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.
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.
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 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 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:
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.
Water scrubbed exhaust gas (also called "inert gas" in the Marine industry) has a high content of nitrogen and carbon dioxide and a low content of oxygen.
The composition varies depending on oil and engine efficiency, but could typically be:
| Component | Concentration, %vol |
|---|---|
| Nitrogen | 80 |
| Carbon dioxide | 12-14 |
| Oxygen | 2-4 |
| Carbon monoxide | 0.01 |
| Nitrous oxides | 0.02 |
| Sulphur dioxide | 0.05 |
If the scrubber is not working properly, acidic gases of sulphur dioxide can be generated. To avoid corrosion, the content of sulphur dioxide must be maximum 200 ppm (0.02%). This is especially critical if the lining is zinc silicate based.
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.
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:
The actually employed detailed procedure depends on the commodity sequence in question, and is based on:
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.
It is generally advisable to avoid operating at temperatures higher than dictated by the handling of the cargo. Unless otherwise stated, the following indicative max. temperatures apply:
| GALVOSIL 15700/15750 | 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.
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.
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.
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 |
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 |
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 |
GALVOSIL 15700/15750 solventborne zinc silicate.
The resistance categories apply to a specified dry film thickness of 1 x 100 micron.
HEMPADUR 15500 epoxy novolac.
The resistance categories apply to a specified dry film thickness of 3 x 100 micron.
HEMPADUR 15400 epoxy.
The resistance categories apply to a specified dry film thickness of 3 x 80 micron.
HEMPADUR 15460 epoxy.
The resistance categories apply to a specified dry film thickness of 2 x 125 micron.
HEMPADUR 15600 epoxy.
The resistance categories apply to a specified dry film thickness of 2 x 125 micron.
All systems must be applied in accordance with "Hempel's Technical Standard for Tank Coating Work".