Surface Preparation Standards Comparison

Pipeline Protective Coatings: Surface Preparation Standards

/in /by

Introduction

Surface preparation is critical in industries like oil and gas, marine, and infrastructure to ensure that protective coatings adhere correctly and perform well over time. Several international standards govern the level of surface cleanliness required before applying coatings. This blog focuses on the commonly referenced Surface Preparation Standards: ISO 8501-1 Sa 2½, SSPC-SP 10, NACE No. 2, and SIS 05 59 00 Sa 2½.

1. ISO 8501-1 Sa 2½: Surface Preparation Standards

Objective:
ISO 8501-1 is an internationally recognized standard that specifies the degrees of cleanliness for steel surfaces after blast cleaning. Sa 2½ refers to a comprehensive blast cleaning that removes nearly all rust, mill scale, and old coatings, leaving only slight shadows or discolorations.
Key Aspects:
Surface Appearance: The surface should be free of mill scale, rust, and old coatings, with only slight residues of stains or discoloration from rust or mill scale remaining. At least 95% of the surface area should be free of visible contaminants.
Visual Standard: ISO 8501-1 Sa 2½ provides visual examples of acceptable cleanliness levels, allowing inspectors to compare the prepared surface against these references to ensure compliance.

2. SSPC-SP 10: Near-White Metal Blast Cleaning

Objective:
SSPC-SP 10, also known as near-white metal blast cleaning, is a standard that specifies the level of surface cleanliness required for steel surfaces before coating. It aims to remove nearly all visible contaminants, leaving a surface with only slight staining.
Key Aspects:
Surface Cleanliness: At least 95% of each unit area should be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter. The remaining 5% may contain slight discoloration but no significant deposits.
Surface Profile: SSPC-SP 10 requires the surface profile to be rough enough to ensure good coating adhesion, typically achieved through abrasive blasting.

3. NACE No. 2: Near-White Metal Blast Cleaning

Objective:
NACE No. 2 is the equivalent of SSPC-SP 10 and describes the same near-white metal blast cleaning level. It is widely used in industries where the corrosion resistance is critical.
Key Aspects:
Surface Appearance: Similar to SSPC-SP 10, NACE No. 2 specifies that at least 95% of the surface should be free of visible contaminants, with only light staining allowed in the remaining 5%.
Equivalency: NACE No. 2 is often used interchangeably with SSPC-SP 10, as they describe near-white metal blast cleaning with minimal residual staining or discoloration.

4. SIS 05 59 00 Sa 2½: Very Thorough Blast Cleaning

Objective:
SIS 05 59 00 Sa 2½ is a Swedish standard describing a thorough blast cleaning process. Like ISO 8501-1 Sa 2½, this standard requires a high level of cleanliness with minimal visible staining or discoloration.
Key Aspects:
Surface Appearance: The steel surface should be free from mill scale, rust, and previous coatings, with only slight residues of rust or mill scale visible in no more than 5% of the surface area.
Usage: SIS 05 59 00 Sa 2½ is widely recognized and used, particularly in Europe and Asia, and is considered equivalent to ISO 8501-1 Sa 2½, SSPC-SP 10, and NACE No. 2.

Comparing the Standards

All four standards—ISO 8501-1 Sa 2½, SSPC-SP 10, NACE No. 2, and SIS 05 59 00 Sa 2½—describe nearly equivalent levels of surface preparation:
Surface Cleanliness: Each standard requires that at least 95% of the surface area be free from visible contaminants like rust, mill scale, and old coatings. The remaining 5% can contain only slight staining or discoloration, which should not affect the coating’s performance.
Surface Profile: While the exact surface profile is not specified in these standards, it is generally accepted that a roughened surface is necessary to ensure proper coating adhesion. The profile is typically achieved through abrasive blasting.
Visual Comparators: Each standard provides visual comparators to assess the level of cleanliness, helping inspectors and contractors ensure that the surface meets the required criteria.

Near White Blast Cleaning (SP 10 / Nace #2 / Sa 2.5)

surface-prep-standards-near-white.jpg
Loosely adhering material: 0%
Tightly adhering material: 0%
Stains, streaks, shadows: SP 10 5%, Sa 2 ½ 15%
Near White Blast Cleaning specifies that shadows, streaks, and stains must be limited to 5% of the surface area. Near White is selected when the added benefit of blasting to White Metal doesn’t justify the added expense.
Near White is typically specified for high-performance coatings over steel exposed to severe environmental conditions, such as chemical spills and fumes, high humidity, and proximity to salt water. It is commonly specified for off-shore platforms, shipyards, and other marine environments.

Practical Implications

Understanding these standards is essential for ensuring the longevity and effectiveness of protective coatings, especially in environments prone to corrosion:
Coating Performance: Proper surface preparation as specified by these standards ensures that coatings adhere well, reducing the risk of premature failure due to poor adhesion or residual contaminants.
Global Applicability: Knowing the equivalence of these standards allows for flexibility in meeting international project specifications, ensuring that contractors and suppliers are aligned on the required level of surface cleanliness.
Quality Control: Adhering to these standards provides a benchmark for quality control, ensuring that surface preparation is consistent and reliable across different projects and environments.

Conclusion

ISO 8501-1 Sa 2½, SSPC-SP 10, NACE No. 2, and SIS 05 59 00 Sa 2½ are critical Surface Preparation Standards in the surface preparation industry. Each defines a similar level of cleanliness required before coating application. Understanding and applying these standards ensures that steel surfaces are correctly prepared, leading to better coating performance and longer-lasting protection against corrosion.

Threads Gauge

API Spec 5B vs ASME B1.20.1

/in /by

Introduction

Regarding threading and connection standards in the oil, gas, and industrial sectors, API Spec 5B vs ASME B1.20.1 are two critical references. These standards govern the specifications for threads on pipes, tubing, and fittings, ensuring threaded connections’ integrity, compatibility, and performance. Although both serve the same general purpose of standardizing threads, they cater to different applications and industries with distinct technical requirements and scopes.

What Are API Spec 5B and ASME B1.20.1?

API Spec 5B is a standard published by the American Petroleum Institute (API), which specifies the threading, gauging, and testing procedures for threaded connections on casing, tubing, and line pipe used in the oil and gas industry. This standard is crucial for ensuring the mechanical integrity of pipe connections in high-pressure, high-stress environments.
ASME B1.20.1, on the other hand, is a standard by the American Society of Mechanical Engineers (ASME) that provides the specifications for general-purpose pipe threads, commonly referred to as National Pipe Taper (NPT) threads. This standard is widely used across various industries, including plumbing, HVAC, and general piping systems, where lower pressures and less demanding conditions prevail.

Key Differences: API Spec 5B vs ASME B1.20.1

1. Scope of Application

API Spec 5B:
Primarily used in the oil and gas industry.
Covers threads for casing, tubing, and line pipe.
Ensures high-performance connections that withstand extreme pressure, temperature, and environmental conditions.
ASME B1.20.1:
They are used in various industries, including construction, plumbing, and general industrial applications.
It governs NPT threads, widely used for low- to moderate-pressure systems.
It focuses on general-purpose applications where the threading does not need to withstand the extreme conditions typical in the oil and gas sector.

2. Thread Types and Design

API Spec 5B:
Specifies threads for casing, tubing, and line pipe, including API Buttress (BC), Long Thread (LC), and Extreme Line (XL) threads.
These threads are designed to provide a tight, leak-resistant seal in environments with high pressures and mechanical loads.
The threads are typically more robust, with higher thread engagement and specific requirements for makeup torque and thread lubrication.
ASME B1.20.1:
Defines the dimensions and tolerances for NPT threads, tapered threads that seal by metal-to-metal contact.
NPT threads are less robust than threads but are suitable for lower-pressure applications where ease of assembly and cost are more critical factors.
NPT threads are more straightforward, emphasizing ease of manufacture and use in general-purpose applications.

3. Manufacturing and Testing Requirements

API Spec 5B:
Includes rigorous testing requirements for thread gauging, including specific API thread gauges to ensure compliance with the standard.
Mandates testing procedures such as leak testing, pressure testing, and sometimes destructive testing to verify the integrity of the threaded connection under field conditions.
Emphasizes the need for precise thread cutting, proper thread lubrication, and appropriate makeup torques to prevent thread galling and ensure a secure, leak-free connection.
ASME B1.20.1:
Provides guidelines for manufacturing and gauging NPT threads but with less stringent testing requirements than API Spec 5B.
NPT threads are usually checked using standard thread gauges, and while testing for leaks is necessary, the testing protocols are generally less rigorous.
It focuses on ensuring that threads are properly formed and that they engage correctly, but compared to API Spec 5 B, the standard assumes a more forgiving application environment.

4. Pressure and Environmental Considerations

API Spec 5B:
It is designed for high-pressure environments such as deep wells, where pipe connections must withstand not only pressure but also thermal cycling, mechanical stress, and exposure to corrosive environments.
API threads must provide reliable performance over extended periods, often in harsh and remote conditions.
ASME B1.20.1:
They are used in lower-pressure applications with significantly less severe environmental and mechanical stresses.
Suitable for systems like water distribution, HVAC, and general industrial piping where pressures and temperatures are within a moderate range and where the threading does not need to resist extreme environmental factors.

Common Misconceptions

1. Interchangeability:

One common misconception is that API threads and NPT threads are interchangeable. They are not. Each type of thread is designed for specific applications, and using the wrong standard could result in connection failures, leaks, or even catastrophic system failures.
API threads and NPT threads have different design criteria, thread profiles, and material requirements, making them unsuitable for substitution without proper engineering consideration.

2. Complexity:

Some may assume that ASME B1.20.1 threads are more straightforward due to their use in less demanding applications, but complexity can arise in the variety of sizes and fittings available. Conversely, while API threads are more complex in design and testing, they are straightforward in their application within the oil and gas industry.

Practical Guidance for Selecting the Right Standard

Choose API Spec 5B when:
I work on oil and gas industry projects, particularly in drilling, well completion, or pipeline construction.
Your application involves high-pressure, high-temperature environments where thread integrity is critical to prevent leaks and failures.
You must meet stringent regulatory and safety requirements for oil and gas exploration and production.
Choose ASME B1.20.1 when:
We design or install piping systems for general industrial, plumbing, or HVAC applications where pressures and temperatures are within moderate ranges.
Ease of assembly, cost-effectiveness, and broad availability of threaded components are important factors.
You are working on projects where NPT threads are the standard specification, and the application environment is not as demanding as in the oil and gas sector.

Conclusion

Understanding the differences between API Spec 5B and ASME B1.20.1 is crucial for ensuring that the correct threading standard is used for your specific application. While API Spec 5B is designed for the rigorous demands of the oil and gas industry, ASME B1.20.1 provides a widely applicable standard for general-purpose piping threads. By selecting the appropriate standard, you can ensure your threaded connections’ safety, reliability, and efficiency, ultimately contributing to the success and longevity of your piping systems.

LNG TANKS

In-Depth Guide to LNG Tank Design, Material Selection, and Applications

/in /by

Introduction

Liquefied Natural Gas (LNG) is an essential component of the global energy infrastructure, stored at cryogenic temperatures to facilitate efficient transportation and storage. LNG tank design and material selection are critical to ensure their safety, durability, and performance. In addition to exploring tank design and materials, it’s essential to understand the various applications of LNG tanks to fully appreciate their role in the energy sector.

Understanding LNG Tank Design

LNG tanks are designed to hold natural gas in liquid form at temperatures around -162°C (-260°F). They must accommodate extreme cold, pressure variations, and potential thermal stresses. Here’s a detailed look at the primary tank types and critical design considerations:
Tank Types:
Single Containment Tanks: These tanks feature a single layer of steel with an outer concrete structure. Due to lower safety margins, they are typically used for smaller storage capacities and are less common for large-scale applications.
Double Containment Tanks: These tanks have an inner steel tank and an outer concrete or steel containment layer. They offer additional safety by managing potential leaks and providing an extra layer of protection.
Full Containment Tanks: These tanks, featuring an inner LNG container and a secondary containment system, are designed to handle any potential leaks, making them the standard for large-scale LNG storage.
Design Considerations:
Thermal Insulation: Advanced insulation materials like perlite, vacuum, or polyurethane foam prevent heat ingress and maintain the LNG at cryogenic temperatures.
Pressure Control Systems: Relief valves and monitoring systems are essential for managing internal pressures and ensuring safe operation.
Seismic and Structural Integrity: Tanks must withstand seismic activity and other structural stresses, so they often incorporate reinforced concrete and detailed structural analyses.

LNG Tank Design

LNG Tank Design

Material Selection for LNG Tanks

Choosing suitable materials is crucial for the performance and longevity of LNG tanks. Here’s a look at the commonly used materials:
Inner Tank Materials:
9% Nickel Steel (ASTM A553): Ideal for the inner bottom plate and inner shell or wall plates, this material provides high toughness and resistance to brittle fracture at cryogenic temperatures.
Low-Temperature Carbon Steel: This is sometimes used with 9% nickel steel for components where extreme cryogenic properties are not as critical.
Outer Tank Materials:
Concrete: Used for the outer containment layer in double and full containment tanks, providing robust structural support and additional thermal insulation.
Steel: Sometimes used in the outer tank for high-stress areas, often coated or treated to resist corrosion.
Tank Roof Materials:
ASTM A516 Grade 70: This carbon steel is suitable for the tank roof plate, offering strength and toughness at lower temperatures.
Insulation Materials:
Perlite: Effective for insulating against cryogenic temperatures.
Glass Fiber and Aerogel: Advanced materials offering excellent thermal insulation but at higher costs.

Applications of LNG Tanks

LNG tanks play a critical role in various applications across the energy sector. Here’s how they are utilized:
LNG Import and Export Terminals:
Import Terminals: LNG tanks at import terminals receive LNG from ships and store it before it is regasified and distributed into the local gas network.
Export Terminals: LNG tanks store liquefied natural gas at export terminals before it is loaded onto ships for international transport.
LNG Storage and Distribution:
Utility Companies: Utilities store and distribute natural gas for residential and commercial use in LNG tanks, ensuring a steady supply even during peak demand periods.
Industrial Applications: Industries use LNG tanks to store and supply natural gas for processes that require a consistent and reliable fuel source.
LNG as a Fuel:
Marine Transportation: LNG tanks are used in ships designed to run on LNG, reducing emissions compared to traditional marine fuels.
Heavy-Duty Vehicles: LNG tanks are used in trucks and buses that operate on liquefied natural gas, offering a cleaner alternative to diesel fuel.
Emergency Backup and Peak Shaving:
Backup Power: LNG tanks provide backup power solutions for areas with unreliable electricity supply, ensuring that natural gas is available for power generation during outages.
Peak Shaving: LNG storage helps manage peak demand by storing excess gas during low-demand periods and releasing it during high-demand periods.
LNG Production Facilities:
Liquefaction Plants: LNG tanks store the liquefied product at production facilities, where natural gas is cooled and condensed into a liquid form for efficient storage and transport.

Design and Safety Considerations

To ensure the safety and efficiency of LNG tanks, consider the following:
Thermal Stress Management: Proper insulation and expansion joints are necessary to manage thermal stresses caused by extreme temperature variations.
Safety Features: To address potential risks associated with LNG storage, incorporate leak detection systems, fire protection, and emergency shutdown systems.
Regulatory Compliance: Adhere to industry standards and regulations from organizations such as the American Petroleum Institute (API), the National Fire Protection Association (NFPA), and the International Organization for Standardization (ISO).

Conclusion

LNG tanks’ design and material selection are fundamental to ensuring their safe and efficient operation. Engineers can create tanks that perform reliably under extreme conditions by selecting appropriate materials like 9% nickel steel for cryogenic components and ASTM A516 Grade 70 for the roof. Understanding LNG tanks’ diverse applications— from import and export terminals to industrial uses and emergency backup—highlights their crucial role in the global energy infrastructure. Careful design, material selection, and adherence to safety standards will support LNG storage and utilization’s continued success and safety. For precise specifications and current pricing, consulting with [email protected] is always advisable to meet specific project needs.

NACE MR0175 vs NACE MR0103

What is the Difference Between NACE MR0175 and NACE MR0103?

/in /by

Introduction

In industries like oil and gas, where equipment and infrastructure are routinely exposed to harsh environments, selecting materials that can withstand corrosive conditions is crucial. Two essential standards that guide material selection for environments containing hydrogen sulfide (H₂S) are NACE MR0175 and NACE MR0103. While both standards aim to prevent sulfide stress cracking (SSC) and other hydrogen-induced damage, they are designed for different applications and environments. This blog provides a comprehensive overview of the differences between these two essential standards.

Introduction to NACE Standards

NACE International, now part of the Association for Materials Protection and Performance (AMPP), developed NACE MR0175 and NACE MR0103 to address the challenges posed by sour service environments—those containing H₂S. These environments can lead to various forms of corrosion and cracking, which can compromise the integrity of materials and potentially lead to catastrophic failures. The primary purpose of these standards is to provide guidelines for selecting materials that can resist these damaging effects.

Scope and Application

NACE MR0175

Primary Focus: NACE MR0175, or ISO 15156, primarily targets the upstream oil and gas industry, including exploration, drilling, production, and transportation of hydrocarbons.
Environment: The standard covers materials used in oil and gas production in sour service environments. This includes downhole equipment, wellhead components, pipelines, and refineries.
Global Use: NACE MR0175 is a globally recognized standard widely used in upstream oil and gas operations to ensure the safety and reliability of materials in sour environments.

NACE MR0103

Primary Focus: NACE MR0103 is designed explicitly for the refining and petrochemical industries, focusing on downstream operations.
Environment: The standard applies to process plants with hydrogen sulfide, particularly in wet H₂S environments. It is tailored to the conditions found in refining units, such as hydroprocessing units, where the risk of sulfide stress cracking is significant.
Industry-Specific: Unlike NACE MR0175, which is used in a broader range of applications, NACE MR0103 focuses more on the refining sector.

Material Requirements

NACE MR0175

Material Options: NACE MR0175 offers many material options, including carbon steels, low-alloy steels, stainless steels, nickel-based alloys, and more. Each material is categorized based on its suitability for specific sour environments.
Qualification: Materials must meet stringent criteria to be qualified for use, including resistance to SSC, hydrogen-induced cracking (HIC), and sulfide stress corrosion cracking (SSCC).
Environmental Limits: The standard limits H₂S partial pressure, temperature, pH, and other ecological factors determining the material’s suitability for sour service.

NACE MR0103

Material Requirements: NACE MR0103 focuses on materials resisting SSC in the refining environment. It provides specific criteria for carbon, low-alloy, and certain stainless steels.
Simplified Guidelines: Compared to MR0175, the material selection guidelines in MR0103 are more straightforward, reflecting the more controlled and consistent conditions typically found in refining operations.
Manufacturing Processes: The standard also outlines welding, heat treatment, and fabrication requirements to ensure materials maintain their resistance to cracking.

Certification and Compliance

NACE MR0175
Certification: Compliance with NACE MR0175 is often required by regulatory bodies and is critical for ensuring the safety and reliability of equipment in sour oil and gas operations. The standard is referenced in many international regulations and contracts.
Documentation: Detailed documentation is typically required to demonstrate that materials meet the specific criteria outlined in MR0175. This includes chemical composition, mechanical properties, and testing for resistance to sour service conditions.
NACE MR0103
Certification: Compliance with NACE MR0103 is typically required in contracts for equipment and materials used in refining and petrochemical plants. It ensures that the selected materials can withstand the specific challenges of refinery environments.
Simplified Requirements: While still rigorous, the documentation and testing requirements for MR0103 compliance are often less complex than those for MR0175, reflecting the different environmental conditions and risks in refining compared to upstream operations.

Testing and Qualification

NACE MR0175
Rigorous Testing: Materials must undergo extensive testing, including laboratory tests for SSC, HIC, and SSCC, to qualify for use in sour environments.
Global Standards: The standard aligns with international testing procedures and often requires materials to meet stringent performance criteria in the harshest conditions found in oil and gas operations.
NACE MR0103
Targeted Testing: Testing requirements are focused on the specific conditions of refinery environments. This includes testing for resistance to wet H₂S, SSC, and other relevant forms of cracking.
Application-Specific: The testing protocols are tailored to the needs of refining processes, which typically involve less severe conditions than those found in upstream operations.

Conclusion

While NACE MR0175 and NACE MR0103 both prevent sulfide stress cracking and other forms of environmental cracking in sour service environments, they are designed for different applications.
NACE MR0175 is the standard for upstream oil and gas operations. It covers a wide range of materials and environmental conditions and has rigorous testing and qualification processes.
NACE MR0103 is tailored for the refining industry. It focuses on downstream operations and uses simpler, more targeted material selection criteria.

Understanding the differences between these standards is essential for selecting suitable materials for your specific application and ensuring your infrastructure’s safety, reliability, and longevity in hydrogen sulfide environments.

Hydrogen-Induced Cracking HIC

Environmental Cracking: HB, HIC, SWC, SOHIC, SSC, SZC, HSC, HE, SCC

/in /by

Introduction

In industries where materials are subjected to harsh environments—such as oil and gas, chemical processing, and power generation—understanding and preventing environmental cracking is critical. These types of cracking can lead to catastrophic failures, costly repairs, and significant safety risks. This blog post will provide a detailed and professional overview of the various forms of environmental cracking like HB, HIC, SWC, SOHIC, SSC, SZC, HSC, HE, and SCC, including their recognition, underlying mechanisms, and strategies for prevention.

1. Hydrogen Blistering (HB)

Recognition:
Hydrogen blistering is characterized by the formation of blisters or bulges on the surface of a material. These blisters result from hydrogen atoms penetrating the material and accumulating at internal defects or inclusions, forming hydrogen molecules that create localized high pressure.

Mechanism:
Hydrogen atoms diffuse into the material, typically carbon steel, and recombine into molecular hydrogen at sites of impurities or voids. The pressure from these hydrogen molecules creates blisters, weakening the material and leading to further degradation.

Prevention:

  • Material Selection: Use low-impurity materials, particularly steels with low sulfur content.
  • Protective Coatings: Application of coatings that prevent hydrogen ingress.
  • Cathodic Protection: Implementation of cathodic protection systems to reduce hydrogen absorption.

2. Hydrogen-Induced Cracking (HIC)

Recognition:
Hydrogen-induced cracking (HIC) is identified by internal cracks that often run parallel to the material’s rolling direction. These cracks are typically located along grain boundaries and do not extend to the material’s surface, making them difficult to detect until significant damage has occurred.

Mechanism:
Like hydrogen blistering, hydrogen atoms enter the material and recombine to form molecular hydrogen within internal cavities or inclusions. The pressure generated by these molecules causes internal cracking, compromising the material’s structural integrity.

Prevention:

  • Material Selection: Opt for low-sulfur steels with reduced levels of impurities.
  • Heat Treatment: Employ proper heat treatment processes to refine the material’s microstructure.
  • Protective Measures: Use coatings and cathodic protection to inhibit hydrogen absorption.

3. Stress-Oriented Hydrogen-Induced Cracking (SOHIC)

Recognition:
SOHIC is a form of hydrogen-induced cracking that occurs in the presence of external tensile stress. It is recognized by a characteristic stepwise or staircase-like crack pattern, often observed near welds or other high-stress areas.

Mechanism:
Hydrogen-induced cracking and tensile stress lead to a more severe and distinct cracking pattern. The presence of stress exacerbates the effects of hydrogen embrittlement, causing the crack to propagate stepwise.

Prevention:

  • Stress Management: Implement stress-relief treatments to reduce residual stresses.
  • Material Selection: Use materials with higher resistance to hydrogen embrittlement.
  • Protective Measures: Apply protective coatings and cathodic protection.

4. Sulfide Stress Cracking (SSC)

Recognition:
Sulfide stress cracking (SSC) manifests as brittle cracks in high-strength steels exposed to hydrogen sulfide environments (H₂S). These cracks are often intergranular and can propagate rapidly under tensile stress, leading to sudden and catastrophic failure.

Mechanism:
In the presence of hydrogen sulfide, hydrogen atoms are absorbed by the material, leading to embrittlement. This embrittlement reduces the material’s ability to withstand tensile stress, resulting in brittle fracture.

Prevention:

  • Material Selection: Use of sour-service-resistant materials with controlled hardness levels.
  • Environmental Control: Reducing exposure to hydrogen sulfide or using inhibitors to minimize its impact.
  • Protective Coatings: Application of coatings to act as barriers against hydrogen sulfide.

5. Stepwise Cracking (SWC)

Recognition:
Stepwise or hydrogen cracking occurs in high-strength steels, particularly in welded structures. It is recognized by a zigzag or staircase-like crack pattern, typically observed near welds.

Mechanism:
Stepwise cracking occurs due to the combined effects of hydrogen embrittlement and residual stress from welding. The crack propagates stepwise, following the weakest path through the material.

Prevention:

  • Heat Treatment: Use pre- and post-weld heat treatments to reduce residual stresses.
  • Material Selection: Opt for materials with better resistance to hydrogen embrittlement.
  • Hydrogen Bake-Out: Implement hydrogen bake-out procedures after welding to remove absorbed hydrogen.

6. Stress Zinc Cracking (SZC)

Recognition:
Stress zinc cracking (SZC) occurs in zinc-coated (galvanized) steels. It is recognized by intergranular cracks that can lead to the delamination of the zinc coating and subsequent structural failure of the underlying steel.

Mechanism:
The combination of tensile stress within the zinc coating and exposure to a corrosive environment causes SZC. The stress within the coating, coupled with environmental factors, leads to intergranular cracking and failure.

Prevention:

  • Coating Control: Ensure proper zinc coating thickness to avoid excessive stress.
  • Design Considerations: Avoid sharp bends and corners that concentrate stress.
  • Environmental Control: Reduce exposure to corrosive environments that could exacerbate cracking.

7. Hydrogen Stress Cracking (HSC)

Recognition:
Hydrogen stress cracking (HSC) is a form of hydrogen embrittlement in high-strength steels exposed to hydrogen. It is characterized by sudden brittle fracture under tensile stress.

Mechanism:
Hydrogen atoms diffuse into the steel, causing embrittlement. This embrittlement significantly reduces the material’s toughness, making it prone to cracking and sudden failure under stress.

Prevention:

  • Material Selection: Choose materials with lower susceptibility to hydrogen embrittlement.
  • Environmental Control: Minimize hydrogen exposure during processing and service.
  • Protective Measures: Use protective coatings and cathodic protection to prevent hydrogen ingress.

8. Hydrogen Embrittlement (HE)

Recognition:
Hydrogen embrittlement (HE) is a general term for the loss of elasticity and subsequent cracking or fracture of a material due to hydrogen absorption. The sudden and brittle nature of the fracture is often recognized.

Mechanism:
Hydrogen atoms enter the metal’s lattice structure, significantly reducing its ductility and toughness. Under stress, the embrittled material is prone to cracking and failure.

Prevention:

  • Material Selection: Use materials that are resistant to hydrogen embrittlement.
  • Hydrogen Control: Manage hydrogen exposure during manufacturing and service to prevent absorption.
  • Protective Coatings: Apply coatings that prevent hydrogen from entering the material.

9. Stress Corrosion Cracking (SCC)

Recognition:
Stress corrosion cracking (SCC) is characterized by fine cracks that typically initiate at the material’s surface and propagate through its thickness. SCC occurs when a material is exposed to a corrosive environment under tensile stress.

Mechanism:
SCC results from the combined effects of tensile stress and a corrosive environment. For instance, chloride-induced SCC is a common issue in stainless steels, where chloride ions facilitate crack initiation and propagation under stress.

Prevention:

  • Material Selection: Choose materials resistant to specific types of SCC relevant to the environment.
  • Environmental Control: Reduce the concentration of corrosive species, such as chlorides, in the operating environment.
  • Stress Management: Use stress-relief annealing and careful design to minimize residual stresses contributing to SCC.

Conclusion

Environmental cracking represents a complex and multifaceted challenge for industries where material integrity is critical. Understanding the specific mechanisms behind each type of cracking—such as HB, HIC, SWC, SOHIC, SSC, SZC, HSC, HE, and SCC—is essential for effective prevention. By implementing strategies like material selection, stress management, environmental control, and protective coatings, industries can significantly reduce the risks associated with these forms of cracking, ensuring the safety, reliability, and longevity of their infrastructure.

As technological advancements continue to evolve, so too will the methods for combating environmental cracking. This makes ongoing research and development vital to maintaining material integrity in ever-demanding environments.

Constructing Oil Storage Tanks: Calculating Steel Plate Requirements

How to Calculate the Number of Steel Plates for Oil Storage Tanks

/in /by

Introduction

Building oil storage tanks involves precise planning and accurate calculations to ensure structural integrity, safety, and cost-effectiveness. For tanks constructed using carbon steel plates, determining the quantity and arrangement of these plates is crucial. In this blog, we will explore calculating the number of steel plates for oil storage tanks, using a specific example to illustrate the steps involved.

Project Specifications

Customer Requirements:

  • Plate Thickness Options: 6mm, 8mm, and 10mm carbon steel plates
  • Plate Dimensions: Width: 2200mm, Length: 6000mm

Tank Specifications:

  • Number of Tanks: 3
  • Individual Tank Volume: 3,000 cubic meters
  • Height: 12 meters
  • Diameter: 15.286 meters

Steps to Calculate Steel Plate Quantities for Three Cylindrical Oil Storage Tanks

Step 1: Calculate the Surface Area of a Single Tank

The surface area of each tank is the sum of the surface areas of the cylindrical shell, the bottom, and the roof.

1. Calculate the Circumference and Shell Area

2. Calculate the Area of the Bottom and Roof

 

Step 2: Calculate the Total Surface Area for All Tanks

Step 3: Determine the Number of Steel Plates Required

Step 4: Allocate Plate Thickness

To optimize the tanks’ structural integrity and cost, allocate different plate thicknesses for various parts of each tank:

  • 6mm Plates: Use for the roofs, where structural stress is lower.
  • 8mm Plates: Apply to the upper sections of the tank shells, where stress is moderate.
  • 10mm Plates: These are used for the bottoms and lower sections of the shells, where the stress is highest due to the weight of the stored oil.

Step 5: Example Allocation of Plates for Each Tank

Bottom Plates:

  • Required Area per Tank: 183.7 square meters
  • Plate Thickness: 10mm
  • Number of Plates per Tank: [183.7/13.2] plates
  • Total for 3 Tanks: 14 × 3 plates

Shell Plates:

  • Required Area per Tank: 576 square meters
  • Plate Thickness: 10mm (lower Section), 8mm (upper Section)
  • Number of Plates per Tank: [576/13.2] plates
    • Lower Section (10mm): Approximately 22 plates per tank
    • Upper Section (8mm): Approximately 22 plates per tank
  • Total for 3 Tanks: 44 × 3 plates

Roof Plates:

  • Required Area per Tank: 183.7 square meters
  • Plate Thickness: 6mm
  • Number of Plates per Tank: [183.7/13.2] plates
  • Total for 3 Tanks: 14 × 3 = plates

Considerations for Accurate Calculations

  • Corrosion Allowance: Include additional thickness to account for future corrosion.
  • Wastage: Consider material wastage due to cutting and fitting, typically adding 5-10% extra material.
  • Design Codes: When determining plate thickness and tank design, ensure compliance with relevant design codes and standards, such as API 650.

Conclusion

Constructing oil storage tanks with carbon steel plates involves precise calculations to ensure material efficiency and structural integrity. By accurately determining the surface area and considering the appropriate plate thicknesses, you can estimate the number of plates required to build tanks that meet industry standards and customer requirements. These calculations form the foundation for successful tank construction, enabling efficient material procurement and project planning. Whether for a new project or retrofitting existing tanks, this approach ensures robust and reliable oil storage solutions that align with engineering best practices. If you have a new LNG, aviation fuel, or crude oil storage tank project, please get in touch with [email protected] for an optimal steel plate quote.