Tank cleaning is one of the most critical operational tasks on chemical and product tankers. Poor cleaning procedures can result in cargo contamination, wall wash failures, charter party disputes and serious operational delays.

Cargo Changeover Planning

Every tank cleaning operation begins with careful analysis of the cargo changeover. Key factors include:

·       Previous cargo characteristics and residue behavior

·       Next cargo purity requirements

·       Compatibility between residues and cleaning agents

·       Required wall wash standards

·       Available tank cleaning equipment and heating capacity

Overlooking any of these factors can lead to unnecessary cleaning cycles, failed wall washes or insufficient tank preparation.

Tank Cleaning Stages

Efficient cleaning follows a structured sequence:

1.      Pre-wash — Removal of cargo residues using hot or cold washing, depending on cargo characteristics

2.      Chemical cleaning — Application of appropriate cleaning agents to remove persistent residues

3.      Hot water washing — To dissolve or loosen stubborn residues where required

4.      Ventilation and drying — Proper ventilation to remove vapours and prepare for inspection

5.      Inspection and testing — Visual inspection and wall wash testing where required

Wall Wash Preparation

Wall wash inspection is required before loading sensitive cargoes such as methanol, ethanol or glycols. Preparation includes:

·       Additional hot washing cycles as needed

·       Careful ventilation of tanks and pipelines

·       Inspection of valves, lines and heating coils

·       Verification of tank coating condition

Even small traces of incompatible residue can cause wall wash failure — and the associated delays and costs.

Common Difficult Cargoes

·       Vegetable oils and palm oils

·       Heavy petroleum products

·       DPP cargoes

·       Certain chemical additives and lube oil components

Incorrect procedures for these cargoes can result in persistent residues requiring demucking operations — adding days and significant cost to operations.