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.



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.



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…





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.





Sandblast for Rubber Lining and Painting


General Sandblasting Information for Code Rubber Lining and Painting

Before beginning any kind of blasting you must verify that the humidity and dew point are at acceptable levels. Not respecting the proper dry bulb wet bulb parameters will only lead to flash rust. This is generally not accepted in the coatings industries and can cause failures between the sub straight and the adhesives. There are charts available to understand this phenomenon and will help you find the acceptable ranges.

The second evaluation most codes require you to do, is to perform a blotter test. A blotter test is usually with a white cotton or white cloth testing that your air is free from oil, contamination or water. Given you have a modern, proper blasting or painting system with an in line air water separator and filter system you can be assured that this test is to reassure your customer that your air is good.

Adding oils and water to a blasted surface will negatively affect the adhesives and the overall performance of the liner.

There are other blast tests required for some specification, such as the soluble salts test. Although this test comes up on occasion, for most rubber lining it is not required. We will cover this subject in another post.

For the lining of steel pipe, tanks and other steel sub straights, you must achieve a blast profile of at least SSPC-SP5 classified as a white metal blast.

There are visual charts such as the example below to visually compare. These also have detailed descriptions to evaluate the blast achieved.


In addition to getting the surface clean you must also provide a profile for the adhesive. You can verify the profile of blast using a Testex strip shown below. This is a common way of evaluating the sandblast profile and proving to your customer the work was performed to specification. This is by far the most important part of the blasting process. Sure, cleaning scale, mill varnish is important, but in order for the adhesive to properly hold  the liner in place, the tooth or profile will give the adhesive a larger surface area to hold onto. Very important.


Blast profiles need to be a profile of 3-5 mils for adhesive as it is required for good surface adhesion. For a paint anywhere from 1.5-4.5 mils is acceptable depending on the specification provided. 

If you glass bead a surface you will get a nice finish, looking like SSPC SP-5 but your adhesion will be terrible due to the profile being flat. You can effectively double your adhesion surface by blasting a proper profile.  Achieving the correct  profile has everything to do with your blasting media and once you find the correct blast media and pressure you can achieve this result 100%of the time. Many option of blast media will create this profile.

For painting the exterior of pipe and tanks most specification call for SSPC SP-6 which is classified as a commercial blast.

The profile for paint is important but not as critical as for adhesives.

Once the proper blast profile has been achieved, adhesive needs to be applied before flash rusting can occur. A good rule of thumb is within 20 min, environmental conditions affect this time one way or another dramatically. On a dry sunny hot day with no humidity the piece can stay without adhesive longer with no risk of flash rusting.

If you have followed all of this you will have an excellent base for which the adhesive can be applied.




Why do bubbles occur in rubber?

bubble liner


Bubbles can occur during the lining process. These become most evident after the curing process.

Why do bubbles occur?

There are many reasons this occurs. The most common reasons are the following. Bubbles occur as the air is heated and trapped. The air will expand and will show up after the cure. The  vulcanization process gives the rubber the memory to keep the bubble in it’s final state after cure.

Trapped air in an autoclave is least likely to occur as a pressurized cure is more likely to keep the bubble small and the air from expanding. An atmospheric on the other hand is prone to bubbles. As there is no pressure to keep the bubbles small they are most likely to show up during this type of curing process.

Where does the air get trapped? 

Often when the rubber get’s calendered, depending on the company doing the calendering, the bubble get trapped between the layers. Often if a rubber sheet supplier will realizes this and they will process their rubber sheet in a piercing roll, prickle roll. They will perforate the sheet to let the bubbles out. Often looking at the exterior of the sheet will not tell you if the bubbles are present.

Other places bubbles can form is between the steel, adhesive layers and the rubber layer. If the adhesive was not off gassed properly or there is a stitching issue, dirt in the adhesive, than rubber can not properly adhere to the sub straight. This can cause an area for the air to be trapped and expand.

Poorly welded seams that have trapped air or porosity, porous castings which get rubber lined are all prone to air bubbles. These types of porosity are better addressed before the adhesive process using a liquid metal epoxy to fill potential air pockets.

Can you repair this?

There are a few ways to properly repair these types of lining failures. The picture above is not repairable the liner should be stripped and the pipe relined. It would never pass a spark test or help in reduction of wear in this pipe.

If it is a problem within the rubber itself and fairly small a 10-12 gauge needle can be used with toluene or SC2000 to shrink and adhere the blister. After every repair a spark test must be performed in order to determine if the liner is compromised. For bubbles below the liner a more aggressive repair is required. the bubble must be cut out. The steel sub straight must be ground or blasted in order to give the steel a clean profile and a tooth. At this point there are two patching methods.A cold patch which can be done with an adhesive like SC2000 and a cured piece of rubber,stitched  subsequently buffed flush and again a spark test performed to validate the patch quality. Or a localized hot  patch be used. Uncured rubber with a Chemlok adhesive system, which is then stitched, cured with steam, buffed flush and then verified with a spark test.