Storage tanks: Conceptually simple, technically complex
Are your tank installations optimising safety and cost-effectiveness by making use of the latest theory and practice for inspection and maintenance? Aboveground cylindrical tanks constructed in steel plate form the mainstay of industrial process plants the world over when it comes to bulk fluid storage. Conceptually simple, the vertical cylindrical tank appears from a distance to be a solid, straightforward and benign item of engineering equipment. Yet this view is dangerously deceptive. The tank inventory may be flammable or have the potential to cause a flood. The weight of liquid stored can generate great pressure on the tank floor and walls. Imperfect foundations can cause structural damage that may lead to leakages or worse. Wind, rain and electric storms will batter a tank as it sits doing its job. And there may be other hidden dangers present, such as invisible gas blankets capable of suffocating and killing those unprepared. The proper inspection, maintenance and repair of these tanks requires serious attention to detail plus a raft of solid technical know-how. The sources of expertise, standards, and guidance relating to storage tanks are many and varied. Together they form a complex web of information with many cross and back references.
A family-based company with global ambition
Figaro den Hollander, owner of Navigator Network, a headhunting office specialised in energy and industry, talks to Daan Vos, MD at Oiltanking Europe about the company’s values and future plans Even at university, Daan Vos was already fascinated by the dynamics of industrial companies and the businessto- business markets. ‘When I was studying economics, my graduation assignment was with DSM in Asia, and I started as a trainee with Van Ommeren in Rotterdam shortly thereafter.’ He joined Oiltanking as its chemicals business manager in 2001. ‘What I like about this business is that it is a global playing field in which so many factors continuously change the prevailing business environment. Traditionally, Oiltanking is a major oil and gas storage company, but it has also successfully managed to build up a chemicals business from 1998 onwards. In Singapore, Oiltanking had a chemical terminal under construction comprising third party and industrial storage infrastructure. It was the perfect mix for me.’
Things can only get better
As we head into another year of backwardation, Amy McLellan talks to terminals across Europe to see how their facilities are faring Ports are useful yardsticks of economic health. Their endof- year score cards lay bare in simple tonnage the consumer goods, foodstuffs and energy products that define a nation’s economic performance and are the lifeblood of its most strategic industries. Statistics from Europe’s main ports show that terminal operators endured, rather than thrived, in 2013, as they battled a weak fuel market, refinery closures and backwardation. Hans Smits, CEO of the Port of Rotterdam Authority, put it neatly when he said at the end of 2013, ‘where in 2012 crude oil and oil products provided growth, they have failed this year’. Crude oil throughput at this important port was down by 7.3% at 92 million tonnes, a historic low. It was a similar story at the Port of Amsterdam, with throughout of liquid bulk cargo down by 5% at 41.1 million tonnes.
From refining to storing and trading
JBC Energy presents its take on the future path of refinery consolidation and the effects this will have on trade flow and storage After a brief moment of respite in 2012, refining margins have done what many expected and returned to rather uncomfortable levels. Due to a cocktail of factors, Europe is suffering the most. The region is the weakest in terms of demand dynamics, while it also has to deal with an increasingly burdensome surplus of petrol. Furthermore, it is strongly dependent on oil imports from areas that are either politically unstable or, in the case of Russia and parts of the Middle East, pressing forward with upgrading their own refining infrastructure. However, the margin situation is problematic in other parts of the world as well. The problems are due to the general overcapacity issue, but some of the facilities out there are also simply too old and thereby structurally uncompetitive. When looking at candidates for shutdowns, market participants usually turn their attention straight to Europe. Since 2 million barrels per day (bpd), out of a global total of 5 million bpd, have been shut down in Europe over the last four years, it comes as little surprise that the old continent takes the centre stage in this issue.
Beware of 'nothing'
‘Empty’ tanks – and, to some extent, empty tanks – pose a variety of potential hazards, which are too often neglected or overlooked A review of storage tank accidents occurring worldwide over four decades found that maintenance, which is generally carried out on empty tanks, is the second most common immediate cause, after lightning strikes. A large proportion of the accidents listed under most of the other immediate causes, especially operator error, static electricity and open flame, are also likely to occur in empty tanks. Experience shows that empty tanks are no less hazardous than full ones. They are often overlooked, partly due to the apparent absence of inventory. What follows is a brief reminder of a selection of these hazards, with particular emphasis on explosion. The quantity of flammable residue needed to destroy an ‘empty’ atmospheric storage tank is alarmingly small; in principle, less than 0.003% of the capacity can be enough. Consider a 6,000m3 tank with a drumful (200 litres) of heptane liquid residue, representing a bottom layer of average depth less than 1mm. At ambient temperature, this residue would yield about 34m3 of heptane vapour, which, if mixed with the equivalent proportion of air, would generate 1,800m3 of flammable mixture. On ignition, this would yield 12,600m3 of burned gases at atmospheric pressure, i.e. more than twice the tank volume, over a period of the order of 10 seconds – easily overwhelming the tank vents.
Guidelines for measuring and improving process safety management
The Energy Institute (EI) has just published the first five of its ‘process safety management guidelines’ series. The EI’s Stuart King, EI Process Safety Survey’s Martin Ball and Leigh Hunt, and independent safety consultant John Pondant take a closer look... Process safety is a blend of engineering and management skills focused on preventing catastrophic accidents and near hits, particularly structural collapse, explosions, fires and damaging releases associated with a loss of containment of energy, or dangerous substances such as chemicals and petroleum products. While maintaining process safety involves doing many things, the defining characteristic of a process safety failure is a major accident or business upset, with lots of potential for large loss of life and major loss of revenue. In this way we distinguish process safety from occupational safety (slips, trips and falls). A number of recent incidents in various parts of the world have highlighted the increasing importance of effective process safety management. The reports into the 2005 Buncefield explosion in the UK and the 2010 Macondo incident in the Gulf of Mexico drew public attention to the issue. In addition to the immediate human, environmental and financial costs of these incidents, there have been escalating effects on the reputations of companies, their senior executives and the industry as a whole. There has also been increased scrutiny by regulators and governments, and impacts upon the share prices of the involved companies, causing investors to question the security of their investments in the high hazard industries.
Blind trust or keeping an eye open?
Nobody doubts the importance of safety in the tank storage industry, although it would be foolish to claim that incidents can always be avoided. The Dutch Association of Independent Tank Storage Companies (VOTOB) was once more confronted with the safety risks of the sector when, in 2012, Odfjell had to shut down a terminal in the port of Rotterdam. Inspections found that there were several breaches of safety measures. Odfjell responded in a press release, saying: ‘We regret the concerns that we have caused in the local community and we hope that this safety shutdown and plan going forward will put minds at ease. Odfjell is determined to improve the integrity of the terminal in order to ensure safe operations.’ But the typical problem with trust is that it is hard won and easily lost. Research into trust invariably draws the conclusion that high-trust societies are much more conducive to economic prosperity: trust is a big asset. But trusting blindly makes no sense when the risks involved are as large as they can be in the tank storage industry.
Regulatory changes in AST corrosion protection
You’ve probably heard the phrase: ‘The only constant is change’. Aboveground storage tank (AST) owners know from experience that best practices and regulations today will be different next year, and again the year after that. Florida has some of the most stringent regulations in the US for field-erected ASTs and many state regulatory agencies look to Florida to plan for their own rule changes. So what has Florida been doing lately? Since 1984 Florida has required tank owners to have and maintain a cathodic protection system as a means of reducing corrosion to the underside (soil side) of AST floors. The 1990 rule revisions specified that each system be designed in accordance with API RP 651 and NACE RP0193-2001 standards. This has been part of the state regulations ever since for all tanks in contact with the soil, and all grandfather clauses have since elapsed.
Storage terminal solves expensive metering problem
United Riverhead Terminal (URT) is located on the north shore of Long Island, 80 miles east of New York Harbour and was built in 1956. All products are received and shipped via marine vessels that load and offload at a deep water platform located one mile offshore in the Long Island Sound. The platform has two berths that can accommodate ships and/or ocean-going barges, including tankers with up to a 62ft draft, making Riverhead the deepest tanker port on the US east coast. The terminal routinely receives Suezmax class tankers and can accommodate very large crude carriers (VLCCs). The terminal also operates a 60ft work boat that transports employees, crews, and supplies to the platform. The work boat is also used for first response to emergencies and can deploy 3,200” of sea spill boom that is stored on the platform. Both the platform and workboat also have foam firefighting systems. URT’s offshore platform is linked to the tank farm by two 24” submarine pipelines that connect to 20 tanks with combined storage capacity of 5.2 million barrels. The tanks range in size from 12,000 barrels to 580,000 barrels. Approximately half are heated by a steam boiler system for use in storing heavy fuels, blend stocks, gasoils, and crude oil. The remaining tanks store distillate, petrol and crudes.
Monitoring flat-bottomed tanks with vacuum leak detectors
The term ‘flat-bottomed tank’ normally refers to tanks standing aboveground, which have a flat bottom and a fixed roof (tank shell and roof firmly attached to one another) or a floating roof (the roof floats on the liquid and rises and falls when the tank is filled or emptied). These tanks are often erected on concrete ring wall foundations or hard core, on a full concrete base or compacted natural ground within catchment areas. Leaks in the bottom area can only be reliably detected if the tank foundation is constructed such that storage medium escaping into the catchment area can be seen from all sides. The alternative is the introduction of a second bottom (this is also known as a leak protection lining) to create an interstitial monitoring space (double bottom) which is then monitored for leaks by means of a vacuum leak detection unit. This double bottom can be implemented using stud or smooth plates with wire mesh as the spacer material. Glass fibre reinforced synthetic resin laminate, flexible plastic sheeting (plastic webs) or rigid plastic sheets with nubs as spacers can also be used. In order to be able to monitor the double bottom using a vacuum leak detection unit, the interstitial monitoring space between the double bottom must offer sufficient passage for stored media, water and air. To ensure the functionality of a leak monitoring system, the liquids stored must neither have a tendency to form solid matter deposits nor to become viscous.
Choosing the optimum tank cleaning system
Over time, usable tank capacity is reduced by the volume of sludge. The tank operator needs then to clean the tank in order to re-establish its full capacity. In addition to this, national inspection regulations require a leak test every five or 10 years (double floor). To perform this inspection, the tank needs to be completely drained and cleaned. Repair work is often performed on this occasion. The petrochemical industry and tank terminals are increasingly choosing the option of automated rather than manual tank cleaning. They look for cleaning methods that achieve the highest degree of cleanliness in the shortest possible time, while offering high levels of recycling valuable hydrocarbons and apply important safety and environmental protection standards.
Expanding storage in Peru
When the Natural Gas Liquids (NGL) fractionation plant in Peru wanted to expand it awarded the turnkey project to OHL Industrial. The project was executed entirely through Ecolaire España (OHL Industrial Oil & Gas).The plant expansion included a third NGL fractionation unit, which is used to obtain propane and butane, and a third primary distillation or ‘topping’ unit, which generates naphtha, diesel, or diesel derivatives such as MDBS, depending on the equipment’s operating mode.A new NGL storage sphere was also built to absorb possible fluctuations or interruptions in the transport pipeline. A new tank for the topping condensate (naphtha) and a new diesel storage tank were also added. The expansion includes a third propane vapour recovery unit (VRU) and a cooling train to expand the system’s capacity to handle the increase in propane production, as well as two new pressurised butane and propane storage facilities (bullets).The expansion project was executed while the existing plant was in operation, including offshore works in a docking unit. The expansion of storage and production capacity consisted of: • NGL (storage: 25,000 barrels) • Naphtha (storage: 13,000 barrels) • Diesel/MDBS (storage: 80,000 barrels, production: 25,000 barrels/day) • Butane/propane (storage: 2,860 barrels, production: 35,000 barrels/day).
One pump, multiple uses
Oil and tank farm installations have experienced a real boom over the past few years. New tank farms are being built worldwide to cover the growing demand for crude and refined oil products. And there seems to be no end in sight to this trend. Innovative and more flexible pumping systems can make big contributions to a flexible, smooth and cost-efficient operation of oil and tank farms. Apart from conventional centrifugal and gear pumps, an increasing number of screw pumps are being used to transport stored oil products. The big advantage is that oil products with various qualities and viscosities, different back pressures and suction conditions such as presence of entrained air or gas can be pumped without difficulties by just one pump. The versatility of the screw pump and its use in low, medium and highpressure applications up to 100bar is a huge advantage. Pump speeds of up to 3,500 rpm are acceptable, depending on the individual application.
Transforming crude sludge deposits into recovered oil
Nowadays millions of barrels of crude oil are stored in different locations worldwide. Most of this oil is found in steel tanks at tank terminals or refineries, where the tanks are filled and emptied on a non-regular basis. Crude oil itself is a mixture of different kinds of hydrocarbons, water and inorganic particles like sand. For the most part, the crude oil remains motionless in the tanks as there is hardly any movement inside them. As a result, gravity affects the crude oil leading to a separation of the components: the heavier, longer-chained hydrocarbons sink to the bottom of the tank and the lighter, shorter-chained hydrocarbons stay on top. The hydrocarbons, which have settled on the bottom of the tank together with the sediment, gradually build up to form so-called sludge. The consistency of this sludge, which is made up almost completely of hydrocarbons, is somewhere between viscous crude oil and dried-out coke plates. As far as the storage tank owners are concerned, this sludge reduces the volume of the tank, can lead to blocked valves and pipes and prevents the tank from being properly emptied before inspection and maintenance work.
Lighter couplings = safer terminal
The physical exertion involved in the positioning, handling, pressurising and bolting of couplings in a tank terminal or tankship setting can present health and safety issues to terminal staff. Although the option of lifting equipment such as trolleys or cranes is generally available, time restraints and poor weather conditions often mean that this is done manually, either by an individual or small group. In these situations, the weight of the coupling can result in injury of the back and sprains and strains of muscles, further resulting in lost work hours due to staff sickness leave. In addition to health and safety issues, heavy steel couplings can put excess pressure on marine loading arms in circumstances where the loading arm is used incorrectly for convenience (e.g. when terminal staff wish to avoid connecting the loading arm whilst bridging between ship and shore.) This can eventually result in damage, incurring maintenance costs and negative environmental impact. Implementing couplings that are more lightweight is a simple preventative solution, to both health and safety and excess maintenance issues, which can be applied to all marine storage terminals that use loading arms. To achieve a lighter coupling, aluminium is used instead of steel, reducing the weight of the coupling by up to 50%. Although aluminium has low elasticity, therefore making it unsafe for use in a pressurised environment, reducing couplings manufacturer Eurad has developed an aluminium alloy with an elasticity of 10% specifically for this purpose.
Homogenising fluids with compressed gas
If fluids have to be mixed regularly, or even permanently, the reliability of a mixing device is vitally important. Pneumatic impulse mixing complies with this requirement as it does not actuate any rotating parts in a storage tank like mechanical agitators Since industry applications often require uninterrupted mixing processes for long periods of time, a breakdown can be costly. After all, not only expenses for spare parts and repair work arise but especially by emptying the tank. This could mean long breakdown times and even losing the medium supposed to be mixed. By using a mixing system without moving parts, there is no risk of anything breaking, which would cause standstill and require tank emptying. The only parts in the tank are compressed-air piping and discs horizontally attached to it, so-called accumulator plates out of which the air bubbles emerge. Moving parts are only outside the tank, e. g. the logic relays in the controller for the air pulses and the injection valves, leading to the tank.
How to deal with shortcomings in regulation? Avoiding a false sense of security
Things can get complicated when certain regulations conflict with each other. As the Netherlands is in the top three of countries with the largest fuel storage capacity in the world, it is a good place to look at. Dutch regulation PGS29 Publication Harzardous Substances: Directive for aboveground storage of flammable liquids in vertical tanks) dictates that storage tanks need to comply with API650, EN14015 or DIN4119. Newly-built tanks need to be in accordance with EN14015. Next to this, the following Eurocodes are applicable in the Netherlands: EN1991-4 for the actions on structures with respect to silos and storage tanks; and EN1993-4-2 for the design and calculations of steel structures for storage tanks. The formulas for the stability of tank shells according to American norm API650 and European norm EN14015 (see below) look more or less the same. Both formulas are tailored at the minimum wall thickness. However if we look at the maximal allowed unsupported height, which is H1 in API650 and HP in the EN1993-4-2, you can see that the set up of both formulas is completely different (see figure below) which influences the outcome of the design of a shell course severely.
Repairing roof top leaks in-service
National Cooperative Refinery Association (NCRA) had two aboveground storage tanks (AST) holding petrol and diesel fuel and scrape, seal and coat the leak using a nonpermanent epoxy solution. The cost, time and safety impacts of this situation resulted in the company planning to take the tank out of service to complete a more permanent repair.
The internet of tanks
The physical world is becoming an information system of sensors and actuators embedded in physical objects. Tanks, for example, are linked through wired and wireless networks via the internet protocol. These so-called web-based technologies are not only changing the technical way of data integration in a vertical sense but also impact the way we do business. The horizontal integration along the supply chain, where material and information flow has to be managed, will be one focus application where these technologies will change the game. People have always communicated to exchange information. For centuries, there have been no real changes in the technologies applied – letters or face-to-face. But in the last few decades communication channels have changed dramatically. Electrical signals took over from pen and paper. Via telegrams, telephone and fax, the era of the internet was entered. In recent years, there was another push coming from the mobile technologies. Now, the internet is everywhere and available at any time. By 2008, the number of devices connected to the internet exceeded that of people. The number of connected devices is estimated to reach 50 billion by 2020.
Unravelling the misconceptions
The past couple of years have seen heightened interest in how to improve the accuracy of emission estimates for storage tanks that either receive hot stocks or heat the stock in the tank. This interest has been driven both byregulatory enforcement and by initiatives to improve the accuracy of estimated emissions for emission inventories. Chapter 7.1 of the US Environmental Protection Agency’s (EPA) AP-42 document provides methodology for estimating emissions from storage tanks, but there is no mention in this document of how to estimate emissions if the stock in the tank is heated. In the absence of guidance from the US EPA, there have been some common misconceptions about heated storage tanks that have contributed to erroneous assumptions with respect to estimating emissions from these tanks. One misconception is that a heated storage tank would not have breathing loss. Breathing loss refers to the cycles of expansion and contraction of the vapours that result from heating and cooling of the vapour space in the tank. In an uninsulated storage tank, heat is readily transferred through the tank shell and roof, and thus the diurnal temperature cycle of the ambient air causes a corresponding diurnal temperature cycle in the vapour space of the tank.
An integrated approach helps fuel growth in Kenya
Despite challenges in 2013, Kenya is among Africa’s success stories. A strong private sector, relative political stability, better literacy levels than its neighbours, market-friendly policies and good trade have helped sustain development. The economy grew 5.1% last year, and can look forward to further expansion of 5.8% in 2014, according to the country’s Ministry of Finance. Already one of the fastest growing economies in Africa, it forecasts growth of 7% a year by 2017. According to the World Economic Forum, Kenya leads the continent as among the top 100 most competitive economies in the world. Demand for oil products in Africa is to grow more than 20% in the next seven years to 4.4 million barrels per day (bpd), according to Vienna-based consultancy JBC Energy, with Kenya among those expected to see the highest growth. The government-owned National Oil Corporation of Kenya expects diesel and petrol imports to rise by a third in the next two years to 6 million tonnes (130,000 bpd).
A faster alternative
When a marine terminal in the UK refurbished its bunds last year the contractor Trant Construction decided to use Concrete Canvas (CC). CC is a flexible concrete impregnated geotextile that hardens on hydration to form a thin, durable, fibre reinforced concrete layer. Used predominately for aboveground drainage applications, the material can also be used for hard armour capping of earth bunds around oil refinery tank farms, munitions depots and flood defences. CC provides high level protection against degradation of earth bunds by preventing surface erosion from wind, rain and freezethaw and significantly extends the operational life span of a bund, reducing throughlife maintenance and rebuild costs.
A safe harbour
Even if there are no visible signs, there is still a lot going on in a tank terminal. They ensure the reliable and constant supply of fuels and raw materials: in ports, refineries, industrial plants and at airports. Any interruption to the supply chain would lead to a bottleneck in the fuel supply chain, and to possible production delays which can be very costly. That is why every pumping, filling and handling operation from the tankers – not only to the individual tanks, but also to tank vehicles– is precisely monitored. All loading units, pipe bridges and pipelines to the storage tanks, pumps and compressors for fast loading and unloading must be integrated into an overall solution. In addition to protection against explosion and overfilling, emergency and shutdown equipment due to the potential environmental hazards of a tank terminal are obligatory for such a facility. And last but not least, plant safety can be increased using access control and fire protection measures.