API 620 Standard Pdf: Design and Construction of Large Welded Low Pressure Storage Tanks

The American Petroleum Institute (API) 620 standard is a critical guideline that outlines the design, construction, and inspection requirements for large, welded, low-pressure storage tanks. These tanks are commonly used in industries such as petrochemical, oil and gas, and chemical processing, where safe storage of materials like liquid natural gas (LNG) and other refrigerated products is paramount. API 620 is essential for ensuring that tanks operating under specific low-pressure and low-temperature conditions meet stringent safety and quality standards.

Established to provide consistent guidelines for constructing these specialized storage tanks, API 620 has evolved to address industry advancements, safety concerns, and the complex requirements of low-temperature storage applications. It serves as a benchmark for engineers, designers, and inspectors, helping them ensure tanks are safe, durable, and capable of handling challenging conditions without compromising integrity. The standard also delineates detailed criteria for selecting appropriate materials, welding techniques, and construction practices to mitigate risks such as leaks, ruptures, and degradation.

Understanding API 620 is essential for anyone involved in the design, construction, or operation of storage tanks for low-pressure applications. As the demand for safe storage solutions continues to grow, this standard remains a cornerstone of industry safety, allowing operators to manage the complexities of low-pressure storage confidently.

I. What is API 620?

API 620 is a standard published by the American Petroleum Institute that specifies the design, construction, and inspection requirements for large, welded, low-pressure storage tanks. These tanks are typically utilized for storing liquefied gases or liquids at relatively low pressures and temperatures, making them suitable for applications in industries such as petrochemical, natural gas, and chemical processing.

Key Aspects of API 620:

• Scope: API 620 primarily applies to tanks that operate at pressures up to 15 pounds per square inch gauge (psig) and temperatures as low as -325°F (-198°C). This makes the standard particularly relevant for the storage of refrigerated products, such as liquefied natural gas (LNG), ammonia, and other volatile or low-temperature substances.
• Materials: The standard allows the use of various materials, including carbon steel and low-alloy steel, which are carefully selected for their ability to withstand the low temperatures and pressures specified by API 620.
• Types of Tanks Covered: API 620 is specifically designed for large, field-erected tanks with welded construction. These tanks often have unique configurations to handle low pressures, such as double-walled or insulated designs, to minimize heat transfer and maintain stable temperatures.
• Applications: API 620 tanks are commonly found in industries where safe and efficient storage of low-pressure materials is essential. Examples include natural gas processing facilities, LNG storage facilities, and large-scale chemical plants.

API 620 sets strict requirements to ensure the integrity and safety of these tanks, covering aspects like structural design, material selection, welding, and inspection practices. As a recognized industry standard, API 620 helps manufacturers and operators comply with best practices and regulatory requirements, ensuring safe storage solutions for a wide range of low-temperature, low-pressure applications.

II. Scope of API 620 Standard

API 620 establishes the essential criteria for the design, fabrication, and inspection of large, welded, low-pressure storage tanks used for products requiring temperatures as low as -325°F (-198°C) and pressures up to 15 pounds per square inch gauge (psig). The standard’s scope covers a wide range of factors that influence the structural integrity, safety, and durability of tanks used in specific low-pressure and low-temperature environments.

Key Elements of the API 620 Scope:

1. Pressure and Temperature Limits:
   • API 620 is designed for tanks that operate at a maximum internal pressure of 15 psig.
   • The standard allows for storage of products at cryogenic temperatures, with limits as low as -325°F, accommodating the requirements for refrigerated and liquefied gas storage.
2. Materials of Construction:
   • API 620 specifies materials like carbon steel and low-alloy steels, selected for their ability to perform under low-temperature conditions without compromising strength or integrity.
   • These materials are chosen to minimize brittle failure risks, especially at cryogenic temperatures.
   • The standard allows for the use of double-walled or insulated designs to further protect against temperature fluctuations and maintain low internal temperatures.
3. Tank Types and Configurations:
   • API 620 applies to large, field-erected tanks, meaning the tanks are constructed on-site, generally for permanent installations.
   • Tanks covered by API 620 often require unique designs, such as vertical, cylindrical, or double-walled configurations, to accommodate low-pressure and low-temperature storage.
4. Design Standards and Structural Integrity:
   • The scope includes detailed criteria for calculating tank thickness, structural support, and stability to withstand external forces such as wind, seismic loads, and potential snow loads.
   • It also includes specific requirements for welding procedures and quality control, ensuring the welded joints maintain integrity at low temperatures.
5. Testing and Inspection Requirements:
   • API 620 specifies testing and inspection protocols for newly constructed tanks to ensure they meet performance standards. These inspections often involve nondestructive testing methods to assess weld quality, wall thickness, and overall tank structure.
   • Additionally, the standard provides guidelines for periodic inspection, maintenance, and recertification to keep the tanks in compliance with safety regulations throughout their service life.
6. Corrosion Protection and Maintenance:
   • API 620 also outlines requirements for corrosion protection, such as coatings, cathodic protection, and regular maintenance schedules to extend the lifespan of tanks operating in challenging environmental conditions.
7. Use Cases:
   • The standard is widely applied across industries that store volatile, cryogenic, or low-temperature products. Typical examples include LNG storage facilities, refrigerated hydrocarbon storage, and chemical processing plants.

API 620’s scope ensures that tanks built under its guidelines meet the stringent demands of low-temperature and low-pressure environments, providing safety, reliability, and compliance across multiple industries.

III. Design Requirements for API 620 Tanks

The API 620 standard sets out comprehensive design requirements to ensure that low-pressure storage tanks operate safely and reliably under specific temperature and pressure conditions. These requirements address factors such as structural integrity, welding, material selection, and environmental considerations, providing a framework for constructing tanks that can withstand the demands of low-pressure, low-temperature applications.

1. Structural Design Criteria:

• Tank Wall Thickness: The standard specifies minimum wall thicknesses based on tank diameter, height, and the internal pressures expected. This ensures that tanks are structurally sound and resistant to buckling or collapse.
• Support and Stability: API 620 includes requirements for tank supports to prevent tipping or deformation under external loads, including wind, snow, and seismic forces. Tanks must also have reinforced foundations to ensure stability, particularly in regions prone to seismic activity.

2. Materials and Toughness:

• Material Selection: Materials used in API 620 tanks, such as carbon steel and low-alloy steel, are chosen for their toughness at low temperatures. The materials must maintain strength and resist embrittlement to prevent cracking or failure in cryogenic conditions.
• Low-Temperature Testing: Materials undergo testing to confirm they meet low-temperature requirements, with procedures like Charpy V-notch impact testing to verify toughness.

3. Welding Standards and Procedures:

• Welding Specifications: The standard provides detailed guidelines for weld types and methods to be used on storage tanks, requiring that welds maintain strength and durability under low temperatures.
• Weld Quality Control: Each weld undergoes inspection, often using nondestructive testing (NDT) methods like radiographic or ultrasonic testing, to detect any imperfections that could compromise the tank’s integrity.
• Weld Toughness and Preheating: Welded areas are often preheated, and post-weld heat treatments may be applied to prevent brittleness, particularly when welding thick sections.

4. Tank Roof and Bottom Design:

• Roof Requirements: API 620 allows for various roof types, including dome, cone, or flat roofs, based on the tank’s purpose and structural needs. Roofs are often designed with insulation for tanks storing refrigerated materials to minimize heat ingress.
• Bottom Plate Specifications: The bottom plate design includes specific thickness requirements and may incorporate double bottoms for additional safety, particularly when storing materials that are highly corrosive or require extra protection from leakage.

5. Environmental and Loading Considerations:

• Wind, Seismic, and Snow Loads: Tanks must be designed to withstand external environmental loads, including wind pressure, seismic activity, and snow accumulation. These design factors vary based on the tank’s geographic location.
• Temperature and Pressure Variability: Tanks are designed to accommodate changes in internal pressures due to temperature fluctuations, with mechanisms to relieve excess pressure, such as pressure-relief valves.

6. Inspection and Testing:

• Initial Testing: Tanks constructed under API 620 undergo rigorous testing upon completion, such as hydrostatic testing, to ensure there are no leaks or structural weaknesses.
• Nondestructive Testing (NDT): The standard mandates NDT methods like ultrasonic or magnetic particle inspection to verify weld and material quality.
• Periodic Inspection Requirements: API 620 requires tanks to be inspected periodically during their service life, ensuring ongoing safety and compliance. This includes checks for corrosion, deformation, and weld integrity.

7. Corrosion Allowance and Protection:

• Corrosion Allowance: Design requirements include an allowance for corrosion by adding extra material thickness to the tank walls, especially when storing materials that may cause corrosion.
• Protective Coatings and Linings: The standard recommends the application of protective coatings, linings, or cathodic protection systems to reduce corrosion and extend the tank’s lifespan.

8. Insulation and Thermal Considerations:

• Insulation Requirements: For tanks storing refrigerated products, insulation is crucial to minimize heat transfer and maintain the product’s low temperature. The design includes guidelines for selecting and applying insulating materials.
• Thermal Expansion and Contraction: The tank’s design must account for thermal expansion and contraction to prevent stresses that could compromise structural integrity.

9. Safety and Pressure Relief Mechanisms:

• Pressure-Relief Devices: API 620 requires tanks to be equipped with pressure-relief devices to prevent over-pressurization. This includes pressure-relief valves or venting systems to safeguard the tank in case of pressure build-up.
• Emergency Shut-Off Systems: For tanks storing hazardous or volatile substances, emergency shut-off and monitoring systems may be recommended to enhance safety.

These design requirements under API 620 ensure that storage tanks operate safely and effectively, accommodating the unique demands of low-pressure, low-temperature environments. The stringent standards for materials, construction, and safety mechanisms help prevent leaks, corrosion, and structural failure, protecting both personnel and the environment.

IV . Fabrication and Construction Guidelines for API 620 Tanks

API 620 provides a comprehensive set of guidelines for the fabrication and construction of large, welded, low-pressure storage tanks. These guidelines ensure that tanks are built to withstand specific low-temperature and low-pressure conditions, ensuring safe and durable storage solutions. The fabrication and construction processes outlined by API 620 cover materials, assembly, quality control, and protective measures.

1. Material Preparation and Handling:

• Material Verification: All materials used in tank fabrication must be verified to ensure they meet the low-temperature requirements and toughness standards specified by API 620. Material traceability is also essential for quality control.
• Pre-Treatment and Cleaning: Before fabrication, materials are cleaned and pre-treated to remove contaminants. This preparation ensures clean welding surfaces and reduces the likelihood of weld defects.

2. Cutting and Shaping:

• Precision Cutting: Tank components are cut with precision to the required dimensions, using techniques like plasma cutting, oxy-fuel cutting, or laser cutting to achieve clean edges that aid in high-quality welds.
• Forming and Shaping: Shaping of plates, particularly for the tank shell and roof, is done through methods like rolling or bending. For domed or conical roofs, specific forming methods are used to achieve the required shape and fit.

3. Welding Guidelines:

• Welding Process Selection: API 620 specifies suitable welding processes, such as shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), or submerged arc welding (SAW), based on the tank’s design and material requirements.
• Welding Procedures and Qualifications: Welders must be certified, and welding procedures must be qualified under specific conditions to ensure they meet the standard’s quality requirements. This involves test welds under simulated conditions to confirm the adequacy of weld strength and ductility.
• Preheating and Post-Weld Heat Treatment (PWHT): For certain materials, preheating is required to prevent cracking, and post-weld heat treatments may be applied to relieve stresses in thicker sections.

4. Assembly and Fit-Up:

• Alignment and Fit-Up Tolerances: Proper alignment of tank sections is critical. API 620 outlines allowable tolerances for the fit-up of components to ensure structural integrity and reduce stress concentrations in the finished tank.
• Tacking and Temporary Supports: During assembly, tacking welds and temporary supports are used to hold components in place, allowing for fine adjustments and maintaining alignment until final welding.

5. Inspection and Quality Control:

• Nondestructive Testing (NDT): API 620 requires various NDT methods, including radiographic, ultrasonic, magnetic particle, and liquid penetrant testing, to inspect welds for defects. These tests identify any discontinuities or weaknesses that could compromise tank integrity.
• Hydrostatic Testing: After assembly, a hydrostatic test is performed by filling the tank with water to a specified level, testing its strength and ensuring there are no leaks or structural weaknesses.
• Dimensional Verification: During and after fabrication, dimensional checks are performed to verify that all components meet the specified dimensions and tolerances.

6. Corrosion Protection:

• Protective Coatings: API 620 recommends applying protective coatings to both internal and external surfaces of the tank, especially for tanks exposed to harsh environmental conditions. This helps prevent corrosion and extends the tank’s lifespan.
• Cathodic Protection: For tanks with external exposure, cathodic protection systems, like sacrificial anodes or impressed current systems, may be used to prevent corrosion on exposed metal surfaces.

7. Insulation and Thermal Protection:

• Insulation Installation: For tanks storing refrigerated products, insulation is applied to maintain low temperatures. The insulation is typically applied in layers and may include protective jacketing to shield it from environmental damage.
• Vapor Barrier: A vapor barrier is often installed along with insulation to prevent moisture ingress, which could degrade insulation performance and lead to corrosion under insulation.

8. Roof and Bottom Assembly:

• Roof Construction: API 620 allows for various roof types, including flat, dome, and cone-shaped roofs. The roof structure is welded in place and may require additional support for insulated tanks to bear the insulation’s weight.
• Bottom Plate Installation: The bottom plate is designed to bear the full load of the tank’s contents. Double bottoms or leak detection systems are sometimes incorporated, especially when storing hazardous or volatile substances.

9. Environmental and Safety Considerations:

• Ventilation and Access: API 620 requires the inclusion of access points, vents, and manholes for safe tank entry, maintenance, and emergency scenarios. These features are critical for both safety and regulatory compliance.
• Pressure Relief Systems: Pressure-relief devices are installed to safeguard the tank from over-pressurization, especially in tanks holding cryogenic or refrigerated substances.

10. Documentation and Certification:

• Inspection and Testing Records: Detailed records of inspections, NDT results, and hydrostatic tests are maintained for certification purposes, ensuring compliance with API 620 standards.
• Compliance Certification: The tank must be certified by a qualified inspector who verifies that it meets all API 620 requirements, including material quality, welding standards, and final testing results.

These fabrication and construction guidelines ensure that tanks built under API 620 are reliable, durable, and safe, providing the industry with low-pressure storage solutions that adhere to strict standards and quality measures.

V. API 620 vs. API 650

API 620 and API 650 are both widely used standards for the design and construction of storage tanks in the petroleum, petrochemical, and chemical industries. However, these standards are suited to different applications due to differences in design pressure, temperature ranges, and tank configurations. Here’s a comparison to clarify when each standard should be applied:

1. Design Pressure

• API 620: Covers low-pressure tanks with internal pressures up to 15 psig. These tanks are typically used for storage of liquefied gases and refrigerated liquids that require a low-pressure environment.
• API 650: Primarily designed for atmospheric pressure storage tanks or tanks with internal pressures up to 2.5 psig. API 650 tanks are commonly used for storing liquids at ambient or slightly elevated temperatures and pressures.

2. Temperature Range

• API 620: Accommodates low-temperature storage, with a design temperature limit as low as -325°F (-198°C). This makes API 620 suitable for cryogenic and refrigerated storage applications, such as storing liquefied natural gas (LNG) and other cold or volatile substances.
• API 650: Intended for tanks operating at near-ambient temperatures, typically from -40°F (-40°C) to 500°F (260°C). API 650 is ideal for general-purpose liquid storage under standard conditions, without the need for extreme temperature considerations.

3. Tank Types and Configurations

• API 620: Primarily used for large, field-erected tanks with welded construction. API 620 tanks often have unique configurations like double-walled or insulated designs to handle low pressures and maintain low temperatures.
• API 650: Also covers large, field-erected welded tanks but for atmospheric pressure applications. API 650 tanks commonly have simpler designs, such as open-top or fixed-roof configurations, suitable for holding liquids at ambient temperatures.

4. Material Requirements

• API 620: Allows for the use of carbon steel, low-alloy steel, and other materials that are compatible with low temperatures. The standard includes stringent toughness requirements, such as impact testing, to ensure that materials can withstand cryogenic conditions without becoming brittle.
• API 650: Primarily specifies carbon steel but also includes options for certain stainless steels. The material requirements are less demanding in terms of low-temperature toughness, as API 650 tanks are generally used in warmer, ambient conditions.

5. Design and Structural Requirements

• API 620: Design calculations for API 620 tanks include considerations for low-temperature and low-pressure conditions, with emphasis on minimizing stress concentrations and ensuring structural integrity at low temperatures. Additional reinforcement may be required for tank bottoms, roofs, and walls, especially for refrigerated or cryogenic storage.
• API 650: The design calculations focus on atmospheric pressure conditions and standard environmental loads, such as wind and seismic forces. API 650 emphasizes simplicity and cost-effectiveness for tanks storing non-pressurized, non-refrigerated liquids.

6. Applications

• API 620: Used in specialized applications, particularly where cryogenic or refrigerated storage is needed. Industries include natural gas (for LNG storage), petrochemical processing, and other facilities handling volatile or low-temperature substances.
• API 650: Commonly used in general storage applications, including water, oil, fuel, and other non-cryogenic substances. It is the standard of choice for tanks in refineries, terminals, and facilities where liquids are stored at ambient temperatures.

7. Testing and Inspection

• API 620: Requires more extensive testing for material toughness at low temperatures, such as Charpy impact testing. It also has specific inspection and testing protocols for ensuring the integrity of tanks designed for low-pressure and low-temperature applications.
• API 650: While thorough, the inspection and testing requirements for API 650 are more straightforward, with a focus on checking for general structural integrity, weld quality, and leakage for tanks operating at ambient conditions.

8. Cost and Complexity

• API 620: Due to the need for more specialized materials, stringent welding requirements, and structural reinforcements, API 620 tanks are generally more costly and complex to build. This added cost is justified by the need to store hazardous or cryogenic substances safely.
• API 650: Simpler in design, with fewer requirements for materials and structural reinforcement, API 650 tanks are typically more cost-effective. They are easier to construct and are widely used for less demanding storage needs.

Summary Table

In summary, API 620 is the preferred standard for tanks used in low-pressure, low-temperature applications, such as cryogenic and refrigerated storage. API 650, on the other hand, is suited for atmospheric tanks holding liquids at ambient temperatures. Selecting between these standards depends on the specific operating conditions, pressures, and temperatures required for storage.

VI. Common Applications of API 620 Tanks

API 620 tanks are specifically designed for low-pressure and low-temperature storage, making them ideal for applications in industries that require safe storage of volatile, cryogenic, or refrigerated products. Here are some of the most common applications for API 620 tanks:

1. Liquefied Natural Gas (LNG) Storage

• Application: API 620 tanks are widely used for storing liquefied natural gas, which must be kept at extremely low temperatures (around -260°F or -162°C) to remain in liquid form.
• Benefits: The standard’s low-temperature design requirements ensure that these tanks can safely store LNG in cryogenic conditions, reducing the risk of leaks or catastrophic failure.

2. Refrigerated Hydrocarbon Storage

• Application: In the petrochemical and oil industries, API 620 tanks store other refrigerated hydrocarbons, such as ethane, propane, and butane, which also need to be kept at low temperatures and pressures.
• Benefits: The tanks’ specialized materials and insulated designs make them suitable for safely storing these gases in liquid form, preventing vaporization and maintaining product stability.

3. Ammonia Storage for Chemical Processing

• Application: Ammonia is frequently used in industrial and agricultural processes, including fertilizer production, and must be stored at low temperatures to maintain stability.
• Benefits: API 620 tanks provide a secure and stable environment for ammonia storage, helping prevent temperature fluctuations that could lead to pressure build-up and increase the risk of hazardous releases.

4. Carbon Dioxide (CO₂) Storage

• Application: For industries involved in beverage production, dry ice manufacturing, or carbon capture and storage (CCS), API 620 tanks store liquefied CO₂ at low temperatures.
• Benefits: The design specifications of API 620 tanks help maintain CO₂ in its liquid form, minimizing the risk of accidental venting or expansion.

5. Ethylene and Propylene Storage in Petrochemical Plants

• Application: Ethylene and propylene are critical feedstocks in the petrochemical industry and are often stored in liquid form at low temperatures to facilitate transportation and processing.
• Benefits: API 620 tanks are ideal for these applications, as their low-temperature design and pressure limits make them suitable for these volatile substances, reducing the likelihood of leaks or ruptures.

6. Cryogenic Oxygen and Nitrogen Storage

• Application: In the healthcare, aerospace, and manufacturing industries, cryogenic oxygen and nitrogen are commonly stored in API 620 tanks for use in various applications, including medical treatments and metal fabrication.
• Benefits: API 620 tanks provide a safe and insulated environment for storing these cryogenic gases, preventing them from vaporizing and ensuring that they remain at stable, low temperatures.

7. Hydrogen Storage for Fuel Cells and Industrial Applications

• Application: Hydrogen is increasingly being used in fuel cell technology for clean energy production, as well as in industrial processes like refining and ammonia production. It requires low-temperature storage to maintain a stable liquid state.
• Benefits: API 620 tanks, with their low-temperature specifications and robust safety standards, are suitable for safely storing liquid hydrogen, which is highly flammable and requires careful handling.

8. Cold Storage in Pharmaceutical and Food Industries

• Application: Certain pharmaceutical and food products, such as vaccines, biological samples, and perishable food ingredients, need low-temperature storage to prevent degradation.
• Benefits: API 620 tanks provide the needed insulation and temperature control, making them valuable for cold storage facilities where stable, low-pressure environments are essential for product quality.

9. Specialized Industrial Gas Storage

• Application: Industrial gases such as argon, helium, and neon are often stored in liquid form for various applications, including welding, electronics manufacturing, and scientific research.
• Benefits: API 620 tanks are suitable for these gases because they maintain low temperatures, helping the gases stay in liquid form, which is more convenient and efficient for storage and transport.

API 620 tanks play a crucial role across various industries where low-pressure and low-temperature storage conditions are required. By meeting stringent safety and structural standards, API 620 tanks offer reliable solutions for storing cryogenic and volatile substances safely and efficiently.

VII. Compliance and Inspection Requirements for API 620 Tanks

API 620 tanks, used for low-pressure and low-temperature storage, must adhere to strict compliance and inspection standards to ensure they remain safe and reliable over their service life. These requirements help prevent leaks, structural failures, and other risks associated with storing volatile or cryogenic materials. The compliance and inspection guidelines outlined in API 620 involve initial testing, regular inspections, and documentation protocols.

1. Initial Testing and Certification

• Hydrostatic Testing: Once the tank is constructed, it undergoes hydrostatic testing, where it is filled with water to a specified level to check for leaks and verify the structural integrity under load conditions. This test is essential to detect any potential weaknesses before the tank is put into service.
• Nondestructive Testing (NDT): Nondestructive testing methods, such as ultrasonic, radiographic, magnetic particle, or liquid penetrant testing, are performed on welds and critical sections of the tank to ensure they meet the quality standards set by API 620. NDT helps identify any internal flaws, cracks, or other imperfections that may not be visible to the naked eye.
• Material Toughness Testing: For tanks storing cryogenic substances, material toughness testing, such as Charpy impact testing, is conducted to confirm that the materials can withstand low temperatures without becoming brittle.

2. Regular Inspections

• External Visual Inspections: Regular external inspections are required to identify signs of corrosion, deformation, or damage to the tank shell, roof, and supports. This inspection is typically done visually and helps detect early signs of deterioration.
• Internal Inspections: Periodic internal inspections are conducted to examine the interior surfaces of the tank for corrosion, pitting, or wear. Internal inspections are especially important for tanks storing corrosive or volatile substances. For safety, these inspections often require the tank to be drained and decontaminated.
• Ultrasonic Thickness Testing (UTT): Ultrasonic testing is used to measure the wall thickness of the tank to detect any thinning due to corrosion or erosion over time. This test is critical for ensuring that the tank maintains adequate structural integrity throughout its service life.
• Leak Detection: Periodic leak tests, such as pressure or vacuum testing, help ensure there are no leaks in the tank’s structure or its fittings. This is especially important for tanks storing hazardous or cryogenic materials.

3. Corrosion Protection and Maintenance

• Coating and Lining Inspections: For tanks with protective coatings or linings, regular inspections assess the condition of these layers to ensure they continue to prevent corrosion effectively. If any damage or wear is detected, repairs or reapplications may be required.
• Cathodic Protection Systems: For tanks equipped with cathodic protection systems, periodic testing ensures the system is functioning correctly to prevent corrosion on external and buried parts of the tank.

4. Pressure Relief and Vent System Testing

• Pressure Relief Valve Inspection: Tanks under API 620 typically have pressure relief valves to prevent over-pressurization. These valves are inspected and tested regularly to ensure they are functioning correctly and will release pressure if it exceeds safe limits.
• Vent System Checks: The venting system, crucial for tanks storing volatile or cryogenic substances, is inspected periodically to confirm that it is unobstructed and operating as designed, maintaining the tank’s pressure and safety.

5. Documentation and Record Keeping

• Inspection Records: Detailed records of all inspections, tests, and maintenance activities are maintained to document compliance with API 620 standards. These records include dates, findings, and corrective actions taken, ensuring a traceable history of the tank’s condition.
• Repair and Alteration Documentation: If repairs or alterations are made to the tank, documentation of these changes, including any re-testing, is essential for compliance. This ensures that any modifications do not compromise the tank’s integrity and that it continues to meet API 620 requirements.
• Certification by Qualified Inspectors: Inspections and certifications are performed by qualified inspectors who are trained in API 620 compliance. Their role is to verify that all aspects of the tank’s design, construction, and maintenance meet the standard’s requirements.

6. Periodic Compliance Audits

• Scheduled Audits: Operators may perform periodic compliance audits to ensure ongoing adherence to API 620 standards, especially for tanks holding hazardous or cryogenic substances. These audits verify that maintenance, inspection, and testing schedules are followed accurately.
• Regulatory Compliance: In addition to API 620 standards, operators may need to ensure compliance with local, state, or federal regulations related to the storage of hazardous materials, especially if the tank is located near populated areas.

7. Corrective Actions and Repairs

• Repairs of Defects: Any identified defects, such as corrosion, cracks, or thinning, must be repaired immediately to maintain the tank’s integrity. Repairs are typically followed by re-inspection and testing to verify effectiveness.
• Replacement of Worn Components: Components such as gaskets, seals, pressure relief valves, and other parts may need periodic replacement to ensure the tank’s safety and functionality.

8. End-of-Life Assessment

• Decommissioning Inspections: If a tank is nearing the end of its service life, a thorough inspection assesses its structural condition. Based on the findings, the tank may either be decommissioned or undergo extensive repairs for continued safe use.
• Life Extension Strategies: If extending the life of the tank is desired, operators can implement additional inspections, reinforcements, or retrofits to ensure it remains compliant and safe.

By adhering to these compliance and inspection requirements, operators ensure that API 620 tanks remain safe, durable, and compliant over their operational lifetime. Proper inspection and maintenance also reduce the risk of failure, protecting personnel, facilities, and the environment.

Conclusion

API 620 is a vital standard in the storage tank industry, providing comprehensive guidelines for designing, constructing, and maintaining large, welded, low-pressure tanks used in low-temperature applications. Its stringent requirements ensure that storage tanks meet high safety and quality standards, making them suitable for the demanding conditions of storing cryogenic and volatile substances, such as liquefied natural gas (LNG), ammonia, and various hydrocarbons.

The standard’s evolving nature, with periodic updates and revisions, demonstrates API’s commitment to keeping pace with technological advances and industry best practices. The latest editions and addenda incorporate improvements in material specifications, design methodologies, and safety protocols, reinforcing the reliability and safety of API 620 tanks in diverse industrial applications.

For engineers, constructors, and operators, API 620 provides a crucial framework that not only upholds safety but also boosts efficiency and cost-effectiveness. By adhering to this standard, industries can ensure that their low-pressure, low-temperature storage needs are met with tanks built to withstand challenging conditions over a long service life. In this way, API 620 continues to serve as an authoritative guide, supporting safe and efficient storage solutions across critical sectors.

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