Intermediate-Level Questions
1. What are the main types of tanks covered under API 650, and what are their typical applications?
API 650 covers vertical, cylindrical, aboveground, closed, and open-top welded storage tanks for storing petroleum, petroleum products, and other liquid products. These tanks are typically used in the petroleum industry for storing crude oil, gasoline, chemicals, and other liquids at atmospheric pressure, making them essential for storage terminals and refineries.
2. Explain the significance of the material selection process in API 650 tank design and the factors influencing it.
Material selection is crucial to ensure structural integrity, durability, and compliance with environmental conditions. Factors influencing material choice include the stored product's chemical properties, operating temperature, design metal temperature, corrosion allowances, and the tank's location. Proper material selection minimizes risks like brittle fracture and corrosion, ensuring long-term performance.
3. Describe the method for calculating the minimum required thickness for the shell of an API 650 tank.
The minimum required shell thickness is calculated using API 650 equations that consider the tank's internal pressure, hydrostatic pressure due to the liquid's height, and the material's allowable stress. The formula accounts for factors like design-specific gravity, tank diameter, joint efficiency, and corrosion allowance. Ensuring adequate thickness is essential for structural integrity under operational loads.
4. What are the welding requirements specified in API 650 for tank construction, and why are they important?
API 650 specifies welding procedures, welder qualifications, and weld inspection methods to ensure high-quality welds. Requirements include prequalified welding procedures, welder certification, and adherence to acceptable welding processes. These standards prevent defects that could compromise tank integrity, such as cracks or leaks, ensuring safety and reliability.
5. How does API 650 address seismic design considerations for storage tanks, and what parameters are involved?
API 650 includes seismic design provisions to ensure tanks can withstand seismic events. The parameters involved are seismic zone factors, importance factors, soil conditions, tank geometry, and contents' properties. Designers calculate seismic base shear and overturning moments to determine anchorage requirements and reinforcement, preventing tank failure during earthquakes.
6. What is the purpose of the hydrostatic test in API 650 tanks, and what procedures must be followed?
The hydrostatic test verifies the tank's integrity under operational pressure by filling it with water to check for leaks and structural performance. Procedures include filling the tank gradually, holding the water level at the top for a specified period, and inspecting for leaks or deformations. This test ensures the tank can safely hold its intended contents.
7. Explain the concept of joint efficiency in API 650 tank design and its impact on shell thickness calculations.
Joint efficiency refers to the strength of welded joints relative to the base metal strength. In API 650, joint efficiency factors are used in shell thickness calculations to account for potential weaknesses in welds. Lower joint efficiency requires thicker shell plates to compensate, ensuring the tank can withstand internal pressures without failure.
8. Discuss the importance of corrosion allowances in API 650 tank design and how they are determined.
Corrosion allowance is an extra thickness added to tank components to compensate for material loss over time due to corrosion. It is important to ensure the tank's long-term integrity. Determined based on the corrosiveness of stored products, environmental conditions, and expected service life, it ensures the tank remains structurally sound despite corrosion.
9. What are the requirements for tank foundations according to API 650, and why are they critical?
API 650 requires tank foundations to provide stable support, prevent settlement, and ensure even load distribution. Foundations must be designed considering soil characteristics, loadings, and environmental conditions. Proper foundation design is critical to prevent tank deformation, leaks, or failure, thus maintaining operational safety and integrity.
10. How does API 650 address wind load considerations in tank design, and what are the key factors?
API 650 provides guidelines for calculating wind loads based on wind speed, tank geometry, and location. Key factors include design wind velocity, exposure category, and shape factors. These considerations help determine the required structural reinforcement or anchorage to prevent tank overturning or damage due to wind forces.
11. Describe the role of the design metal temperature (DMT) in API 650 tank design.
Design Metal Temperature (DMT) is the lowest expected metal temperature during operation, influencing material selection to prevent brittle fracture. API 650 requires materials to have suitable notch toughness at the DMT. Considering DMT ensures that the tank material maintains ductility and toughness under the coldest operating conditions, enhancing safety.
12. What is the significance of the allowable stress values in API 650, and how are they determined?
Allowable stress values are maximum stress levels that materials can safely withstand. In API 650, they are determined based on material properties, temperature, and safety factors. These values are critical for calculating minimum thicknesses and ensuring components can handle operational stresses without yielding or failing, thus ensuring structural integrity.
13. Explain the purpose and application of Annex E in API 650 regarding internal pressures exceeding atmospheric pressure.
Annex E provides design provisions for tanks with internal pressures above atmospheric but not exceeding 2.5 psi. It includes guidelines for reinforcing roofs and shells to handle additional pressure, calculation methods, and construction details. Applying Annex E ensures tanks are properly designed to safely contain products under slight internal pressure.
14. How does API 650 address the inspection and testing of welds during and after tank construction?
API 650 mandates various non-destructive examination (NDE) methods, such as visual inspection, radiographic testing, and magnetic particle testing, for welds. Inspections occur during and after welding to detect defects like cracks, porosity, or incomplete fusion. Compliance ensures weld quality, preventing failures and ensuring the tank's structural integrity.
15. What are the design considerations for roof structures in API 650 tanks?
API 650 provides design criteria for various roof types, such as cone roofs, dome roofs, and floating roofs. Considerations include structural loads (dead, live, snow), wind uplift, internal pressure, and material selection. Proper roof design ensures protection from environmental elements, containment of vapors, and structural support.
16. Describe the importance of settlement considerations in API 650 tank design and the types of settlement that may occur.
Settlement considerations are vital to prevent tank distortion, leaks, or failure. API 650 addresses uniform settlement, differential settlement, and edge settlement. Designers must evaluate soil conditions and foundation design to mitigate uneven settling. Monitoring and adjusting for settlement ensures long-term tank integrity and operational safety.
17. What is the purpose of nozzle reinforcement in API 650 tanks, and how is it calculated?
Nozzle reinforcement strengthens the tank shell around openings to compensate for the material removed and stress concentrations. API 650 provides calculation methods to determine the required reinforcement area based on nozzle size, shell thickness, and material properties. Proper reinforcement prevents failures at nozzles due to internal pressures and external loads.
18. How does API 650 guide the design of anchorage systems for tanks, and when are they necessary?
Anchorage systems prevent tank uplift due to wind, seismic forces, or internal pressures. API 650 specifies when an anchorage is required based on calculations of overturning moments and stability criteria. It provides guidelines for anchor design, materials, and installation to ensure the tank remains secure under various loading conditions.
19. Explain the considerations for thermal expansion in API 650 tank design.
Thermal expansion affects tank dimensions due to temperature changes. API 650 requires designers to account for expansion in material selection, joint design, and structural allowances. Provisions include flexible connections, expansion joints, and proper spacing to prevent stresses or distortions that could compromise tank integrity.
20. What are the requirements for cathodic protection in API 650, and why is it important?
While API 650 does not provide detailed cathodic protection requirements, it acknowledges the need to protect tanks from corrosion, especially the bottom plates in contact with the soil. Cathodic protection systems, designed per NACE standards, mitigate corrosion by making the tank the cathode of an electrochemical cell, prolonging tank life.
Advance-Level Questions
1. What are the key considerations for selecting materials for API 650 tanks?
Material selection depends on factors like stored fluid properties, temperature, pressure, corrosion resistance, and regulatory compliance. Typical materials include carbon steel for general use and stainless steel for corrosive or high-temperature environments.
2. Explain the concept of hydrostatic testing in API 650 tanks.
Hydrostatic testing ensures structural integrity by filling the tank with water or another non-hazardous liquid and checking for leaks, deformation, or other issues under design pressure conditions.
3. How is the thickness of the shell plates determined in API 650 tanks?
Shell thickness is calculated based on internal pressure, material strength, joint efficiency, and corrosion allowance using formulae specified in API 650 standards.
4. What are the seismic design considerations in API 650 tanks?
Seismic design involves evaluating seismic forces, anchorage requirements, and tank stability using seismic coefficients, site conditions, and fluid dynamics to prevent overturning or sliding.
5. How is the tank roof type selected according to API 650 standards?
Roof type selection depends on operational needs, such as a fixed roof for general storage, an external floating roof for volatile liquids, or a domed roof for high-pressure or large-diameter tanks.
6. What are the welding requirements specified in API 650?
Welding must follow prescribed procedures, using qualified welders and materials. Welds are inspected visually, radiographically, or using ultrasonic techniques to ensure compliance with joint efficiency factors.
7. Describe the importance of corrosion allowances in API 650 tank design.
Corrosion allowance compensates for material loss due to corrosion over the tank's lifecycle, ensuring structural integrity and safe operation even after prolonged exposure to corrosive environments.
8. How is the tank foundation designed to meet API 650 standards?
The foundation must provide uniform support, prevent settlement, and withstand loads from the tank and stored contents. It typically includes compacted soil, concrete ring walls, or reinforced slabs.
9. What is the purpose of wind girders in API 650 tanks?
Wind girders prevent deformation or buckling of the tank shell due to wind loads, particularly in large-diameter tanks, by providing additional structural reinforcement.
10. Explain the importance of shell course arrangement in API 650 tanks.
Shell courses are arranged with varying thicknesses, with thicker plates at the bottom to withstand higher hydrostatic pressure, ensuring both structural efficiency and cost optimization.