Saturday, December 25, 2010

COLOUR ON CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL

Colour is an indicator of the purity of the  cargo. Any deviation from the known color of a cargo indicates contamination.

When water ingresses certain chemicals it is easy to find out by visual means ( milkiness  , without any elaborate tests.

Majority of the chemicals are clear, and a haze of milky color should be investigated.

Testing of color should be always be done on a white background.

Discoloration of methanol wash during WWT , means that the tank requires further cleaning.

APHA ( hazen ) used for light products such as aromatics and Ketones.

Colour  5 Apha   (or Saybolt ASTM D12095)   is required for the MEG fg wash  ( highest spec.) . Methanol requires only 15 Apha.

Apha solution is platinum chloride solution. The number of cc Apha solution ( min is 5 cc ) for Apha 5 added to distilled water gives the APHA colour shade number.

Apha zero means clear. In your wall wash lab you must have comparator nessler tube ready made solutions of A5  A10  and A20 ( always in multiples of 5 ).

The standard apha solutions are stable for many days but should be done again after one week. The stock solution is stable for an indefinite period if kept in a refrigerator.

Proforma: ml of 500 APHA Stock Solution Diluted to 100 ml with Distilled Water/ APHA number
1/5
2/10
3/15
4/20

SAYBOLT scale is NOT used by shipstaff. Lightest is +30 Saybolt and darkest is -16 used only in the petroleum industry.   Water White standard colour is in the range of  +30 to +20. 


Gasolenes contain dyes  will turn a methanol wall wash to a pinkish color. It is very important that the dye is removed prior to loading subsequent cargoes, since with time the dye is harder to remove. The dye can be removed by recirculating an oxidizer solution or bleach.


Acid Wash Colour 
Done to test the cleanliness of a tank by wiping one M2 of tank bulkhead with a cotton swab dipped in Toluene. The liquid is then wrung out and tested,as  below. Done by ship staff.

This method is used for analysing aromatic hydrocarbons, like toluene and xylene or to check is petroleum HC are present in aromatic HC. Aromatics are unaffected by Sulphuric acid , but oils and other contaminants are affected.  


A certain amount of sample (21 ml) is mixed in a specified glass cylinder with 7 ml sulphuric acid. The acid will remove impurities present in the sample and will discolour. The colour of the acid-layer, at the bottom of the tube  is compared with standard colours in the range of 0 ( water color ) till 14( dark yellow color ). The higher the colour number, the worse the sample.


ASTM or NPA colour 
This method is used to analyse lubricating oils, diesel fuels, etc. The oil is compared in a colorimeter with standard glasses, marked 0, 0.5, 1, 1.5, etc. to 8.  There is a relationship between NPA and ASTM 1500.  However, below colour 3.5 NPA glasses are darker than ASTM glasses, while above colour 3.5 ASTM is darker than NPA.

ASTM D 1500, previously called NPA defines colour scale and an apparatus suitable for field work and application on board. A test sample is compared with coloured glasses in a revolving magazine. The scale goes from I (water) to 8 (extra dark red). The name "NPA grade…..” is still often used in shipping when a prospected cargo is circulated or when a vessel's cleanliness is described. A cargo may be accepted at NPA 2, with discharge permitted at NPA 2.5. A certain amount of degradation in such a case can be permitted.

With a colorimeter on board one can take samples and by experience get an idea of how much of the previous cargo residues can be left unattended without risk for cargo claims (refers to petroleum cargoes rather than to chemical products). The colour of a product is used as a measure for the quality of that product. The following systems are used.


FAC colour
The FAC colour will be mainly analysed in animal fats. The molten fat is compared with standard colours numbered 1, 3, 5, 7 etc.


GARDNER SCALE AND LOVIBOND SCALE ARE USED FOR VEGETABLE OILS.


Lovibond colour
Generally, this method is used for analysing animal and vegetable oils and fats. The colour is determined with a Lovibond Tintometer.  In this apparatus, red, yellow and blue coloured standard glasses are matched which glasses can be slided one after each other. The sample is poured into a glass cell of a specified length, viz. 1/4, 1/2, 1, 2 or 5 1/4''.  The colour of the oil is compared with the standard glasses by sliding these glasses in such way that the mixture of the three colours matches the colour of the oil.

Example: 
The glasses no 20 yellow, no 4 red and no 0.1 blue together give the same colour as the oil sample in an 1" cell.
The colour is noted as :
Colour in Lovibond 1'' cell : 20 yellow, 4 red, 0.1 blue.


Gardner colour
The Gardner-scale uses sealed reference tubes for comparison with samples in a tube of the same diameter. (The FAC-method resembles the Gardner method but has a different graduation). The Gardner scale goes from 1 - 18 and is defined in ASTM 1544-63T.

This colour will be mostly determined in animal and vegetable oils and fats. The colour of the sample is compared with standard Colours in the range 1 - 18.


Saybolt colour
This colour determination is used to measure the colour of refined petroleurn products, like aviation gasoline, jet fuels and naphthas. In a colorimeter the height of a column of sample matching standard glasses is read.  From a table the colour Saybolt is found.

The Saybolt colour scale uses coloured classes against which the sample is compared in a defined apparatus. The colour scale goes from plus 3 )0 (lightest) to minus 16 (darkest). The Saybolt scale is widely used in the petroleum industry The method is defined in ASTM D 156-64. The Saybolt method requires a special apparatus, is somewhat complicated and not particularly suited for use on board ships.


APHA-colour 

Apha solution is platinum chloride solution. The number of cc Apha solution ( min is 5 cc )for   Apha 5 added to distilled water gives the shade number.

Lightest is +30 Saybolt and darkest is -16 used only in the petroleum industry.   Water White  standard colour is in the range of  +30 to +20.

Apha zero means clear. In your wall wash lab you must have comparator nessler tube ready made solutions of A5  A10  and A20 ( always in multiples of 5 ).

The standard apha solutions are stable for many days but should be done again after one week. The stock solution is stable for an indefinite period if kept in a refrigerator.
Proforma: ml of 500 APHA Stock Solution Diluted to 100 ml with Distilled Water/ APHA number
1/5
2/10
3/15
4/20

A method called APHA (Hazen) is often used for very light products, defined in ASTM D1209, viz aromatics, ketones

This colour is analysed in water white chemicals and solvents, like methanol, VAM, glycols, etc. 
This colour scale is defined with an origin in 100 cc distilled water (value 0) to successively higher values (max 500) by adding APHA-solution (a platinum-cobolt salt solution). The number of cc APHA-solution (min 5 cc) added to the distilled water gives the APHA-colour shade number. A comparison is made against a white background with a product sample in one test tube and a matching APHA-solution in another100 ml of a sample in a specified glass cylinder is compared with a standard colour solution in water. 

1 ml of the standard colour in 99 ml water has a colour APHA of 5; 2 ml standard in 98 rnl water gives colour 10, etc.

This method can easily be carried out on board. APHA-solutions are best bought from a laboratory, already premixed for a number of shades.


Standard Test Method for Colour of Clear Liquids - APHA Colour ( pt-co)

(PLATINUM – COBALT SCALE)
ASTM – D1209

This test method describes a procedure for the visual measurement of the color of essentially light coloured liquids.

1. From the stocks solution prepare standards in accordance with Table I by diluting the required volumes to 100 ml with distilled water in the Nessler tube. Cap the tubes and seal the caps with shellac or a water proof cement if long term storage is desired (Note: This standard would be stable for at least at year).

2. Wall wash the tank using the appropriate solvent (e.g. Acetone or Methanol or Para-xylene etc as applicable) and introduce 100 ml of the sample into a Nessler tube (Use a filter if the sample has it has any visible turbidity.)

3. Report as the color the number of the standard that most nearly matches the specimen.  In the event that the color lies midway between two standard, report the darker of the two or otherwise report the range over which an apparent match is obtained.

TABLE 1
COLOR
STOCK
COLOR
STOCK
STANDARD
SOLUTION
STANDARD
SOLUTION
NUMBER
( ml )
NUMBER
( ml )




1
0.20
25
5.00
2
0.40
30
6.00
3
0.60
35
7.00
4
0.80
40
8.00
5
1.00
50
10.00
6
1.20
60
12.00
7
1.40
70
14.00
8
1.60
100
20.00
9
1.80
150
30.00
10
2.00
200
40.00
11
2.20
250
50.00
12
2.40
300
60.00
13
2.60
350
70.00
14
2.80
400
80.00
15
3.00
450
90.00
20
4.00
500
100.00

As a very general rule, if the wall wash sample is coloured, the colour will usually be caused by an unsaturated dye material and if there is significant colour in the sample, then it is quite usual that the PTT test will also fail.

Platinum Cobalt Colour 

Ref. ASTM D 1209 - Typically Colour should be < 15 APHA

Common sense tells us that any previous cargo(s) that were not water-white will potentially result in the wall wash becoming discoloured.

Inorganic zinc coatings that tend to adsorb contamination onto the coating surface are most likely to show the worst effects of discolouration. This is why it is quite useful to have a source of colour remover on board a vessel with zinc coated tanks, because even the slightest colour in the previous cargo can cause problems with this wall wash test.

On the other hand, organic epoxy coatings tend to be quite smooth and the discolouration can be far more easily washed away.


CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )
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4 comments:

  1. Dear Captain,
    My 2 year old daughter, suddenly 2 days back she started stuttering. We are worried. Any remedy for this? In one of your comments I read that Amla-Ghee combination can cure it. Is it advisable for a 2 year old?
    Please help me...

    ReplyDelete
    Replies
    1. hi vvp,

      In Kerala we give vayambu ( dried root powder of Acorus Calamus ) and honey quarter teaspoon to be licked off a fresh plucked peepal leaf..

      You may NOT have access to vayambu—in which case substitute it with fresh turmeric juice.

      DO NOT WORRY !

      Note: Vayambu is the name in Malayalam. The british took this plant to other lands. English-Sweet Flag.; Chinese-Shi chang pu; Arabic-vash, vaj; French-acore calame; German-Kalmus; Italian-calamo aromatic; Dutch-kalmoeswortel; Hindi-Bajai, Gora-bach, Vasa Bach; Marathi-Vekhand; Tamil-Vashambu; Telugu-Vadaja, Vasa; Kannada-Baje; Malayalam-Vayambu; Sanskrit- Bhutanashini, Jatila. Vacha


      Capt ajit vadakayil
      ..

      Delete
  2. Dear Captain,
    My daughter is now talking almost OK, with a small level of stammering.. ..... hope that too will be cleared soon...
    exactly after I received your message "DO NOT WORRY", my wife called me up and said she has improved a lot!!!!!!!!
    Thanks a lot

    ReplyDelete
  3. Wow Ajit , Good Man,
    my e mail
    ops@ackm.com.sg

    ReplyDelete