How important are anchoring systems on your refractory linings?
- How does your company engineers this systems?
- Can you trust on your suppliers for technical advice? Wich alloy suits best your lining, your equipment, etc.
- Is anchoring systems a matter of price, do you look at it as a commodity?
the anchor system is critical to the success of the Furnace Lining.
Indeed, you get what you pay for but anchoring will be a fraction of your build spend so to 'pinch pennies' in this area is a false economy, resulting in premature failure perhaps.
Key points which determine the engineering of you anchor system:
* Lining thickness & construction - What material(s) are you retaining?
* Operating Conditions - Temperature, thermal cycling, atmosphere, mechanical stress
* Plane of Refractory - Roof, wall, bull-nose?
* Openings within the refractory body - flue opening
This determines the type of anchor (material) & quality (grade) you should be expecting to use.
I would suggest that the anchoring design is based on experience and good practice.
Additional to what has been said already. Your total lining needs to be designed for its purpose. Thermal expansion can destroy a lining regardless of the anchors system while it may appear to be anchor failure. Consideration of refractory load on any give area is also a consideration for anchoring design. If the vertical load is not transferred back to the shell with shelf supports, you may see failures that look like and anchor failure, when reality is improper anchor application. Shelf supports are also used to isolate areas which may be exposed to thermal expansion from two walls. Bull noses and corner are examples that one would isolate.
It is difficult to find installation companies that will offer anchor design because they do not want to be exposed to any liability. Some do.
We have improved the performance of one of our client calciners to operate continuously for 3-4 years. Improved from have outages every 6 months. A huge factor in the improved performance was changing the anchor design.
a change from standard 310s to 253MA in many industries. This could be for several reasons. Having worked at Rolled Alloys and knowing the differences between each alloy I think one needs to have a good understanding of metals and their behaviour and to know when and where to apply which alloy. One furnace is not the same as another. I have seen anchor failures in 253MA and 310s in similar applications but all for very different reasons that the applicator thought they would survive. I don't always understand why suddenly an alloy is 'in' but it could well be because of lack of understanding of the alloy or just 'everybody is going that way' or some sort of hype, so "lets follow". My experience is that the life time of an alloy actually depends on the alloy chemistry AND the condition in which it is furnished. Both play about a 50-50 part as opposed to just the chemistry. Alloy content determines strength as well as the corrosion resistance of the elements it is endowed with but the surface tension determines the rate at which corrosion takes place. A rough surface will be more susceptible to attack than a smooth surface and a black solution annealed surface wll be attacked/corroded faster than a bright annealed surface. Bright Solution Annealing od a cold drawn or rolled surface is usually the way to go. What people also forget is that each alloy needs to be solution annealed at different temperatures for different lengths of time. If the recepie for all the above is not correct one will not have the full benefit out of any alloy and remain in the dark as to why it worked one time and not the next. One usually forgets he paid the cheapest supplier to get him something he thought was the same as anothers.
There is also lot of misunderstanding about Sigma forming in stainless steel alloys and very little written about it. I have seen write ups and theories that are totally incorrect and others usually prior to 1970 that would be closer to the truth. One such belief is that 253MA is immune to Sigma formation. This is not true. I have seen annealing bells crack like glass in cold swedish winters after only months of service. Immunity to Sigma is only offered by sufficient Nickel or Cobalt content. There are a few other elements but due to the commercial nature of these alloys it is usually shyed away. I think the industry may reconsider 253MA as an anchoring alloy unless it is used for the purpose for which it was designed. This was to offer better sulphadation and oxidation resistance against 310 and 310s. Not to offer better sigma formation resistance as many believe with such certainty. It would be a great alloy for incinerators and SO2 containing gasses. One must consiously know one has selected the right alloy. If one has not, that will be the time it bites back at him.
When deciding which alloy to go for, it is absolutely critical to know the how each alloy will behave under the various conditions it is exposed to. It not just a matter of price. We have noticed that certain markets prefer to use Grade 304 because it is cheaper yet most don't realise that is grade is not suitable for excessive temperature exposure or aggressive corroding atmosphere therefore increasing their maintenance and labor cost in the long run.
the Sigma phase formation and susceptibility as well as the lack of sufficient publications to support the arguments. 253MA is not immune but it is less susceptible than 310. Incoloy DS and Inconel 601 are better alternative but at premium price due to the higher Ni content.
Special alloys such as Haynes 160 and 120 can offer even better solutions however they do come at relatively higher prices.
- How does your company engineers this systems?
- Can you trust on your suppliers for technical advice? Wich alloy suits best your lining, your equipment, etc.
- Is anchoring systems a matter of price, do you look at it as a commodity?
the anchor system is critical to the success of the Furnace Lining.
Indeed, you get what you pay for but anchoring will be a fraction of your build spend so to 'pinch pennies' in this area is a false economy, resulting in premature failure perhaps.
Key points which determine the engineering of you anchor system:
* Lining thickness & construction - What material(s) are you retaining?
* Operating Conditions - Temperature, thermal cycling, atmosphere, mechanical stress
* Plane of Refractory - Roof, wall, bull-nose?
* Openings within the refractory body - flue opening
This determines the type of anchor (material) & quality (grade) you should be expecting to use.
I would suggest that the anchoring design is based on experience and good practice.
Additional to what has been said already. Your total lining needs to be designed for its purpose. Thermal expansion can destroy a lining regardless of the anchors system while it may appear to be anchor failure. Consideration of refractory load on any give area is also a consideration for anchoring design. If the vertical load is not transferred back to the shell with shelf supports, you may see failures that look like and anchor failure, when reality is improper anchor application. Shelf supports are also used to isolate areas which may be exposed to thermal expansion from two walls. Bull noses and corner are examples that one would isolate.
It is difficult to find installation companies that will offer anchor design because they do not want to be exposed to any liability. Some do.
We have improved the performance of one of our client calciners to operate continuously for 3-4 years. Improved from have outages every 6 months. A huge factor in the improved performance was changing the anchor design.
a change from standard 310s to 253MA in many industries. This could be for several reasons. Having worked at Rolled Alloys and knowing the differences between each alloy I think one needs to have a good understanding of metals and their behaviour and to know when and where to apply which alloy. One furnace is not the same as another. I have seen anchor failures in 253MA and 310s in similar applications but all for very different reasons that the applicator thought they would survive. I don't always understand why suddenly an alloy is 'in' but it could well be because of lack of understanding of the alloy or just 'everybody is going that way' or some sort of hype, so "lets follow". My experience is that the life time of an alloy actually depends on the alloy chemistry AND the condition in which it is furnished. Both play about a 50-50 part as opposed to just the chemistry. Alloy content determines strength as well as the corrosion resistance of the elements it is endowed with but the surface tension determines the rate at which corrosion takes place. A rough surface will be more susceptible to attack than a smooth surface and a black solution annealed surface wll be attacked/corroded faster than a bright annealed surface. Bright Solution Annealing od a cold drawn or rolled surface is usually the way to go. What people also forget is that each alloy needs to be solution annealed at different temperatures for different lengths of time. If the recepie for all the above is not correct one will not have the full benefit out of any alloy and remain in the dark as to why it worked one time and not the next. One usually forgets he paid the cheapest supplier to get him something he thought was the same as anothers.
There is also lot of misunderstanding about Sigma forming in stainless steel alloys and very little written about it. I have seen write ups and theories that are totally incorrect and others usually prior to 1970 that would be closer to the truth. One such belief is that 253MA is immune to Sigma formation. This is not true. I have seen annealing bells crack like glass in cold swedish winters after only months of service. Immunity to Sigma is only offered by sufficient Nickel or Cobalt content. There are a few other elements but due to the commercial nature of these alloys it is usually shyed away. I think the industry may reconsider 253MA as an anchoring alloy unless it is used for the purpose for which it was designed. This was to offer better sulphadation and oxidation resistance against 310 and 310s. Not to offer better sigma formation resistance as many believe with such certainty. It would be a great alloy for incinerators and SO2 containing gasses. One must consiously know one has selected the right alloy. If one has not, that will be the time it bites back at him.
When deciding which alloy to go for, it is absolutely critical to know the how each alloy will behave under the various conditions it is exposed to. It not just a matter of price. We have noticed that certain markets prefer to use Grade 304 because it is cheaper yet most don't realise that is grade is not suitable for excessive temperature exposure or aggressive corroding atmosphere therefore increasing their maintenance and labor cost in the long run.
the Sigma phase formation and susceptibility as well as the lack of sufficient publications to support the arguments. 253MA is not immune but it is less susceptible than 310. Incoloy DS and Inconel 601 are better alternative but at premium price due to the higher Ni content.
Special alloys such as Haynes 160 and 120 can offer even better solutions however they do come at relatively higher prices.
As far as I know, using traditional V-anchors really can do a good job if you don't need a lifespan of more than a year in very harsh conditions. If one wants a long life time and the temperature is too high for anchors to survive (in my opinion above furnace temp of 1200 degrees C or more), then one should consider ceramic anchor systems. If the chemicals are the problem, then one can look at exotic anchor materials. Another solution is changing the geometry and make a self load bearing brick solution.
Another aspect that goes wrong many times, in my opinion, is the amount of used anchors. Rule of thumb for me is the anchor distance should be the same as the lining thickness with anchor length being 2 cm shorter than the lining thickness.
Sigma phase cannot be tackled other than assuring the anchor is either not susceptible to that or not used in the wrong temperature range or replaced before the anchor went too many time through the sigma phase related temperature.
Another aspect that goes wrong many times, in my opinion, is the amount of used anchors. Rule of thumb for me is the anchor distance should be the same as the lining thickness with anchor length being 2 cm shorter than the lining thickness.
Sigma phase cannot be tackled other than assuring the anchor is either not susceptible to that or not used in the wrong temperature range or replaced before the anchor went too many time through the sigma phase related temperature.
the anchoring system you choose will determine the life of the monolithic lining. You must also take care about anchoring if you are gunniting, or shotcreting, as long as ceramic anchors do not retain the gunned material as well as V-shaped metallic anchors. Generally, the V-shaped corrugated free-moving system is a very good option, provided your welders will not close the movable parts with a strong weld seam.
You should also take care about the environment in which you are installing the monolithic linings. At temperatures below 600-700 °C, I don't see a mechanical problem in installing 310S or 310, but at higher temperatures you should really consider a better alloy, such as Inconel, or 253MA. From the discussion, I believe your major concern are cement kilns. In this case, you should check if there is sulfate or chlorine gas attack in the anchor. Against chlorine very little can be done, thus I recommend a mix of ceramic and metallic anchors (guarantee the clips are of 310S or superior quality and that the anchors do not have their movement restricted. Good wedging is essential!). In this case, you may also consider the change from the V-Shaped anchors to the flat bar concept. I agree 100% that this concept is old-fashioned and lead to higher stresses in the lining, but if an expansion joint is carefully prepared, you have a much larger corrosion area. This concept should be tried if corrosion of the V-shaped 10 or 12 mm anchors is excessive.
For sulfate, the information from Wouter Garot is perfect. You should avoid nickel in the alloy, thus 253MA is far better than 310 or supperalloys.
Anyway, wherever corrosion is an issue, the mix of ceramic and metallic anchors is geneally advantageous.
You should also take care about the environment in which you are installing the monolithic linings. At temperatures below 600-700 °C, I don't see a mechanical problem in installing 310S or 310, but at higher temperatures you should really consider a better alloy, such as Inconel, or 253MA. From the discussion, I believe your major concern are cement kilns. In this case, you should check if there is sulfate or chlorine gas attack in the anchor. Against chlorine very little can be done, thus I recommend a mix of ceramic and metallic anchors (guarantee the clips are of 310S or superior quality and that the anchors do not have their movement restricted. Good wedging is essential!). In this case, you may also consider the change from the V-Shaped anchors to the flat bar concept. I agree 100% that this concept is old-fashioned and lead to higher stresses in the lining, but if an expansion joint is carefully prepared, you have a much larger corrosion area. This concept should be tried if corrosion of the V-shaped 10 or 12 mm anchors is excessive.
For sulfate, the information from Wouter Garot is perfect. You should avoid nickel in the alloy, thus 253MA is far better than 310 or supperalloys.
Anyway, wherever corrosion is an issue, the mix of ceramic and metallic anchors is geneally advantageous.
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