Rubber Compounds and Properties Archives • Rubber Lining

Rubber Linings for FGD Systems

Posted on November 4, 2015 by Dan Denault

Introduction
Power facilities are the largest generators of Sulfur Dioxide (SO2), which may cause acid rain. In 2012 Power Plants were required to meet the tougher air quality emission standards. Adding Flue Gas Desulphurization Units (FGD) to clean or scrub the exhaust gases reduces SO2 emissions by 98%. By FGD units reduce the emissions by this amount, they have become the most common type of technology used for reducing sulfur oxide emissions from bituminous and coal fired power plants.

There are two different designs used for FGD systems:

Dry: This is used to heat up the incoming flue gas to vaporize the liquid in the lime slurry, used to scrub the sulfur dioxides from the gas, resulting in a dry waste stream.
Wet Scrubber: This uses an excess of slurry and produces a wet waste stream. All internal surfaces as subjected to a saturated environment or are in immersion. This type of system is the most common.

A FGD system and its auxiliary equipment provide a wide range of parameters, which must be evaluated to tailor the proper lining system to the required process conditions. The following is a list of the parameters which should be considered as a minimum: Chemical Exposure, Temperature, Immersion, Impingement and, Sliding Abrasion.

Rubber Linings

Rubber linings are used where abrasion is a major concern. Typically used in scrubber absorption zones, and slurry piping. There are 3 commonly used rubber linings in the FGD units:

Natural Rubber (60 Shore A Durometer): This has the lowest cost out of the 3 styles. This lining is easy to apply for a qualified applicator and will have the highest degree of abrasion resistance, but is limited in heat / hydrocarbon resistance.
Neoprene (60 Shore A Durometer): This lining is the most costly but will offer a degree of fire and oil resistance, which is the advantage where oil fired start up systems are in place.
Chlorobutyl / Bromobutyl (60 Shore A Durometer): This is the most common lining choice because of the low permeation. The abrasion resistance is not as strong as the NR, but is acceptable and the oil resistance is better than the NR but not as good as the neoprene.

Summary

Rubber has advantages so that physical or chemical properties of the scrubbing liquid have any major effects on the service life. Because rubber has good resistance to sulfuric acid, rubber lined steel has been consistently used, especially where abrasion resistance is needed. The key ingredients for a successful FGD lining project are the correct lining specification and the proper rubber lining applicator. With the proper specification and application one can expect to achieve a performance life of 15-20 years with extremely low maintenance costs.

Rubebrsource

Buck Meadows / Rubber Technologist

Technical Sales Manager

RubberSource Inc.

519-620-4440

How to rubber line pitted and corroded tanks!

Posted on July 13, 2015 by Dan Chamberland

Rubber lining a pitted and or corroded tank can be a challenge at the best of times…

There are many considerations in order to evaluate what materials to use. The most important part of repair, re-line, remediation of a tank is to have a good clean surface.

Blasting the sub-straight to a near white metal is important to remove, dirt, scale, residual chemicals which would all affect adhesion to the sub-straight. After blasting you can also determine the amount of good steel left. Many times repairs will need to be done in the most problematical area’s.

Once the sub-straight has been deemed sound all slag, debris blasting media must be removed and thoroughly cleaned. Suction companies are readily used in order to remove waste materials. Note when cleaning with solvents ensure the solvents are compatible with the adhesive system being used. For more reference on this see the post on Toluene and Trichloroehtylene.

Also note that dehumidifiers, heaters and hording of the tank are important in order to control the internal temperatures and climate to avoid flash rusting subsequent to blast.

After the sub-straight is clean you have to decide if you will fill in all the voids. There are several ways and materials you can choose. Bondo has been used, epoxy fillers such as Devcons have been used and ultimately as long as the filler used is stable over time, adheres to the sub-straight and is spread extremely smoothly and you can get a nice final finish, than you can use it to fill in the voids. The reason you need to fill the voids is if you use pre-cured sheet rubber for your application than the amount of surface the backing will be in contact with can be as little as 30%. By filling in the voids you can have 90-100% of the backing surface being properly adhered.

The next part of this equation is what method of lining and curing to choose.

1- The best possible liner you can put into a tank is a raw rubber liner that gets vulcanized after installation.

Pro’s

-Raw un-cured rubber has good malleability in order to get into all the scaling crevasses.

-You will get the best adhesion using uncured rubber.

-Ultimately an installed and cured liner will have more homogeneous seems.

Cons’s

-Small tanks are the only practical sizes for this type of rubber application

-Rubber cures in sun and in UV, depending on site conditions and storage, the top layers may cure while waiting to be installed, you may lose rubber square footage depending on your application time and conditions.

-Any pits not filled with an epoxy can be prone to blistering as the air trapped in hole will expand during the cure and may set that way.

-The limitation of course of this type of lining style is the availability size of your boiler. ex. 60′ X 65′ Dia. high tank would require a 300 HP boiler to overcome the heat loss of a hoarded tank. The boiler would consuming approx a swimming pools worth of diesel in order to provide a 24 H cure.

2- The most common method of handling tanks is using cured rubber.

Pro’s

-The rubber can not go bad on site.

-You save all the curing time, diesel costs, hording, setup for the cure.

Cons’s

-You must buff the backing or have the backing pre-buffed for good adhesion to the sub-straight.

-Adhesion to the sub-straight is more difficult as the rubber is rigid. Extra time needed for good stitching to ensure proper adhesion.

3- The least desirable are the chemical cure liners.

Pro’s

-You get to use semi-uncured material which is generally easier to line with.

-You will get better adhesion to the surface.

Cons’s

-After the initial chemical kick for curing the liner takes approx 18 days for a full cure. People are generally in a rush to add the liquid back into the tank. Filling the tank prior to the full cure will halt the cure and you may not get durometer or the intended performance out of the rubber required.

4- Using uncured rubber and curing the rubber using hot water.

Pro’s

-Raw un-cured rubber has good malleability in order to get into all the scaling crevasse.

-You will get the best adhesion using uncured rubber.

-The rubber will cure very consistently.

Cons’s

-Difficult to get that large of a volume of water.

-Heating that much water requires alot of energy, and that can get very expensive.

As you may have noticed we did not go over any of the nuances of lining on site. We focused primarily on the types of method applications and none of the health and safety, site requirements unique to every site.

In the end lining a corroded tank is not for the faint at heart. It requires years of field experience in order to perform these jobs on time and on budget.

PH and rubber lining

Posted on December 17, 2014 by Dan Chamberland

PH and Rubber Lining

The PH levels in the transport fluids is always a concern when selecting the proper rubber liner for pipe or chutes. If the transport fluid is Acidic, natural rubber can be the right selection. When using natural rubber with acids, swelling occurs dependent on concentration and you may not get the same abrasion resistance you would normally get from a liner. Alternately extremely alkaline solution or caustic materials can also be problematic.

As a general rule of thumb, any high corrosive or caustic application, will change the rubber selection from Natural rubbers to Chlorobutyls or Bromobutyls which can handle high chemical compositions and higher temperatures. The challenge with the Butyl family is that they sometime have difficulties adhering to sub-straights.

Rubber manufacturers know the adhesion problem and will some time use a pure natural gum layer on the bottom of the sheet. This helps adhere the sheet to the sub-straight. Liner applicators must be aware, that the natural rubber layer (tie gum layer) is there. If this is the case closed skives are recommended for all chemical applications.

When a rubber sheet has a tie gum layer it is susceptible to chemical and temperature attack. Many liners have failed due to this layer being dissolved or weakened because of the lower chemical resistance and temperature threshold of the tie gum layer.

When selecting rubber liners an understanding of the PH levels and the effect on the liner is critical to the selection of rubber for the application. Being able to describe the PH, material particle size and velocity can help you in designing the perfect piping system.

What elastomeric lining material is appropriate for what service?

Posted on October 31, 2014 by Dan Chamberland

Rubber selection can be intimidating as there are a number of engineered high performance linings which can have several different applications. I will list a few different elastomers and durometers as a general guideline.

There can be many different formulations of the compounds listed below with different physical properties than what is listed.

Soft Natural Rubber, 30-60 Duro Shore A, Temp Limit 160 Deg F, Resistance to Hydrocarbons Poor

Typical Uses: Acid Storage depending on concentration, Transportation equipment, Abrasive Services, Sulphur dioxide scrubbers.

Semi Hard Natural Rubber, 80-85 Duro Shore A, Temp Limit 180 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses: Chemical Processing and Plating

Hard Natural Rubber, 90-100 Duro Shore A, Temp Limit 200 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses: Chemical Processing, High temperature nickel-copper plating, steel pickling, vacuum service.

Graphite Loaded Hard Rubber, 90-100 Duro Shore A, Temp Limit 212 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses: Special lining for wet chlorine gas, in chlorine cells and associated equipment. High wear applications.

Three-ply (Soft, Hard, Soft) 40-50 Duro Shore A, Temp Limit 230 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses:Steel pickling lines, Phosphoric Acid

Neoprene 40-70 Duro Shore A, Temp Limit 230 Deg F, Resistance to Hydrocarbons-Very Good

Typical Uses: Chemical or abrasive services with oil present, best for strong bases, good weather resistance, fire retardant.

Nitrile, 60-90 Duro Shore A, Temp Limits 200 Deg F, Resistance to Hydrocarbons-Excellent

Typical Uses: Aliphatic hydrocarbons, kerosene, animal, vegetable and mineral oils.

Butyl, 50-75 Duro Shore A, Temp Limits 225 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses: Oxidizing acids, 70 percent hydrofluoric acids, super phosphoric acid, best water resistance, good for alternative service.

Chlorobutyl, 40-60 Duro Shore A, Temp Limits 200 Deg F, Resistance to Hydrocarbons-Fair

Typical Uses: Much the same as butyl but easier to apply and faster curing, sulfur dioxide scrubbers.

EPDM, 40-60 Duro Shore A, Temp Limits 180 Deg F, Resistance to Hydrocarbons-Poor

Typical Uses: Hypochlorite bleach, ozone and weather resistant.

Feel free to ask about applications and we can suggest compounds.

How to compare rubber compounds for slurry applications.

Posted on July 7, 2014 by Dan Chamberland

Rubber specifications are confusing and some of the properties described in some specification sheet do not help evaluate the wear characteristics of the compound.

In fact most of the time the important lab tests, which tell you how well a rubber will perform in a slurry application are left out.

Specification sheets contain many characteristics which are elemental by definition. In other words the fact that the rubber is tan in color has no relevance to the actual wear “the undesirable mechanical removal of material in fine particle from from the surface.”

Here are some of the common specification criteria and their relevance.

Durometer: (Elemental Property)

In a slurry wear application the fact that a rubber is softter than another may indicate that it may be perfom better or worst but that would be opinion. Harder compounds generally perform better under cut and chip situations but there is a lab test for cut and chip as well as wet sliding abrasion. Durometer is not really the deciding factor. This rubber just happens to be a given duro shore A.

Tensile Strength: (Elemental Property)

Tensile strength is very useful when comparing rubberized tracks and track pads for tanks. As the ability not to rip apart is important. When comparing an elastomeric lining which is adhered to a steel sub-straight it’s tensile strengthen is not relevant factor in this application.

Ultimate Elongation: (Elemental Property)

Going back to my previous example when a snowmobile takes off the ultimate elongation is very important so that engineers and designers can calculate if this track will perform correctly. In a rubber lined wear application this factor is not relevant. It will never achieve it’s ultimate elongation adhered to a metal sub-straight.

Specific Gravity: (Elemental Property)

This is the actual density of the product. In the olden days the buoyancy of rubber was a good indicator of how many rubber fillers were in the product. Floating rubber was regarded as good rubber. Dense rubber was thought to have more clay which would adversely affected it’s wear performance. This day and age with material sciences helping to improve material quality, adders like carbon is common. Carbon increases wear characteristics in some cases. Therefore the specific gravity is simply that, what it’s density is. Not a good wear performance indicator.

Performance properties are “Real factors which can be tested and directly speak to the wear performance in a slurry application.”

Cut and Chip: (Wear Performance Property)

Cut and chip is a test performed in a lab where you can accurately compare compounds and find which is the best in a cut and chip application. This is completely relevant when you are trying to increase the longevity of a liner in a slurry application. This was a test devised by BF Goodrich in order to evaluate how good the tires would perform on the road. A very good indicator of wear life.

Wet Abrasion: (Wear Performance Property)

A test to determine the exact resistance in wet abrasion. It’s a sliding plate that cycles on the rubber in a container of a known wear slurry and the removal of the material is then measured to determine is wear performance characteristics. This is very relevant to wet sliding abrasion test to determine the rubber wear.

Water Resistance: (Wear Performance Property)

Also known as the percentage of swell. The reason this is important is the amount of swell will adversely affect wear within certain services such as acid. The more a rubber will swell the less it will perform in that situation.

Resilience:(Wear Performance Property)

The ability to return to it’s original shape is a huge factor in determining if this rubber will be suitable for wear. The more resilient the better the rubber will perform in a slurry application.

Tear (Die C):(Wear Performance Property)

This is another important performance criteria as the ability for the rubber to hang on to the straightaway is important. This is a relevant value when considering rubber for slurry wear applications.

Conclusion

Rubbers with high Cut an Chip resistance and Wet Abrasion resistance will perform better in wet slurry application. Elemental properties such as density are interesting and mater of fact but should not be deciding factors when choosing rubber compounds for wear applications.

Shelf Life Of Uncured Protective Rubber Linings

Posted on June 16, 2014 by Dan Chamberland

In determining the shelf life of uncured rubber linings, several instances but be understood:

The level of heat memory built into a compound (ex. Synthetic Rubber takes more heat to break down than a Natural Rubber)
The lower the storage temperature, the longer the rubber lining will be useable.

As a rule of thumb the average uncured rubber linings (NR, IIR) will have a shelf life of approximate shelf life of 9 to 12 months if stored at a temperature of 10°C (also out of sunlight). If the linings are stored at a lower temperature the rubber lining will much longer the 12 month period. Please note that Neoprene (CR) and Nitrile (NBR) compounds have a typical shorter shelf life than the above mentioned compounds. In dealing with these compounds a great of caution is to be used as they can cure much faster. If storing rubber at a lower temperature that the recommended 10°C the rubber may become frozen, if this was to happen the roll will need to be unrolled and left at an ambient temperature for 2 weeks to thaw the rubber. After the 2 week interval the rubber will need to go on a hot table to help facilitate any shrink that might of occurred during the freezing process.

Any Questions please contact RubberSource @ 519-830-0546.

Buck Meadows / Rubber Technologist

Technical Sales Manager

RubberSource

Bromobutyl Rubber Linings

Posted on June 2, 2014 by Dan Chamberland

Bromobutyl is a derivative of the halobutyl family, which is structurally similar to chlorobutyl rubber and produced through the same halogenation process: Brominated (BIIR) to Chlorinated (CIIR). By using the brominated process allows the same workability in the lining as a chlorobutyl. The Bromobutyl polymer will exhibit stronger physical characteristics over Chlorobutyl. Bromobutyl Linings are either blended with Natural Rubber for ease of application or made pure in polymer content, which means there is no other polymer in the formulation which gives the lining stronger permeation and heat resistance.

Advantages

• Tight knitting of the molecular cross link which results in an extremely low permeability rate.

• Low glass transition temperature

• Wide vulcanization versatility

• Fast cure rates

• Higher Heat Resistance

o Other Bromobutyl linings have a maximum heat resistance to 121°C as to the pure bromo can run at a constant temperature of 127°F and handle spikes up to 150°C

• Stronger bond strength to substrates

• Excellent Oxidation / Ozone Resistance

• Good Abrasion Resistance

Common uses of Bromobutyl linings are:

– Scrubber Towers

– Piping,

-Storage Vessels

– Chutes

– Thickeners / Clarifiers

Any questions on our Bromobutyl linings please feel free to contact

Buck Meadows / Rubber Technologist

RubberSource

Ph# (519) 620-4440

Email: buck@rubbersource.ca

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