ASTM B117 PDF : Standard Practice for Operating Salt Spray (Fog) Apparatus

ASTM B117 is a standard practice developed by ASTM International for operating salt spray (fog) apparatus. This practice provides a standardized method for creating a controlled corrosive environment to evaluate the corrosion resistance of materials and coatings. Here are some key points about ASTM B117:

1. Purpose: The primary goal is to test the relative resistance of materials and surface coatings to corrosion, often used for quality control and to compare the effectiveness of protective coatings.
2. Test Apparatus: The test uses a salt spray cabinet, where a saline solution (typically 5% sodium chloride) is atomized to create a mist that settles on the samples. The environment inside the cabinet is maintained at a constant temperature, usually around 35°C (95°F).
3. Procedure:
   • Preparation: Samples are prepared and cleaned according to the standard’s guidelines.
   • Exposure: Samples are placed in the salt spray chamber, and the duration of exposure depends on the requirements of the test, which can range from a few hours to several thousand hours.
   • Evaluation: After the exposure period, samples are evaluated for signs of corrosion, such as rust or pitting, and the results are recorded.
4. Applications: This test is widely used in various industries, including automotive, aerospace, marine, and construction, to ensure that materials and coatings will withstand corrosive environments.
5. Limitations: While ASTM B117 is a useful accelerated corrosion test, it may not always predict actual field performance since real-world conditions can be more complex.

I. Introduction

Brief Overview of ASTM B117

ASTM B117, “Standard Practice for Operating Salt Spray (Fog) Apparatus,” is a widely recognized standard developed by ASTM International. It outlines the procedure for conducting a salt spray test, which is an accelerated corrosion test used to evaluate the corrosion resistance of materials and coatings. The standard provides detailed guidelines on the equipment setup, test conditions, and methods for assessing the results, ensuring consistency and reliability across different tests and laboratories.

Importance of Corrosion Testing

Corrosion testing is critical for understanding how materials and protective coatings will perform in corrosive environments. Corrosion can lead to significant material degradation, structural failures, and economic losses. By simulating harsh conditions through accelerated tests like ASTM B117, manufacturers and engineers can predict the lifespan of their products, improve material formulations, and develop more effective protective coatings. This proactive approach helps in preventing potential failures, ensuring safety, and reducing maintenance costs.

Applications in Various Industries

ASTM B117 is utilized across a multitude of industries, each with unique needs for corrosion resistance:

1. Automotive Industry: In automotive manufacturing, components are frequently exposed to harsh conditions such as road salts and moisture. Salt spray testing ensures that vehicle parts, like body panels and fasteners, can withstand these corrosive elements, leading to longer vehicle lifespans and reduced warranty claims.
2. Aerospace Sector: Aircraft materials and components are subjected to extreme environments, including salty marine atmospheres and high humidity. Corrosion testing helps in the selection and validation of materials that can maintain integrity and performance under such conditions, ensuring passenger safety and aircraft longevity.
3. Marine Industry: Marine vessels and offshore structures are constantly exposed to seawater, a highly corrosive environment. ASTM B117 testing is crucial for evaluating the durability of ship hulls, offshore platforms, and marine equipment, aiding in the design of corrosion-resistant structures.
4. Construction and Infrastructure: Building materials and infrastructure components, such as bridges and pipelines, must endure various environmental challenges. Corrosion testing helps in selecting materials that offer superior durability, contributing to the safety and longevity of critical infrastructure.

By employing ASTM B117, industries can ensure their products meet high standards of corrosion resistance, ultimately leading to better performance, reliability, and customer satisfaction.

II. History and Development

Origin of ASTM B117

ASTM B117 was first introduced in 1939 by ASTM International, an organization dedicated to developing and publishing voluntary consensus technical standards for a wide range of materials, products, systems, and services. The creation of ASTM B117 stemmed from the need for a standardized method to evaluate the corrosion resistance of materials and coatings in a controlled environment. This need arose during a time when industrialization and the use of metals in manufacturing were rapidly increasing, leading to greater awareness of the detrimental effects of corrosion.

Evolution of the Standard Over Time

Since its inception, ASTM B117 has undergone several revisions to enhance its precision, reliability, and applicability. These revisions have included updates to testing procedures, equipment specifications, and evaluation methods, reflecting advancements in technology and a deeper understanding of corrosion mechanisms. Each update has been aimed at improving the reproducibility of the test results and broadening the standard’s applicability to different materials and coatings. The standard has been periodically reviewed and updated to incorporate new research findings and industry feedback, ensuring it remains relevant and effective in addressing modern corrosion challenges.

Contributions to Industry Practices

ASTM B117 has significantly influenced industry practices by providing a common framework for corrosion testing. Its widespread adoption has led to greater consistency in how corrosion resistance is assessed across different sectors, facilitating better comparison and validation of materials and coatings. The standard has also driven innovation in corrosion protection technologies, as manufacturers strive to meet the rigorous requirements set forth by ASTM B117. Moreover, it has played a crucial role in regulatory compliance and certification processes, ensuring that products meet specific corrosion resistance standards before entering the market.

III. Purpose and Scope

Objective of ASTM B117

The primary objective of ASTM B117 is to establish a controlled, repeatable method for conducting salt spray (fog) testing. This test is designed to accelerate the corrosion process in a laboratory setting, allowing for the rapid evaluation of a material’s or coating’s resistance to corrosion. The results provide valuable insights into how these materials will perform in real-world corrosive environments, aiding in material selection, quality control, and product development.

Scope of the Standard

ASTM B117 covers the apparatus, procedure, and conditions required for conducting a salt spray test. The standard specifies the following key elements:

• Test Apparatus: Detailed description of the salt spray (fog) chamber, including its construction and operational requirements.
• Saline Solution: Composition of the saline solution, typically 5% sodium chloride, and the method for its preparation.
• Environmental Conditions: Maintenance of a constant temperature, usually around 35°C (95°F), and consistent salt spray (fog) generation.
• Testing Procedure: Guidelines for sample preparation, placement, and exposure duration.
• Evaluation of Results: Criteria for assessing and recording the extent of corrosion observed on the test samples.

Importance in Quality Control and Product Development

ASTM B117 is integral to quality control processes, ensuring that materials and coatings meet specific corrosion resistance criteria before they are used in production. By identifying potential corrosion issues early, manufacturers can make informed decisions about material selection and protective coatings, ultimately improving product durability and performance. In product development, ASTM B117 testing helps in comparing different materials and coatings, guiding the optimization of formulations and the development of new, more effective corrosion-resistant solutions. The standardized nature of ASTM B117 allows for consistent and reliable results, facilitating industry-wide benchmarking and continuous improvement.

IV. Test Apparatus and Materials

Description of the Salt Spray (Fog) Apparatus

The salt spray (fog) apparatus is a specialized chamber designed to create a controlled corrosive environment. Key components of the apparatus include:

• Test Chamber: An enclosed space where the samples are exposed to the salt spray. It is typically constructed from corrosion-resistant materials like plastic or stainless steel.
• Atomizer: A device that generates a fine mist of saline solution, creating the corrosive fog. The atomizer ensures uniform distribution of the salt spray within the chamber.
• Heating System: Maintains the chamber at a constant temperature, usually around 35°C (95°F), which is critical for consistent test conditions.
• Solution Reservoir: Holds the saline solution, which is fed to the atomizer. The reservoir is also constructed from corrosion-resistant materials.
• Control Systems: Monitors and adjusts the temperature, humidity, and spray density to ensure compliance with the test parameters set by ASTM B117.

Specifications for the Saline Solution

The saline solution used in ASTM B117 testing is a critical component, formulated to simulate a corrosive marine environment. The specifications for the solution are as follows:

• Concentration: A 5% sodium chloride (NaCl) solution, prepared by dissolving 5 parts by weight of NaCl in 95 parts of distilled or deionized water.
• pH Level: The pH of the solution should be maintained between 6.5 and 7.2. This can be adjusted using dilute hydrochloric acid (HCl) or sodium hydroxide (NaOH) if necessary.
• Purity: The NaCl used should be free from heavy metals and other impurities that could affect the test results.

Environmental Conditions Maintained During the Test

The test conditions are tightly controlled to ensure reproducibility and accuracy:

• Temperature: The chamber temperature is maintained at 35°C (95°F) to accelerate the corrosion process.
• Humidity: Relative humidity within the chamber is kept at 95-100%.
• Salt Spray Density: The apparatus is set to produce a fog with a collection rate of 1.0 to 2.0 ml per hour for each 80 cm² of horizontal collection area.

V. Testing Procedure

Sample Preparation Guidelines

Proper preparation of test samples is crucial for accurate results:

• Cleaning: Samples should be cleaned to remove any contaminants such as oils, greases, or dirt. This can be done using solvents or detergents.
• Labeling: Samples must be labeled with non-corrosive materials to ensure they can be identified after the test.
• Handling: Care should be taken to avoid touching the test surface with bare hands to prevent contamination.

Steps to Conduct the Salt Spray Test

1. Preparation of Saline Solution: Prepare the 5% NaCl solution, ensuring it meets the specified pH and purity requirements.
2. Setup of Apparatus: Fill the reservoir with the saline solution and set the chamber conditions (temperature, humidity, and spray density) as per ASTM B117 guidelines.
3. Placement of Samples: Place the prepared samples in the chamber, ensuring they are positioned at a specified angle (usually 15-30 degrees from the vertical) to allow uniform exposure to the salt spray.
4. Initiation of Test: Start the atomizer to generate the salt spray and maintain the environmental conditions throughout the test duration.

Duration and Exposure Settings

• Duration: The test duration depends on the specific requirements of the material or coating being tested. It can range from a few hours to several thousand hours.
• Monitoring: Regularly check the chamber conditions and ensure the saline solution reservoir is adequately filled throughout the test period.
• Termination: At the end of the specified exposure time, stop the test, remove the samples, and proceed to evaluate the extent of corrosion.

This detailed procedure ensures that the salt spray test is conducted consistently, providing reliable and comparable results for evaluating the corrosion resistance of materials and coatings.

VI. Evaluation of Results

Methods for Assessing Corrosion

After completing the salt spray test, the samples are evaluated for signs of corrosion. The following methods are commonly used:

• Visual Inspection: Observing the surface of the samples for signs of rust, blistering, pitting, and other forms of corrosion. A magnifying glass or microscope may be used for detailed examination.
• Weight Loss Measurement: Weighing the samples before and after the test to determine the mass loss due to corrosion. This method quantifies the extent of material degradation.
• Surface Profiling: Using tools like profilometers to measure changes in surface texture and roughness caused by corrosion.
• Coating Adhesion Test: For coated samples, adhesion tests (like cross-hatch adhesion test) may be performed to assess the coating’s integrity after exposure to the corrosive environment.

Criteria for Determining the Extent of Corrosion

The criteria for evaluating corrosion depend on the specific material and application requirements. Common criteria include:

• Rust Grade: Using standardized rust grading systems (e.g., ASTM D610) to rate the extent of rusting on a numerical scale.
• Blistering Degree: Evaluating the size, frequency, and distribution of blisters using standardized charts (e.g., ASTM D714).
• Pitting Depth: Measuring the depth and density of pits formed on the sample surface.
• Adhesion Strength: Assessing the adhesion strength of coatings through peel or cross-hatch tests, comparing results against specified acceptance criteria.

Recording and Interpreting Test Results

• Documentation: Detailed records of the test conditions, sample preparation, and observations during and after the test should be maintained. This includes photographs and detailed descriptions of corrosion features.
• Data Analysis: Analyzing the recorded data to identify trends, compare the performance of different materials or coatings, and determine the effectiveness of corrosion protection methods.
• Reporting: Preparing comprehensive test reports that include test parameters, observations, data analysis, and conclusions. Reports should clearly state whether the materials or coatings meet the specified corrosion resistance criteria.

VII. Applications of ASTM B117

Use in Automotive Industry

In the automotive industry, components are frequently exposed to harsh conditions such as road salts and moisture. ASTM B117 testing ensures that vehicle parts, like body panels, fasteners, and undercarriage components, can withstand these corrosive elements, leading to longer vehicle lifespans and reduced warranty claims. This testing is crucial for developing corrosion-resistant paints, coatings, and materials that contribute to vehicle durability and safety.

Applications in Aerospace

Aircraft materials and components are subjected to extreme environments, including salty marine atmospheres, high humidity, and varying temperatures. ASTM B117 testing helps in selecting and validating materials that can maintain integrity and performance under such conditions. This ensures the reliability and safety of critical components such as airframes, fasteners, and avionics housings. The aerospace sector relies on this testing to develop coatings and treatments that protect against corrosion, thereby enhancing the longevity of aircraft.

Importance in Marine Environments

Marine vessels and offshore structures are constantly exposed to seawater, a highly corrosive environment. ASTM B117 testing is crucial for evaluating the durability of ship hulls, offshore platforms, marine equipment, and underwater pipelines. The marine industry uses this testing to develop and validate protective coatings, anti-corrosive materials, and cathodic protection systems that can withstand prolonged exposure to saltwater, ensuring the safety and operational efficiency of marine infrastructure.

Role in Construction and Infrastructure

Building materials and infrastructure components, such as bridges, pipelines, and reinforced concrete structures, must endure various environmental challenges, including exposure to deicing salts, coastal environments, and industrial pollutants. ASTM B117 testing helps in selecting materials that offer superior durability, contributing to the safety and longevity of critical infrastructure. This testing supports the development of corrosion-resistant construction materials, protective coatings, and maintenance strategies that minimize the impact of corrosion on structural integrity.

By employing ASTM B117, these industries can ensure their products meet high standards of corrosion resistance, ultimately leading to better performance, reliability, and customer satisfaction.

VIII. Benefits of ASTM B117

Standardization of Corrosion Testing

ASTM B117 provides a consistent, repeatable methodology for conducting salt spray tests, which is crucial for ensuring that test results are reliable and comparable across different laboratories and industries. This standardization helps manufacturers, researchers, and quality control professionals to benchmark materials and coatings against a common set of criteria, facilitating industry-wide acceptance and recognition of test results.

Comparison of Material and Coating Performance

By adhering to the standardized procedures outlined in ASTM B117, different materials and coatings can be evaluated under identical conditions. This enables direct comparison of their corrosion resistance, helping manufacturers choose the most suitable materials and coatings for specific applications. It also assists in identifying the strengths and weaknesses of various corrosion protection strategies, guiding improvements in material formulations and coating technologies.

Accelerated Testing for Faster Results

ASTM B117 is an accelerated corrosion test that simulates long-term exposure to corrosive environments within a relatively short period. This allows for rapid assessment of material and coating performance, providing valuable insights during the product development phase. Accelerated testing helps in identifying potential corrosion issues early, reducing the time and cost associated with long-term field testing.

IX. Limitations and Considerations

Limitations of Accelerated Testing

While ASTM B117 is a useful tool for evaluating corrosion resistance, it has limitations:

• Simplified Conditions: The test creates a controlled salt spray environment that may not fully replicate the complexities of real-world corrosive environments, which can include varying temperatures, humidity levels, and the presence of multiple corrosive agents.
• Accelerated Nature: The accelerated nature of the test might not accurately predict long-term corrosion behavior, as some corrosion mechanisms may not be fully represented or accelerated differently in the test chamber.

Differences Between Lab Conditions and Real-World Environments

The controlled conditions of the ASTM B117 test chamber differ significantly from real-world environments, where materials and coatings are subjected to a range of variables such as fluctuating temperatures, mechanical stresses, and varying concentrations of corrosive agents. Consequently, while the test provides valuable comparative data, it may not fully predict the actual performance of materials and coatings in their intended applications.

Complementary Tests for Comprehensive Evaluation

To obtain a more comprehensive understanding of corrosion resistance, ASTM B117 should be used in conjunction with other tests and evaluations. These might include:

• Field Testing: Long-term exposure studies in actual service environments to observe real-world corrosion behavior.
• Electrochemical Tests: Techniques such as electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization to study corrosion mechanisms at a microscopic level.
• Environmental Simulations: Tests that replicate specific environmental conditions, such as cyclic corrosion tests that combine salt spray with other environmental factors like UV exposure and temperature cycling.

By combining ASTM B117 with other test methods, a more robust and accurate assessment of corrosion resistance can be achieved, providing better insights for material selection and product development.

Conclusion

ASTM B117, the “Standard Practice for Operating Salt Spray (Fog) Apparatus,” is a cornerstone in the field of corrosion testing, providing a reliable and standardized method for evaluating the corrosion resistance of materials and coatings. Its widespread adoption across various industries highlights its importance in ensuring the durability and longevity of products exposed to corrosive environments.

Key Takeaways:

• Historical Significance: Since its introduction in 1939, ASTM B117 has evolved to become an essential tool for quality control and material development, influencing industry practices and driving advancements in corrosion protection technologies.
• Purpose and Scope: The primary objective of ASTM B117 is to offer a controlled, repeatable method for accelerated corrosion testing. It provides detailed guidelines on apparatus setup, saline solution preparation, environmental conditions, and evaluation of results, ensuring consistency and reliability in corrosion assessment.
• Applications Across Industries: From automotive and aerospace to marine and construction, ASTM B117 plays a critical role in assessing the corrosion resistance of materials and coatings, guiding material selection, product development, and quality assurance.
• Benefits: The standardization of testing procedures, the ability to compare material performance under identical conditions, and the accelerated nature of the test contribute to faster and more efficient product development cycles.
• Limitations and Considerations: While ASTM B117 offers valuable insights, it is important to recognize its limitations and complement it with other testing methods to obtain a comprehensive understanding of corrosion behavior in real-world environments.

In conclusion, ASTM B117 remains a vital standard in corrosion testing, providing a robust framework for evaluating the corrosion resistance of materials and coatings. By understanding its scope, applications, benefits, and limitations, manufacturers and researchers can effectively utilize this standard to improve the durability and performance of their products, ensuring they meet the demands of corrosive environments. Combining ASTM B117 with other complementary tests allows for a more holistic approach to corrosion assessment, ultimately leading to safer, more reliable, and longer-lasting products.