Safely storing chemicals - because accidents do happen

Safely storing chemicals is an essential cog in the wheel of an efficiently run global chemicals industry. Muriel Axford reports on the dangers of chemicals storage and finds out how new technologies are protecting the environment, as well as the health and safety of employees and the general public.

High profile incidents, such as the 2005 explosion at the Buncefield fuel depot in the UK, put storage and safety high on the agenda. The explosion was found to have occurred when an overfilled tank caused the formation of a rich fuel air vapour.

As the tank continued to take on fuel, the vapour cloud increased and spread across the site which led to a major explosion and fires, which affected the depot and surrounding area.

In the US, the collapse of a two million gallon liquid fertiliser storage tank at the Allied Terminals distribution facility, located in Virginia, US, during 2008 was another incident that highlighted the importance of safe storage.

The subsequent investigation by the US Chemical Safety Board concluded the tank, which contained an aqueous solution of urea and ammonia nitrate fertiliser, collapsed due to defective welds on the tank walls.

Technology is helping to improve health and safety

There are stringent regulations in place at national and international levels which mean companies involved in incidents where there is a loss of containment either through, for instance, leakage or explosion, are likely to be hit with heavy fines.

"There are stringent regulations in place at national and international levels."

But legislation, good practice and the use of many current technological innovations are making incidents involving chemical tanks less frequent. One of the potential hazards involving storage tanks is related to the monitoring of conditions within a tank. This could be related to, for example, the level of the substance, the presence of vapours or tank pressure.

Emerson Process Management has been among the leaders in the development of wireless instrumentation technology for the automated inventory management of tanks and the company's solutions have found widespread applications.

During 2010 Emerson's Smart Wireless technology was installed by Nynas AB, an international group that refines heavy crude oil to produce bitumen and naphthenic speciality oil products. The wireless monitoring technology was installed to upgrade at the company's underground storage tanks located in Nynashamn, Sweden.

Morten Hansen, the senior instrument engineer at Nynas, said failure of a signal cable on one of the tanks switches prompted the company to seek a solution that would bring tank data directly into the plant's control room. "We were interested in trialling wireless technology and this application presented the perfect opportunity," Hansen said.

The speed and ease of the installation impressed Nynas, but the cost saving was particularly impressive. "Using Emerson's wireless solution we have been able to significantly reduce the cost of upgrading the pressure measurement to an online system. Installing new cabling would have cost more than the wireless solution," Hansen said.

Honeywell has also been at the forefront of developing wireless instrumentation to help process manufacturers monitor tank levels and prevent hazardous incidents. One such development is the FlexLine Wireless Radar Gauge, which the company says captures a wide array of tank measurements and quickly transmits them across the dedicated OneWireless network to control rooms.

This system, says Honeywell, reduces overall operating costs and improves safety by eliminating the need for manual data collection. "Terminals today are striving for more efficient production, which means operators need more information and diagnostics from the field to better understand how their assets are functioning," said John Joosten, radar and safety product manager at Honeywell Enraf. 

Honeywell's FlexLine solution has been approved by the TUV for use in safety integrity level-2 (SIL-2) rated loops, allowing industrial facilities to use the FlexLine devices in applications that require stringent certification to prevent safety incidents.

"Safety is on everybody's minds due to several recent incidents," said Joosten. "So there is naturally an awareness of process safety and how it can better protect people, the environment and assets."

"Legislation, good practice and use of many current technological innovations are making incidents involving chemical tanks less frequent."

It's not just the contents of a tank that can prove hazardous; the integrity of the storage vessel is also a major consideration. Silverwing UK Ltd has many years experience providing its non destructive testing (NDT) equipment and systems.

The company specialises in the design, development, manufacture and supply of NDT systems and equipment for the above ground storage tank (AST) and pipeline inspection aimed specifically at the petrochemical industry.

The company produces a range of magnetic flux leakage corrosion detection, sizing floor scanners and ultrasonic wall crawlers.

Silverwing recently released the latest version of its ultrasonic corrosion mapping system, the rapid motion scanner (RMS2), which can now inspect critical pipe work with a minimum diameter of 6 inches.

Silverwing says the RMS2 is designed for rapid large scale inspection of ferrous structures, such as storage tanks, pipe-work, pressure vessels and other critical equipment.

Coatings and development

Coatings have a crucial role to play in tanks where corrosion is an issue. During the first half of 2011, International Paint introduced a new bimodal epoxy coating for cargo tanks of chemical tankers. The Interline 9001 coating has enhanced cargo resistance, zero absorption for cargoes and fewer cycling restrictions.

The company explains that modern chemical tankers are designed to handle a wide range of liquid cargoes, ranging from vegetable oils to more aggressive cargo such as ethylene dichloride and caustic soda. Most vessels have coated mild steel tanks, stainless steel tanks or a combination of both.

Epoxy phenolic resin is commonly used to coat mild steel tanks but it can absorb and retain certain cargoes, which can lead to difficulties in cleaning to minimise the risk of contamination.  Tank cleaning costs can add in excess of $100,000 to an operator's expenses.

"It's not just the contents of a tank that can prove hazardous; the integrity of the storage vessel is also a major consideration."

International Paint says that Interline 9001 has been designed to deliver greater efficiency and flexibility in the operation of chemical tankers, easily switching from one cargo to the next with minimal down time.

It can also carry all of the cargoes that standard epoxy phenolic technology can, plus a further 25% of the large-volume cargoes that epoxy phenolic technology cannot handle.

International Paint said the technology opened up new, previously restricted cargo sequences for the carriage of aggressive cargoes.

For example, methanol to fatty acids to ethylene dichloride back to back, with no coating recovery required.

The new coating has been snapped up by bulk carriers with Stolt-Nielsen BV being the first company to benefit from Interline 9001. During June 2011 the Stolt Jade chemical tanker was docked at Dubai Drydocks World, where the coating was applied to one of the tanker's 600m² tanks.

Neil McGurk, managing director of Coating Consultants Ltd, who acted as Stolt's coating superintendent, said "Stolt's sophisticated tanker fleet can handle virtually any liquid cargo. Because it can switch easily from one cargo to the next, with minimal downtime and tank cleaning, Interline 9001 was the natural choice and will help Stolt to continue to meet their customers' stringent demands."