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Floating focus

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Hydrocarbon Engineering,

An increased focus on the environment and pressure on profitability has encouraged the use of internal floating roofs (IFRs) in fixed roof tanks in the terminals industry.

Highly volatile products, such as gasoline or gas condensate, have vapour pressures greater than the design pressure of most atmospheric storage tanks (ASTs) at ambient temperatures. Therefore, the use of pressure/vacuum vents set to the maximum allowable working pressure (MAWP) of the tank will not stop the majority of the vapours escaping the tank. This results in large quantities of hazardous volatile organic compounds (VOCs) leaking into the atmosphere.

These vapour clouds affect profitability and the impact on the health of people, animals, birds and plant life in the vicinity of the tank farm. They also present a significant fire hazard, as has been demonstrated by numerous high profile tank farm incidents around the world.

The most volatile elements in flammable liquids are the ones that are most likely to evaporate first. Loss of these light ends, such as butanes, result in reduced product quality. This could lead to rejected deliveries, damaged reputations and legal action.

IFRs are specified in preference to normal venting because they significantly reduce vapour loss and protect profitability, the environment and assets.


IFR technology dates back to the 1950s and has evolved in line with the demands of customers and to keep abreast of legislation. Tank inspections are now routinely performed in 15 – 20 year intervals. Therefore, it is important that the IFR performs effectively throughout this period, without the need for intervention and maintenance. Pressure on profit margins can drive cost cutting on capital equipment purchases and concurrent pressure to prevent production outages, so inspection schedules are likely to be pushed out even further. It is, therefore, important that any IFR technology meets those demands and performs robustly at optimum level for longer periods of time than ever before.

The technology has evolved incrementally over time with the occasional key step change. Two of the largest recent developments have been the introduction of full contact IFRs and stainless steel shoe seals.

Written by Ewart Cox, Assentech, UK.

This article was originally published in the Winter 2017 issue of Tanks & Terminals. To read the full article, sign in or register for a free trial subscription.

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