Lesson Above-Ground Storage Tanks in the Houston Ship Channel

Learning Objectives

After this lesson, students are expected to:

• Describe above-ground storage tanks.
• List where and why above-ground storage tanks are used and the associated environmental issues.
• List and explain the different types of failure associated with above-ground storage tanks.
• Use engineering terminology to explain how Pascal's law and Archimedes' principle relate to the use of above-ground storage tanks.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Pre-Req Knowledge

Basic knowledge of algebra and simple geometry is needed to understand the concepts in this lesson and will be needed to solve and manipulate the equations in the corresponding activity.

Introduction/Motivation

(Have the 13-slide Above-Ground Storage Tanks Presentation, a Microsoft PowerPoint® file, projected in the classroom, with slide 1 of a painted above-ground storage tank showing. The slides are animated, so click to reveal the next text or image.)

What is this? Who knows what is shown on this slide? (Expect most students to say "water tower," so ask questions to guide them to reach the correct answer, which is an above-ground petrochemical storage tank. Expect students to make guesses that include the words "chemical," "gas," and/or "petroleum." Ask them to combine those terms to "petrochemical.") What is a petrochemical? (Listen to student answers.) Petrochemicals are very much what the word sounds like—chemicals obtained from petroleum or natural gas. Later, you all will get to share with the class the different types of petrochemicals in your projects.

(Move on to show students the rest of the slides, engaging them and encouraging student-led discussions throughout the presentation on the topic of above-ground storage tanks in the Houston Ship Channel and what happens when they are destroyed or damaged in big storms. The slide images and information serve as the foundation for the upcoming design challenge; they enable students to "understand the need" — the first step of the engineering design process. Some examples questions to ask students include the following:

Slides 2-3: What do you see in these pictures? What might be happening or have happened?

Slides 7-8: What do you think causes these types of failures?

Slide 10: Take a look at this map and guess: How many above-ground storage tanks are on the Houston Ship Channel?

Conclude the presentation by asking students the questions provided in the Lesson Closure section). Then have students complete the Above-Ground Storage Tank Design Project activity to test their own calculations and designs.

Lesson Background and Concepts for Teachers

Above-ground storage tanks (ASTs) are essential in the production and storage of petrochemical within ~300 industrial facilities along the Houston Ship Channel. Because the Houston Ship Channel is the largest port of foreign water-borne cargo in the U.S., and the nation's largest petrochemical producer (producing nearly half the nation's supply of gasoline and petrochemicals), it is disastrous when any of the 4,200 above-ground storage tanks rupture. Not only might the facility that owns the storage tank be closed for an extended amount of time, but the entire Houston Ship Channel might shut down. This can cost millions of dollars per day—the loss of goods being transferred or shipped, the costs of ships sitting unproductively outside the channel, the costs to clean the hazardous material from the environment, as well as costs to repair or replace the tank(s). During most hurricanes along the southern U.S. coastlines, above-ground storage tanks have displaced and buckled. Some examples of hurricanes that have damaged above-ground storage tanks include Hurricane Katrina along the Atlantic coast in 2005, Hurricane Rita in the Gulf of Mexico in 2005, Hurricane Gustav in the Gulf of Mexico in 2008, and Hurricane Ike in the Gulf of Mexico in 2008.

The storage tanks are of high concern because many facilities are only protected to 14–16 feet above mean sea level and damage to the region and national economy could be catastrophic in the event of major storms or hurricanes. During flood events, it is common for these storage tanks to uplift, displacing and crashing into nearby objects, and buckle from wind, waves and moving debris. The resulting shut-down of facilities and environmental impacts associated with tank failures are insurmountable. The spillage of hazardous materials incurs numerous costs to clean up the material from the environment, repair or replace storage tanks, and make up for losses due to contaminated produce and destroyed vegetation. Specific code instruction manuals include provisions for external pressure and floatation, anchorage due to seismic activity, and anchorage due to internal pressure, but no provisions for shell buckling or uplift due to flooding.

Displacement of above-ground storage tanks is explained by Archimedes' principle. This type of failure occurs when the weight of the above-ground storage tank plus the weight of the liquid contained within the above-ground storage tank weighs less than the weight of the water displaced by the above-ground storage tank during a flood event, causing it to float. Buckling is another type of failure that occurs in above-ground storage tanks, and can be explained by Pascal's law. Buckling occurs when the external water pressure on the tank shell caused by flooding is greater than the internal pressure of the above-ground storage tank, or when debris, waves and wind continually strike the outer shell of the tank. The pressure caused by flood water, debris waves and wind is applied only at a certain point on the tank shell, but is distributed to all points inside the tank, a closed tank system, as explained by Pascal's law.

Typical above-ground storage tank dimensions are:

• Fixed roof tank (flat roof)
• Aspect ratio (height to diameter ratio): 0.4
• Tank height: 25 feet
• Tank diameter: 62 feet
• Shell thickness: 0.394 inches

  

The surge height and liquid level inside the tank vary daily. For the Above-Ground Storage Tank Desigm Project associated activity, the diameter range for the above-ground storage tanks were assumed to be 20-300 feet and the height range for the tanks were assumed to be 10-30 feet, based on information presented at the SSPEED Center Conference: Hurricane Ike 5 Years Later at Rice University on September 24, 2013. Shell materials were extracted from Section 4.2.2 ASTM Specifications in the API Standard 650: Welded Tanks for Oil Storage, and petrochemicals were chosen randomly.

Associated Activities

• Above-Ground Storage Tank Design Project - Students derive equations to determine the stability of specific storage tank scenarios with given tank specifications and liquid contents. They analyze the tank stability in specific storm conditions. A related design project challenges them to improve storage tank designs to make them less vulnerable to uplift, displacement and buckling in storm conditions. Teams present their analyses and design ideas in short class presentations.

Lesson Closure

Based on what you have learned today, why it is important to include provisions for AST shell buckling or uplift due to flooding? (Answer: The failure of above-ground storage tanks is very common in powerful storms and hurricanes. When ASTs fail, they create environmental problems and result in great costs. It is important to include provisions for shell buckling or uplift due to flooding especially in coastal areas because large-force storms and hurricanes are so common.)

What are some of the scientific concepts that we have seen acting upon these storage tanks during major storm forces. (Listen to student ideas. Then correct and amend with additional explanations.) The displacement of above-ground storage tanks is explained by Archimedes' principle. This type of failure occurs when the weight of a tank plus the weight of the liquid contained within it weighs less than the weight of the water displaced by tank during a flood event, causing it to float. Buckling is another type of failure that occurs in ASTs and can be explained by Pascal's law. Buckling occurs when the external water pressure on the tank shell caused by flooding is greater than the internal pressure of the storage tank, or when debris, waves and wind continually strike the outer shell of the tank. While the pressure caused by flood water, debris waves and wind is applied only at a certain point on the tank shell, it is distributed to all points inside the tank, a closed tank system, as described by Pascal's law.

If you were the engineer in charge of writing provisions in the API 650 instructional manual, what would you write to encompass these provisions? (Listen to student answers and examples of what they might write in the code book to improve the rules protecting the tanks, but be sure not to give away any ideas to prevent buckling or uplift because that is part of the associated activity's design project.)

Now, it is your turn to analyze an above-ground storage tank in given storm conditions to see if your tank will displace. Your challenge is to come up with an engineering design for a new and/or improved tank, perhaps by an addition or change to an existing tank design that prevents it from buckling or displacing. (Move on to conduct the associated activity.)

Vocabulary/Definitions

above-ground storage tank: A storage tank that is unburied (above ground) and used to contain fluids such as petrochemicals and petroleum. These tanks are more susceptible to damage and failure from flooding, displacement and buckling since they do not have much storm protection, if any.

buckling: When an AST shell caves in due to external and internal pressure changes, hydrostatic pressure due to flooding, debris, wave impact and/or external wind pressure.

buoyancy: The ability of an object to float in a liquid.

density: A measurement of the compactness of an object.

Houston Ship Channel: The 50-mile long, largest port of foreign water-borne cargo and largest petrochemical production zone in the U.S.

mass: A measurement of the amount of matter in an object.

mass density: Mass per unit volume of a substance.

petrochemical: A chemical obtained from petroleum and natural gas.

pressure: A measurement of force per unit area.

storm surge/surge height: The height of the flood water during a storm.

uplift/displacement: When an AST lifts up during a flood and travels while floating on the water.

volume: A measurement of the amount of space an object occupies.

weight: A measurement of force on an object due to gravity.

Assessment

Pre-Lesson Assessment

What Is This!? Show students the first slide of the Above-Ground Storage Tanks Presentation, a photograph of an above-ground storage tank. Ask them: What is this? Expect most students to answer "water tower," so guide them to reach the more specific and correct answer—an above-ground petrochemical storage tank. Students' answers help to reveal their base knowledge of the lesson topic.

Post-Introduction Assessment

Discussion Questions: Throughout the Above-Ground Storage Tanks Presentation, engage students by asking questions, such as: What do you see in these photographs? What is happening in these pictures? (slides 2-3), What might cause these types of AST failures? (slides 7-8), Looking at the map, make a guess: How many ASTs are on the Houston Ship Channel? (slide 10). Students' answers reveal their engagement with and comprehension of the subject matter.

Lesson Summary Assessment

Transition to Design Project: At presentation end, ask students the questions in the Lesson Closure section. This primes them to conduct the associated activity.

References

Copyright

Contributors

Supporting Program

Acknowledgements

This digital library content was developed by the University of Houston's College of Engineering, based upon work supported by the National Science Foundation under GK-12 grant no. DGE 0840889. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.