overlay on boiler tubes

Date 08-07-2003 11:42

There are several issues you have to be clear on before you start:
- You must have an R stamp to do repairs in a boiler, unless you are covered under the owner user clause.
- The client may have ideas that are a little different than yours (one example we ran into: we have an SMAW WPS for F43 over P1; the client insisted we use GTAW, with F43, including a 175F preheat, all welding must be done vertical down). Those ideas may require you to qualify a new procedure and/or your welders.
- When you get into the work itself, remember there is a minimum allowable wall thickness required for the tubes. It is not permissible to include the thickness of the F43 overlay in the "overall" thickness of the pressure retaining part (ie boiler tube wall thickness). F43 may not be used in a wetted environment in a Section I application.
- If the client wants either corrosion resistant or hardfacing overlay, the welder must test in accordance with those requirements (ie, a butt weld WPQ does not cover that type of weld). If you can call the work "weld build up to restore dimensions", a welder who has tested on a butt weld coupon is covered (within the other essential variables).
- Pay close attention to the essential variables in Section IX for the PQR if you have to do one for overlay. Filler metal diameter for the first pass, number of layers required, minimum thickness of the base metal, and a couple more are not usual. You'll have to make sure you have them all straight or your carefully prepared PQR may not cover exactly what you need to do in the boiler.

Charles Hall

By brande

Date 08-10-2003 03:10

Thanks much for your reply.

These tubes are customer specified equipment with their own proprietary specs. They are done in a code shop.

I was looking for any tips or tricks to shorten my development time.

Anyway, I'll keep the group posted on developments!

Good Luck

brande

By colins

Date 08-07-2003 14:32

Brande,

I used to do QA/QC for a large company that performed mainteneance and repair on Large boilers in Alberta, Canada. Depending on the base material, We would match the filler material accordingly. (P1 to P1) etc.... . Is this requirement for the customer ? One problerm with using an alloy to overlay carbon steel tubing, is the risk of running into Dilution of the base material in to the deposited weld metal, maybe this is a concern for you maybe not, just thought i would throw it out there.

There is a company in Florida, Southeastern Mechanical Services that specializes in overlay of tubing for boilers and Furnaces. They do fantastic work. Maybe get in touch with them or check their website out.

By insp76

Date 08-07-2003 23:15

Brande, I`ve been involved in many boiler repair jobs and I can`t say that I have ever heard of using 309 ss or 625 inconel to over lay P1 boiler tubes but I am curious as to why and what would the advantages be. The problem you could experience is galvanic corrosion attack of the P1 material due to the high chrome content in these filler materials but then again maybe I`m wrong. Lord knows it wont be the first time. Have a good day

By pipewelder_1999 (****)

Date 08-08-2003 02:42

Hi Insp,

One application of this is in Waste to Energy boilers. An article that breifly describes the situation is at http://www.asme.org/research/imw/boilertube.pdf

Have a good night

G Austin

By ssbn727 (*****)

Date 08-09-2003 16:34

Hello Insp76!

Check out the websites listed in the other posts on this thread...

I think that after you do, you'll have a better understanding of what's involved, the different schools of thought, and the reasoning behind all of this...

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By insp76

Date 08-09-2003 19:25

SSBV727, Thanks for the help. Although I am very famillar with alloy overlay of vessel and tank walls ,I didn`t realize ss and inconel overlay of carbon tubes were a popular method of extending the life of boiler tubes. It`s a known fact that high chrome content has a resistance to heat and corrosion, it is also a fact that carbon to high chrome overlay or even in close contact are subject to galvanic corrosion. My question to you is : If galvanic corrosion is not a concern is it because of the excessive heat and the lack of oxygen in the fire box? Thanks again and have agood day.

By ssbn727 (*****)

Date 08-10-2003 00:31

Hello Again Insp76!

Galvanic corrosion is always a concern but, in this weld overlay application it's already known beforehand that one can prevent this from occuring afterwards to a degree, and if applied properly to the suspect material, then the effective rate of galvanic corrosion can be often minimized, and neutralized or immunized to a great extent whereby the end result is increasing the working life of "insitu" waterwall boiler tubes when compared to the original CS or low alloy tube's working life!!!

I'll try to elaborate by first saying that three conditions must be met in order to determine as to whether or not Galvanic corrosion is actually occurring and not some other form of corrosion. These are the the three conditions: (1) There must be two electrochemically dissimilar metals present. (2) There must be an electrically conductive path between the two metals. (3) There must be a conductive path for the metal ions to move from the more anodic metal to the more cathodic metal.
If any one of these three conditions do'nt exist, galvanic corrosion will not occur.

At first glance, one would say that this will (typo) or will not occur after joining either 309, and 312ss or Inconel 622, and 625 to carbon or low alloy steel as in the case of performing the weld overlays on boiler tubes but, if the thickness of the overlay material, and the amount of dilution is controlled, then galvanic corrosion will in effect be minimized!
Other additional considerations in design can further decrease the amount of galvanic corrosion

please let me explain the thickness aspect first - of this phenomenon:
One of the two metals is more "noble" than the other... In other words, one is the anode (less noble) and one is the cathode (more noble).

Basically, one can control the amount of galvanic corrosion by using a variety of methods to be incorporated into the design.

Galvanic compatibility of the two metals is important and varies in different environments. By matching the two metals anodic index values as closely as possible, one can prevent the galvanic corrosion potential after applying this method of extending the working life of waterwall boiler tubes and membranes...

Controlling the thickness of the weld overlay is another method because, if the carbon steel boiler tube wall (Anode) thickness is greater than the weld overlay (Cathode), then galvanic corrosion will be minimized to a degree. Therefore it is important to avoid making combinations where the area of the less "noble", anodic metal is relatively small compared with the area of the more "noble" material...
Therefore it's important to inspect waterwall tube thicknesses throughout in order to determine whether or not to build up certain areas where this condition is'nt present before performing the weld (clad) overlay...

Minimizing dilution will maintain galvanic compatibility and consistency at the boundries where the two metals are fused together.
Making sure the suspect material's surface is relatively smooth is also important in order to maintain consistent dilution and galvanic compatibility... Minimizing dilution itself is done by the use of depositing multi-pass weld layers. (Zues process does this in two passes as compared to three with GMAW-P which also means less heat input)

Finally if possible, cathodic protection can also be applied to further protect from possible galvanic corrosion by the use of an impressed current(DC)...

So, to answer your question. The answer is yes and (I should've put this in originally) no because the heat or in combination with the lack of oxygen in the firebox, by itself really does'nt prevent the Galvanic corrosion from occuring...

The Math and physics involved with galvanic corrosion is explained at:
http://www.corrosion-doctors.org/Thermo/FreeEner.htm

All of the above info can be found in this website:
http://www.corrosion-doctors.org/Aircraft/galvdefi.htm

Hope this website and others that explain the various types of galvanic corrosion conditions can help you understand this better...

Respectfully,

SSBN727 Run Silent... Run Deep!!!

P.S. Do a Google search and you'll find out more about galvanic corrosion!!!

By Niekie3 (***)

Date 08-10-2003 15:54

Hi insp76

For galvanic corrosion to occur, you need an electrolyte in which the metal ions can be transported from the one electrode to the other. Under high temperatures in a furnace, you typically do not have such an electrolyte present. (It has evaporated.)

Galvanic corrosion therefore becomes a problem when the boiler is undergoing start-up or shut-down, or standing idle. Galvanic corrosion can also become a problem in "stagnant" areas of the boiler where the design is such that condensation can occur on the outside surfaces of the tubes, or there is such a great build-up of soot and other contaminats that an electrolyte can form under the layer. Under these conditions, you will in any case get rather serious corrosion with or without the galvanic effect.

As long you have a well designed boiler that is operated correctly, (Including start-up and shut-down) these problems should not be a great issue.

Regards
Niekie Jooste
Fabristruct Solutions

By insp76

Date 08-10-2003 17:52

NIEKIE3, your statements reinforced what I beleived all along, during operation the exterior of the tubes should be in a non aqueous enviroment due to the excessive heat, therefore galvanic corrosion attack should be kept in check. I know API codes state that temp. below 25f and above 250f disapate moisture and corrosion should not be a problem. Is this above 250f also true for galvanic corrosion ,if not do you know the above temp? Thanks for your time, have a good day

By Niekie3 (***)

Date 08-11-2003 20:26

Hi insp76

I believe that in the case of boilers, it would be difficult for me to give a definite upper temperature. This is because it depends on the humidity of the boiler atmosphere (keeping in mind that water is a product of combustion) and "hidden" places where this moisture could potentially accumulate.

None-the-less, I find it difficult to imagine that at a temperature substantially above the boiling point of water at the pressure present in the fire box, you could have much of an electrolyte present. Obviously there are other problems such as acids forming which may have relatively speaking higher boiling points. They could be electrolytes where enough soot is present to act as a "blanket". Some of this "soot" can also have water of crystallization present which can be given off slowly. Most of this is however mostly theoretical. (I say this, because at the typical surface temperatures of the tubes, they will be substantially above 250°F.)

Then we also need to keep in mind that there are high temperature oxidation type degradation mechanisms which are not necessarily based on electrolytic action. - This is another story.

Regards
Niekie Jooste
Fabristruct Solutions

By insp76

Date 08-12-2003 01:01

Niekie, thanks to you and SSBN727 I have a better understanding of the overlay application and why galvanic corrosion on the OD of boiler tubes in most cases are not of great concern.

High temp. material degradation, that`s a horse of a different color isn`t it.
Thanks and have a good day

By jwright650 (*****)

Date 08-12-2003 11:18

Insp76,
This forum is a great source of info. There is so much to learn and no time to digest it all. Hopefully, I'll be able to keep up with some of these discussions. Boiler work has never been in my line of work and it is interesting reading.
Thanks to all for posting,
John Wright

By insp76

Date 08-12-2003 23:05

Hello John, Yea your right my freind the learning never ends does it. I spend my day`s at work actually working with codes, standards, publications and owner specifications and some of my free time visiting websites like this one accumulatng even more information (this site is by far the best). I would like to know everything that there is to know about inspection and codes but that is not possible, still that will not stop me from trying. We can all spend a lifetime trying to accomplish that. Thanks and have a good day.

ps. you don`t have to answer the e-mail I sent you,but did you recieve it?

By jwright650 (*****)

Date 08-13-2003 11:30

No, I sure didn't receive any emails from you. I looked again and refreshed my mailbox and I have nothing. Send it again and I'll take a look JWRIGHT650@AOL.COM
John Wright

By ssbn727 (*****)

Date 08-11-2003 05:58

Hello Niekie!

Long time no read!!!

I was going to give Insp76 a "double"(yes and no) answer but, I decided to answer his question with an explanation...
In an attempt to avoid any possible confusion, I'm going to give what I did originally write as the answer to insp76's question by stating that prevention of galvanic corrosion must be first incorporated into the design of any system first!!! A multi-pronged approach will produce the best results... First of all, I mean no disrespect when I comment below, to anyone But, I must warn everybody that this will take some time to explain so prepare for a long reply...
By consolidating all of your bets on or in other words, "putting all of your eggs in one basket" as far as relying on the heat, and lack of oxygen in the fire box as the only means of protection or as the only reason for the absence of galvanic or any other form of corrosion would be oversimplification to say the least!!! What I'm trying to get at is that steam is still water only in a vaporous state, and even though in comparison to all natural types of water (whether it be from a river or the sea in it's liquid state) or ultra-pure water, steam is still an electrolyte because, until the elements that make up water, separate from each other, then we're still dealing with water only in a different state ...
Therefore, the steam is still water, which means that it's still an electrolyte!!!
The amount of galvanic corrosion would decrease as compared with water in it's liquid state and yet, Galvanic corrosion is still occuring, just on a smaller scale, and mainly in the interior of the tube!!! Sure, the exterior is protected by the heat, and lack of oxygen in the environment of the "fire box". However, one must consider what has already occured within the interior, and in the thickness of the tube prior to the weld overlay, and afterwards... This is where corrective measures to diminish this are important!!!
Dissolved oxygen refers to the volume of oxygen that is contained in water. Oxygen enters the water by photosynthesis of aquatic biota and by the transfer of oxygen across the air-water interface. The amount of oxygen that can be held depends on the water temperature, salinity, and pressure. Gas solubilty increases with decreasing temperature (colder water holds more oxygen). it also increases with decreasing salinity (fresh water holds more oxygen than saltwater). Both the partial pressure and the degree of saturation of oxygen will change with altitude. Finally, gas solubility decreases as pressure decreases. Thus, the amount of oxygen absorbed in water decreases as altitude increases because of the decrease in relative pressure.
A key point to remember is that in modern boiler systems, dissolved oxygen (DO) is handled by first mechanically removing most of the dissolved oxygen, and then chemically scavenging the remainder. The mechanical degasification is typically carried out with vacuum degasifiers that reduce oxygen levels to less than0.5-1.0 mg/L or with deaerating heaters that reduce oxygen concentration to the range of 0.005-0.010 mg/L. Even this small amount of oxygen is corrosive at boiler system temperatures and pressures. Removal of the last traces of oxygen is accomplished by treating the water with a reducing agent that serves as an oxygen scavenger. Hydrzine and sulfite have been widely used for this purpose, but they have shortcomings. Sodium sulfite, although an effective scavenger, is not recommended for use in systems operating above 1,000 psi because breakdown occurs to form corrosive hydrogen sulfite and sulfer dioxide. Also, sodium sulfite increases the amount of dissolved solids, as well as the conductivity, in the water.
Hydrazine efficiently eliminates the residual oxygen by reacting with the oxygen to give water and gaseous nitrogen. Unfortunately, hydrazine is an extremely toxic. This is where Erythorbic acid and it's sodium salt are replacing sulfite and hydrazine as oxygen scavengers in boiler water treatment. Based upon the Stoichiometric relationship, it should take about 13 parts of sodium erythorbate to react with one part of dissolved oxygen. However, actual lab and field test data shows that much less erythorbate is needed than what the theoretical results to scavenge oxygen (DO). Further scavenging occurs from the breakdown products of the erythorbic acid. Field trials in large utility boilers show the intermediate breakdown products to be lactic and glycolic acids. The ultimate breakdown product is carbon dioxide... Also, a thin film of hydrogen will form to protect the interior surface initially...
Erosion corrosion can also wear out the interior's protective coating, applied intially by the manufacturer/supplier of the tubes, and some of the older tubes have coatings that actually did more harm than what they were intended to protect!!!
How does all of the above relate to galvanic corrosion or any other form of corrosion? Well - just look at all of the different types of water treatments that were and are currently either being used or are being tested... If you look closer, you'll see that this is another consideration that must be taken into account when designing, by using a multi-pronged approach. Thermal cycling (coefficients of thermal expansion differ when comparing the filler metals used as the overlay) results in accelerating certain forms of localized corrosion as do other environmental factors. The entire circumference, wall thickness, surface (both internal and external) finish, and length of each tube will not be uniform, metallugically speaking. Furthermore, no two tubes are exactly alike as far as metallurgical (microstructural) uniformity is concerned so because of this, various forms of localized corrosion has already occured prior to applying the weld overlays on existing boiler tubes, and there are a variety of reasons for this which I wo'nt get into as it's becoming apparent that I've spent too much time on this attempt to explain that initially, galvanic corrosion may not occur where one might expect, and that environmental factors that are preventing this from happening when one looks at the exterior, can be decieving. One must also look at what forms of corrosion has occured at the interior of the tubes... Finally, if different forms of corrosion are already present, and originating from the interior surface, the potential for galvanic corrosion to also occur as a result of previous localized corrosion is a real possibility!!! Erosion corrosion is an example of this. If the thin protective hydrogen layer or film which forms between the steam and the tubes interior surface erodes then, the potential for the electrochemical reaction which results in a form of galvanic corrosion increases (erosion of the protective coating or laquer applied to the tube prior to installation is also a factor), especially in carbon or low alloy steels!!!
For instance, if one localized area of a previous form of corrosion has formed in a small area of the interior surface of the tube, and another one has also formed on the opposite location on circumference of the interior surface of the tube or tubes then, because of this relative close proximity to each other, and yet not actually making contact with each other, the end result will be that galvanic corrosion can occur!!! Now this may not be important in the short term but, we must look at this from a long term perspective in order to decide whether or not to either replace a section of tube or tubes instead of just blindly applying weld overlays only, wherever without looking at the root causes of this phenomenon in order to formulate a more effective strategy that results in reduced repetitive maintenance...
I can go on, and on but, I think I'll stop here so, if anybody wants a further explaination, you can go to the corrosion doctors website which I had posted in my previous reply on this topic...

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By Niekie3 (***)

Date 08-11-2003 20:13

Hi SSBN727

You obviously have a lot of experience with boiler corrosion, but unless I am missing something, I believe that you may be complicating what is actually a relatively simple situation.

If the overlay is merely on the outside of the boiler tubes, then nothing happening on the inside of the tubes can lead to galvanic corrosion, unless you have corrosion penetrating the entire thickness of the tube from the inside. The reason being that the metal ions have no path to move from the cathode to anode. (The atmosphere on the outside of the tube is not connected to the atmosphere inside the tube.)

Obviously there is a hundred other corrosion mechanisms that can still take place inside the tubes, but these will not be galvanic corrosion due to the overlay.

Let me know if I am missing the point?

Regards
Niekie Jooste
Fabristruct Solutions

By ssbn727 (*****)

Date 08-12-2003 06:00

Hello Niekie!!!

I agree with you as far as the overlay not being the concern for galvanic corrosion originating from the tubes outside diameter's surface.

However, as you pointed out so elequently, there is around a hundred or so other corrosion mechanisms that can take place inside the tubes. For this very reason, the potential of galvanic corrosion can increase when one considers the non-uniform localized variety (some of these cells will be anodic while other cells in close proximity will be cathodic, even though the material is the same at both locations) of corrosion cells. Their close proximity to each other with the electrolyte (steam) flowing under pressure in between or adjacent to these different corrosion cells, of which have originated from the same metal inside of the tubes (the temperature is less inside the tubes when compared to the exterior) or through the thickness of the original tubing... This has already been found to happen in some "older" boiler tube sections prior to the application of weld overlays.

Only afterwards was it later discovered through inspection that galvanic corrosion was still present at certain locations inside some of the tubes. Prior to the application of the disimilar metal weld overlays, and without considering the existing corrosion dynamics that were present inside the original (before being overlayed) tubes, the different corrosion cells in close proximity to each other were found to be the source of this anomoly, and the reasoning behind why there was still Galvanic corrosion present.

You could imagine what the initial reactions were from the different parties involved but, upon closer analysis, the weld overlays were ruled out as the cause for the galvanic corrosion. No sir, the explanation of the root cause for galvanic corrosion to still exist was a very complicated, and yet very logical one at that, based on what I previously attempted to explain...

The point I'm trying to show is when a thorough (both NDE and DE) inspection of the tubes is'nt performed prior to the application of weld overlays, then the reasons other than the obvious ones for Galvanic Corrosion to be present afterwards, can be overlooked...
I hope I was able to clarify my point to you... If not, then maybe I'm missing something? Oh well, in any event, I look foward to reading more from you Niekie, and everyone else for that matter!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

P.S. I noticed that in my original response (less in the second one) to Insp76 that there were some typo's which regrettably I overlooked, and I believe that some of these typo's caused alot of the confusion... Oh well, some days I'm better than others... Another reason why this forum is such a great place to be!!!

By dasimonds (**)

Date 08-12-2003 08:41

I definately agree with Mr. Jooste on this subject.
I'd be more concerned with thermal expansion coefficients that with galvanic corrosion. As Mr. Jooste pointed out, at the tube metal temperatures seen inside a fossile fuel fire box, I wouldn't expect to see a lot of electrolytes present to facilitate galvanic corrosion. And as Mr. Jooste pointed out, if you have corrosion penetrating the entire wall thickness of the tube , then more than likely, overlay shouldn't even be an option. As this point, replacement of the tube section would definately be the best route to consider.
Inconel has a thermal expansion coefficient almost matching carbon steel, making it a better choice than say 309.
Another thing to consider is the AI(Authorized Inspector). I believe he has the final say as to whether to repair or replace. Also, I believe, ( I may be wrong), you must contact the AI if you are considering overlaying more than 100 sq. in.
There have been other discussions on overlay concerning boiler tubes in this forum, and an "overlay" search might prove fruitful.
Also, for some excellent reading, "Metallurgical Failures in Fossile Fired Boilers" by David N. French, ISBN number 0-471-55839-7 will give you some good insight as to the different mechanisms that lead to in-service tube failures.
Hope this helps.
Dale Simonds

By ssbn727 (*****)

Date 08-12-2003 17:27

Hello Dale!

I did'nt know that Niekie and I were in disagreement!

I was merely pointing out a different perspective to this topic...

Brande mentioned that these tubes were to be overlayed in a code shop in a later post in this thread so, obviously these overlays will be applied prior to the installation of these tubes on site...
Check the dates and times of each reply, and you'll see that I was responding to a question from Insp76. I have to admit that my original answer caused some confusion from others when they read it initially so, I decided to take another stab at it afterwards...
If you read my previous posts again regarding this matter, you'll see that we are also in agreement!!! Hopefully, the end result of all this will be that Brande has been exposed to the necessary info available, in order to make the proper decisions regarding the application itself...

Btw, the book you mentioned is very good one at that, as I've had the priviledge to read it before, and if you see some of root causes for these metallurgical failures, then you'll see where I'm coming from...

Btw, what took you so long to respond to this thread?
I mean no disrespect in my comments to you so, please do not misunderstand me... I hope that we all operate under the premise that we can all agree to disagree and visa-versa...

Respectfully.

SSBN727 Run Silent... Run Deep!!!

P.S. Remember, Corrosion, is like cancer!!! It usually starts out very small in scale. It then grows, and sometimes, if the conditions are present, mutates into different forms of cancer from the original form, and eventually complicating the patients condition... The same analogy can be used for my explanation of the various corrosion cells that can be found in suspect boiler tubes... It's for this reason that thorough inspection is necessary in order to determine whether or not these conditions exist in the already installed, previously used in service, boiler tubes...

By dasimonds (**)

Date 08-13-2003 08:27

Hi SSBN727,
I didn't say I thought you and Niekie were in disagreement, just that I don't see this as an overly complicated issue. Especially considering the tubes being considered for cladding are new, and have never seen any service. As such, the tube stock should be relatively free from corrosion, unless they were improperly stored.
I agree with you that there are many corrosion mechanisms involved with in-service failures of boiler tubes, but most of them would have very little to do with this issue.
Galvanic corrosion is definately something to consider when selecting the correct filler metal for the intended service conditions. Obviously, one would not want to choose an alloy with a greatly different level of nobility. Historically, the stainless and Inconel alloys used in the past have had good results.
I've seen the replacement of 2 floors in recovery boilers which had stainless clad composite tubes originally installed, but had to be replaced with inconel clad composite tubes, due to sever cracking in the cladding, which can be deadly in a recovery boiler, considering the temperature of the smelt, and close proximity to the cracking, attributed to the differing thermal expansion coefficients between carbon steel and stainless steel.
I think the main issues here are correct filler metal for the application and compatibility with the carbon core, method of application, and quality of weld metal deposited.
I think you definately presented some good information, and intend no disrespect to you.
It wasn't mentioned, but I am very curious as to what kind of boiler the clad tubes are going to be installed into.
Hope this helps,
Dale Simonds

By ssbn727 (*****)

Date 08-13-2003 19:31

Hello again Dale!

Thanks for the clarification!!!

I just thought that I goofed somewhere in my previous replies, and when I reviewed them, I noticed that there were some typo's, and yet what I was stating was sound so, I guess my knee-jerk reaction was that you were challenging me (must be all the stress I'm going through with my disability)... I guessed incorrectly, and I apologize to you in earnest for this!!!

I can also remember when alot of the boiler tubes were being clad with stainless steel, and I could'nt get a word in edgwise, about using Inconel 625 or an equivalent because, I was'nt a metallurgist so, nobody wanted to listen... Oh well - Their loss but, what a wierd way to be vindicated... Who knows, maybe some day they'll replace these rather obsolete and relatively inefficient boilers (Although, they did serve their purpose) with some newer technologies like for instance, Fuel cells!!! (Siemens/Westinghouse already has tested some pilot plants in Germany and the U.S. in conjunction with the D.O.E. with some very encouraging findings) That would definitely put alot of people out of work as far as the boilers are concerned but, fortunately that might not happen until very late in our lifetime, and by then, I plan on going fishing myself for quite some time in place where I can finally relax... I hope to read more from you and others... Thanks again!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By brande

Date 08-10-2003 03:18

Thanks much for the reply. This is a bit of an odd app.

These are proprietary items made exclusively to customer specification.

There is a very narrow tolerance for dilution (i.e. iron% and carbon% content in the overlay itself) between the two materials. Perhaps thisis to minimize galvanic action.

Also the overlay thickness is to be rigidly controlled (heat transfer concerns, I am told).

I'll keep all posted as we progress.

Good Luck
brande

By ssbn727 (*****)

Date 08-08-2003 01:05

Hello brande!

I read an abstract in Power plant Chemistry 2002,4 (12) that "on a couple of boilers of one boiler design (Coal-fired), have been found to show circumferential cracking for the 625 overlay using GMAW.

It has been found that this circumferential cracking was the result of preferential sulfidation attack due to overheating of the overlay surface
layer to possibly 593 degrees C (1100 F)."

I also think that if the waterwalls are in bad shape (too thin), the thermal stresses can pose a hazard to the structural integrity enough to cause distortion and in extreme cases buckling of the waterwalls...
A possible solution may be using GMAW-P instead in order to control heat input but careful analysis is in order
FEA (Finite Element Analysis) can predict this distortion issue to a degree so, careful planning is necessary before any work is performed in fact there's an article written about this in Mechanical Engineering's website, and here's the address: http://www.memagazine.org/backissues/september99/features/weld/weld.html
Check out this very informative article... "A weld in time"

I found out some more interesting info but, if you can wait a little bit, I'll sort it all out and post it either tomorrow or the latest, on saturday...

I'll tell you this, the most commonly used alloys for overlays on CS boiler tubes are: 309 & 312 stainless, Inconel 625 & 622.

Anywho, I'll get back to you as soon as I sort all of this data out...

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By pipewelder_1999 (****)

Date 08-08-2003 02:36

Welding Services out of the Atlanta had done this before on a Garbage burner in Nashville using Inconel. It was done using GMAW Downhill if I remember right. There are a few sources on the internet with information that may be of help

See http://www.weldingservices.com/Newsletters/Combustion%20Power/Coal%20Fired%20Boiler%20and%20BOP/Power%20NL%208.pdf

There is also an article at http://www.boilermakers.org/6-Reporter/6-Archives/V42N1.pdf but it appears to be more related to safety issues.

New waterwall panels are sometimes manufactured and then overlayed as part of the process or manufactured out of composite tubing.

This is mentioned at the bottom of the following article http://www.power-technology.com/contractors/Cathodic/ge_welding/

I have worked on black liquor recovery boilers with composite tubes consisting of a SA210 A1 Core and a 304 or 309 overlay. In the case of replacements of these sections, amperage, voltage and travel speed were controlled more closely than normal to minimize dilution of the base metal. On those tubes which were tangent (No Membrane) these were done as window welds. The circumferential weld was made with the 1st pass of E-308-16, the second was a VERY low carbon steel rod and the remainder E-7018. Then the window was installed. The root was put in either using GTAW and ER 70 Wire or 5/64" Dia E-7018. The joint was filled out flush on the carbon steel. The stainless han been removed by machining/grinding and verification with copper sulfate.

If anyone is interested here is a VERY limited sketch of the above item at http://www.weldinginspectionsvcs.com/WindowWelds.htm
Sorry for rambling

Have a nice day
G Austin

By bspeirs (*)

Date 08-08-2003 03:17

This is an article about overlaying 625 on boiler tubes. The pictures are not very good on the website, but the hardcopy available was very good.
http://www.weldreality.com/clad1.htm

The powersource from Zues (www.zuescorp.com) has proven to be excellent for alloy overlays, with very low dilution.

By jwright650 (*****)

Date 08-12-2003 17:33

bspeirs,
Good link, Thanks for posting. I was very interested in the difference in the two processes of cladding.
John Wright

By brande

Date 08-10-2003 03:23

Thanks Gerald,

All good info-as always!

I'll keep you posted as we go.

Good Luck

brande

By jfolk

Date 08-08-2003 03:41

Gerald (pipewelder) is correct about Welding Services, Inc. in Norcross, GA. I, in fact, was there today to witness the overlay technique they perform. Contact Bruce Newton at 678-728-9271.Or visit weldingservices.com.

John Folk

By ssbn727 (*****)

Date 08-09-2003 15:28

Hello brande!

I checked out the Zues Corporation's website and I was impressed!!!

The comparison between the amount of heat input and dilution is dramatic!!!
Especially when applying the "Rapid Arc" to boiler tube overlays where, both of these factors are pretty relevant!!!

If I were you, I'd definitely look more into this... Ed Craig likes this over GMAW-P so, I've gotta bleieve him because, he does'nt pull any punches or promote any bull!!!

Here's the website: http://www.zuescorp.com/index.html

I think you'll like what you find in here... Anywho, let me know if I could be of some assistance with this.

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By brande

Date 08-10-2003 03:05

ssbn-
yes that Zues machine is really something. Currently we are doing an 140 degree (radius) using pulse. Trying to talk client into Zues, however.He might go for it-if so-I'll have a performance review for the group.

The biggest hangup, though is dilution. Too much and the overlay alloy is greatly compromised. Too little would be better, but is sometimes difficult to do in conventional pulse spray. Seems the Zues is just the ticket.

Yes-I have agreat deal of faith in Ed Craig. I've used his books both in teaching and onsite seminars.

Anyway-I'll keep in touch and keep you posted!!

Good Luck

brande

By boilermaker (**)

Date 08-21-2003 17:53

deleted

By weldguard Date 09-02-2003 13:11

Brande:

We have been using 309LSi, Alloy 625 and other alloys for the 'restoration' and 'protection' of the fireside of boiler tubing for many years. We find greater and greater acceptance of the automated weld overlay process as the years go by and the number of successes increases. The particulars of the application depend somewhat on the material to be used, whether you are after a corrosion resistant overlay or a weld metal build up, and the environment in which you are operating. However, we can report successes in most major types of boilers throughout North America and the world.

Our process is employed both in the field for in-situ repairs and in our weld shop for the protection of individual tubes and tube panels prior to installation in the boiler environment.

We can offer a wealth of information on the history of this process, process details, project management, etc., etc., should you so desire. I can also offer a website to allow you to browse much of the information at your leisure.

Thanks,

WeldGuard

By weldguard Date 09-02-2003 13:11

By brande

Date 09-06-2003 05:57

Weldguard-
Thanks much for your reply.

I would be very much interested in that website and any history you could provide.

We have our process close, but still have to get some chemical concerns addressed.

As always, I find this group a great source of info, and hope you can help.

Keep in touch, as I most certainly will!

Good Luck

brande