Saturday, December 4, 2010


                    SULPHURIC ACID

Sulphuric acid is a rogue cargo and many seamen have been injured badly.

It is the free flowing high density property that makes the cargo dangerous especially on the maiden trip with Teflon gaskets being inserted not bolted.

The only time Chemical carriage becomes more dangerous is when you discharge highly toxic , high MP cargoes like Phenol or HMD in freezing weather.

Imagine a slug of free flowing Sulphuric acid being projected through a pipe by compressed air of 7 kg which you deliberately introduce into the pipelines at stripping time. It will smash into all corners like a bullet. Stripping the stack is hence a dangerous job ( especially on the maiden voyage ) and the person doing it must wear proper PPE.

IT TENDS TO GET INTO THE HYDRAULIC SYSTEM OF JAPANESE DEEPWELL PUMPS. The Frank Mohn system has a jockey pump which keeps 2 kg pressure in the system at all times—this is something which the Japanese pumps do not have. They are solely dependant on the air buffer inside the cofferdam which can leak out slowly as air tends to find the highest point. Also it is difficult to find out if the air pressure has reduced—as there is no pressure guage.

Since Sulphuric acid is highly reactive with water causing exhothermic reaction when water to added to acid , it follows that the double skin must not have any water. This is an item the port state inspector can check.


Colourless or clear brown depending on purity.
Dense oily liquid
Normally carried at concentration >90% at temp < 35C
Marpol cat/ Y
UN number/ 1830
Fosfa approved
MP/ 10.4C
Surface tension/ high
SG/ 1.84
AH/ 30C
Sulphuric acid is Non-flammable
Has no odour but when hot the odour is choking.
It is a good last cargo for WWT
Completely water soluble.

Sulfuric acid will not bum. It will react with many metals, giving off hydrogen gas that is highly flammable. If hydrogen is trapped in a confined space, it can form an explosive mixture with air.

Do not use water to put out fire if the water can get into concentrated Sulfuric acid. Use respiratory protection against fumes.

May cause moderate irritating, unpleasant at high concentrations

Severe skin irritant, causing second and third-degree bums on short contact and very injurious to the eyes

Some hazard, typically having threshold limits of 100 to 500 ppm.

Odor threshold (ppm)    Greater then 1 mg/m3

Permissible exposure limits/TWA    1 mg/m3

Liquid causes severe bums with destruction of tissue. Vapor is very irritating.

The inhalation hazard is slight at ordinary temperatures. The skin on which acid is spilled may feel hot or it may sting or itch. Drench  with  water. 

Skin  contact:   remove contaminated clothing and flush affected areas gently with large amounts of water.

Eye contact: immediately flush eyes gently with water, continue to flush for 15 minutes. Get medical attention.

Stable, but can react very easily with many other materials.

Highly corrosive to most metals, particularly at concentrations below 60 %. May cause wood or cellulose to ignite.

USCG/ Group 2. See also exceptions to the chart

Wear rubber gloves, protective clothing. Have body shield available. Avoid contact with liquid. If there is a leak on cargo transfer system, stop the transfer and empty the line system. Secure ignition sources. Flush contaminated area with large amounts of water.

MARPOL Pollution category  / Y

Have on board sufficient acid resistant hoses , Polypropelene or SS for the cargo transfer.
Have on board sufficient SS acid spray shields to cover flanges on manifold and hose connections according to IBC code.

Sulfuric Acid is normally carried in stainless steel tanks with a minimum concentration of 90% and at temperatures not exceeding 35C.
The tank must be cleaned to "Visual Water White Standard", and free of any residues from previous cargoes, chlorides and any other foreign matters.
It is a good idea to passivate the tanks with 14% cold nitric acid to build up the passive layer of Chromium oxide which can get denuded by hot salt water wash.
Heating coils to be pressure-tested for leaks, blown empty and dried with nitrogen. The tank must be dry before loading is permitted.
The surrounding cofferdams and double bottoms must be empty and dry.

Because of the high gravity of Sulfuric Acid, very high pump pressure may be experienced. In such cases care must be taken not to quickly open or close valves in the pump system as this causes pressure surges that may rupture lines or hoses.

Sulfuric Acid in less than 30-70% concentrations is non-oxidizing and attacks the steel rapidly, particularly at elevated temperatures.
When concentrated Sulfuric Acid is diluted the reaction is exothermic and the temperature of acid will rapidly increase. If the tank is cleaned with inadequate quantities of water, the acid will become hot, as it is diluted, and rapid attack will occur on the stainless steel until sufficient water is introduced. Large quantities (preferably fresh water) must be put into the tank to rapidly pass the dangerous concentration range and heat increase. Preferably if stainless steel hoses were used on the manifold for discharge should be replaced with non-stainless steel acid resistant hose(es) before the cleaning operation starts.
Preferably, fresh water should be used as cleaning medium but if not available large amounts of sea water must be used/added to the tank. Cleaning must start as soon as possible after discharge, but do not commence cleaning unless slop disposal is available, either to shore or as per Marpol regulations.
Sulfuric Acid slops should normally not be kept on board as diluted acid slops arc very aggressive to all metals.
Cleaning with water (adding water to acid) will generate much heat with release of Hydrogen gas.
Cleaning must be started with as much water as possible introduced into the tank from the beginning. If it is not possible to pump washings overboard after water quenching , leave the tank alone. Close all inlets to prevent moisture ingress into tank.
Continuously drain the tank, do not allow acid/water mixture to collect in the tank. Do not stop cleaning before the pH check reads 7.
If seawater was used, the tank must be immediately desalted with freshwater.
Ensure that the line systems, including the vent system, are cleaned out and free of any acid remains.
Flush out the heating coils with freshwater and check for acidity using pH paper.

When diluted to 50% Sulphuric acid becomes the most corrosive.  Don’t EVER retain slops on board.

Sulphuric acid is hygroscopic. When you load slack tanks due to the load density—bear this in mind.

Sulphuric acid has the tendency to eat away the under water Annex 2 pipeline, on the section below the water level to the overboard  .



Date: Wed, 20 Apr XXX 02:55 +0100 Msg: A03153-48145
Subject:   XXX/ XXX VISIT
dear XXX,

XXX visited the ship at odfjell terminal houston on XXX .

needless to say, he is a easy bloke to get along with and we had a free
exchange of ideas.

of all these only one i would like to put on record-- for posterity.



XXX does NOT have superstrip lines on tanks aft of the manifold.  as
i showed you when you vistited the ship at new york --our
aft framo pump delivery pipelines go up into the air, and slopes down
hill towards the manifold.

this does away with superstrip lines-- which are small dia ss lines
which run piggy back to delivery pipes on all tanks aft of the manifold.
so after stripping the stack-- hardly any sulphuric acid remains inside
the framo sump.

so after discharge of sulphuric acid, with very little ROB , it is NOT a
huge crime to quench this small quantity rob with sea water-- in case
tank cleaning fresh water is unavailable.



narrated by the sacked chief officer of the ship -- who came on MY ship
in another company as my chief officer. he told me certain truths about
himself--more to LEARN and not as a confession.

this is a brand new stainless steel chemical tanker belonging to a
prominent shipmanager in hongkong . the maiden voyage was to discharge
sulphuric acid to brazil.

this ship did NOT have piggy back fixed ss superstrip small dia lines on
aft tanks . neither did they have polypropelene superstrip portable
hoses to do the job.

this ship has a very large quantity of sulphuric acid after completion
of discharge-- as the shore back pressure was high, the ship did NOT do
internal stripping and the shore tank dry surveyor was not interested in
doing his job the right way.

so-- as per the usual golden rule--the chief officer took in a suitable
quantity of SALT water -- to quench the tanks.

there was huge sputtering hiss-- with enormous hydrogen gas release.

the safety superintendent of this shipmanagement company was in brazil
for the next 6 MONTHS. i know this man well-- he is senior to me .

all clad steel SUS316L of the sulphuric acid tanks were destroyed .

the framo pumps were jammed-- as water was taken in via the drops-- NOT
the pump. the exhothermic heat warped everything inside the pumps.


i usually do a small demonstration , so that my officers/ crew respect
sulphuric acid.

after this NO amount of arm twisting by any cheap skate charterer can
make them change ideas engraved on their spleens .

take a SS drum put 6 inches sulphuric acid inside.

put a used teflon seat ring, a used teflon gasket and a used teflon
single lip/ double lip seal inside .

pour water into the drum taking care not to be too close . water into
acid is dangerous.

keep the mixture between 30 to 70% concentration , to make it NON-
oxidising. sulphuric acid is 100% soluble in water

after one hour -- see the condition of the teflon and the SS drum.

it will be a revelation -- as seeing is believeing!

capt ajit vadakayil
mt xxx
" manage inventories-- lead the men "


  1. Sir, can we access some pictures of the actual ship that got destroyed or of the demo.

    With respect.

    best regards,
    Capt. Himanshu Shekhar
    +91 80977 15412
    Skype : himu1978
    email :

  2. hi himanshu,

    i lost the pictures when i lost my pen drive.

    the ship at brazil was a univan ship.

    capt ajit vadakayil

  3. sir can you suggest the best way to introduce tank clng water into sulphuric acid tanks for first time during tank cleaning ops.Butterwoth machines output is not very large so i doubt there is a chance of exothermic reactions happening.

    1. hi s,

      make sure there is NO acid at the suction and that the pipelines are well blown.

      introduce water into tank in good quantity and flow volume-- to prevent exothermic reaction.

      by TC hoses through butterworth ports - through drop line-- whatever.

      capt ajit vadakayil

    2. good day sir,

      well noted the above method, and one more thing, should we keep butterworth ports and tank domes open initially to vent off gas accumulated.

  4. Hi Ajit;
    I need some information about your Tanker for sulfuric acid, can you please give me your email address for me to send you my question in detail? my email is

  5. Hi Ajit,
    Can we do any backhaul on sulphuric acid cargo ships. If yes, can you share any example where it is in practice, and what type of cargo can be backhauled.
    Kanwaljeet Singh

  6. Easy readable post with many important information. I must back again for something new. Keep up posting and share with us. Thanks for your great staff....
    Safety Spray Shields

  7. Sir good day,

    I just want to clarify, what if discharge of tank cleaning water ex sulfuric acid cargo is not available due to vessel is still in a channel / river (ex rio parana). Can I introduce nitrogen into the tank (ex sulfuric acid cargo tanks) to avoid the tank from moisture? By the time the vessel is off or clear from the channel/river and meet with Marpol Regulations, I can start/proceed washing of my tanks.
    If after discharge sulfuric acid is not possible due to the vessel is still in the river channel, how long does the tank must be cleaned ex sulfuric acid cargo.
    Sir your reply is highly appreciated.
    Thank you and God bless.