What is ullage?
In shipping, ullage pertains to the empty space in large containers transporting liquids (like crude oil) or bulk solids (rice, wheat, etc.). The term is increasingly used in shipping contracts and marine settings. It is also called headspace.
Keeping this space is required as per standards set by the International Maritime Organization (IMO), Code of Federal Regulations, and several other regulatory bodies. These directives require the carrier that the pressurized tanks or containers should be a maximum of 98% full (also called sounding). The extra 2% space here is referred to as ullage.
Ullage v/s Sounding
Sounding refers to the height from the bottom of the tank to the upper surface of the liquid. Ullage, on the other hand, refers to the void space between the surface of the liquid to the top of the tank.
The opposite of ullage is sounding. By summing up sounding and ullage, you get the total height of the container tank.
Why Ullage is important?
Keeping free space, or ullage is necessary to ensure that the gas or vapor being transported is always in contact with the pressure relief valve.
Secondly, this specific space is left to allow for the expansion of liquids or gasses during transportation. This might happen due to variations in ambient temperature or movements during freight shipping.
Thirdly, while transporting liquid cargo, the master of the vessel, surveyor, and the boarding officer sign the Ullage Survey Report to note the exact volume of the stocks. The quantity of liquid bulk cargo received at the port is included in this discharge port report.
If there is a discrepancy in the documented quantity loaded at the shipment port, and the Ullage Survey Quantity received at the destination port, it is regarded as a short landing of the expected quantity of cargo — for which the person in charge of the vessel can be penalized.
Ullage V/s Pillage
Pillage is often confused with Ullage.
Pillage is a term often used in reference to pirates and their loot. By extension, pillage emphasizes the actual theft or loot of the loaded cargo (liquid, gasses, or bulk solids).
Whereas, ullage explains the mysterious loss or damage to the goods — by measuring the extra space left in the loaded vessel or container.
In other words, pillage is intentional (and bad!), while ullage is mostly unintentional (and necessary).
Terms related to Ullage
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