P&ID Typicals and Symbols Process Deliverables Process Design Process Equipment

Storage tanks / vessels P&ID symbols

As a process engineer, it is very important to know storage tank/vessel P&ID symbols, because storage tanks and vessels play a crucial role in various industrial processes, as they are used to store and hold materials such as liquids, gases, and other substances. In this blog post, we will be taking a closer look at the storage tanks & vessels P&ID symbols. We will study the different types of storage tanks and vessels, their features, and the symbols used to represent them in P&IDs.

These are the commonly used P&ID (Piping and Instrumentation Diagram) symbols for storage tanks and process vessels or drums. Note that they may differ slightly from one project to another.

Horizontal Vessel / drum

In a P&ID diagram, a horizontal vessel symbol is used to represent a horizontal storage tank or pressure vessel. The symbol typically consists of a cylinder that is oriented horizontally. Both semi-circles represent the ends of the vessel.

Horizontal vessel with boot

A horizontal vessel with a boot refers to a type of storage tank or pressure vessel that has a protruding section, or "boot," at one end. This boot is used for connecting the vessel to other components in the piping system, such as a pump or piping.

Vertical vessel / drum

The vertical vessel has a very similar p&id to a horizontal vessel. The only difference is that the vessel is drawn vertically.

Closed Tank

Closed Tank

A closed tank refers to a type of storage tank that is designed to be completely sealed and not allow any exchange of material or fluid with the environment. In a P&ID, the symbol for a closed tank is typically a rectangle that is oriented vertically or horizontally, with no open nozzles or connections visible.

Open Top Tank

Open Tank

The top side of the open-top tank is covered with a removable, weatherproof tarpaulin that can be secured with ropes. The top of the open-top tank does not have a solid roof. In a P&ID, the symbol for an open-top tank typically consists of a rectangle that is oriented vertically or horizontally, with the top of the rectangle represented as an open area, rather than a closed line.

Dome Roof Tank

Dome Roof Tank p&id symbol

A dome roof tank is a type of storage tank that has a dome-shaped roof, rather than a flat or sloped roof.  The P&I symbol for a dome roof tank is typically a rectangle, with a circular or semi-circular shape added on top to represent the dome roof.

Double Wall Tank

Double Wall Tank

A double wall tank is a vessel that has two walls, with a space between the two walls. The P&ID symbol for a double wall tank is typically a rectangle, with two parallel lines or shapes inside the rectangle to represent the two walls.

Conical roof tank

A conical roof tank is a type of storage tank that has a conical roof. The conical roof design provides increased stability and strength. The conical roof tank P&ID symbol is typically a rectangle, with a triangular or conical shape added on top to represent the roof.

Conical roof tank with boot

It has a conical roof and a cylindrical extension, or "boot," at the bottom of the tank. The boot provides additional storage space for the tank and helps to prevent the buildup of liquids or solids on the bottom of the tank. It has a similar P&ID symbol as a conical roof tank with an added boot at the bottom.

Floating roof tank

This type of storage tank has a floating roof, which rests on the surface of the stored liquid and rises or falls with the level of the liquid. The P&ID symbol for a floating roof tank is typically a rectangle, with a smaller open-top rectangle shape added inside to represent the floating roof.

Spherical storage tank

The symbol for a spherical storage tank is typically a circle, with additional lines or shapes added to indicate the inlet and outlet nozzles, and any other components of the tank, such as a pressure relief valve.



A clarifier is a type of process equipment used to separate solid particles from a liquid, resulting in a clearer liquid. In a P&ID, the symbol for a clarifier typically consists of a rectangular tank. The bottom part of this rectangle consists of a triangular shape to represent the scraper mechanism and inlet/outlet points.

Man way

A manway, is an opening in a storage tank that provides access for maintenance, inspection, cleaning, or other tasks. Manways are typically located near the top of the tank and are designed to be large enough for a person to enter and exit the tank. In a P&ID, the symbol for a manway is typically a circular shape, with a cross or hatch pattern added inside to indicate the opening.

Vortex breaker

A vortex breaker is a device that is used in tanks, vessels, or pipelines to prevent the formation of vortices or swirling eddies, which can cause problems with fluid flow and mixing. The P&ID symbol for a vortex breaker of a cross-type baffle is typically a rectangle with diagonal lines inside it.



A bin is a type of storage container or vessel used for storing and transporting bulk materials, such as powders, granules, or small objects. The bin P&ID symbol is similar to the shape of a pencil.



A bag is a type of flexible container made of materials like cloth, paper, or plastic, which is used to store, transport, or package small to medium-sized items.

Gas Cylinder

Gas Cylinder

A gas cylinder is a high-pressure container used to store and transport gases, such as oxygen, nitrogen, or propane. In a P&ID, the symbol for a gas cylinder is typically a cylinder shape with a taper at one end, which represents the valve or outlet of the cylinder.

Gas Holder

Gas Holder

A gas holder, is a large, vertical storage tank used to store gases such as natural gas, biogas, or other industrial gases. They typically have a floating roof, which allows the tank to expand and contract in response to changes in the gas pressure inside, and also helps to minimize the amount of gas that is lost due to evaporation. In a P&ID, the symbol for a gas holder is typically a tall, cylindrical shape with a floating roof.

Tray column

A tray column is a type of vertical process equipment used in chemical and petrochemical processes to separate and purify liquids, gases, or mixtures of both.

Tray columns are usually tall, cylindrical vessels with a series of horizontal trays, or platforms, that are used to hold process components, such as distillation trays or packing material. The P&ID symbol for a tray column is typically a cylindrical shape with a series of horizontal lines, to represent the trays.

Check this post to study P&ID arrangement for storage tanks.


Sign up for free if you are not a member already.