Friday, February 18, 2011

LATEX ON CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL

LOADING LATEX-


The ships deepwell framo pumps and lines are not used for discharge . Latex is ,loaded right into the dank dome (99.9%) and the PV vents are plugged. Steam the tanks just prior loading to keep bulkheads wet, but NOT warm >30C

As soon as you get orders to load latex, you need to get the following ready---
Paraffin wax
Wooden plugs to fit into the PV vent hole of tank dome
Blanks for cargo line drops
Blanks for Framo bell mouth ( ships Framo pump is never used )
Extra fresh water
Long portable telescopic aluminium ladders
Framo screw portable pump
Fresh water recirc arrangement for portable pumps cofferdam
Sufficient 200 litre empty drums
Chlorinated solvent like perchloroethylene
Ammonia to fill in void space of tankdome and to spray during discharge of natural latex. For synthetic latex it is enough to steam ( supplied by charterers )
Wilden M15 pump.

Natural Latex is white, sticky ,milky slow moving paste of a rubber produced from bark of rubber tree. It is grouped as USCG group 30 as an Olefin.  SG is around 0.93. It polymerises at temperatures >30 deg C.

Synthetic rubber is a white milky emulsion of carboxylated Styrene-Butadeine Copolymer or hydrocarbon polymer . It is grouped as USCG group 43 or Misc water solution.  The colloid size is smaller than natural latex and is around 10 microns. SG/ 1.01

Ammonia is used as an anti-coagulant (<2% if it is epoxy ).

Chris code/ LTX
Marpol cat/ Y
Odour is strong ammonia
VP/ 1mm HG @20C
Expansion factor/ almost NIL
Melting point/ -7C
Boiling point/204C
Heat adjacent/38C for synthetic latex. Nil for natural.
Solubility in water/ insoluble and is an emulsion in water
Not flammable unless coagulated. Heat may coagulate the latex and form sticky plastic that may burn
Extinguishing agent/ water spray
Health Hazard/ Due to the ammonia additive vapour may cause irritation of eyes
No reaction with fresh water. Coagulation may develop when mixed with salt water.  Heat , acetic, formic acids will coagulate the latex.
Coating/ SS, Epoxy ( Zinc cannot handle Ammonia inhibitor )

Visible water white standard is required. Wet tank surface with fresh water prior to loading for synthetic latex . Wetting is being carried out light steam which should be cool prior loading.

Ships in Latex trade have special latex impellers. Japanese Kosaka pumps have a special latex box. Other ships need to blanked off at the impeller end. Bellmouth should be removed  and stainless steel blank with teflon gasket installed to seal pump bottom.

Upper opening of pump casing should be sealed with rubber and silicon and threaded hole for flushing to be plugged.

You will need ladder telescopic aluminium ladders to access any spot inside the tank if cargo dries on tank sides and overhead after discharge.

Steam coils should be filled with fresh water as usual.

Diffusers, if installed to be removed from tank and stored for voyage. Drop lines should be blinded or plugged securely with wooden plugs.

Hi level alarm and floats should be removed from tank for the voyage. Sounding pipes  and vent lines should be plugged / corked with wooden plugs or scupper plugs of appropriate size. If latex gets into line then this will coagulate and it is easier to renew the line, than trying to remove the solidified latex.

Shippers sometimes insist that the coating failure spots should be painted with hot paraffin wax. The wax will have to be melted and painted over the rust spots with hand brushes. It dries up almost immediately. It is better that the whole tank is  sprayed with hot paraffin wax.

Sometimes the shipper may insist on formaldehyde fumigating epoxy tanks. Stainless steel does not require fumigation.  This will be done by shore personnel.

Vessel should be supplied with 4-5 drums of Aqueous Ammonia ( Ammonium hydroxide ) to form seal and stop coagulation

The coefficient of expansion is negligible. Since the latex will coagulate in the void space between the tank overhead and level of the liquid , the tanks should be always full loaded up into tank dome. To avoid air pockets it is better that the trim is even keel during loading.

The cargo is dropped into the ships tank by a hose supplied by the Charterer. The outlet of the dropline must be submerged into the cargo throughout the loading to prevent foaming.

Upon completion of loading the aqueous ammonia should be poured  on top of latex into the tank dome  to form seal and prevent coagulation.

Since the latex coagulates, any heat adjacent must be avoided. Heat or dryness turns the latex into rubber.

Since vent lines will be plugged, ullage caps or vapour locks can  be cracked open daily for pressure release

Vessel will be provided with portable hydraulic screw Framo pump on rent basis with hydraulic pressure and return hoses, cargo hoses and associated equipment, designed specially for latex.

Ship’s hydraulic system will be used, therefore suitable coupling should be on board  to connect rented pump to ship’s hydraulic lines.

Sufficient quantity of fresh water should be on board for pre washing cleaning the tanks .

Prepare portable pump hired from shore, lower down into the tank through aft butterworth hatch.
Open tank lid, there will be solid layer on top of cargo . Remove to at open drum.

Start discharging. Portable pump should be fully submerged into the latex throughout the discharge to prevent clogging by floating scum.

Fresh water should be recirculated through the screw pump cofferdam seal during the discharge. If water flow stops or gets milky the discharging should be stopped and pump opened and cleaned of latex.

Prior to completion of discharge two men will need to enter tank to position pump in aft end for stripping while squeezing the tank top. All necessary precautions to be taken for entry into the tank with unsafe atmosphere .Ammonia can irritate the eyes.

Keep tank wet with ammonia spray during dischg. This way the coagulated rubber on bulkheads can be minimised. As soon a squeezing is over the surveyor must give tank dry certificate. Quickly give a FW cycle with one machine in all ports and leave the water at the bottom of tank.

NEVER EVER let the discharged tank become dry as Latex will polymerise.

After sailing, outside 12 mile /25 metre zone, pump  out fresh water using portable eductor or Wilden  M15 pump.  Make tank gas free. 

Put into tank the hose and wash ladder, heating coils u-bolts, pump with sea water

Remove coagulated latex from the tank top .

Using ladder peel out  rubber skin from the tank overhead, bulkheads and collect all latex from  heating coils.

Unseal cargo pump, remove blind flanges from drop lines, sounding pipe and vent line. Recirculate  pure chlorinated solvent ( Perchlorethylene ) for 3 hours.

This solvent can be reused for 2 tanks provided a drum is added to each next tank.

Ensure that a cone A filter is installed on pump stack elbow to prevent butterworth machines clogging. 

Butterworth with ambient sea water with graco injection of 0.5 % teepol .

Flush with fresh water.

Re install Install level gauge float and Hi and Hi-Hi alarms floats.

Make sure the PV plugs are removed and no latex clogs vent lines.

Note:
If the shippers want to use the ships manifold pipelines Immediately after loading fill the manifold lines with fresh water. If no ammonia is available then steam the tank for 15 min prior loading. During voyage steam the tank 10 min daily to keep the ullage space moist. During dischg steam via butterworth ports for 10 minutes every one hour . Prewash the tank immediately to shore after the tank dry cert is issued. Use can use toluene to wipe out latex if you do not have a chlorinated solvent.

CAPT AJIT VADAKAYIL ( 28 YEARS IN COMMAND )
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