Rubber Linings for FGD Systems

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:

  1. 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.
  2. 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.



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.


Buck Meadows / Rubber Technologist

Technical Sales Manager

RubberSource Inc.



How to rubber line pitted and corroded tanks!


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.


-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.


-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.


-The rubber can not go bad on site.

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


-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.


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

-You will get better adhesion to the surface.


-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.


-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.


-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.



Inspection of Rubber Lined Vessels

lined 3

An inspection of a rubber lined vessel should be conducted once per year and never delayed. A close check should be maintained on operating procedures and conditions at all times. If a problem is going to occur with a rubber lining, generally it will happen within the first 3 months of service, which is why it is important to check a lined vessel after the first 3 months of service.
This is likely to be true whether the problem is caused by workmanship or by misapplication of material choice.
In some cases, the solution for which the tanks were originally lined for will have little detrimental effects on the rubber while the increase of a few percentage points in the service condition (added heat, less of more concentration, introduction of new chemical) may have a definite deteriorating effect of the rubber.
The tank must be clean, degassed, and dried before a proper inspection can be made.

A full visual inspection should be conducted, being aware of:
– Any loose seams
– Blisters
– Cracks
– Cuts
– De-lamination of the sheet surface
– Discoloration or suspicious areas

Notes of the date of the inspection should be entered within a log book which is kept on each rubber lined tank and should be updated each time the tank is inspected. The areas which were described as suspicious on the previous should be identified by some means of a reference of a location and rechecked with each additional inspection.
***Note: On entering a rubber lined tank, workmen MUST wear smooth sole shoes (no contamination is acceptable) and be very cautious not to drop sharp or heavy tools onto the lining or place hot electrical lights against the rubber linings. Ladders MUST have padded feet (both top and bottom) and placed gently inside the tank.

Any questions on inspections of rubber lined vessels or repair procedures please consult



Buck Meadows / Rubber Technologist

RubberSource at 519-620-4440.


Victaulic XL Fittings vs Additional Rubber on Elbow Extrados


Victaulic XL Fittings vs Additional Rubber on Elbow Extrados

Victaulic has come up with an interesting way to increase the longevity of fittings for mining and wear applications. For those of you who haven’t hear yet, the concept is to produce a larger ID fitting in order to add more rubber in the critical fittings, enabling your fittings to last longer. These fittings will than mate up to your standard sized ID, OD pipe.  Using a stepped XL coupling it bolts up to your existing pipe with the same ease of all 07 and 77 couplings. The ID of the thicker lined fittings matches up perfectly to your thinner lined pipe.

The majority of wear occurs in changes in direction. Elbows are particularly vulnerable to wear do to this fact. By increasing the rubber in the fittings from 1/4″ thick rubber to 1/2″ rubber you get two benefits. You get a thicker wear sub-straight and a better cushion for the forces on the liner. The result is a significant increase in lifespan from these fittings.

The down side to these fittings is that you can no longer use the standard 77 or 07 couplings in your system. You will need to get the stepped XL couplings. Since these fittings are unique to rubber lined systems the availability and lead time on these components can be a challenge.

Traditionally the way to increase the life in your elbows is to add an additional layer of 1/4″ rubber on the extrados of the elbow. This created the 1/2″ of rubber desired. This allows users to keep their existing couplings and adds longenvity to the elbows..

The downside to this type of additional wear material is the transitions are not always made the same. Depending on the rubber liner installer, you can get  various transitions in the rubber, some better than others. If a bad transition is made in the rubber, you can get an undesired turbulent effect. This will result in eddy currents in the elbows and fittings and this effect will prematurely wear out the liner.

Victaulic has created a good system which addresses the additional material required in high wear situations. It is an effective way to increase the life span of your fittings. The ID’s of the fittings and pipe having no transitions which ensures no unintended premature wear.



Celebrating 1 Year for RubberLining.org

1 Year Celebration

Celebrating 1 year for RubberLining.org

We have had a fun year blogging about rubber lining and the associated disciplines.

More and more followers have been coming to visit our blog every month, averaging 300+ views per month. We are happy and able to help with any of the industries technical questions. If we don’t know the answer we are definitely able to point people in the right direction.

We want to send out a special thanks to Rubber Source for contributing articles to this open forum of rubber knowledge. If any of our readers feel inclined to submit a rubber lining industry articles, we would be happy to post them. We plan on having many more years of blogging to share in our industry specific knowledge. The more people who get involved in sharing rubber lining industry knowledge the better the industry will be.

Stay tuned for more articles on rubber lining.

Thanks for following along.

from the Rubberlining.org team.


Compressed Air Blotter Test for Rubber Lining and Painting


Compressed Air Blotter Test

What is it checking for?

The background behind this specification, which is becoming more and more prevalent in engineering documentation, has to do with the presence of oil and water in the air stream. As you can imagine having oil sprayed onto a surface prior to painting would be terrible. It would immediately create fish eyes, lack of adhesion and all types of terrible things for the paint. Water  is just as bad as flash rusting can occur.

Rubber and hydrocarbons for the most part don’t get along. So the presence of oil on a surface will definitely have a negative impact on the adhesion and longevity of rubber on a steel sub straight.

Why would water be in the air line?

Humidity (water molecules suspended in the air) is found in the air all around us. When compressed the moisture forms into water. Most compressors are equipped with a water separator. But water separators are not all created equal. Based on the volume of blasting or painting, your air water separator may not be able to process the volume of water. Winter is a good gauge of if your water air separator is working for your setup. If your lines freeze in winter yours is not adequate for your work load.

Why would oil be in the air line in the first place?

Not all compressors are made the same. Piston compressors are more prone to oil in the air than screw compressors. Although all compressor designs offer various risk to oil in the air lines, there are many inline solution to capturing any residual oil left  in the air.

How is the testing done?

You can use a 4″ X 4″ clean cotton cloth. Spray for a duration of  1-5 minutes and look to see if you any oil or water. This only needs to be done once per shift as objective evidence for your client if required. Otherwise it’s good practice to monitor your compressor air as well as you oil separation for long term performance issues.

For the exact specification the standard would be according to ASTM D 4285

The net result of good clean air! 

A clean well blasted metal with no surface impurities will enable you to create a perfect adhesive bond that will ensure a rubber coating will last forever.

Good process equals good results…





Bends and Rubber Lining



Bends and Rubber Lining

The use of bends in a designed piping system is critical to managing wear in piping directional changes.

In short the longer you can make the directional transition, the less wear you will ultimately have in your elbow. Induction bent elbows provide engineers and designers an infinite degree of adjustment and allows the elbow to have any sweep dia,  limited only by the sweeping arm of the induction bending machine.

Although there are very little limitation of what can be fabricated as an elbow, lining these elbows with rubber can be a challenge.

Here are some general rules of thumb.

Positive: Larger diameters elbows are easier to line as you can reach the inside to stitch and work out possible air pockets.

Negative: Large diameter tubes are very heavy and hard to manage, sometimes difficult not to create wrinkles

Negative: Small diameter long swept bends are challenging as you cannot manually adjust the tube in the swept section. Difficult to stitch in corners.

Negative Small long swept bends can hide bubbles and wrinkles as they can be hidden in the inside radius which is impossible to see with the naked eye.

Positive: Small diameter tubes are generally easy to handle.

Thick liners in small diameter bends are difficult, due to the tube not wanting to turn the corner and kinking when folded in half. The liner has tendencies to create large wrinkles.

New trends is to have thick liners in pipe and elbows. Engineers are using the additional rubber thickness in order to match flow calculations and standardize pipe size. An example of this would be using a 30″ dia. pipe and lining it with 2″rubber. The engineering design recommended 28″ pipe for the flow. But 28″ pipe is not common  and 28″ flanges and valves are not commonly stocked and are very expensive. Using 2″ rubber would accomplish the reduction in interior diameter.

Other times the belief is that a thicker liner will make the elbow last longer, this is inaccurate. If using the correct compound for the fluid with particle size and flow taken into consideration than 1/2” rubber sub-straight is ample for best performance.

Lining with 2″ thick material is extremely in-practical. The weight of the tube would exceed the tear strength of the silk required to pull the tube through the elbow. The tube would weight in the area of 700 lbs. The other challenge with such a thick liner, the sag created in the material during the vulcanization process will create an uneven liner. The top of the part would thin and the lower section would increase dramatically. An uneven liner generally created uneven wear.

From a designing perspective, 3D bends should generally have a minimum 1D tangent. Anything less and the end of the pipe will result in an elliptical form. An elliptical end will create challenges with the termination, flanges and grooved ends. This generally doesn’t affect rubber lining but 1D tangents are good design practices.

 Pro Tip.

-Although 6 D bends are great for wear, the most common swept bend ordered are 3D 45’s and 90’s. These are common and stock in most location have a 1D tangent. Even if the site has a 1 deg slope try to standardize all bends to normal standard angles for ease of replacement and interchangeability.

-3D Bends 8″ and below 1/4″ liners

-3D Bends above 8″ 1/2″ Liners.

-3D Bends above 16″ if required 1″ liners are possible

-On cyclone under-flows where the material if very coarse like 3’/4″ ,minus allow for the longest possible Radius such as a 5D or 6D elbow.



PH and rubber lining


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.




Toluene and Trichloroethylene

toluene TriCHloro


Toluene, Trichloroethylene and Rubber


Toluene (recommended for raw rubber use only) 

The most common solvent in the sheet rubber industry has to be Toluene. For those of you that don’t know Toluene is used for tackifying raw rubber sheets, or to clean any surface impurities prior to application. In order to tackify the sheet a “GAS” is created to better promote adehsion. Gas is a slurry of rubber crumbs dissolved in Toluene. Toluene effectively breaks down the surface of the rubber sheet compound and makes it extremely sticky. It is a very flexible and forgiving solvent. Chemlock 289, 290, 286 etc.. is a commonly used Toluene based rubber adhesion systems, therefore it is a natural solvent for that application.

Some of the properties of Toluene are the following.

-Clear and water-insoluble

-Toluene is heavier than air so when it off gasses it falls to the ground.

-It is an aromatic hydrocarbon, meaning it is a derivative of oil product in particular a Benzine derivative.

-Smells like paint thinners

-Can be used in an internal combustion engine.

One of the negative side Toluene it is generally not good for you. Respirators face shields and gloves are recommended for handling it.

It is also not recommended to clean buffing’s off of a cured rubber sheet. What can happen is that by buffing a cured rubber sheet you effectively make the surface porous. The toluene will saturate and enter the rubber sheet. If not given enough time to evaporate out of the sheet, toluene will affect the adhesive layer negatively in a cured rubber sheet, cold bond cement is Trichloroethylene and zinc oxide based.

Check your adhesive system base solvent before deciding which solvent to use.


Trichloroethylene (recommended solvent for cured rubbers)

Anybody who has ever has spliced and bonded conveyor belting is familiar with this solvent. Trichloroethylene is actually part of the Halocarbon family. Halocarbons are used as an industrial solvents. When cleaning rubber buffing or removing surface impurities, in a cured sheet this is the solvent to use.  When using SC2000 or any equivalent adhesive system the only solvent you should use is Trichloroethelene. These type of adhesive systems are 60-90% trichlorethylene with a zinc oxide.

-Trichloroethylene is a good solvent

-Great degreaser for hydrocarbons.

-Clear and water insoluble.

-Smells like paint thinner.

-Heavier than air and will pool at the bottom

One of the negative sides of this chemical is that it can react to soda lime. Can cause depression due to is’t general anesthesia effects. Respirators face shields and gloves are recommended for handling it.

Please consult manufacturers and available MSDS sheets for more information.





What elastomeric lining material is appropriate for what service?

Rubber Types


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.