With over 6000 identified liquid bulk chemicals currently transported by sea PPG's Marine Tank Coating Resistance Information Service (TRIS) provides practical information on appropriate coatings suitable for the widest range of individual cargoes.
PPG TRIS uses the following features for chemical resistance suitability of the coating system:
|
Feature |
Explanation |
|
|
Resistance Code |
+ |
Coating system is suitable for storage/carriage of this cargo. Notes and temperature limitations may apply. |
|
- |
Coating system is unsuitable for storage/carriage of this cargo. |
|
|
N |
No information is available on resistance |
|
|
Note(s) |
1, 2, 3 etc. |
Coating system is suitable subject to reference notes 1, 2, 3 etc. |
|
Temperature |
T (°C) |
Generally cargoes are stored and transported at ambient temperatures up to 35°C. For highly viscous cargoes, maximum storage/carriage temperatures are indicated in degrees centigrade (°C). Loading and discharge temperatures may be up to 10°C higher. However the period for which the cargo is kept at these higher temperatures should be kept as short as possible and must not exceed 48 hours. Where an * is mentioned with the temperature, an additional 10 days per month up to 5°C above the mentioned temperature is allowed as operational flexibility in case of a heating overshoot or pre-heating before discharge. See "Temperatures, storage/loading" for more details. |
The maximum acid value refers to the free fatty acid content in a cargo for each coating system and is detailed in Note 3 with the acid value being determined by the ISO 660 (1996) method.
For guidance only, the acid values determined by ISO 660 (1996) are related to the approximate weight percentage of free fatty acid as mentioned below:
|
System |
Maximum Acid Value |
Approximate Percentage Free Fatty Acid (FFA) |
|
PPG PHENGUARD series |
No limit |
Up to 100% |
|
PPG NOVAGUARD 840 |
100 |
30 - 50% |
|
PPG SIGMAGUARD 720 |
20 |
6 - 10% |
|
PPG SIGMAGUARD 750 |
5 |
1.5 - 2.5% |
TRIS is based on practical tests carried out on pure and/or commercial cargoes. The composition of many commercial cargoes contained in this resistance service are subject to change and therefore may vary in composition. PPG has no control over the composition of these cargoes, their sequence or the conditions of service and expressly disclaim any responsibility for the results obtained from their use or for any incidental or consequential effects of any kind. Concentrations mentioned are expressed in weight percentage.
Absorption of cargo by the coating may occur and subsequent desorption is dependent on factors such as temperature, ventilation, humidity, absorbed components, tank cleaning procedures etc.
Contamination of cargo by the coating may occur but is usually limited to the first cargoes after application of the coating and should be taken into account for sensitive cargoes such as edible and potable cargoes and cargoes with a high purity such as fiber grade glycol. Such cargoes should be avoided in the early life of the coating system.
Given the subjectivity of taint and taste, where this may be relevant it is recommended that the client first carries out testing of cured panels of the chosen coating in contact with the cargo, to ensure suitability.
Chemical reaction between cargoes may well result in the formation of products which may cause breakdown of the coating.
To avoid cargo contamination, care should be taken that any previous cargo retained in the coating is desorbed prior to loading of the next cargo and that effective tank cleaning procedures are used. PPG does not accept any responsibility or liability in relation to cargo contamination whatsoever.
While PPG tank coating systems are resistant to many edible and potable cargoes, PPG shall not bear any responsibility or liability for any odor, taste or contamination imparted to either edible or potable cargoes from the coating or products retained in the coating. It shall be the buyer's and/or user's responsibility (but in any event not the responsibility of PPG PMC), to ensure that any use of the product in connection with the shipping of edible or potable cargoes complies with any applicable laws under the relevant jurisdictions.
CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS #s. Chemical Abstracts Service (CAS), a division of the American Chemical Society, assigns these identifiers to every chemical that has been described in the literature. The intention is to make database searches more convenient, as chemicals often have many synonyms.
A synonym is another name for the same chemical or composition. One chemical can have a number of different names or synonyms, e.g. Methyl Alcohol is a synonym for Methanol.
To enable better identification of the cargo to be transported/stored, CAS numbers can be used to find chemicals in TRIS and synonyms are listed on the results pages.
Isomers are molecules with the same molecular formulas: the number of atoms of each element is the same — but the specific arrangements of atoms and bonds differs. In TRIS, several isomers or mixtures of such compounds may be mentioned in the synonym list even though they are not one exactly same chemical, if the coating systems are considered to have the same resistance to these chemicals.
Some products may cause surface discoloration of the coating, which is difficult to remove by tank cleaning operations, and subsequent cargo contamination is possible. Discoloration is normally a surface phenomenon and in itself does not necessarily constitute a defect. See also Note 2.
PPG does not accept responsibility for coating discoloration and cannot be held liable for any aspect of cargo tank or cargo acceptance and consequences thereof.
There are 3 distinct curing states; Full Cure, Post Cure and Hot Cure. All three states do not always apply to all coatings.
This applies to all coatings mentioned in TRIS and is the minimum curing time required for carriage of non-aggressive cargoes (cargoes without notes 4, 7 and/or 11). These minimum times are detailed in the curing tables found in the product data sheets of the respective products.
For PPG SIGMAGUARD 750 the full cure is equivalent to full resistance and no further curing is required for service.
This applies to the epoxy coating systems in TRIS and relates to carriage of aggressive cargoes (cargoes with notes 4, 7 and/or 11). Before carriage of aggressive cargoes, a full cure is required followed by 3 months service (also see Note 4) after which carriage of all acceptable aggressive cargoes compatible with the specific coating system with the exception of Methanol and Vinyl Acetate Monomer for which PPG PHENGUARD products require a hot cure before carriage.
This is only required for PPG PHENGUARD series tank coating systems and only a requirement when Methanol or Vinyl Acetate Monomer are to be stored/carried (also see Note 4) and cannot be substituted by a carriage/storage period of 3 months of non-aggressive products.
However, to obtain maximum resistance in the shortest possible time a hot cure is generally recommended.
Prior to the hot cure, in all cases, the full cure must have already been achieved.
For double hull vessels, hot curing can be carried out using hot water and the butterworth system as detailed in the PPG PHENGUARD TANK COATING - HOT CURE.
All references to "gas-free" refer to a steady state gas free condition. The most common value taken for gas free and that recommended by PPG is below the LEL (Lower Explosive Limit) however, the MAC value (Maximum Allowable Concentration) is also sometimes used. For further details on gas-free recommendations and ventilation guidelines see Ventilation. However, this information is only given as a guide and PPG cannot be held responsible for the effectiveness of ventilation procedures.
This categorization is shown in TRIS for information purpose only and should be validated by the client via IMO, relevant agencies or organizations.
The information below is taken from the IMO 'International Code for the Construction and Equipment of Ships carrying Dangerous Chemicals in Bulk' (IBC Code 2007 Edition). Please note that IMO should be consulted to confirm the classification. PPG will not accept responsibility for specification changes of cargoes or conditions of transport due to changes in classification by IMO.
Note: cargo classification to a certain ship or tank type does not indicate a cargo's aggressiveness to a coating system.
Cargoes listed in Chapter 17 of the IBC Code have been evaluated with regard to environmental and safety hazards and subsequently assigned for carriage in vessels meeting a certain design specification. The design criteria for the 3 various ship types 1, 2 and 3 are detailed in the IBC Code and are as follows:
A type 1 ship is a chemical tanker intended to transport chapter 17 products with very severe environmental and safety hazards which require maximum preventive measures to preclude an escape of such cargo.
A type 2 ship is a chemical tanker intended to transport chapter 17 products with appreciably severe environmental and safety hazards which require significant preventive measures to preclude an escape of such cargo. 2(k) denotes that ship type might be subject to regulation 4.1.3 of Annex II of MARPOL 73/78.
A type 3 ship is a chemical tanker intended to transport chapter 17 products with sufficiently severe environmental and safety hazards which require a moderate degree of containment to increase survival capability in a damaged condition.
Thus, a type 1 ship is a chemical tanker intended for the transportation of products considered to present the greatest overall hazard and type 2 and type 3 for products of progressively lesser hazards. Accordingly, a type 1 ship shall survive the most severe standard of damage and its cargo tanks shall be located at the maximum prescribed distance inboard from the shell plating.
Chapter 18 chemicals (denoted by a * in the IMO column) are those which have been reviewed for their safety and pollution hazards and determined not to present hazards to such an extent as to warrant application of the IBC Code.
After carriage of alkaline cargoes, wash water generated by tank cleaning operations will be alkaline. The wash water residues must be completely removed and not left in the tanks or loading pipes.
Although the organic coatings themselves are resistant to several inorganic acids in various concentrations, PPG cannot accept these chemicals as cargoes. This being due to the very serious pitting of the steel and undercutting of the coating system that can be caused by the inorganic acid, in areas of damage to the applied system.
PPG SIGMAGUARD 750, PPG DIMETCOTE 9 and other zinc silicate coatings, are not resistant to acids or alkalis. Their suitability is limited to products in the pH-range between 5,5 to 9. The use of acidic or alkaline tank cleaning products must also be avoided.
For regular transport of Methanol and Ethanol, PPG SIGMAGUARD 750 or PPG DIMETCOTE 9 zinc silicate coated tanks are recommended.
A non-aggressive cargo is defined as a cargo detailed in the resistance list which is not accompanied by any of the following notes: Note 4, Note 7 and/or Note 11.
Conversely, cargoes with any of the above notes are considered to be aggressive cargoes.
Tank repair should be carried out with compatible coating systems of the same or better chemical resistance. For more information contact your PPG representative.
Application of the systems must be carried out in accordance with the respective product data and relevant information sheets.
For the information from the TRIS system to be valid, the first coat of the system must be applied directly to the steel substrate which has been abrasive blasted cleaned in-situ to a minimum of ISO 8501-01 SA 2½, freed from rust, scale, water soluble salts and other foreign matter. For more information and allowed soluble salt levels, see Information Sheet "Cleaning of Steel and Removal of Rust".
After application of the full system has been completed, the system has to be cured under specified conditions (see also above CURING).
Exposure of the coating to an aggressive cargo before the coating has obtained the required cure, may permanently affect the resistance properties of the system.
This list is not valid when shop primers are present under the coating system. Shop primers must be completely removed.
When part of the structure is of stainless steel, the blasting profile of the stainless steel substrate should be the same as for mild steel as is specified in the respective product data sheet.
Whilst a list of tank cleaning chemicals suitable for use with our tank coatings is available, PPG does not advise on specific tank cleaning procedures or regimes. For detailed advice on this subject we recommend contacting one of the specialist tank cleaning companies.
Generally cargoes are stored and transported at ambient temperatures up to 35°C.
For highly viscous cargoes, maximum storage temperatures are indicated in degrees centigrade (°C). Loading and discharge temperatures may be up to 10°C higher. However, the period for which the cargo is kept at these higher temperatures should be kept as short as possible and must not exceed 48 hours.
The temperature to which high viscosity cargoes have to be raised for loading and discharging have been obtained from organizations engaged in the transport and manufacture of such chemicals. PPG cannot be held responsible for the consequences of changes to the chemical composition or quality due to heating of cargoes.
For less viscous cargoes, which do not require heating to reduce viscosity, no maximum temperatures are stated. This means that, for these cargoes, no higher temperatures are allowed than those occurring in world-wide storage or transport under ambient conditions. For cargo temperatures above 35°C PPG should be consulted.
Aggressive cargoes (which reference notes 4, 7 and/or 11 in TRIS), should not be carried in tanks adjacent to those having higher temperatures than allowed for these aggressive cargoes.
The resistance code refers to bulk storage or transport of cargoes for a maximum period of 6 months unless a shorter time is specified. For extended storage or transport times PPG PMC must be consulted.
In order to extend the service life of the coating, after carriage/storage of aggressive cargoes (which reference notes 4, 7 and/or 11 in TRIS) and before carriage of another cargo or water contact, it is necessary to allow release of absorbed cargo by fully ventilating the tank followed by storage/carriage of a non-aggressive cargo for at least 10 days.
The measures detailed below are given as a guideline for a suitable ventilation procedure, they should not be interpreted as a comprehensive set of instructions for every vessel as the requirements and procedures vary from vessel to vessel and are dependent on / influenced by such things as cargo store/carried, tank size, tank configuration, pump capacity, ambient temperature, relative humidity etc.
These guidelines are also not intended to have priority over any local, national or international rules or laws.
After complete discharge of cargo, the tank should be ventilated until gas free. The most common value taken for gas free and that recommended by PPG is 1% of the LEL (Lower Explosive Limit) however, the MAC value (Maximum Allowable Concentration) is also sometimes used. The gas concentration should be measured at different levels and different locations.
Complete discharge of cargo means that no residual cargo should be present on the tank bottom, in the by-pass pump, the stripping line, the drop line and that the deep-well pump must be completely emptied.
After the tank has been made gas free, it should then be ventilated for at least 24 hours.
There are two main methods for ventilation, dilution and displacement.
Dilution is the least efficient method and involves blowing air into the tank at the top thereby forcing air out through other tank openings. Here the dilution is very slow and inefficient, with gas pockets likely to remain in the bottom corners of the tank etc.
Displacement is by far the quickest, most efficient method for ventilation and is therefore strongly recommended. For cargo vapors heavier than air (most cargoes), these heavy vapors settle on the tank bottom and should be extracted by means of an extraction fan connected to flexible trunking which is lowered into the tank until just above the tank bottom. It is strongly recommended to reposition the flexible trunking during extraction/ventilation. Fresh/dry air, to replace the extracted vapors, should simultaneously be allowed to enter the tank through fully opened tank covers, sampling holds and Butterworth lids in the top of the tank.
It is important to prevent condensation forming on the paint film and therefore the relative humidity of the air used should be kept as low as possible. Under normal circumstances use of the heating coils during ventilation is strongly advised, as it reduces the risk of condensation forming on the paint film and will accelerate desorption of the cargo.
After ventilation has been carried out, the tank should be closed for 8 - 12 hours and then opened and measured to see if it is gas free (as due to release of absorbed cargo during this period, the gas concentration could have increased above the specified limit and therefore further ventilation is required.)
a) If gas free, then the tank is suitable for loading of a non-aggressive cargo.
b) If not gas free, then the ventilation procedure detailed in 2) should be repeated and thereafter the tank should be measured to see if it is gas free.
The following points are general and apply for all ventilation processes:
Ambient air with a high relative humidity (such as that found during adverse weather conditions - mist, rain, spray etc.) should not be used for any ventilation process.
All times quoted are for an ambient temperature of 20°C.
Tank size and configuration play an important role and it is advisable, if possible, to reposition the flexible trunking and fan periodically in such a way that gas pockets are avoided.
Air used for tank ventilation should not be recirculated.
The above procedure does not guarantee complete removal of absorbed cargo from the coating and is provided as a guide only.
Further guidance on tank ventilation and safety matters can be found in the International Safety Guide for Oil Tankers & Terminals (ISGOTT).
Below generic illustrations are given for descriptive purpose only and are not to imply detailed work procedures.
Zinc pick up by the cargo in tanks coated with PPG SIGMAGUARD 750 or PPG DIMETCOTE 9 zinc silicates may occur, depending on the cargo in question.
