Notes

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

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

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

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.

 

 

Gasfree

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).

Inert gas

Inert gas is commonly understood as water scrubbed exhaust gas, with a high content of nitrogen and carbon dioxide, and with a low content of oxygen.

The composition varies depending on oil and engine efficiency, but could typically be:

Component Concentration, %vol
Nitrogen 12-14
Carbon dioxide 80
Oxygen 2-4
Carbon monoxide 0.01
Nitrous oxides 0.02
Sulphur dioxide 0.05

To avoid corrosion, the content of sulphur dioxide must be maximum 200 ppm (0.02%).

Sequences

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

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.

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.

 

 

Ventilation

See: Tank cleaning

Washing

See: Tank cleaning

Temperature

It is generally advisable to avoid operating temperatures higher than dictated by the handling of the cargo. Unless otherwise stated, the following indicative max. temperatures apply:

  GALVOSIL 15700 HEMPADUR 15500 HEMPADUR 15400 HEMPADUR 15600 HEMPADUR 15460
Water containing cargoes Max. 40°C/104°F Max. 40°C/104°F Max. 40°C/104°F Max. 40°C/104°F Max. 40°C/104°F
Water-free cargoes (acceptable Resistance Notes) Max. 90°C/194°F, (+, +3, +9, +23) Max. 90°C/194°F, (+, +11, +15, +29) Max. 65°C/149°F, (+, +14) Max. 70°C/158°F, (+, +14) Max. 70°C/158°F, (+, +14)
Loading and discharging for water-free cargoes,short term Max. 90°C/194°F Max. 100°C/212°F Max. 85°C/185°F Max. 85°C/185°F Max. 85°C/185°F

For some cargoes, the resistance category is accompanied by a maximum temperature, e.g. "+, max. 35°C", meaning that the lining is fully resistant at and below 35°C/95°F.

In case of transport or storage of water containing cargoes at temperatures higher than ambient, all adjacent cargo tanks should in general be either empty or contain cargo with the same temperature, and all adjacent ballast tanks must be empty. This is in order to avoid excessive temperature gradients across the paint film resulting in excessive absorption of cargo, which is fatiguing for the paint film.

In case of transport or storage of water containing cargoes at temperatures higher than 40°C, Hempel must be consulted unless otherwise stated.

 

Resistance table

References

Resolution MEPC.225(64): 2012 Amendments to the International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code) as amended by MEPC.2/Circ.18 and MEPC.2/Circ.19.

When consulting data for IMO Ship Type and MARPOL Pollution Category in the present guide, it is recommended to check that the above references are still valid. In case of discrepancy between the present guide and the references, the latter prevail.

Name

The cargoes are arranged alphabetically according to their name, including both the common name and the most frequently used synonyms (Index Names). The common names are generally the Product Names used in MARPOL and in the IBC Code. Ref. 1 Chapter 17 and 18. Most Index Names are from the IBC Code, Chapter 19.

"TM" after the cargo name means that the name is a trade name.

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.

MARPOL Pollution Category

The following notation is used in the Cargo List of this guide:

Pollution category Description
X, Y, Z Substances posing a threat of harm to the marine environment are divided in three categories, X, Y and Z. Category X substances are those posing the greatest risk to the marine environment, whilst Category Z substances are those posing the smallest threat. Ref. MARPOL Annex II, Regulation 6.1 and chapter 17 and 18 of the IBC Code.
OS Substances denoted "OS" (Other Substances) in chapter 18 of the IBC Code have been evaluated and found to fall outside Category X, Y or Z.
L The cargo is included in List of Oils. Ref. MARPOL Annex I, Appendix I.
* The cargo is not included in chapter 17 or 18 of the IBC Code or in MARPOL

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

IMO Ship Type

Chapter 2.1 of The IBC Code defines three ship types designed to one of the following standards:

Cargo ship type notation Description of notation Ship type description
1 The cargo to be transported in ship type 1 only A type 1 ship is a chemical tanker intended to transport products with very severe environmental and safety hazards which require maximum preventive measures to preclude an escape of such cargo
2 The cargo to be transported in ship type 1 and 2 only A type2 ship is a chemical tanker intended to transport products with appreciably severe environmental and safety hazards which requiresignificant preventive measures to preclude an escape of such cargo
3 The cargo to be transported in either ship type 1, 2 or 3 A type3 ship is a chemical tanker intended to transport products withsufficiently severeenvironmental and safety hazards which require a moderate degree of containment to increase survival capability in a damaged condition
- The cargo is not assigned a ship type in chapter 17 of the IBC Code
* The cargo is not listed in the IBC Code

Formula

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

HEMPEl's GALVOSIL 15700 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 15500 phenolic epoxy

The resistance categories apply to a specified dry film thickness of 3 x 100 micron, applied in accordance with "Hempel's Technical Standard for Tank Coating Work".

 

HEMPADUR 15400 amine cured epoxy

The resistance categories apply to a specified dry film thickness of 3 x 80 micron, applied in accordance with "Hempel's Technical Standard for Tank Coating Work".

 

HEMPADUR 15600 amine cured epoxy

The resistance categories apply to a specified dry film thickness of 2 x 125 micron, applied in accordance with "Hempel's Technical Standard for Tank Coating Work".

 

HEMPADUR 15460 amine cured epoxy

The resistance categories apply to a specified dry film thickness of 2 x 125 microns, applied in accordance with "Hempel's Technical Standard for Tank Coating Work".