4xx series martensitic and ferritic stainless alloys that, with exceptions, contain no Nickel. They only have11.5% and up of Chromium for the invisible shield.

    These metals are magnetic, and they are hardenable and sharpenable for making the better kitchen knives, however, you can't bend and fold and weld them as casually as you would the austenitic pots and pans and the Viessman alloys. One main characteristic of the Nickel-less martensitic alloys that manufacturers find irresistible is that they are less costly. I can stick all the fridge magnets I want on the stainless muffler under my car and it doesn't rust, it doesn't cost all that much more, and it shines to the envy of all the other drivers. What better could we all want?

    Better choices are made by default in finding the lower cost. Is the plate exchanger attracted by the irresistible lure of a magnet? we might have some answers.

    Another plus in heat transfer applications: Chromium only martensitic alloys are near doubly good at spreading heat compared to the austenitic 18-8, this means less heat stress and less stress induced Chloride corrosion (less, not none) and the Molybdenum antidote still works... so... duh... where's the down side? Well, there's always an itch.

    Chromium only alloys develop sensitized areas wherever they've been welded or significantly bent into shape. Working with kid gloves is not good enough, careful treatment has to be extended to prevent sensitization... costly treatment... see where I'm going...

    And so, these sensitized areas left on their own will develop a rash because the invisible Chromium effect is turned off. The rash then turns into the plainest most common perforating rust. My muffler shows rust stains where it is welded. :(

    The secret to getting your bacon done right: the tinned Copper pan, that, and all the trapping of shiny Nickel. But if you have stainless stuff, your austenitic pans will be non magnetic while your martensitic knives will be magnetic. Ask a manufacturing engineer.

    Please HR, tell us more whether your failed gadget is magnetic or not? and if so, how strongly compared to live steel? and whether only magnetic in some corners? Is it all shiny like a frying pan or are there rust spots and blemishes along the seams? Did the perforation occur where you'd think warping stresses would collide? ... Minute chloride was there, we know that. In all likelihood, if non magnetic, it is probably Moly and her friend Titania that never showed up in the kitchen; if magnetic, then non politically correct manufacturing procedures were used and the now sensitized Chromium got offended into a rust hole.

    I bet people all over this site will go stick magnets on their pots and pans and knives and mufflers this beautiful Sunday morning - like I just did... :)

    Christian Egli

  • Perry_3
    Perry_3 Member Posts: 498
    The complexities of alloys and their degradation

    This is really a science that needs carefull tending to in order to produce long life items in many areas. Most people have no idea what goes into some of these alloys and the specific heat treatments they go through in order to minimize problems - or to maximize certain properties.

    I have seen 304 SS that was as rusty as any steel. The fabricator was looking for a cheaper way to clean scale off of it after it was hot formed into a hemisphere... and used some stuff on it that prevented the formation of the chromium oxide layer... We endid up shipping it back - half way across the US so they could chemically clean and treat it.

    I have seen 400 series SS that was heat treated to restore the corrosion resistant properties after forming and welding; only to be made to brittle for its application.

    I can't count the number of 300 series SS failures I have seen in numerous applications - and while chlorine is the most common there are many things that were not chlorine related (zinc, mercury, and other things cause a different kind of failure). Lets not forget bacteria attack in raw water or stagnant service lines (commonly called Microbioligic Influenced Corrosion - MIC).

    You are right that how stressed the part is plays a role - especially Stress Corrrosion Cracking (SSC). However, you can still get SSC on low stressed 300 Series SS with the right combination of cholride level and temperature. I've seen it - and I've seen it where it cost millions to replace the equipment (and the SS tubes were carefully annealed to eliminate any major stresses up front).

    Let's just say that it does not take too much imagination on my part to speculate several failure modes of a 300 series SS boiler HX. While chlorine is my first guess and probably the most likely, there really are several other things out there.

    Personally, In the HX world I tend to quickly transition to the superferritics. Not cheap, but they work. I note that AL29-4C is in this class of materials. I also note that these materials often require special heat treating after forming in order to bring out their corrosion resistant properties. Of course, even with a material like 316T - I would look at heat treating after forming as well.

  • Maine Doug_52
    Maine Doug_52 Member Posts: 71
    Always an educational experience

    coming to the Wall.

    I cook the bacon wrapped in paper towels in the microwave. Zap, change towels, zap, one more sequence if needed.
    Crisp, dry, flat and one now has a pre-warmed plate. Playing with magnet will have to wait a bit.

    >>>>The secret to getting your bacon done right: the tinned Copper pan, that, and all the trapping of shiny Nickel.<<<<
  • Glen
    Glen Member Posts: 855
    SS cleaning & passivation

    We service a large number of VSB boilers, and a growing number of Vitodens. I see various degrees of combustion chamber cleanliness, the least clean being LPG fired units and secondly almost anything in a heavy agricultural area, regardless of crop or type of animal husbandry. We use a wonderful cleaner called Citrisurf 3050, and when mixed and used as per instructions does a really nice job. Better yet its organic. And yes - stress cracking of some s s's and chlorine is well documented. Pic attached is a NG fired VSB - post cleaning, 8 years young, still looks new. For more info re stress cracking google society of corrosion engineers.
  • Dave_4
    Dave_4 Member Posts: 1,405
    Progress goes BZZZ, ding :)

    Copper is the connection. What might we say makes the microwave box possible? A whole bunch of copper wiring all crunched up into the magnetron - copper wiring with the ends tinned so that good electrical connection may be had.

    It still seems it's all about Tin and Copper for the best cooking environment. We're on the same page Maine Doug :) Microwaves are real cool.

    Now, I hope nobody handles the bacon in cooking tongs, usually the articulated stainless ones, those things are only meant for the amateurs and for weeding out the fake cooking experts on TV. Don't be caught wearing them.

    Simply wield, single handedly, a fork and a spoon; it is also the only way to be served a dinner roll at the table, tonged waiters do nothing for me... and of course, at the table, silver plate always trumps solid stainless. One exception, sweet mini tongs are fun to use on sugar cubes while having tea. Where do I get this stuff? It amazes me. I love my boiler room steak.

    Metals matter.
  • hr
    hr Member Posts: 6,106
    copper is the cookware choice for candy

    makers from what I have seen on various TV shows. Seems it conducts the heat most evenly.

    Hense my copper transfer plate idea :)

    Thanks all for the info.

    hot rod

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  • Maine Doug_52
    Maine Doug_52 Member Posts: 71
    Metals do wonderful things

    Copper in thin narrow strips allow me to solder glass. Now that is amazing.

    A big copper based Wok and a gas monster burner, some good spirits and some friends, mix and enjoy.

    But we digress.

    Long live the metals!
  • mtfallsmikey
    mtfallsmikey Member Posts: 765
    Just saw a blurb on copper cookware for candy making

    On "Good Eats", Food TV,last week. Alton Brown mentioned a favorable reaction between the copper and sugars in the basic syrup mix. I'm facinated by this thread! Don't know the differences between different grades of stainless, but 12 years ago while working for a medium-sized mechanical contractor, they remanned some stainless cooking vessels for a local pasta manufacturing plant. Seems the calcium laden slightly acidic water coming from the locality's system had eaten holes in the vats. The company ordered some kind of special stainless steel from Germany to make new ones out of, which worked and held up great.
  • Bob Harper
    Bob Harper Member Posts: 977
    a very reactive element

    Batelle Labs did some extensive studies on stainless alloys for use in HX. AL29-4C was tied for first place. It is very hard to drill, is not malleable, and doesn't do well at high temps. However, it handles a chloride environment pretty well. A lot of chimney sweeps specify AL29-4C if the boiler is co-located with the laundry room. There is some discussion about ionized chloride being capable of getting into the liner to wreak havoc but that's another discussion. Most sweeps now use 316Ti for their gas and oil liners. The original stainless liner, Ventinox, is 321 alloy, then came 300 low carbon and now titanium stabilized. The Ti also helps if you weld stainless. I've seen Cat. IV boilers vented with AL29-4C where a drip in condensate ate up the concrete floor but the stainless was tight.

    Two of the most common problems we see with chlorides vs. stainless is from soap testing for gas leaks using corrosive soaps instead of commercial non-corrosive soln.s and masons washing down brick fireplaces with muriatic acid splashing on the stainless flex connectors on gas controls. I brought this up with the mfr. I used to work for and got it changed in the install manuals to avoid corrosive soap test solutions. From other chat sites, the word still has not gotten out.

    Back to the original discussion: If you put stainless steels into high temps, usually above 1385F, you can get carbon to bond with chromium forming chromium carbides. The stainless undergoes intergranular corrosion and becomes sensitized. Then your steel is no longer very "stainless", which is a terrible moniker. Most people think stainless means the steel is like Superman's cape.

    The heat conduction properties were mentioned. Most pellet stove mfrs. now use thick aluminum tubes as heat exchangers or cast iron studs. In fact, Quadrafire's newest stove uses laminar flow technology in shaping their HX studs like tear drops.

    There was a class action lawsuit with Class A chimney mfrs over chloride action eating them up. Apparently, the mineral fiber insulation they used for solid pack insulation contained chloride. If rain seeped into the pipe joints, the chimney corroded away. Also, these chimneys don't do well on seacoasts as you can imagine. Take a ride down the shore and you'll see most of the factory built fireplace chimney terminations rotted away. Actually, the aluminized steel ones fair pretty well. Also note most direct vent gas fireplaces and wood burners now use aluminized steel for their fireboxes with good results as long as the temps don't exceed 1220F

    Fun discussion.
  • Perry_3
    Perry_3 Member Posts: 498
    HX Alloys

    In commercial tubed HX's. The most common superferritic tube alloy is called Sea-Cure; a propriatary mix developed by Trent Tube. It is similar to AL29-C4 in chemical composition.

    Plymouth tube purchased the Trent Tube operations and the rights to Sea-Cure. They are selling lots of it. That was the specialty alloy I refered to above.

    There is more Sea-Cure tubing made than all the rest of the superferricts and AL6XN combined (AL6XN is not considered a superferritic but has wonderful corrosion resistant properties and often pops up as an option in the metalurgy charts). I note that AL6XN is very sensitive to proper heat treating after forming - and there has been some problems with that that keep reoccuring. So while the base AL6XN alloy has great propeties; getting it properly fabricated has been enough of a problem that a lot of people steer away from it.

    For flate plate or some formed HX's Sea-Cure will not work as you cannot properely heat treat it in many of those forms.

  • bob_50
    bob_50 Member Posts: 306
    I can't help but

    wonder how well a cast iron boiler and a glazed tile chimney
    would hold up. I know this is a smart a## remark,but I just don't trust new stuff until it's been around a long time. bob
  • Cast iron boilers and chlorides...

    DON'T hold up well at all...

    Case in point, floor drain trap lost seal right below Buderus (doesn't matter who's cast iron boiler), and within 2 years, boiler looked like it was a condensing boiler, about 100 years old. Laundry (chlorox) drain was right next to the boiler room.

    I'll see if I can dig up the pictures, but it is NOT a pretty scene.

  • Gordy
    Gordy Member Posts: 9,537
    What to do???

    So whats a person to do. It seems AL HXs are finicky about water quality, and it would seem from what I have read here, and else where that SS HXs are not bullet proof either specifically chlorides. So whats the safe bet for material in HX longevity. Or is it a matter of close monitoring of the systems water quality as usual?

  • Gordy
    Gordy Member Posts: 9,537
    What to do???

    So whats a person to do? It seems AL HXs are finicky about water quality, and it would seem from what I have read here, and else where that SS HXs are not bullet proof either. Specifically chlorides. So whats the safe bet for material in HX longevity? Or is it a matter of close monitoring of the systems water quality as usual?

  • Perry_3
    Perry_3 Member Posts: 498
    Viessmann wins again?

    Viessmann uses 316T.

    As a 316 SS has a bit higher resistance to low level chloride attack as 304 SS (it will not withstand high levels of chloride attack at the temperatures in the boiler coil and burner box).

    I have just read the reports from 3 different websites on the properties of 316T versus 316. Unfortunately, non of them claim that adding titanium increases chloride resistance. It does increase general corrosion resistance at higher temperatures - such as what you would find in a burner box. The Titanium also increases high temperature strength - so that it maintains it shape better at higher temperaturs (again in the burner box).

    Here is a really good Technical Date Sheet on 316T (also known as 316Ti):


    My guess is that the 316T will probably stand up to normal levels of city water chlorination. However, it might not stand up to the highest concetrations found in some cities where the water is not that great and they use a lot of chlorine.

    You might want to install a carbon based water filter on the boiler fill line: That will take out the vast majority of the chlorine in city service. Change the carbon filter every year or so (say during normal boiler maintenance).

    You should only clean SS burner boxes and coils with a chlorine free cleaning solvent. You should only do air pressure leak checks using a commercial leak check compound such as "Snoop."

    Do not use any ordinary household soap, detergent or cleaner or any comercial cleaners that are not labled as chlorine free.

    Avoid being real close to a laundry area that uses a lot of chlorine bleach. Suggest to the homeowners to switch to non-chlorine bleaches.

    Edited to add: I note that the primary increased chemical resistance of 316T is to sulpheric acid. That is what forms from sulfer contamination of fuel. Especially prevalent in fuel oil, slight amount in natural gas and propane. If I were a betting man... I'd guess this was the reason that Viessmann adopted 316T. It works well for oil fired appliances - and has added protection from poorly purified natural gas.

  • hr
    hr Member Posts: 6,106
    Clean them properly at installation,

    use good quality fill water, buy some if you need to. Add a hydronic systen treatment compatiable with the boiler HX material. Test the fluid ocassionally.

    Be sure it has a source of fresh outside air only, look for a brand that has a good sealed case, or the Lochinvar with air piped to the fan.

    Then open them up yearly to inspect and clean out the HX if needed.

    Re-check with a combustion analyzer after cleaning and re-assembly.

    Those would be my suggestions for getting a long life cycle from todays mod cons.

    hot rod

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  • archibald tuttle
    archibald tuttle Member Posts: 1,033
    nother smart axxed question - why not copper hx

    I get if you have chlorine vapors from dry floor trap inundating cast iron boiler, it may not do so well, but I haven't heard that the failure that started this thread had anything like that kind of vapor trail.

    We don't yet know if it was a magnetic alloy or if the cause of the failure was chloride, but the thread here is regarding even levels in treated water, as well as the possibility of chloride based cleaners. I think the cast iron comment/clay tile comment is right on insofar as the number of cast iron and tile lined chimney failures I would ever attribute to treated water and cleaning.

    Interestingly, I put in my 'found' cast iron boiler in my house and cleaned it with a pressure washer into the floor drain while I had the skin off and before I put a new redipak in it, but with no cleaning agent, just water. It kept the dust down. It got me thinking about regular wet, rather than dry cleaning. But I digress.

    My smart axxed question is, what about copper heat exchangers as on laars ne:heatmaker style units. I know you can melt them if there is no circulation, but I have units in service for 15 years or more now with no leaks. Are they all waiting to go tomorrow or was the copper HX bypassed too quickly as a long lasting technology?

    And, depending on near boiler piping, and a little never seize on the bolts, they did manufacture those units for relatively easy replacement of the hx. Don't have any mod cons in service so can't compare hx replacement ease. It's pyschologically dissappointing to the kind of do it once do it right technician if the very core of the boiler is a sacrificial part, but if replacement is easy and parts rationally priced then it is just a different philosophical approach.


  • hr
    hr Member Posts: 6,106
    copper could not handle the ph

    of the condensate in a condensing boiler. But if I'm not mistaken the first pass coils in the MZ are copper and the second condensing chamber is aluminum and stainless.

    hot rod

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  • Perry_3
    Perry_3 Member Posts: 498
    Copper HX's

    Copper could work well in the right situation.

    It however has its own list of chemical issues - and stress corrosion cracking of copper is not unheard of (but not from chlorine).

    I would hesitate to put copper into a condensing boiler without some good data on copper leaching rate in the acidic condensate environment...

    Please note that I addressed up front on this issue that there were other things other than chlorine that could cause the failure of a SS boiler HX, and it would take a metalurgical analysis to really know (which would also tell you which side of the HX it started from). However, over 90% of all SS failures I have seen were chloride related. That is why it's my first guess - especially knowing that it could easily have been exposed to chlorides.

  • archibald tuttle
    archibald tuttle Member Posts: 1,033
    hr and perry

    got the ph problem for oil units.

    but I'm talking the early natural gas condensing boilers that were copper hx. they are not mod con and may not really see that much condensing in the hx but more in the vents which are trapped and drained. Copper has seemed to be very serviceable in these applications.

    Maybe this chloride related stainless steel failures are rare and can be controlled by water filter and cleaner selection so it remains material of choice, especially for other than nat. gas, maybe for natural gas as well.

    Assume it is the temperatures and temperature shock/expansion contraction that is the villain so that these concerns would not apply to indirect hot water heaters with stainless elements or jackets because the ranges of temperature swing are lower and no direct exposure to combustion. Certainly going to get plenty to chlorine treated water through the domestic side.

    Since we're on the subject, I did notice that you said other causes besides chloride are possible. Lets have a few more to worry about....

  • Bob Harper
    Bob Harper Member Posts: 977
    swimming pools?

    Anyone know if the ladders and rails are 300 series in pools? If so, why don't they corrode away from the chlorine? Don't say it's because all the kiddies pee in the pool and turn it into chloramines, which gives you that wonderful aroma of public pools, which we all thought was from too much chlorine. Yeah, right.
  • Gordy
    Gordy Member Posts: 9,537
    Hot Rod ...How long in service?

    Hot Rod you never mentioned in your original post, How long these HXs have been in service. Or was the water in the systems city, or well water. Was the water treated upon initial install or not.

    You did note that you thought it was maybe a failure from the inside out.

    I don't expect you to mention brand names of boilers, but are they interested in helping with finding possible causes. You did mention warranty was void I think. What was reason for denial?

  • Perry_3
    Perry_3 Member Posts: 498
    Its a temperature related phenomina...

    Swimming pools rarely get about 85 F. You would have to have a chlorine concentration so high at those temperatures that no one would get near that pool...

    Raise the temperature to 120F or higher... and things start to happen. Perfect firebox temperatures... even on low system temperature for a mod/con.

  • Perry_3
    Perry_3 Member Posts: 498
    Other chemical issues with 300 series SS

    Mercury and zinc off the top of my head... Again it takes temperauters; and in those cases somewhere above 200 F.

    There are others as well; but not worth my time to look up.

  • Intergranular corrosion

    Stainless steel is used in sensitized temperature, easy to produce carburizing, the occurrence of intergranular corrosion, stress is generated, it must be separated and carbon(carbon steel pipe), when the medium is non-corrosive and non-existence of the electrolyte of the electrochemical corrosion environment, does not produce intergranular.corrosionthe.
  • Zman
    Zman Member Posts: 7,446
    No Ads


    I am sure your commercial pipe is wonderful.

    Please look at the forum rules NO ADS

    There is no need to dig up 10 year old threads for the sake of SPAM
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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