Scanning Tunneling Microscopy (STM)

In line with the industry requirement for continuous improvement, a higher quality of cargo is demanded year after year- no matter whether it is a chemical product, animal or vegetable oil. The latter is for human consumption and contamination by any possible foreign substances harmful to health must be prevented. In the case of the former, its high quality on delivery is a prerequisite for the end product to be of good quality.

Of course, we can control only quality of carriage. Chemical cargo maybe rejected due to impurity, whatever the size of the parcel; in some cases impurity detected by chromatography constitutes a reason for rejection.

To meet the severe requirements for cargo quality control, cargoes must be handled with the greatest possible care. For this purpose, the vessel should check and eliminate all that may deteriorate cargo quality. A proactive, rather than reactive attitude is a must. Any problem related to cargo tank preparedness needs to be attended to overall, rather than with the approach of just passing cargo surveys.

1. Cleanliness (This should be ascertained at the time of tank cleaning, and to be confirmed before loading.)

a. Tank: Not only the tank bottom but also the following places which tend to collect cargo residues, should be checked. The middle and upper sections of tank walls, The blind sectors behind the inner structural members, lower part of the heating coil, pipe supports, behind pipe stacks, around pipe flanges, gaps between pipes and U-shape bolts, inside of sounding pipes and bell mouths, under floats, behind longitudinals etc.

b. Cargo line: Cargo pipes are enclosed and thus almost preclude visual checks from outside. Accordingly cleaning should be conducted carefully; and their cleanliness, visually checked as far as possible. Cleaning water trapped in the line should be removed by air blow or draining.

c. Strainer: After tank cleaning the strainers must be removed to clean their elements, etc. When they are open the cleanliness of the relevant pipes connected thereto should be checked.

d. Cargo valve: Cargo valves which prevent internal visual inspections, should be drained by removing their bottom plugs, and checked by inserting a finger in their bottom holes. When the bottom recess is found extremely stained, It can be cleaned to some extent in the following manner. The valve is closed and line is under pressure, open the bottom plug first to discharge water inside the recess and then open the valve slightly to wash the seat and recess with water under pressure and discharge it through the bottom hole. As complete cleaning is difficult, it should be cleaned by opening the bonnet.

e. Spool, spectacle flange, reducer, etc. It is recommended to remove them to check the cleanliness from inside.

Reducers are generally attached to cargo pipes at the manifold for connecting cargo hoses. And if they are dirty, they may give an unfavorable impression that the entire piping systems are stained.

Spectacle flanges and spool pieces are used for segregating lines. When they are disconnected the inside cleanliness of the relevant lines should also be checked.

It is absolutely necessary to use normal flange packing in order to connect them to pipes securely, for which purpose they should be tested under air pressure for air leaks after they are fitted in place.

f. Cargo hose: The Terminal usually arranges connecting hoses from the shore to the manifold. However, the vessel should check the cleanliness of the hose from inside.

If found stained the vessel should request the terminal to clean in the charterer's time or replaced with clean hose.

If neither of the above requests has been accepted, a surveyor's inspection should be requested and the fact should be acknowledged both by the surveyor and shore side representative.

2. Line-up of cargo tanks and lines: For cargo quality control and to prevent contamination the following should be checked:

a. Is the bulkhead between consecutive cargo tanks in good condition?

The bulkhead must not have cracks, pin holes and other defects causing cargo leaks, which must be checked at the time of pre-loading survey as well as on all other occasions including tank cleaning.

b. Is the cargo piping system properly set to the relevant cargo tank?

pipes and tanks should be confirmed, as their combinations are very complicated.

At the same time, checks should be given whether spool pieces and spectacle flanges are properly fitted in position.

In the case of vessels equipped with the independent cargo line system, contamination with other cargo occurs only through the common manifold, which requires checks to proper setting of the spool pieces.

After spool pieces have been disconnected, the relevant flanges should be covered with blank flanges using proper flange packing. Blank flanges should be fitted to unused and uncovered flanges on the cargo line.

It is desirable to check by air pressure, the tightness of such spectacle or blank flanges as set in position.

6.14.1 Inerting

Inerting is a process of controlling the cargo tank environment, i.e. Replacement of the air in the tank by an inert gas.

1. Inerting cargo tanks may be for the reasons of quality control, for example to reduce oxidization or to remove moisture in the ambience of the tank when a cargo is water sensitive.

2. The normal media used for inerting is Nitrogen. Pure Nitrogen is obtainable from some shore terminals and, on some vessel banks of Nitrogen storage bottles will be provided. Other vessels may be fitted with an inert gas/nitrogen generator, which supplies Inert gas, of a lower quality than Nitrogen.

3. For certain products including those reactive with water, dry nitrogen will be required. Where inert gas is used for quality control only, the tank need not be inerted until after it has been filled with cargo, thus only the ullage space required inerting.

4. Inerting is to be continued until the oxygen content of the tank atmosphere is reduced below the safe limit. Generally this limit is less than 8% oxygen. The oxygen content must be measured using the oxygen meter.

5. During loaded passage, precautions must be taken to prevent the ingress of air into a tank, through the vacuum side of the PV valve, tank lids gaskets or valve glands. Air can be prevented from entering inerted tanks by maintaining a slight positive pressure in the ullage space.

Company's instruction and it must be recorded in the record book for the whole period of inerting operation maintained.

6.14.2 Stabilisation / Inhibition

If the cargo loaded is inhibited or requires inhibition for safe carriage, the Master must ensure that an inhibitor or stabilization Certificate is received and that the cargo is properly inhibited for the intended voyage.

A certificate of inhibition from the manufacturer of the cargo should specify the following information.

a. Date inhibitor / stabilizer added to product b. Type of inhibitor / stabilizer added to product c. Quantity of inhibitor / stabilizer added to product

d. Effective duration of the inhibitor / stabilizer added to product e. Temperature limits of the inhibitor / stabilizer added to product

f. The effects of elevated temperature on the inhibitor / stabilizer added to product g. Action to be taken in case of abnormal temperature rise of the product.

h. Emergency contact numbers for shore advise/ assistance.

i. Action to be taken if the lengths of the voyage exceed the effective life of the inhibitor j. Recommended method for determining inhibitor / stabilizer level and continued

effectiveness.

Master must exercise his utmost to comply with these requirements; however, he must exercise discretion where a certificate is not available. The last resort will be to refuse to load such cargo.

If difficulty is experienced in obtaining a certificate or any information needed to satisfy the requirements, Company must be informed immediately, where the matter will be taken up directly with the shippers.

During a voyage the quantity of inhibitor may decrease as it is used up/or lost in vapourisation. More inhibitor may need to be added. This will be carried out by ships personnel and supplies of inhibitor and special instructions regarding the addition will be supplied at the time of loading.

Care must be taken when handling the inhibitor because of its toxicity. Special attention must be given to the tank venting system which may become blocked by uninhibited cargo vapour condensate.

List of chemicals for which inhibition / stabilization certificate required

1. Acetone cyanohydrin 10. Isoprene

2. Acrylic acid 11. Methyl methacrylate M

4. Butadiene 13. Styrene monomer

5. Butyl acrylate 14. Vinyl acetate monomer

6. Decyl acrylate 15. Vinyl chloride

7. Ethyl acrylate 16. Vinylidene chloride

8. 2 ethyl hexyl acrylate 17. Vinyl toluene 9. 2 hydroxyethyl acrylate

NOTE: Some of the Inhibitors require Oxygen to stabilize the cargo, hence, do not purge tank or lines with Nitrogen in such cases. However where Inhibitors do not require O2, some of the terminals do purge the tanks and lines with N2.