Wednesday, January 12, 2011

MEG FIBRE GRADE ON CHEMICAL TANKERS -- CAPT AJIT VADAKAYIL


This post is written in great detail , to show the uninitiated that MEG FG is a special cargo. There are many who have learnt it the hard way.

MEG industrial grade is NOT a difficult cargo-- BUT Union carbide coprn MEG fibre grade is!

MEG FG is by far the cleanest cargo a chemical man will carry. 

The Wall wash specs for UCC are very stringent.

Chris/ EGC
Pollution category/ Y
USCG group/ 20
BP/ 197
MP/ -12 C
FP/ 240 C
AH/ 40 C
SG/ 1.13

Basic items required to properly clean to MEG FG specifications:--

Sufficient low ppm (less than 10 ppm) chloride fresh water
A properly functioning fresh water generator (evaporator), and a proper functioning compressor and air supply system able to supply clean air.
Proper equipment with which to clean and test the tanks.
A proper functioning steam system producing steam with nil hydrocarbon, nil chlorides. With sufficient capacity to heat the coils to dry tanks,  and a proper functioning butterworth heater.
Sufficient cleaning chemicals to clean the tanks.
An enthusiastic and trained crew

Let us first look at the cleanliness requirements, wall wash specifications, foot sample specifications and final specifications. We will also look at the methods of conducting the wall wash and shipboard equivalents to the shore lab so that we may duplicate the tests as close as possible.

A typical wallwash procedure or MEG FG is given in my blog site.

Wall wash specifications for union carbide MEG FG:
Chlorides  :  less than 0.249 ppm ( ridiculous but true! )
Color: less than 10 platinum cobalt
Suspended matter: less than 6-8 particulate that are no greater than the diameter of a common pencil lead in size.
Hydrocarbons: nil, clear and no foam remaining on top when vigorously shaken.  50% di-water/ 50% wall wash solution.  Look down through the liquid from the top of cylinder to the bottom and compare to a cylinder with pure test methanol only. Do this in against a black and white background. (you can put a white paper with writing on it underneath)

Note: if you have the presence of slight hydrocarbons you may find out that you have left over cleaning chemicals on the bulkheads by making 90% di water and 10% wallwash. Then shake vigorously. The presence of foam remaining on top for over 30 seconds indicates some cleaning solution or detergent left in the coating.

It is important to have sufficient di water in order to spray all tanks at least twice for 3 hrs. Each. Low chloride water can be made on board in the following manner:

Start with 10-15 ppm water and recirculate on a continuous basis through a di-water generator. This can be done by placing a di-water generator near an outside faucet or use a wilden M-2 pump and suck up from the fresh water tank and run the water through the filter and return to the fresh water fill line.  It is important that this system is isolated from the rest of the ships supply so that it is not inadvertently contaminated.  Also you can speed the process along by entering newly produced water from the evaporator and consuming from this tank. This must be monitored very closely.

Make sure everyone is aware of the process so that everyone understands the importance of what is going on. You must test the water every few hours (both inlet and outlet) so that you can be sure that the di -water generator is not saturated with chlorides and not working.

You should be able to reduce chlorides in approximately 150 mt fresh water from 10-15 ppm to less than 4 ppm over a 5-10 day period.

Of course the best way to have good water is to use ships FWG water.

Air supply system- this must be able to deliver sufficient air to run four Dasic jet fan 65 tank vent fans. Also it must be able to supply clean air for airline breathing apparatus and to run the 10:1 ratio barrel pump to full pressure (7kg/cm2)

Any leaking hoses or equipment that must be worked on continuously is unacceptable.

All air and  steam driven equipment used in and around the cargo tank should have an exhaust hose attached to direct waste air or steam away from the tank so that it is not drawn back into the tank.

Compressed air from the ships supply contains vaporized oil and other contaminants that may contaminate your tank.

If the weather is  rainy and cold  it is almost impossible to dry tanks without the heating coils properly functioning.the steam system must be able to produce steam that is chloride and hydrocarbon free.  This is accomplished by stopping the use of boiler treatment chemicals two-three days prior to use. You must carefully test the condensate before use for hydrocarbons and chlorides. Once free of chlorides and hydrocarbons, the steam can be used to steam tanks and cargo lines. 


A careful check of steam condensate will also alert you to possible leaks in heating coils and contamination of same. During steaming, the steam should be tested at least once per day and always upon restarting steaming after shutting down.  All steaming of tanks, cargo lines, p/v vent lines should be completed prior to using the heating coils to dry tanks. The reason for this is there may be contamination of heating coils by previous cargo and if coils are opened prior to completion of steaming tanks, you may end up contaminating all cargo tanks being steamed.while steaming your tanks the cargo pumps should be run intermittently in order to avoid buildup of condensate in the tank.

When determining the cleaning chemicals required, there are several factors which come into play.
Last three to five cargoes carried in each tank to br prepared
Coating condition of cargo tanks
Cargo line condition
Present tank cleanliness
Cargo vent line condition

Remember, there is no substitute for hot butterworth. The most important thing to remember is to order cleaning chemicals at least two weeks prior to requiring them. This is to allow your ship operator to make necessary arrangements.

The participation of the Master and all crew members working together as a team is the key to success. You must keep an exact record of your daily cleaning progress and what was or was not accomplished each day. Include time used for rigging, equipment breakdowns etc.

Typical wall wash lab items:-

1) Reagent Silver Nitrate—strength 10% /  250 cc –2 Bottles
2) Reagent Nitric acid --- strength 20% / 500 cc- 2 bottles
3) Reagent Potassium Permanganate crystals – 0.1 gms in stoppered tubes/ 12 tubes
    for making 0.02% solution on the spot.
4) Reagent Standard chloride solution ---strength 10 ppm/ 500cc—2 bottles
5) 5 Apha, 10 Apha, 15 Apha--Standard comparator solution in stoppered tubes
6) pH value paper colour comparator strips 1 to 14—4 boxes
7) Nessler tube with round bottom 100 CC  and white markings / 16 nos
8) Stand for above tubes
9) Nessler tube with flat bottom stand 50 CC/  24 nos
10) Polyethylene methanol wall wash squirt bottles 500 cc/ 4 nos
11) Polyethylene wall wash funnel with flat side and 60 deg angle short stem/ 4 nos
12) Pipette glass pyrex brand 5 CC/ 4 nos ( graduated)
13) Pipette glass pryes brand 10 cc/ 4 nos  ( graduated )
14) Conc Hydrochloric acid/ 500 CC
15) Lab grade methanol  chlorides < 0.05 ppm / 60 litres
16)  DI water/ 60 litres
17) Thermometer 0 to 100 deg C/ 3 nos
18) Ice box portable with white interior to hold at least 12 nessler 100 CC tubes vertically
19) Sample bottles wide mouth transparent glass 500 CC/12 nos
20) Wall wash plastic bucket/ 2 nos
21) Parasol wide 2 metres dia/2 nos
22) Washing brush for nessler tube/ 2 nos
23) Penlite torch / 2 nos
24) Disposable vinyl gloves/ 100 nos
25) Disposable shoe covers plastic—lint free / 100 nos
26) Filter paper 5A and Whatman 42# 10 cm paper filter qualitative, white / 100 nos each
27) Palladium chloride solution/ 50 cc
28) Disposable 5CC pipettes—100 nos
29) Lab grade acetone ( for NVM and Plankton of sea water )— 20 litres
30) Stainless steel funnel / 2 nos
31) Sponges for Lint free mopping and wiping steam coil bottoms.
32) Methanol Draeger tubes  50ppm –3000 ppm range / 50 nos ( expiry dates to note )


Reporting your results.
While preparing your tanks you will send a daily progress report to your ship operator. You will advise him on your tank cleaning progress to date and any wall wash tests results. It is important that you advise the cleaning methods used, number of hours butterworthed( hot or cold), any problems you are having. This will enable us to help you with cleaning advice and assist with solutions to your problems. We are also in contact with the supercargo who will also advise on cleaning. Wall wash test results should be reported as follows:
Tank        HC            Cl         PTT        Color
Nbr
1P         slight        1 ppm      47 min       10

***you will also keep a daily cleaning log with test results .
***reporting on color: this may be difficult to determine to the untrained eye.

 You should compare to a methanol standard with a white background and white florescent light.  It may be beneficial to report if you can see evidence of color in the wall wash collection jar. Also you can report for example: same as standard : clear,  almost as clear as sample: slight. 

When you are at the loading port, if the ship operator or supercargo is not present, the master or chief officer should go with the surveyor to the lab to witness the testing. 

This is important especially in the event tanks fail for foam or hydrocarbons.

The reason for this is so that you can see  how bad the foam is and also same for hydrocarbons. If you don’t go, then all you will have to work with just the report from surveyors that tanks have failed.There are degrees of how bad the foam is (heavy foam, light, very light)

Sometimes the tank will fail on hydrocarbons, chlorides, foam) if the test was taken with damp bulkheads.  We have had this happen and all that was done was to let the tank dry out more (with heating coils on and vent fans running) and retest and the tank passed.

Cargo tank dryness is one of the most important keys to getting your wallwash passed if your tanks are clean.
If your bulkheads are wet, you will most likely show presence of chlorides and sometime hydrocarbons. If you are close on your chlorides (less than 1 ppm) and your bulkheads are damp, sometimes all that is needed is longer drying time.  You can accomplish this by turning on heating coils and running your tank vent fans.
In rain and cold, drying tanks is difficult and care must be taken to cover tank tops with tarps and the same goes for your fans. The other problem with the weather and cold in the winter is the possibility of condensation freezing in the cargo pipelines. It is important to keep all drains open and let drain during the day.


After spraying tanks with di-water and ready for wall wash test

All cargo line and vent line drains and manifolds open to drain out condensation.

Turn on heating coils to aid in drying tanks

Have airline ready to blow down drop line into cargo tanks. This is so surveyors can check to see if the line is clear. Make sure spray equipment is ready in case of tank failure.

Seal with silicon all butterworth plates except forward most plate. Leave tank top unsealed. ( Silicon work is NOT necessary on butterworth ports with double seal and check nuts )

Once tank has passed wallwash seal up the forward butterworth plate. Remove all water from tanks, mop and dry.

Also remove any dust and contaminants. Check all drain lines to remove every drop of water. Look from tank top into vent line.

Blank steam coils only after the WWT has passed. Surveyor will not enter unless the TLV of methanol ( if methanol sparyed ) is >70% of methanol used. Same way cargo hoses must not be connected till the wall wash has passed. Once hoses are connected no entry is allowed into tank.

Once all tanks have passed wall wash make a final check again of all tanks, lines for water. Close all drains and tank tops. Do not seal tank tops yet, this will come after final nitrogen purging.

Have airline breathing apparatus ready for use on deck. Once cargo hose is connected and airblow is done, and nitrogen purge started look down into each tank and see if any free water has come out of cargo drop line into tank. If so, tell shore to stop nitrogen purge, disconnect cargo loading hose and put on air breathing apparatus and mop up water in tank. Then, when all out of tank you can reconnect loading hose and resume purging. If spare tank is available, the take first shot of nitrogen into that tank

Sometimes a small amount of meg is blown into the cargo tanks from the shore hose. Only cargo lines are blown with nitrogen before loading. All nitrogen purging and blanketing is done after loading completes.

Initially the cargo is taken into the pipelines and contents deslopped. It is vessels responsibility to provide deslopping drums.

It is ships call when to stop loading for taking the first foot sample.

Upon completion of loading the cargo tanks will be purged down to 7% oxygen content. The best way to do this is to start this in a slack tank so that the loading line can be cleared of product without risk of overflow.

When purging with nitrogen keep pv valve lifted and the tank dome open by 2 inches to prevent structural damage to tank.

Pressurize each MEG FG tank in turn after all  tanks have been taken down to 7% oxygen.  When last tank is being taken down to 7% oxygen have a person stand by the first tank to be pressurized and have dock close down nitrogen pressure to about one quarter open.

Reduce nitrogen flow to 20% open.  Tank valve and start pressurizing have a person near p/v valve to make sure it is lifting . When relief valve lifts , open next tank and close down tank valve.

When last tank’s p/v valve lifts, have shore shut down nitrogen and close tank valve.

Have shore bleed off pressure and disconnect shore hose.

Test all deck openings for leaks with ultrasonic probe.  You will keep a daily nitrogen pressure log of the nitrogen pressure in each tank during the loaded voyage. If a tank falls to zero pressure introduce enough nitrogen to raise pressure to a positive pressure.

Also you will make daily rounds on deck to check for leaks with the ultraprobe.

Regarding ultraprobe:  this unit is a very sensitive listening device that picks up leaks around seals and joints. This unit is fragile so care must be taken to keep it from banging around. This ultraprobe costs around $4500.00 USD to replace. 
  
Before discharge checklist:--

Approximately 1-2hrs prior to picking up pilot at first discharge port open all MEG FG manifolds and drains.

Start each pump and run a small amount of cargo out through each manifold. Examine for particles and floaters.

If everything is clear, then shut down and drain lines.

When surveyor comes on board, you will note his method of sampling. Any deviation from sampling methods employed by the surveyors from the way it is usually  done will be noted with a protest.

Also fax to ship operator the statement of sampling methods as shown below signed by chief officer and surveyor.


Statement of sampling methods

Ship name:_________________________      voy:________________
Port: ______________________________
Date: ______________________________
Cargo:____________________________

Material of sample bottle: (glass, plastic)_________________________________

2. Material of sampling apparatus  pot           _________________________________

Material of sampling line (s.s., cotton, fiber)______________________________

Were bottles flushed with product (yes,no)_______________________________

5. Were sample bottles new (yes, no)                       ________________________________

Were bottles checked for foreign particles______________________________

Material of gloves used (plastic,rubber, none)____________________________

8. Depth of cargo where sample was drawn      ________________________________

9. Samples taken in the presence of                        ________________________________

10. Other observations:
(oxygen content of each tank opened   tank- o2

(weather conditions at time of sampling)
_____________________________________                   ______________________________________
Chief officer                                                              surveyor


The supercargo or chief officer is always to follow the surveyor inside the tank and observe the surveyor.

Watch and make sure the surveyor cleans and rinses all equipment such as the bottle, funnel, cap, hands with methanol prior to taking wallwash in each tank.
Be diplomatic when asking the surveyor to do the above when he forgets.

If the surveyor scrapes or slides the funnel against the coating there is a good possibility that the wall wash test will fail on suspended matter, especially on zinc coating. Request a retest if the tank fails. Also you may ask the surveyor to “jump” the funnel down the side of the tank rather than to scrape it down. (this means to bring the funnel away from the wall and bring it against the wall at a lower place).

Watch for the surveyors touching the funnel with their hands when putting the funnel back into the plastic bag.
(if they do touch with their hands, make sure they wash with methanol before reuse in the next tank.

Assume that the surveyors oxygen meter does not work very well during final purging, and double check with the vessels oxygen meter.  This is especially important during wet weather when their sensor is thrown off by moisture.


Maintenance of cargo quality during the voyage:---

The following procedures will be carried out on all vessels carrying MEG FG

Our main problem at this time is elevated chlorides at discharge port.  It should be noted that the chloride spec is considered to be elevated if the discharge tank sample has 0.10 ppm increase in chloride as compared to the final load sample at load port.  The main source of increase in chlorides would be a leak of salt water into the tank on the voyage or chlorides remaining on the overhead and ullage space of the tank that are not immersed in product at the load berth but get “washed down” while the vessel is at sea.  Therefore, it is imperative that tanks are di-water washed completely (not just areas accessible to wall washing) during final cleaning.  Tanks will be sealed with silicon or shrink wrap if necessary on completion of loading and nitrogen pressure maintained during the voyage.  To accomplish this zero tolerance level of cargo quality, we require the following procedures to be followed:

The chief mate or other designated cargo officer must maintain a cleaning and sealing record/log of each MEG FG tank and must sign off on this document that all cleaning and sealing has been witnessed in person.  We can not accept the word of the crew member doing the work, it must be witnessed. 

After completion loading, the cargo officer will personally witness the nitrogen purging and oxygen level and check each tank for leaks with the ultra sonic probe.  The vessel is to stay at the load berth until the cargo officer is convinced that the tanks are tight and the nitrogen pressure is holding.  The results of this inspection will be the first entry on the vessels’ nitrogen log and is to be signed by the cargo officer.  Once again if this procedure takes more time than anticipated and the vessel misses the tide, so be it. Let nobody rush you.

During the voyage, the cargo officer must record daily nitrogen pressures and check for leaks with the ultra sonic probe each day when weather permits.  Nitrogen log entries are to be factual and signed daily by the cargo officer and record days when weather did not permit actual on deck checking.  If a tank loses pressure, it should be recorded together with action taken to find the leak. It is foolishness to have a “perfect” nitrogen log unless it actually happens. 

At the discharge port, the cargo officer must personally supervise ullaging and sampling and insure that the discharging surveyor draws an extra sample and seals it for the vessel to retain.

Tankcleaning after discharge:

Cold wash for 30 minutes
Hotwash for one hour
FW rinse
Steam
Vent



CAPT AJIT VADAKAYIL ( 28 years in command )
..

12 comments:

  1. Dear Capt Ajit,

    Could you kindly enlighten on the following points:
    1. How does oxygen content in the tank lead to failure of UV test?
    2. Under normal circumstances what precautions should the Ch Off take to ensure the cargo samples pass UV test at discharge port?
    3. If the receivers surveyors insist and do open sampling ports which leads to breach of positive nitrogen pressure in the tank will it lead to failure of UV test of cargo samples?
    4.Under above circumstances how can one ensure that cargo samples pass UV test?

    ReplyDelete
    Replies
    1. hi milind,

      UV test is not done on board the ship.

      Aromatics Benzene, Toluene and Xylene , Chlorinated solvents , all inhibited products and petroleum products show up in the UV test ( if they are previous cargoes )

      Mono Ethylene Glycol and Methanol are tested for UV transmittance and UV absorbance.

      UV spectrometers are used in the 200 to 750 nm range. UV light is visible between 400 nm and 750 nm.

      So if you do tankcleaning for MEG FG using toluene ensure a final job is done with an UV neutral solvent like acetone, MEK , MIBK or methanol.

      A photospectrometer is used for sending UV light. Results are given in transmittance ( light allowed to pass through ) or absorbance ( light trapped in sample ).

      if you have passed the line samples and first foot you cannot fail the UV test at disport.

      this is the reason why ship's manifold valve is NOT opened till chief officer collects the FOOT sample ( of shore line ) .

      requests for open sampling of cargoes whose UV tests are to be done, must be taken in writing-- where a PROTEST remark is made that " ship will not be responsible for direct and indirect consequences due to shore request to do open sampling "

      in reality ship CANNOT fail just because you opened out a tank for a few minutes to do open sampling-- and direct sunlight came in contact with cargo and nitrogen pad escaped.

      capt ajit vadakayil
      ..

      Delete
  2. Dear Captain Ajit, Thanks a Ton for your kind response.

    Regards

    Milind Tambe

    ReplyDelete
  3. My dear Captain Ajit
    In one of the tanker out of 10 tanks MEG failed in three tanks in test UV at 220nm.At load port tank,pipeline,loading arm,one foot,pump stack & all tanks sample was passing.
    The cleaning was customary but UV neutral or chemicals used for cleaning were not recorded by attending surveyors & last cargo was Naptha. Why cargo from 3 tanks failed in UV at 220nm is it because of oxygenation or preshipment cleaning problems
    With Kind regards
    G.A.Manohar

    ReplyDelete
    Replies
    1. hi ashok,

      VERY POOR cleaning when you prepared the naphtha tank to load MEG FG.

      naphtha due to its benzene content ,shows up in the UV test.

      a chemical man must never fall in this hole.

      capt ajit vadakayil
      ..

      Delete
  4. Dear Captain Ajit
    Million Thanks for promt responce
    With kind regards
    G.A.Manohar

    ReplyDelete
  5. Dear Sir,

    One of my chemical tanker,45000dwt,Zn coated, failed the 1st foot sample due to moisture content and other tank failed the swab test while loading MEG FB.
    Pls advise what need to be done during tank cleaning and tank preparations it becoming very serious issue while loading in KSA.
    brgds
    Capt.Vishal

    ReplyDelete
    Replies
    1. hi v,

      first of all zinc tanks are NO suitable for MEG FG.

      yet i am NOT saying it is impossible.

      i have loaded MEG FG at houston after disch of molasses.

      the first foot failure is due to water in pipelines .

      swab test failure is die to using tank cleaning chemicals outside 6 to 9 pH --NON zinc safe.

      capt ajit vadakayil
      ...

      Delete
  6. Dear Sir,

    Thanks for your prompt response.

    To remove any moisture from pipelines, we blow lines by dry air and than blow nitrogen also.

    For Tank cleaning no chemical is used.

    We fail the in the moisture limit and 2nd time failed in swab test, i have contacted super cargoes but no one could give me a solution.

    Appreciate if you can guide what need to be done to pass moisture and swab test.

    Thank you.

    Brgds
    Capt.Vishal

    ReplyDelete
    Replies
    1. hi v,

      i do NOT take such questions.

      however , what was your last cargo?

      capt ajit vadakayil
      ..

      Delete
  7. Replies
    1. hi v,

      i get the feeling that the tanks were NOT washed after methanol . methanol leaves a sediment on surfaces with are NOT exactly vertical.

      i have carried methanol from San Jose in venezuela to El Segundo-- 40000 tons shipload in zinc tanks.

      and the swab test could be failing ( same colur as paint lining ) because someone used tank cleaning chemical outside the pH range of 6 to 9 in the past--before the previous cargoes.

      check the tank cleaning chemicals--have you ever supplied the ship with TC chemicals outside the 6 to 9 range -- have you always supplied the ship with ZINC SAFE CHEMICALS?

      tell you ship staff to do a proper wall wash before offering the tanks again - check the steam coils.

      http://ajitvadakayil.blogspot.in/2010/02/wall-wash-method-chemical-tankers-capt.html

      zinc is porous-- it holds moisture.

      capt ajit vadakayil
      ..

      Delete