EPOXY TANK LINING
NO EPOXY PAINT MANUFACTURER WILL EVER DECLARE IN WRITING HOW MUCH ACID PH VALUE THEIR PAINT CAN ENDURE.
If you ask them bluntly , they will stone wall you.
Do not load any cargoes in epoxy tanks which are not allowed by the paint manufacturer of your tank specific paint. Epoxy tanks can carry all types of cargoes from 4.5 to 14 pH.
This means it cannot handle acids-- unless it is Siloxirane . Has limited resistance to Aromatics, Alcohols and Esters.
This means it cannot handle acids-- unless it is Siloxirane . Has limited resistance to Aromatics, Alcohols and Esters.
Pure epoxy paints are un-suitable for really corrosive liquids. All epoxy manufacturers specify that no aggressive cargo ( Ketones , Alcohols, Nitrites, Esters etc) should be loaded in the first 3 months . The next cargo after a previous aggressive cargo should be a fully approved non-aggressive cargo without any remark in the cargo resistant list.
After carriage of “aggressive water soluble cargoes”, no steam, ballast water, wash water, slops or aqueous cargoes must come into contact with the epoxy coating before its original coating condition is restored by ventilation.
When using Verveys guide pl remember –it has not been made for smooth SS without internal framing—and you will notice that no provision is made to remove aBsorbed chemical by venting. Indiscriminate jet impingement on unrecovered coating causes blisters and coating breakdown.. When an organic coating which is saturated with a water soluble solvent like Methanol or Ethanol is washed with water, severe blistering of the epoxy coating is sure to happen.
More dangerous—retained absorbed cargo in the epoxy coating film may cause a chemical reaction, and produce products, which cause total breakdown of the tank lining.
Cargoes such as Methanol and Benzene and Diethylene glycol are absorbed into the coating film to a higher degree than other chemicals .
Remember the list of chemicals shown in the COF on a full epoxy coated ship is not the same as the resistance list of the paint manufacturer. Sometimes it is possible on a old ship to have three types of epoxies (Choguku/ Sigma --- pure/ phenolic/ isocyanate/ modified ) applied in different drydocks during her life time. When loading in epoxy tanks it is most necessary to see previous cargoes and check for footnotes in paint manufacturers list as to restrictions for next cargo.
Epoxy paint is organic. It is a three dimensional “cross linked array” of chemical bonds between resin molecules. Amine cured epoxy is used on chemical tankers. Polyamine cured epoxy having no resistance to Aromatics is used on oil tankers usually. The DFT of an epoxy coating is usually specified to be between about 270 microns in a 3-coat system—in unavoidable overlap areas and in unavoidable stripe coat areas it may be around 480 microns. These thick DFT areas are the vulnerable spots which take longer time to restore and remains soft . Doubling the DFT means desorbsion /drying times are four times longer.
The paint is applied on a grit blasted to SA 2.5 surface. If the coating is too thick it will fall off when softened and pores opened by solvent cargoes like methanol, benzene and methyl acetate. High DFT causes longer time to cure after an aggressive cargo and can cause alligoration ( formation of cracks ). High film thickness requires longer ventilation than a low film thickness to get rid of entrapped solvent / cargo.
Sunlight can discolor the epoxy surface due to UV rays of the sun, but it should not affect the protective properties of the paint.
Cargoes tend to be aBsorbed like a sponge rather than aDsorbed. It reacts with water/ solvent mixtures which penetrate coating. So if ethanol is discharged the coating must not be allowed to get wet prior to venting. Unlike zinc silicate epoxy is usually touched up at sea ( on a degreased metal surface ) provided the curing time is sufficient. Phenolic and isocyanate epoxies are better than normal epoxy. Never recoat an epoxy coat on top of an old coat for the risk of poor bonding is too great. Degreasing must be done.
Aromatics like Benzene softens and swells epoxy. Do finger nail test prior tankwashing after aromatics, alcohols, esters and high FFA animal and veg oils. If your finger nail is not long enough use HB, 2B,4B, 6B pencils on breaking stress.
Enter tanks with soft soled shoes. If you make the mistake of speeding up recovery by application of heat from within the tank—the top skin of coating will harder first thus trapping the solvent underneath. This solvent has to breakthrough and will bust the coating with flaking as a result. Recovery must be done by venting with application of heat from the other side, to increase VP and induce faster evaporation. I remember one of my past companies getting a horrendous claim of a couple of million dollars for loading Styrene Monomer in an epoxy tank after Benzene without extracting the aBsorbed Benzene by venting . One % absorbed previous cargo could cause a concentration of 10 ppm in the next cargo if completely dissolved. aBsorbsion always takes at a faster rate than release due to hydrostatic pressure or force feeding of sponge. Permeation is generally facilitated by increasing pigment content ( reduces when paint gloss reduces ). Absorbsion reaches equilibrium level in a few days and then remain constant.
A 1000 cum tank AFTER 20 hours of ventilation can still contain 12 litres of methanol which can be released into the next cargo causing contamination and rejection of entire parcel. While a stainless steel tank or zinc tank after methanol discharge is ready for next cargo.
The best way to restore epoxy coating is with an air temperature of about 30C-- dry air with a relative humidity below 45%. At 15 C it takes more than 3 times the time.. Paradoxically too high ventilation temperature does not speed up the restoring process and the epoxy film will remain soft even after the absorbed cargo is ventilated out of the coating
When an organic coating saturated with a water soluble sovent like Methanol or Ethanol is washed with water jets, severe blistering of paint takes place. Remember long term ventilation of empty tank at 30 deg C is required before water is introduced in the tank. Ventilate with dehumidified air for fast results. This is the reason why epoxy coated chemical tankers must have dehumidifier and heater inherent with the fixed blower.
Retained (aBsorbed ) cargoes which are water mixible or water reactive should NOT be removed by steaming or water jets . They also should not be followed by aqueous cargoes or ballast. Such a consideration is not there for Zinc Silicate which aDsorbs cargo ( aDsorbsion is a surface phenomenon). Empty epoxy cargo tanks which are not ventilated can sometimes be dangerous wrt explosion or toxicity. Entering such an ex Benzene tank is a sure way to invite cancer.
Adhesion of paint is tested by glued on tablets which are pulled off with a means of recording the force. Don’t allow butterworth portable machines to bang during rolling. Epoxy coating should never be heated more than 80 degrees C during tankcleaning.
Methanol steaming is never done in epoxy tanks. No pure steaming must be done when the coating is soft. Solvent cargoes like Methanol ( moisture <0.1% or 1000 ppm ) when mixed with water form aggressive acidic mixtures . Esters, Acetates, Chlorinated/ Brominated compounds, Pthalates will react with moisture to form acidic compounds ( moisture <0.02% or 200 ppm ).
When oils and fats are contaminated with water they become more aggressive than their acid value alone would indicate. For this reason moisture content should not exceed 0.25%.
It is better to do prompt and constant touch up when curing time is available , than to leave the damaged spots without touch up. Usually curing at 20C takes 10 days while at 30 deg C it takes 7 days. Spot portable grit blasters which do not allow grit to fly around are available in the market. Disc grinding causes poor adherence and paint will fall off contaminating cargo. While airless spot spraying remove adjacent cold ballast from adjacent tank and wrap steam coils in vicinity with old wire hoses. Stripe coating is applied on edges, welds and difficult to spray on areas.
Resistant to: Normal epoxy has good resistance to Alkalies , veg oils and Luboil. Vegetable oils , animal oils and fats may be carried in epoxy tanks irrespective of acid value. For animal/ veg oils with a free fatty acid content content >50% the temp of 50c must NOT be exceeded. Epoxy has good chemical solvent and water resistance.
Not resistant to: ( only for reference , for application CONSULT YOUR PAINT RESISTANCE TABLES INCLUDING EXCEPTIONS WRT WATER CONTENT ) all acids of pH less than 4.5 , Benzene, Toluene, Ethanol, Methanol, Esters, Ketones, Calcium Hypochlorite, HMD, Phosphoric acid , Nonyl Phenol, Sodium Hypochlorite soln <15% , Sulphuric acid, 28% or less aqueous Ammonia, Chloro Toluene, Cyclo Hexylamine, Di Ethylamine, Diphenyl Ether, Di n Propylamine, Dodecyl Alchohol, Ethanolamine, Ferric Chloride soln, Furfural, Maleic Anhydride, Nonyl Phenol, Potassium Hydroxide soln, Sodium Hydrosulphide soln < 45% , Sod Hydroxide soln, Tall oil, Undecyl Alcohol, Vinyl toluene, Xylenol, Acetone, Amyl alcohol, Alkaline Glycol Monoalkyl Ether, Bsolve, Di Ethyl Sulphate, Di isobutyl Ketone, Ethyl Acetate, Ethyl Acrylate, Ethylene Diamine, Ethyl Hexyl Acrylate, Isobutyl Acetate, Polyethylene Polyamine, Isobutyl mix, Brake fluid, Polythelene Polyamine, Propionic acid, Triethylene Tetramine, Propelene Glycol, Methyl Ether Acetate, Vinyl Acetate etc etc .
Epoxy and modified epoxy are resistant to very few amines ( Zinc is better only if theses Amines are water free ) . Steaming of tanks for prolonged periods can cause damage. The thing to make sure is that the steel temp does not exceed 50 deg C.
If the difference between cargo temp and empty tank temp is >55 deg C it is recommended that preheating of tanks is done prior loading to prevent thermal shock. In case of Aliphatic petroleum products example: Crude oil, Waxes, Bitumens, a max carriage temp of 70 deg C may be accepted
The hardener and resin mix has a low pot life. Coating chalks and yellows on ageing . Acetic acid can be used to refresh and to remove lead from Gasoline trapped within. Some companies suggest recirc of Metalbrite / Phosphoric acid . REMEMBER any acid of less pH than 4.5 will damage the epoxy coating . You have to use the pH value paper. Remember DILUTING STRONG ACIDS BY A FACTOR OF TEN INCREASES pH VALUE BY A MEASLY ONE.
Paint manufacturers indicate suitability based on max transport temperature. They usually mention higher heating limits for a limited number of days. Example: can be heated to 75 deg C for 10 days. Consult paint manufacturers resistance suitability notes for such information. A paint manufacturers resistance list footnote might say—
Tank must be left dry prior loading.
Next cargo must be a hot cargo of Lubes / Mineral/ Veg / Animal oil for min 5 days at 50 deg C or 43 days at 60 deg C. OR
Non aggressive , non aqueous cargoes must be carried for 30 days.
Water mixible cargoes must be carried in perfectly dry tanks and water must be excluded during carriage. Prior tankcleaning ,vent the tank etc etc.
If you ballast epoxy cargo tank the ballast water surface must be chased down using tank cleaning machines during the deballasting process lest you get a stained /discoloured coating. During long voyages change the ballast every 10 days. Epoxy is however the best for salt water ballast followed by Zinc and last stainless steel.
Epoxy does not absorb oils, they absorb only solvents. During wall wash test the “test Methanol” swells the coating and extracts the residues. Some cargoes get chemically bonded to the coating by molecular forces.
Liquid is absorbed by the binder phase of the coating through the diffusion process till it is saturated.. Desorbsion also takes place by the diffusion process..
The following cargoes swells epoxy and MUST be ventilated prior washing with jets.
Ekta solve DP
Ekta solve EB
Ekta solve EE
Vinyl acetate monomer
In general cargoes having small molecular structures are able to penetrate organic coatings to a greater extent than those cargoes with larger molecules. So Methanol is a very penetrative cargo.
Since epoxy is like a sponge –to lessen absorbsion of cargo into the paint layer, it is better to carry cargo ( in shipowners interests ) at the lowest possible practical temperature.
Wall wash surveyors are quite particular about odour in an epoxy tank when sensitive odour absorbing cargoes such as edible oils, potable Ethanol, MEG FG etc are to be carried. A strong smelling cargo like Styrene Monomer absorbed into coating can still give potent odour and contaminate a sensitive heated vegetable oil after 2 voyages. This is the reason why FOSFA has banned Styrene/ EDC as the LAST TWO cargoes in epoxy tanks. Heating increases the rate of desorbsion
Two successive cargoes may require to be chemically compatible with each other.
WARNING:--Epoxy paint is non toxic only after curing. Be aware of the curing time in case you need to spot touch up. The time versus temperature scale is always given in the paint tables.
Epoxy systems do not absorb oil-like substances. Epoxy coatings tend to absorb solvent-like cargoes. Some chemicals may even be chemically bonded to the coating by molecular forces. Typically, the cargo is absorbed within a couple of days to the maximum level (equilibrium) and stays constant for the remainder of the voyage. The absorption rate and the amount of cargo absorbed depend on the type of cargo. After transporting agressive cargoes (methanol, EDC, acetone, vinyl acetate monomer, cyclohexanone), the coated tank has to be ventilated until the cargo has been desorbed (released) from the coating film, which results in hardening and decreasing swelling.
The desorption (removal) of the cargo residue from the coating by ventilation begins rapidly. After a couple of days, there is no significant further loss of the retained cargo. The desorption comes to a standstill before all cargo has been released by the coating. The amount remaining varies, depending on coating type, film thickness and type of cargo.
Check the graph of desorbsion from the lists given in this Chemical Handbook.
Water may not be used for cleaning until this ventilation process is finalized. If residues remain they will probably be solved during a wall-wash with methanol, because the methanol causes the coating to swell again and the high solvency power will extract the residues.
IT IS THE MASTERS DUTY TO ADVISE WHOM SO EVER IT MAY CONCERN ABOUT THE DANGERS OF DESORBED CARGO (FROM SPONGY EPOXY CONTAMINATING THE WHOLE SHIPMENT). WHEN THINGS GO WRONG ALL AND SUNDRY (WHO WERE AVERSE TO TIME LOSS DUE TO VENTILATION) NOW WILL WASH OFF THEIR HANDS LEAVING THE SHIPOWNER ALL ALONE WITH A HUGE FINANCIAL BURDEN AND LOSS OF IMAGE.
Phenolic resins can handle strong solvent chemicals which epoxies and polyurethane coatings cannot . it has the highest resistance to chemicals.
Phenolic epoxies are better for low molecular weight Alcohols, Ketones , Aromatics like BTX. Esters (Acetates, Pthalates ) Chlorinated / Brominated materials that react with water to form acidic compounds. Water content greater than 200ppm or 0.02% must be avoided. When Methanol and Vinyl acetate monomer is carried in Phenolic epoxy tanks a hot cure is required. Example: the paint resistance tables might talk about carrying heated LO , Veg oil or animal oil at 60 deg C for 5 days. Phenolic resins are expensive . They can load solvents which cant be loaded in epoxy and polyurethane.
After carrying Ketones, Ethers and Esters the tank should be well ventilated to remove all traces of the previous cargo prior to cleaning—and the next cargo should not be diluted aqueous solutions like latex or fertilizer solutions.
The absorbsion of epoxy is faster than desorbsion due to hydrostatic pressure of cargo. Epoxy acts like a sponge, especially if the pigmentation is good. The organic molecules of the epoxy coat is permeated by the cargo of low molecular structure causing softening. Modified epoxies are most exposed to this problem—as they are ABLE to carry such products
Normal epoxy has limited time exposure to high acid animal and vegetable oils. But Polyurethane can stand acid conditions from free Fatty acids. But it is not as good as normal epoxy for Caustics. Also it can take the Ketones and Alcohol solvents epoxy cannot handle.
Another good thing is that the polyurethane lining has a smooth finish , it wont have too much clingage and so it is easy to clean. Urethane epoxies do not absorb and hold much solvents—--but Amine epoxies and Phenolic epoxies hold nearly double the content.
Can be provided as one or two pack product. One pack depends on atmosphereic moisture to produce polymerisation. Two pack is more common.
Camrex camcote MX is resistant to Ethanol and Methanol.
Rubber is used for highly corrosive cargoes which cannot be handled by Epoxy, Phenolic epoxy, Polyurethane and even stainless steel.
Rubber is suitable for Phosphoric acid. But not for Nitric acid and Sulphuric acid. It is used primarily for Hydrochloric acid and waste acids. The rubber lining is usually 6mm thick and can be of the Neoprene, Chloroprene, Nitryl and Butyl variety. There can be no perforation in the coating. Rubber coating is expensive. And must be done at drydock in ideal conditions ( temperature and humidity controlled ) on ideal surface, gritblasted , dust free ( vacuumed ) and degreased.
Rubber is not suitable for Nitric and Sulphuric acids as they oxidize rubber. Rubber is not suitable for vegetable oils , animal oils or solvents
Has better resistance to acids than epoxy or polyurethane but has poor resistance to solvents and alkalies. So used in organic acid trade –limited use.
CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )