Glossary > #SSPC-PA 2

SSPC-PA 2

SSPC-PA 2 is a widely recognized standard developed by the Society for Protective Coatings (SSPC) to determine compliance with dry film thickness of coatings on ferrous and non-ferrous metal substrates. This standard provides comprehensive guidelines for non-destructive measurement of coating thickness, ensuring that coatings meet established thickness requirements. SSPC-PA 2 is key in industries where protective coatings play a crucial role in protecting materials from corrosion and other environmental factors.

What is SSPC-PA 2?

SSPC-PA 2 is a procedural standard that establishes methods for measuring and ensuring compliance with dry film thickness of coatings. It is used primarily in the context of protective coatings applied to metal substrates. The standard is applicable in both manufacturing and field conditions and provides instructions on how to measure coating thickness using non-destructive testing methods.

The standard is key in quality assurance and control processes, ensuring that coatings applied to structures such as bridges, pipelines, and industrial equipment are within the specified thickness range. This is essential for performance, service life, and the ability of the coating to protect the underlying substrate.

Key Components of SSPC-PA 2

Types of Gauges

SSPC-PA 2 specifies the use of two types of gauges for measuring dry film thickness:

  1. Type 1 – Magnetic Pull-Off Gauges: These gauges use a permanent magnet to measure the force required to separate it from the coated surface. The force is interpreted as coating thickness. These gauges are simple but require careful handling, as they are non-linear and cannot be adjusted by the user.
  2. Type 2 – Electronic Gauges: These gauges use electronic circuits to convert a reference signal into a coating thickness measurement. Generally, they are more accurate and easier to use than Type 1 gauges and are capable of performing multiple measurements quickly.

Calibration, Verification, and Adjustment

Accurate measurement of coating thickness requires careful calibration, verification, and adjustment of gauges:

  • Calibration: Performed by the gauge manufacturer or an accredited laboratory, ensuring that gauge readings are traceable to national standards.
  • Accuracy Verification: Performed at the beginning and end of each work shift, or more frequently if a large number of measurements are being performed. This involves using certified coating standards or shims to ensure that the gauge is measuring accurately.
  • Adjustment: For Type 2 gauges, adjustment may be necessary to compensate for substrate characteristics, such as roughness, metallurgy, or curvature.

Measurement Procedures

SSPC-PA 2 provides detailed guidelines on the number and frequency of measurements required to ensure compliance:

  • Gauge Reading: A single measurement at one point on the surface.
  • Local Measurement: The average of at least three gauge readings in a circle 4 cm (1.5 inches) in diameter. This accounts for local variations in coating thickness.
  • Area Measurement: The average of five local measurements on a defined area, typically 10 m² (100 ft²).

The standard specifies various measurement frequencies depending on the size of the coated area. For areas smaller than 30 m², each 10 m² area must be measured. For larger areas, a statistical sampling approach is used.

Coating Thickness Limit Levels

SSPC-PA 2 provides five limit levels relating to the allowable deviation in coating thickness. These levels range from Level 1, the most restrictive, to Level 5, the least restrictive. In practice, if no limit level is specified, Level 3 is used as the default.

Compliance with Specified Thickness

To determine whether a coating meets the specified thickness, SSPC-PA 2 describes a process that includes:

  • Measuring thickness using defined procedures.
  • Comparing measurements to established minimum and maximum thickness values.
  • Using statistical methods to ensure that the overall area meets the established thickness requirements.

Practical Application

SSPC-PA 2 is used in various industries, including construction, automotive, maritime, and oil and gas industries, where protective coatings are essential. The standard ensures that coatings are applied correctly and fulfill their purpose, thereby extending the service life of coated structures and reducing maintenance costs.

Application Example

Consider a project involving the coating of a bridge. The specified dry film thickness is between 200 and 250 microns. Using SSPC-PA 2, inspectors would:

  1. Divide the bridge into sections of 100 ft².
  2. Perform five local measurements in each section, with each location containing at least three gauge readings.
  3. Calculate the average thickness for each section and compare it to the specified range, allowing for a certain deviation according to the chosen limit level.

Significance of SSPC-PA 2

Compliance with SSPC-PA 2 ensures that coatings provide the required level of protection and performance. It helps with:

  • Preventing premature coating failures.
  • Ensuring compliance with industry standards and specifications.
  • Reducing the risk of corrosion and damage to structures.

SSPC-PA 2 is a key standard for anyone involved in the application and inspection of protective coatings. By providing a structured approach to measuring coating thickness, it helps maintain the integrity and durability of coated structures. Understanding and implementing SSPC-PA 2 is essential for achieving high-quality coating applications that meet established requirements and function effectively in their operating environment.