Tank Barge

Overview

A tank barge carries liquid bulk, petroleum products, chemicals, or edible oils, along rivers and inland waterways inside a set of tanks built into a flat-bottomed steel hull. It has no engine, so a pusher tug or towboat moves it, and the barge itself is essentially a floating set of tanks wrapped in a protective double hull with the piping, pumps and safety systems needed to load and discharge liquid cargo. The core of the vessel is the Double-Hull Structure enclosing several Cargo Tank compartments, served by the Cargo Piping System and the Pump Room.

Because the cargo is often flammable or hazardous, much of the design exists to keep it contained and to manage the vapor it gives off. A Vapor & Inert Gas System handles tank breathing and inerting, a Firefighting System foam system protects the deck, and a Deck Outfit with spill coamings keeps minor leaks aboard. Power for pumps and controls comes from the Electrical & Control System system, and the Mooring & Coupling Set both ties the barge up and couples it to the pushing tug.

Double-hull structure

The Double-Hull Structure is a double-skin steel box. An outer Side Shell Plating and Bottom Shell Plating form the part that contacts water, river bed and quay, while an Inner Skin Plating inboard of them actually holds the cargo. The void space between the two skins is the spill barrier: if the barge grounds or is struck and the outer hull is breached, the cargo behind the intact inner skin stays put. This double-hull arrangement is now standard for liquid cargoes precisely for that reason.

Inside, Transverse Bulkhead walls divide the length into separate tanks, and a centerline Longitudinal Bulkhead often splits each into port and starboard halves. Beyond their role as tank boundaries, these bulkheads are major strength members and they cut the free-surface effect, the destabilizing slosh of a half-full tank, by limiting how wide any single liquid surface can be. The Raked End Section sections taper the bow and stern so the barge can be pushed cleanly through the water.

Cargo tanks

Each Cargo Tank is a liquid-tight compartment of welded plate, internally braced by Tank Stiffener Web webs and protected inside by a Tank Coating / Lining chosen for the cargo, an epoxy or specialty lining that resists chemical attack and keeps the product uncontaminated. A raised Tank Dome & Trunk over each tank carries the loading hatch, the gauging point and the vent connections in one accessible trunk.

Every tank is instrumented. A Tank Level Gauge with a non-contact Radar Level Gauge reads the liquid surface through a closed hatch, an independent High-Level Alarm Switch guards against overfill, and a Pressure/Vacuum Valve lets the tank breathe safely as it fills and empties without venting freely to atmosphere. For heavy, viscous cargoes a Cargo Heating Coil keeps the product warm enough to pump.

Piping, pumps and vapor control

Loading and discharge run through the Cargo Piping System. A main Cargo Pipe Run line links every tank, Cargo Valve valves isolate them individually, and port and starboard Loading Manifold connections are where shore hoses or loading arms couple on, each over a Drip Tray (Save-All) save-all to catch connection spills. A Stripping Line drains the last residue that the main pumps cannot lift.

The Pump Room holds the Cargo Pump units, centrifugal pumps with a Mechanical Seal on the shaft to keep cargo from leaking, turned by a diesel or hydraulic Pump Driver. Because the compartment can collect flammable vapor, it is force-ventilated by a Pump Room Ventilation Fan fan and watched by fixed Gas Detector sensors. Above deck, the Vapor & Inert Gas System routes displaced vapor through Flame Arrester elements to a high High-Velocity Vent Mast or back to shore via a Vapor Return Line, and an Inert Gas Connection lets the tanks be blanketed so their atmosphere never sits in the flammable range.

Outfit, power and safety

The Deck Outfit is built around safe access and containment: a raised Raised Catwalk catwalk over the tank deck, guard rails, tank access hatches and a perimeter Spill Coaming that holds spills on board. The Mooring & Coupling Set combines bitts, fairleads and a powered Mooring Winch for handling lines with Push Coupling Fitting notches that let a pusher tug lock to the stern.

Onboard power comes from the Electrical & Control System system, where an auxiliary Diesel Generator Set feeds the cargo pumps, the Cargo Control Console and the navigation lights. Fire protection is treated as a primary system rather than an afterthought: the Firefighting System arrangement keeps foam concentrate, a fire pump and deck-mounted Foam Monitor nozzles ready to blanket a hydrocarbon fire on the cargo deck.

Use and operation

A tankerman oversees each transfer, lining up valves so the right tanks fill or empty, watching the radar gauges and the high-level alarms, and managing tank pressure through the vent system. Once loaded and inspected, the barge is coupled to a tug and pushed to its destination terminal, where the cycle reverses. Tank barges are valued for the same reason as other liquid carriers: a single pushed tow of several barges moves an enormous volume of product with very little fuel per ton-mile, which is why inland waterways carry so much of the bulk-liquid trade. The trade-offs are the strict procedures around flammable cargo and the cleaning needed between incompatible products, both of which the vapor, pumping and safety systems are designed to handle.