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Loading, carrying & discharging of Sulphuric acid - regulatory requirements & special handling methods

Chemical tankers safety guide

Loading , carrying at sea & discharging of Sulphuric acid involve high risk and require sophisticated handling for safety, health and loss prevention reasons. They need careful consideration prior loading , tank coating compatibility, cross compatibility with other cargoes carried, environmental controls if required (inerting).

ACID Product Characteristics

Product safety data sheets may be available from various sources. For safety preparation, until the specific product safety data sheet can be obtained, the Chemical Data Guide for Bulk Shipment by Water (U.S. DoT), should be used. Concerning the IBC/BCH code (respective 16.2/5.2) the master should request the specific product safety data sheet before commencement of loading. The safety data sheet posted must be in a language understood by ship's Officers and Crew (English).

Regulatory requirements

Sulphuric Acid is regulated for bulk transportation by the IMO, BCH and IBC codes. Following is the summary of the codes' minimum requirements
  1. UN number : 1830
  2. Pollution category: Y
  3. Hazards Pollution and safety hazard : (S/P)
  4. Ship type : 3
  5. Tank type : Integral gravity tank
  6. Tank vents : Open venting
  7. Tank Environment : No special requirement
  8. Electrical equipment : No special requirement
  9. Gauging : Open
  10. Vapour Detection : No
  11. Fire Protection : No
  12. Material of construction : See special requirements
  13. Respiratory and eye protection : Individual units not required for emergency escape purpose
  14. Special Requirements : See IBC Code: 15.11, 15.16.2, 15.19.6 and the BCH Code: 4.8, 4.15.2, 5.2.7, 5.2.8.

Special arrangements - Sulfuric acid

Ensure that there is on board sufficient acid resistant hoses for the cargo transfer. Ensure that there is on board sufficient acid spray shields to cover flanges on manifold and hose connections according to IBC code 15.11.4 and BCH code 4.8.4.

Preloading precautions & loading sulfuric acid

  • Sulphuric Acid is normally carried in stainless steel tanks with a minimum concentration of 90% and at temperatures not exceeding 35C.
  • Highly concentrated, sulphuric acid may be carried in mild steel tanks, but only after obtaining special permits from the class.

Preparations for Loading

  • The tank must be cleaned to "Visual Water White Standard" and free of any residues from previous cargoes, chlorides and any other foreign matters.
  • A thorough inspection of the tank's lower areas and tank top must be carried out, with special emphasis on steel defect detection. Any suspected areas, and welding seams, must be "dye- checked" for cracks.
  • 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.

Discharging Sulfuric acid

Because of the high specific gravity of Sulphuric 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

Cleaning and slop

Sulphuric Acid in 30-70% concentrations is non-oxidizing and attacks the steel rapidly, particularly at elevated temperatures. When concentrated Sulphuric 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(s) before the cleaning operation starts.

Cleaning process

  • 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.
  • Sulphuric Acid slops should normally not be kept on board as diluted acid slops are very aggressive to all metals. In cases where acid slops must be retained on board, consult the Ship Operator for advice.
  • 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.
  • Continuously drain the tank, do not allow acid/water mixture to collect in the tank. Do not stop cleaning before a litmus paper check of the drain water reads neutral. 6. If seawater was used, the tank must be immediately desalted with freshwater or di-water.
  • 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 litmus paper.

Slop disposal and arrangements :

The slops are to be disposed according to: Regulations for control of pollution by noxious liquid substances in bulk, IMO, MARPOL Annex II.

Acid resistance of stainless steel

Due to various resistance of stainless steel materials consult the specific manufacturer's manual/information when necessary.

We have summarized below some of the special chemical cargoes frequently carried onboard chemical tankers

Recommended guideline:

Handling benzene & methanol safety precautions

Handling carcinogens requirements for certain chemical cargoes

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