Refinery Storage Tanks Basics

• Operators monitor storage tanks, prepare them for maintenance, and support their use in routine and emergency conditions.
• Knowledge of storage tanks helps avoid spills and ensures safe use of feedstock and products.
• Storage tanks in Valero refineries hold crudes, intermediate hydrocarbons, finished products, plant water, treatment chemicals, and additives.
• This information enhances understanding of tank use in a refinery and promotes safe work practices.

Course Objectives

• Identify common storage tank designs and explain how they function to safely store different fluids.
• Define major storage tank components and explain their function.
• Describe tank operation during routine and emergency conditions.
• Explain how storage tanks are prepared for inspection and maintenance.

Types of Storage Tanks and Their Functions

• Refinery storage tanks store feedstock, intermediate stocks, finished products, plant water, fire water, and purchased chemicals.
• Storage tank designs vary based on their purpose, but have similarities in basic construction.

Function of Storage Tanks

• Storage tanks contain large volumes of fluids for inventory and processing, protecting contents from evaporation, leaks, deterioration, contamination, and fire.
• Storage tanks store potentially hazardous materials like crude oil, diesel, gasoline, propane, butane, and nitrogen.
• Storage tanks also store non-hazardous liquids like plant water, fire water, and treated wastewater.

Types of Storage Tanks

• Storage tanks are classified as atmospheric or pressurized.

Atmospheric Storage Tanks

• Atmospheric storage tanks are upright steel cylinders with varying capacity.
• Atmospheric storage tanks are designed to operate at or close to atmospheric pressure (14.7 psia or 0.0 psig).
• Design accommodates the density and hydrostatic head of the liquid.
• Atmospheric storage tanks have three common roof configurations: fixed roof, external floating roof, and internal floating roof.

Fixed Roof Tanks

• A fixed roof tank features a cone or dome-shaped roof made of steel that is permanently affixed to a cylindrical tank shell.
• Fixed roof tanks are also known as "cone roof" tanks.
• Fixed roof tanks have a pressure equalizing device,like a breather valve, to allow for pressure changes within the tank.
• Some fixed roofs are engineered to fail at the roof-to-shell weld to relieve internal pressure before the tank shell ruptures.

External Floating Roof Tank

• An external floating roof tank has a roof that floats on top of the stored liquid and closely fits the tank's cylindrical walls.
• A roof-seal fills the space between the floating roof and the tank shell.
• The roof rises and descends with the liquid level, keeping contaminants out, minimizing vapor, and minimizing vapor losses..
• By floating the roof directly on the liquid, there is no place for vapor to accumulate, which minimizes vaporization.
• Confining liquids beneath floating roofs reduces the risk of fire or explosion.
• A drawback to the external floating roof tank is that the roof is not protected from external loads, such as snow, ice, and rain.
• External floating roof tanks have protections like drains to minimize the chance of the roof sinking due to external loads or loss of buoyancy.
• All areas on top of a floating roof is considered a confined space.

Internal Floating Roof Tank

• An internal floating roof tank has both a floating roof and a fixed roof.
• The internal floating roof rises and descends with the fluid level.
• he fixed roof minimizes vaporization and protects from external loads.
• Internal floating roofs do not require a drain system.
• Adding an internal floating roof to a fixed roof tank minimizes vapor losses.

Pressurized Storage Tanks

• Pressurized storage tanks store Highly Volatile Liquids (HVLs) under pressure to maintain their liquid phase.
• Products stored in pressurized tanks are typically liquefied petroleum gases (LPGs) like propane and butane.
• The shape of pressurized storage tanks is affected by the economic need to design the most efficient storage capacity for the required storage pressure.
• The three principal shapes for pressurized storage tanks are spheres, spheroids, and cylinders (vertical and horizontal).

Sphere Tanks

• Spheres, or ball tanks, store large quantities of LPGs that are supported by steel legs.
• Spherical shapes provide strength to resist vessel failure and offer the greatest volume capacity for the amount of steel it takes to build them.

Spheroid Tanks

• Spheroid tanks, or mushroom tanks, are circular or oval-shaped containers used for lower pressure liquids that must have a vapor pressure maintained on top.
• Strength is added to the spheroid by dishing the individual horizontal courses of steel that are used to construct the tank which allows for a larger diameter tank and a larger volume.
• Spheroid tanks have a flat bottom and usually sit on a foundation of concrete rather than having support legs attached to them.

Cylindrical Tanks

• Cylindrical tanks, or bullet tanks, are constructed from heavy steel plates that are rolled into a cylinder and welded.
• Heads are shaped as an ellipse or a hemisphere based on the rated pressure of the tank.
• Cylindrical tanks may be erected either horizontally or vertically.

Construction Codes

• Pressurized and atmospheric storage tanks are built to specific codes and standards and are inspected regularly.
• Pressurized storage tanks are built according to the ASME Boiler & Pressure Vessel Code.
• Atmospheric storage tanks are built according to the API 620 code, and large storage tanks are built to the API 650 code.
• Storage tank inspections ensure code requirements and maintain safety and integrity, as outlined in the facility’s mechanical integrity management plan.

Lesson 01 Recap

• Storage tanks differ in design according to their purpose.
• Storage tanks are used to safely contain fluids stored for inventory and processing
• Recognize the different types of storage tanks used at this facility and how they operate.

Storage Tank Components and How They Work

• Tanks have common parts that serve the same functions.
• Reviews components specific to certain types of tanks.
• Storage tanks perform the functions for which they were designed.

Major Components of Storage Tanks

• Common components to most atmospheric storage tanks: bottom, shell, and roof; stairway and landing; water drain; product inlet pipe; product outlet pipe; gauge hatch; breather valve; vapor recovery system; manway; mixer and agitators; tank heater; grounding straps; fire protection foam system; corrosion control; dike area.

Bottom, Shell, and Roof

• The bottom, shell, and roof of an atmospheric storage tank form a totally enclosed container that keeps contents from escaping and contaminants from entering.
• Tanks are constructed of metal plates that are welded together at their edges.
• The bottom plate is a flat circular disk laid on a foundation of concrete or compacted sand to support the tank.
• The side walls, or shell of a tank, are metal plates welded in sections as the tank is being built.
• Designed with different thicknesses of metal plate to accommodate the hydrostatic head of the fluid the tank is going to contain.
• The bottom of the shell is thicker to handle the higher hydrostatic head with higher liquid levels.
• The roof is designed to minimize vapor escape (floating roof), protect contents from weather (fixed roof), and prevent vapor loss and protect contents (internal floating roof).

Stairway and Landing

• The stairway provides access to the top of a storage tank.
• The stairway will typically wrap around a portion of the tank rather than extend straight up.
• The landing is a small area of several feet at the top of the stairway that is partially or totally enclosed with a hand railing.
• The landing provides access to the tank roof where permitted or provides an area for viewing when access is not permitted.

Water Drain

• The water drain, or water draw, is a shallow catch basin built into the floor near the edge of the tank.
• The purpose of the water drain is to remove water that has settled out of the tank contents.
• A pipe connection is inserted into the catch basin and is routed through the tank shell to an outside sump drain.
• A valve on the outside of the tank is manually operated to drain any water that has settled into the catch basin which then drains to a collection sewer system.

Product Inlet Pipe

• The product inlet pipe is installed in the tank shell 3 or 4 feet above the bottom.
• The product inlet pipe configuration is meant to keep the inlet flow from stirring any bottom sediment during filling.

Product Outlet Pipe

• The normal product outlet pipe is installed in the tank shell 3 or 4 feet above the bottom to prevent the removal of water or sediment that settles to the tank bottom.
• The valve in the normal product outlet pipe is normally open (N.O.).
• A second product outlet pipe is installed closer to the tank bottom to enable lowering the level in the tank and the valve in the pipe is normally closed (N.C.).
• The product outlet pipe is normally orientated directly across from the product inlet pipe to maximize settling time and prevent the incoming product from immediately passing out of the outlet pipe.

Gauge Hatch

• A gauge hatch allows personnel to drop a gauge tape into the tank to manually measure the level in the tank.
• The gauge hatch is usually located near the tank stair landing, positioned near the edge of the roof, and may be set up to be opened by a foot operated lever.
• The weighted cover closes vapor-tight and is designed so that it cannot be accidentally left open after use.

Breather Valve

• A fixed roof tank, including internal floating roof tanks, may be equipped with a breather valve.
• This is an automatic valve designed to either relieve pressure from the tank or admit nitrogen gas or air into the tank.
• Relieving pressure prevents the tank from over-pressurizing, while admitting gas/air prevents a vacuum from forming within the tank.
• Automatic breather valves have the advantage of controlling environmental emissions.
• This is especially true if the automatic valve is connected to a tank-blanketing-gas system or a vapor recovery unit.

Vapor Recovery Systems

• One type of vapor recovery system consists of a compressor that compresses the excess vapors above a set point and delivers them into the plant’s light gas processing section.
• Make-up natural gas, or blanket gas, is supplied to the tank if the pressure falls below a set point.
• Set points are set at ounces of pressure (less than 14.7 pounds per square inch absolute-or-psia) or inches of water column.

Manways

• Manways are large diameter connections welded to a tank to allow entry for inspection or internal maintenance work.
• A manway is fitted with a flat plate used to cover and seal the manway when the tank is in service.
• Typically, manways are a minimum of 16 to 18 inches in diameter for personnel entry but may be larger to allow large internal devices to be installed.
• Entry into a storage tank requires a confined space entry permit.

Mixers and Agitators

• Mixers and agitators are devices that stir a liquid in a tank to ensure uniform composition throughout the tank.
• A jet mixer is a high-pressure nozzle installed near the bottom of a storage tank to agitate and mix the contents that is typically furnished by an outside pump that circulates the tank contents through the jet nozzle.
• A mechanical mixer is a motor-driven propeller installed near the bottom of a storage tank to agitate and mx the tank's contents.

Tank Heating Devices

• Tanks that contain viscous materials are equipped with heating devices to keep the contents fluid or at the proper viscosity.
• The heating source is usually steam.
• Heaters can be steam coils in the bottom of the tank or a heat exchanger tube bundle flanged to the tank wall near the bottom.
• Tanks are sometimes insulated to help control the temperature.

Grounding Straps

• Tanks are usually grounded with heavy bonding cables to dissipate static charges to the grounding system.
• The friction of flowing fluids generates static electricity, and tall structures can gather electrical charges during a thunderstorm.
• Grounding straps prevent dangerous sparks around explosive hydrocarbon vapors and interference with sensitive electronic control devices by attaching the bonding cables to a network of buried cables or grounding rods.

Fire Protection Foam Systems

• Some storage tanks are equipped with foam-type fire protection where the foam forms a protective layer between the storage tank contents and air.
• Spray nozzles are connected to pipes near the top of the tank side walls that are routed to a safe location so fire trucks can connect to them.
• Angled nozzles spray the foam fire extinguishing agent into the tank above the liquid level.

Corrosion Control

• In most cases, the tank bottom is protected from external corrosion with a cathodic protection (CP) system, which includes instrumentation to verify it is functioning properly.
• Storage tanks are also painted to minimize corrosion, usually in a light color to reduce the radiant heat effect of the sun which allows the stored fluid to remain cooler to minimize vaporization losses.

Dike Area

• A dike is a raised wall surrounding one or more storage tanks, and its purpose is to contain the contents of a storage tank if a spill or tank rupture occurs.
• The area within the dike is usually large enough to contain the contents of a full storage tank, and most dikes are dirt levees.
• Some storage tanks are surrounded with concrete dikes, typically for tanks that contain liquids that are more damaging to the environment.
• Storage tank dikes usually have a drain that allows rainwater to be drained into the collection sewer system.

Instrumentation

• Several variables can be monitored on a storage tank depending on the material it contains; however, the most common variables measured are the level of the material and the temperature.
• Three level measurement methods that are frequently used include radar, displacement, and float-and-tape.
• The most common temperature measuring device is a thermocouple

Components Specific to External Floating Roof Tanks

• Specific components to external floating roof tanks: pontoons, roof supports, roof drain, stiffening ring, roof seal, roof guide columns, roof stairway.

Pontoons

• Floating roofs use pontoons to create the buoyancy needed for the roof to float on the liquid in the tank.
• Pontoons can be a hollow ring around the perimeter of the floating roof, tubular sections spaced out under the roof, or both.
• The circular steel plate roof sits on top of the pontoon, covering the liquid to prevent the escape of vapor.

Roof Support Legs

• Roof support legs hang down through the floating roof to support the floating roof when the storage tank is at a low level and are usually adjustable.
• During routine operations, the supports may allow the floating roof to come within 3’6” of the tank floor, but when preparing the storage tank for maintenance, the supports may be set to hold the roof up 6’6” above the tank floor.
• Vapor space will be created under the floating roof as the level continues to drop below the roof support leg setting.
• Breather valves prevent vacuum buildup under the roof.

Roof Drain

• The roof drain on an external floating roof consists of a flexible conduit or pipe that can pivot as the roof moves up or down with the contained fluid.
• The conduit or pipe is in the interior of the tank, and it transfers the water from the floating roof to the outside of the shell at the bottom of the tank.
• Water from the roof is usually routed to the oily water sewer system which ensures that any hydrocarbons that may be in the drain water are properly disposed of.
• The roof drain is also provided with a shut-off valve if a leak should occur.
• If a roof drain is plugged and fails to release the water off of the roof, the roof can tip, lose buoyancy, and sink into the fluid.

Stiffening Ring Wind Girder

• The stiffening ring or wind girder adds support to the shell of an external floating roof tank.
• Loads, such as high winds, are transferred to the stiffening ring instead of adding stress to the tank shell.
• The stiffening ring is constructed of steel plates and encircles the tank.

Seal

• The seal between the floating roof and tank shell is flexible and able to conform to the irregularities of the shell.
• It seals the void space between the floating roof edge and the shell.
• This minimizes escaping vapors and prevents rainwater, dust, and other substances from contaminating the liquid.
• Tank seals are usually inspected on a routine basis.

Roof Guide Columns

• Vertical guide columns are provided to guide the roof as it moves up and down to prevent the roof from rotating and from moving side-to-side

Roof Stairway

• The stairway on an external floating roof is connected to hinges on the top of the tank shell, which allows the stairs to pivot up and down as the roof rises and falls.
• The stairway is used to access the floating roof and should be monitored on a routine basis.

Components Specific to Internal Floating Roof Tanks

• Specific components to internal floating roof tanks: tank vent and internal floating roof.

Tank Vents

• Tank vents are required on internal floating roof tanks to allow the space between the floating roof and the tank roof to breathe.
• As the level in the tank decreases, a volume of air equal to the amount of liquid taken out will be pulled into the tank through the vents.
• When the level rises, a volume of air equal to the amount of liquid added is forced out, which maintains a stable pressure in the tank.
• Some internal floating roof storage tanks are connected to vapor recovery systems.
• In this case, a blanket gas, such as nitrogen, is used to maintain the pressure rather than air.

Internal Floating Roof

• The internal floating roof is designed and built differently than the external floating roof, because the internal floating roof does not need the elaborate drainage system since the fixed roof will shed precipitation.
• It is possible to retrofit a fixed roof tank to include an internal floating roof.
• The floating roof helps to minimize vapor losses of the stored fluid.

Components Common to Pressurized Storage Tanks

• Pressurized storage tanks include many of the same components that are foundin pressure vessels.
• Additional components that are important to pressurized storage tanks include temperature instruments, level instruments, and pressure instruments.

Lesson 02 Recap

• Major components of atmospheric storage tanks.
• Components of pressurized storage tanks.
• Differences between external and internal floating roof storage tanks.

Storage Tank Operation

• Addresses how tanks operate under normal conditions.
• Explains how tanks are manually gauged.
• Introduces the topics of sampling and draining water.
• Identifies issues observed during routine monitoring and the safety precautions to take.
• Reviews types of emergencies that can involve tanks and the actions taken.

Operation of a Tank

• Tank farm operators perform several tasks, including filling and emptying storage tanks, gauging (measuring) storage tank levels, sampling storage tank contents, draining water from the bottom of atmospheric tanks, monitoring storage tanks, and responding to emergencies.

Filling and Emptying a Storage Tank

• Filling and emptying a storage tank means adding or removing a quantity of fluid to/from the tank.
• Transfer of fluid into or out of a tank is controlled by valves and pumps (or compressors when moving a gas).
• Devices may be controlled manually in the field or remotely from a control board.
• Operators must line up the pumps and compressors properly by opening the correct valves to send fluid to the desired location and should double-check valve lineups before starting a movement.
• Mistakes can lead to spills or contamination.
• Each storage tank type has specific filling and emptying considerations.

Fixed Roof

• Fixed roof tanks and internal floating roof tanks have breather valves to maintain stable pressure while filling and emptying and opens automatically to release or admit air or nitrogen gas during level changes.
• If the tank does not release the same volume of gas as the volume of liquid it is taking in, the internal pressure in the tank will increase.
• This is caused by the compression of air or blanket gas in the vapor space of the tank.
• If the tank does not release the same volume of gas as the volume of liquid that is being emptied, a vacuum will be created in the vapor space.
• Atmospheric storage tanks are not designed for high pressures or vacuum pressure; monitor the storage tank pressure during liquid movement. Breather valves should be periodically checked to ensure that they are not plugged.

External Floating Roof

• When the liquid level in a floating roof tank changes during filling or emptying, the roof rises and descends with the level, requiring the roof seal to move freely against the inside of the tank shell.
• In the event that the roof seal should catch and hang up against the shell during a level change, the roof may tip.
• This can cause the top of the roof to become flooded with the tank’s contents, and the roof can lose buoyancy and sink.
• During large level changes in external floating roof tanks, the roof operation should be monitored carefully.

Internal Floating Roof

• Filling and emptying an internal floating roof tank is similar to filling and emptying an external floating roof tank.
• The internal floating roof will typically not have weather seals and drainage piping, resulting in the roof moving up and down more freely.
• The fixed roof on this type of tank will have a breather valve or be connected to a vapor recovery system which maintains a stable pressure within the void space of the tank.
• It is important to ensure that the breather valve is operating properly.

Pressurized

• The purpose of a pressurized storage tank is to allow enough pressure to be maintained inside of the tank to keep most of the product in its liquid phase.
• When liquid is pumped into the tank, the pressure of the vapors within the tank must be held relatively constant.
• If the pressure increases above a set point, vapors are released and sent to the process, flared, or sent to a vapor recovery system.
• The tanks are generally filled to a maximum of 85% capacity to allow adequate vapor space above the liquid.
• When the liquid is pumped out of the tanks, the decrease in pressure in the tank allows some of the remaining liquid to vaporize, which re-establishes the equilibrium vapor pressure in the tank.

“Safe Fill” Limit

• Operations typically specify a limit on the amount of liquid that can be added to a storage tank.
• The maximum fill level in a tank is called the “safe fill” limit.
• Storage tanks that meet original design specifications normally have a safe fill limit located near the top of the tank.
• As a storage tank ages, corrosion or other factors can sometimes affect the integrity, which leads to design limits being reviewed and the safe fill level being lowered, if necessary.
• Storage tanks are designed to contain liquids within a range of densities and specific gravities.
• Occasionally, a tank is removed from one service and placed in another service, such as from crude oil storage to gasoline storage.
• When this occurs, the tank’s safe fill limit may be changed to ensure that the tank continues to operate within safe design limits.
• Nearly all tank levels are measured in feet, inches, and eighths of inches.
• Charts, called Strapping Tables, are available for each storage tank, and these charts accurately list the tank’s volume at each eighth of an inch of level.
• Strapping tables are used to estimate the duration of product transfers.
• It is common practice to equip storage tanks with remote level indicators that transmit all tank levels to a remote-control board or console.
• Operators need to ensure these remote indicators are working by comparing the reading with the local gauge at the tank.
• Pressure tanks that are designed to contain an HVL are filled to a maximum level of 85% of capacity.
• The extra 15% of vapor space provides room for the liquid to expand if the ambient temperature rises.
• Hydrocarbon tanks often have redundant level measurement.
• Overfilling can be prevented by monitoring the flow rate, knowing the capacity, knowing the vapor space, estimating fill time, monitoring the tank level, manually gauging the tank.
• If an atmospheric storage tank is overfilled, the liquid inside the tank may overflow the top of the tank, or it can enter the vapor recovery system which constitutes an unplanned release.

Manual Gauging of Tanks

• Continuous measurement of the liquid level inside storage tanks is often done by automatic devices; however, manual gauging should be performed regularly to ensure that the automatic devices are working properly.
• The gauge hatch provides an opening at the top of the storage tank to manually gauge the tank with a gauging tape to take an innage or an outage.
• The innage measurement is a measure of the height of the liquid in the storage tank, where the gauging tape is lowered to the bottom of the tank, and the liquid height from the bottom of the tank to the top of the liquid is measured.
• An outage is a measurement of the vapor space above the liquid, where the gauging tape is lowered to the top of the liquid and the height of the space between the top of the liquid and the bottom of the tank roof is measured.
• Safety precautions include: following facility safety procedures for respiratory protection, standing upwind of the gauge hatch, keeping the gauging tape grounded, using only approved intrinsically safe flashlight.

Sampling

• The quality of stored liquids is determined by analyzing samples of the material.
• Because material in a storage tank may vary at different locations within the storage volume, multiple samples from different levels and locations within the tank are taken to ensure representation of the total volume of the material.
• The methods used to obtain the sample depend upon the nature of the material being sampled, the type of storage tank, and the available features of the storage tank that allow access to the stored material.
• Sampling is scheduled on a routine basis per operator’s monitoring duties.
• Many storage tanks are filled with product waiting to be transported to the customer and the contents are certified to be on specification, for which the storage tank is sampled after it is filled, and the laboratory runs analysis tests to ensure the quality of the contents.
• Once a storage tank has been certified, no liquid can be added to the storage tank until all of the desired contents have been removed; otherwise, the tank will have to be recertified.

Draining Water

• Storage tanks accumulate water during operation, and they may be introduced with the stored liquid, or the water may come from rain leaking through a faulty roof.
• Water must be kept drained from tanks to prevent it from being included with the product transfer through the water drain into a catch basin, or a vacuum truck can be used to draw water directly from the water drain.
• Water that is not removed can cause major upsets in the process units.
• Water in the product liquid can also create problems in transfers if temperatures are low enough for the water to freeze.
• Water content is one of the elements in determining the quality of the product.
• Water draining should never be left unattended.
• Because the water may be contaminated with toxic substances like hydrogen sulfide, operators should wear proper PPE when draining water and perform the task in accordance with site procedures.

Routine Monitoring of Tanks

• Each refinery has specific routine monitoring tasks, and should act upon any issues that are observed, even if they are not specified in the monitoring plan.

Roof Guide Columns

• Floating roofs require frequent monitoring to ensure they are working properly because they may be damaged during the filling and emptying process

Damage can occur if:

• the tank is overfilled
• the roof is landed on its legs or supports during the emptying process
• the roof seizes and stops its travel during a level change
• the water drain plugs up or freezes and allows water to accumulate on one side of the roof, potentially sinking it

Leaks

• The most common locations for storage tank leaks are at piping connections to the tank, especially in pipe threads, flange gaskets, or manway gaskets.
• A more serious leak is one that appears in a welded or riveted seam in the tank shell, which may indicate internal corrosion or embrittlement (cracking) of the metal and can lead to catastrophic consequences.
• A tank leak must be immediately reported to the appropriate personnel, because minor leaks in pressurized tanks can become major leaks in a relatively short period of time.
• Major failures of atmospheric storage tanks may be signaled by minor leaks.
• If you must work in the area of a leak, ascertain what might be leaking and determine what protective equipment is appropriate for the leaking material.

Personnel Access Ways

• Personnel accesses consist of walkways, ladders, and stairways, which should always be inspected before use.
• Inspect for any signs of excessive corrosion; for broken or damaged rungs, pipes, or plates; for damaged or missing hardware; and for obstructions to the accessways.
• Damaged walkways, ladders, and stairways should be repaired.

Foundations and Supports

• The foundation is usually a concrete pad upon which vessels are installed.
• Cracks, crumbling, severe corrosion, or any other sign that a foundation might be failing must be immediately reported to the appropriate personnel, as well as wet spots or discoloration around tank foundations which usually indicate the start of a tank floor leak.

Outer Indications

• The shells and heads of vessels should appear relatively uniform.
• Irregularities, such as bulges or blisters, should be reported so that proper analysis and corrective actions can be taken as they are often early warning signs of vessel failure.

Emergencies Involving Tanks

• A storage tank may be part of an emergency: being the point of the emergency (such as being on fire or rupturing), being in the vicinity of the emergency, or being a part of the process that is undergoing an emergency.

Actions to Take

• If a storage tank is part of an emergency, the tank is normally isolated from the rest of the system by: shutting down associated pumps and closing all of the accessible inlet and outlet valves to the tank.
• If the tank is at the site of the emergency and it is equipped with critical protective or trip systems, this equipment will be activated as appropriate for the emergency.
• If the tank is threatened by fire, fire monitors and/or foaming agents will be placed at the tank to reduce the likelihood of it adding to or increasing the severity of the incident.

Lesson 03 Recap

Learned how storage tanks operate under normal conditions

• Tasks of an operator monitoring tanks.
• Reporting situations that may indicate developing problems.
• The process for filling and emptying storage tanks and how to prevent overfilling.

Maintaining Storage Tanks

• How to prepare a storage tank for inspection/maintenance work.
• Storage tanks may need to be prepared for entry and/or hot work which requires that storage tanks be free of any hazardous materials and that the atmosphere inside the tank is safe for human occupation.

Draining Liquid Completely

• Most of the liquid is removed through the discharge piping and drain connections, or called “stripping” a tank.
• Complete draining is often not possible due to sediment trapping the liquid.
• Installing a water nozzle in the tank can help push the sediment to a low point where is will be processed and disposed of properly with the water being re-circulated for continued cleaning.

Floating Roof Tank Safety

• Floating roof tanks require special safety procedures regarding roof support before entry into the tank, for which the floating roof should be supported by roof support legs and temporary supports called “cribbing."
• Entering a tank is considered a confined space entry, and employees who enter these tanks must be trained on and fully understand the required procedures.

Purging Hydrocarbon Vapors

• After all drainable residual liquid is removed through diesel washing and degassing, wet (liquid) spots and vapors are purged with steam or another inert gas to free the equipment.
• Steam's heat helps vaporize liquid hydrocarbons.
• The steam or inert gas is fed into the storage tank to displace the remaining hydrocarbons, and special cleaning chemicals may also be used to enhance the vapor degassing activity.
• Purging should be continued until a gas detector test shows that the tank is free of hazardous vapors.
• Employees will be trained on gas detector operation.

Safety Check Prior to Entry for Maintenance Work

• Before personnel enter a storage tank for cleaning or maintenance, must know that each refinery has strict procedures to ensure safety.
• Safety checks include: storage tank isolated from all energy sources; lock Out / Tag Out” (LOTO) procedure complete; proper documentation is in place; atmosphere verified free of hazardous vapors and a gas monitor is used to continuously monitor the tank atmosphere; atmosphere contains sufficient oxygen to sustain human life; continuous draft established.
• Temperature within the storage tank is not excessive for personnel entry.

Lesson 04 Recap

• Actions taken to prepare a storage tank for inspection, cleaning, maintenance and/or entry.
• Tanks must be free of any hazardous materials and the atmosphere inside the tank must be safe for the operators to enter.
• Basic safety checks on and around storage tanks.

This lesson covers the basics of storage tanks in Valero refineries. It discusses the purpose, types of materials stored, operator responsibilities, and monitoring tasks related to storage tanks. Understanding storage tank operations is crucial for refinery operators to ensure safety and efficiency.