Notes

General notes

Discolouration during storage

Storage of some chemicals (such as strong acids (hydrochloric, sulphuric and phosphoric acids), some oils, coal tar, bitumen and their derivatives) may cause discolouration of the lining with no influence on the corrosion protection. However, if purity of the chemical is a requirement an alternative storage solution may be required.

Chemical variability

Commercial substances vary in composition and they can also contain impurities which can be detrimental to the coating and thus must be avoided. It is always recommended to check the full specification of the chemical to be transported/stored and ensure that it does not deviate significantly from the pure chemical listed in this guide.

Sensitive chemicals

Very pure or sensitive chemicals should not be transported or stored until the coating system has been conditioned.

For GALVOSIL, conditioning will in general be achieved after 3 months in service. During this period the coating must have been water washed at least once.

For HEMPADUR 15400,15460, 15600 and HEMPALINE DEFEND epoxies, conditioning will in general be achieved after 3 months in service.

For HEMPADUR 15500 and 85671 conditioning will be achieved after 3 months in service or after heat curing (see Specific Note 19).

Before loading a sensitive chemical, the potential contamination from a previously stored chemical must be taken into account. Effective tank cleaning is always mandatory prior to loading sensitive chemicals.

For edible chemicals, information on relevant regulations and certificates must be obtained. Hempel does not accept liability for these chemicals being affected by the coating or previously stored chemicals.

GALVOSIL

GALVOSIL is Hempel's trade name for zinc silicate coatings. 

Zinc silicates may be waterborne or solventborne. Both are, when fully cured, purely inorganic, and as such have excellent resistance towards organic solvents and related products.

They have a certain open structure and thus evaporation of the chemical absorbed in the lining is quite fast, especially if it is assisted by ventilation. When the tank is used for different chemicals, this generally allows faster loading/unloading sequences between them.

Due to the nature of zinc silicate, its resistance is limited to chemicals within the pH range 6 to 9. At pH outside this range, the zinc is dissolved and the silicate network destroyed, so the coating loses its protective action. Therefore transportation/storage of chemicals or any other exposure outside this pH range must not take place.

Zinc pick-up by the chemical may occur during its transportation/storage in a zinc silicate coated tank, even if the coating is resistant to the chemical. In case it is considered this zinc pick-up may take place it is advisable to check with the receiver if this could have a negative impact on the quality of the chemical. Specific Note 9 is a guidance for some relevant chemicals.

HEMPADUR AND HEMPALINE DEFEND epoxy

HEMPADUR is Hempel's trade name for epoxy coatings. HEMPALINE DEFEND is also Hempel's trade name for some solvent free epoxies, as well as vinyl esters.

A distinction is commonly made between three types of epoxies:

  • epoxies
  • phenolic epoxies
  • novolac epoxies

The three of them cure to give a dense network, generally resulting in slow absorption and low maximum absorption of the stored chemical. Therefore desorption is also slow and this has to be taken into consideration in loading/unloading sequences involving different chemicals.

Crosslinking of phenolic epoxies and thus their chemical and temperature resistance is higher than epoxies', as they cure into a denser network. Chemical and temperature resistance of novolac epoxies is even higher than phenolic epoxies due to higher crosslinking, especially after heat curing (see Specific Note 19), after which they achieve their maximum resistance. 

HEMPALINE DEFEND vinyl ester

HEMPALINE DEFEND is Hempel's trade name for vinyl ester coatings, as well as some solvent free epoxies.

Vinyl esters provide excellent chemical resistance, especially to organic and inorganic acid compounds. If based on novolac, they are able to withstand high temperatures and pressures and their chemical resistance is even better due to the higher crosslinking. Those linings containing the suitable fillers can also provide high abrasion resistance.

Sequences

In some cases, loading/unloading sequences involving water or aqueous chemicals, either as previous or subsequent chemical, may be detrimentally fatiguing for the coating. For these chemicals the Specific Notes advise on safe handling.

It is impossible to give any general advice on the effect of chemical sequences due to the innumerable permutations of chemicals.

For advice on specific sequences, please contact Hempel.

Tank cleaning (including ventilation and washing)

For chemical tankers and some storage tanks it is a common standard to clean the tanks after discharge of the chemical, irrespective of its type.

The purpose is to minimize contamination of the following chemical by residues of the previous one. Besides, the cleaning will also prolong the service life of the tank lining, provided that proper precautions are taken not to damage the lining mechanically or chemically.

In general, one or more of the following operations are involved:

  • Ventilation to "gas free"
  • Wash for debris using seawater and fresh water, or fresh water only
  • Wash for residues of previous commodity using detergents and/or chemicals
  • Ventilation to "dry".

The actually employed detailed procedure depends on the commodity sequence in question, and is based on:

  • Instructions from client/owner/charterer
  • Guidelines from independent tank cleaning guides (e.g. Dr. Verwey).
  • Recommendations by Specific Notes to the Resistance Table.

Some general remarks to the procedures are given below:

Ventilation.

Ventilation to "gas free" aims at lowering the concentration of the chemical vapour to a predefined, acceptable level. It is most effectively done by suction from the bottom of the tank, while introducing fresh air at the top at a relatively low flow rate.

Ventilation to "visibly dry" aims at removing water adhering to the tank surfaces. Possible pools of water on the bottom are removed by mopping. It is most effectively done by suction from the top while introducing fresh air at the bottom at a relatively high flow rate. Drying will be facilitated by the use of heat (from heating coils) and by the use of dry air for replacement.

Ventilation to "completely dry" aims at removing all chemical absorbed in the tank lining, and is arranged as for ventilation to "visibly dry". For zinc silicate, which releases the absorbed chemical quickly, the high flow rate itself will affect the drying. For epoxies, which release the absorbed chemical through diffusion, heat is the determining factor, and the flow rate could be kept relatively low. The rate of diffusion is first and foremost controlled by temperature, and the effect of ventilation is mainly to distribute heat.

Washing

For some commodity sequences washing with water can be done without any implications for the tank lining, whereas for others it may have a detrimental effect. The use of chemicals and cleaning agents must be in accordance with the Chemical Protection Guide. If in doubt, please obtain Product Data Sheet and Material Safety Data Sheet and consult Hempel.

It is generally recommended to keep the washing time as short as possible and the temperature of the wash water as low as possible. As a rule of thumb, a high temperature is only justified if the cleaning efficiency is doubled by a 10°C/18°F increase in temperature.

 

 

Temperature

It is generally advisable to avoid operating at temperatures higher than dictated by the handling of the chemical. Unless otherwise stated, the temperature mentioned in resistance category should be considered as maximum temperature.

Resistance table

Resistance category

The Chemical Protection Guide operates with the following resistance categories:

Resistance category Explanation
+ Fully resistant
+, "Note" Conditionally resistant, referred to by Specific Notes
- Not resistant
¤ Resistance not measured

Hempel's tank lining systems for Protective

GALVOSIL 15700 and GALVOSIL 15680 solventborne zinc silicates.

The resistance categories apply to a specified dry film thickness of 1 x 100 micron.

HEMPADUR 85671 solventborne epoxy novolac.

The resistance categories apply to a specific dry film thickness of 3 x 100 micron

HEMPALINE DEFEND 400 solvent free epoxy.

The resistance categories apply to a specific dry film thickness of 1 x 500 micron.

HEMPALINE DEFEND 630/640 solvent free phenolic epoxy.

The resistance categories apply to a specific dry film thickness of 1 x 500 micron.

HEMPADUR 35760 solvent free phenolic epoxy.

The resistance categories apply to a specific dry film thickness of 1 x 500 micron.

HEMPALINE DEFEND 500 flake filled vinyl ester.

The resistance categories apply to a specific dry film thickness of 2 x 400 micron.

HEMPALINE DEFEND 560 trowable glass flake filled vinyl ester.

The resistance categories apply to a specific dry film thickness of 1 x 500 micron.

HEMPALINE DEFEND 740 glass flake filled novolac vinyl ester.

The resistance categories apply to a specific dry film thickness of 2 x 625 micron.