General notes

Acid value

The acid value is defined as the number of milligrams of potassium hydroxide required to neutralize the free acids present in 1 gram of oil, fat or other product.

The test method is described in e.g. ISO 660:2009.

Chemical variability

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


PH is a measure of the acidity or alkalinity of an aqueous solution. The PH scale is a logarithmic scale meaning that one pH unit corresponds to a ten times higher or lower concentration.

pH value Type of solution Examples
7 Neutral Pure water
Lower than 7 Acidic Citric acid Hydrochloric acid
Higher than 7 Alkaline Caustic soda Ammonia (aqueous)

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 been achieved after 3 months in service, during which period the coating must have been water washed at least once.

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

For HEMPADUR 15500 and 85671 conditioning will have be achieved after three months in service or post-curing (see Specific Note 19).

Before loading a sensitive chemical, the possible contamination of the chemical from a previous harmful commodity must be taken into account. Effective tank cleaning is always mandatory prior to sensitive chemicals.

For edible chemicals, information on relevant regulations and certificates required should be obtained. Hempel does not accept responsibility for chemicals being affected by the coating or retained previous commodities.


GALVOSIL is Hempel's trade name for a zinc silicate coating.

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

They have a somewhat open structure and therefore evaporation of commodity absorbed in the lining is quite fast, especially if the evaporation is assisted by ventilation. This generally allows a close sequence of commodities.

Due to the nature of zinc silicate, their resistance is limited to chemicals within the PH range 6 to 9:

  • Chemicals with PH below 6 will dissolve the zinc pigment, resulting in a coating without protective value.
  • Chemicals with PH above 9 will dissolve the zinc and break down the silicate network.

Transport or storage of chemicals, or any other exposure outside this PH-range must not take place.

Inert gas systems may, if the scrubber is not functioning correctly, generate acidic gases of sulphur dioxide which may damage the zinc silicate coating. The inert gas for use in zinc silicate coated tanks must contain max. 0.02% (w/w) of sulphur dioxide.

Zinc pick-up by a cargo may occur during transport or storage in a zinc silicate coated tank, even when the coating is resistant to the chemical. It is advisable to check with the receiver of the commodity if a possible zinc pick-up is considered to have a negative effect on the quality of the chemical. Specific Note 9 is a guidance note for a number of relevant chemicals.


HEMPADUR is Hempel's trade name for epoxy coatings.

For use as tank coating, a distinction is commonly made between two types of epoxies:

  • amine cured epoxies, and
  • phenolic epoxies, also sometimes termed Novolac epoxies.

Both cure to give a close network, generally resulting in a slow absorption of chemical and a low maximum absorption. Desorption, however, is correspondingly slow, which has to be taken into consideration for some commodity sequences.

Phenolic epoxies can be given an even denser network and broader resistance by a heat treatment after normal curing. See post curing, Specific Note 19.

Both types have quite versatile resistance. However, the phenolic epoxies, especially when post-cured, have a significantly higher degree of resistance than that of the amine cured epoxies.

The differences in resistance may be illustrated by their typical areas of use:


Amine cured epoxies:

Oil tankers, product tankers and storage tanks for mineral oil products and a wide range of inorganic chemicals.

Phenolic epoxies:

Chemical tankers and storage tanks for a wide range of highly refined products, vegetable oils and derivatives as well as inorganic chemicals.




Hempaline Defend is HEMPEL's trade name for protective tank linings based on solvent free epoxy or vinyl ester resin.


Gasfree in the sense "safe for man-entry" means that the tank atmosphere fulfils the following requirements:

  • Oxygen content is 21%.
  • Gas and vapour concentration is less than 1% of LEL (Lower Explosive Limit).
  • Content of "Toxics" is less than TLV (Threshold Limit Value).

Safe entry of tanks is described in guides such as International Safety Guide for Oil Tankers and Terminals (ISGOTT).


For some chemicals, sequences involving water or aqueous chemicals, either as previous or subsequent commodity, 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 commodity sequences, please contact Hempel.

Tank cleaning

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

The purpose is to avoid contamination of the following commodity by various debris and to minimize contamination of the following commodity by residues of the previous chemical. The cleaning, however, 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 to "gas free" aims at lowering the concentration of 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 through evaporation, 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.


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.




See: Tank cleaning


See: Tank cleaning


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

Important note

In accordance with our policy of continuous product development the information in this guide may be modified from time to time and you should check with your local Hempel representative that you have the most up-to date version.

Failure to comply with the requirements of the latest version of this chemical resistance guide that apply to the products to be stored will invalidate any guarantee given by Hempel for the coating system as applied to the storage tank or vessel.

Resistance table

CAS numbers

CAS registry numbers are unique numerical identifiers for chemical compounds etc. The internet version of this Guide provides the CAS number for a number of products and chemicals. Ref. GESAMP/EHS Composite List 50/8, 2013. CAS numbers are given for information only. They cannot be used as the only entry for evaluating the resistance category.

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


The chemical formula provides the elementary composition of those commodities which are well defined as chemicals.


"(sol)" after the chemical formula or alone in the column means that the commodity is water containing, either an aqueous solution or dispersion.

Hempel's tank coating systems

HEMPADUR 85671 epoxy phenolic Novolac lining


The resistance categories apply to a specific dry film thickness of 3x100 microns



HEMPALINE DEFEND 400 solvent free epoxy lining


The resistance categories apply to a specific dry film thickness of 1x400 microns



HEMPALINE DEFEND 500 vinyl ester glass flake filled lining


The resistance categories apply to a specific dry film thickness of 2x400 microns



HEMPALINE DEFEND 560 vinyl ester glass flake filled lining


The resistance categories apply to a specific dry film thickness of 1X500 microns



HEMPALINE DEFEND 630/640 solvent free epoxy phenolic lining


The resistance categories apply to a specific dry film thickness of 1X500 microns



HEMPALINE DEFEND 740 Novolac vinyl ester glass flake filled lining


The resistance categories apply to a specific dry film thickness of 2x625 microns


HEMPEL's GALVOSIL 15680 solvent borne zinc silicate


The resistance categories apply to a specified dry film thickness of 1 x 100 micron, applied in accordance with Hempel's Technical Standard for Tank Coating Work.



HEMPADUR 35760 is a solvent-free, two-component, high-build phenolic epoxy tank lining

The resistance categories apply to a specific dry film thickness of 1X500 microns