The evolution of the API 579-1 / ASME FFS-1 Fitness-For-Service standard has been enormously beneficial to a broad range of industries.
API 579 provides a structured, quantitative methodology for assessing the structural integrity of steel pressurized tanks, pipes and other equipment to determine whether it is still fit to do what it was designed to do.
One reason for API 579’s success is its versatility.
It provides multiple assessment levels, from simple to complex. This provides inspectors with the flexibility to collect more data and perform more detailed evaluations when needed to provide the most accurate picture of an asset’s condition and remaining life.
The team developing the proposed new API 579-1 / ASME FFS-1 “Part 16 – Assessment of Fiber Reinforced Polymer Equipment” has continued with this approach.
Part 16, which is being prepared for ballot in 2026, describes the methods, tools and calculations needed to perform three levels of assessment:
Level 1 FRP Assessment
Level 1 assessment is the simplest, most conservative assessment that you can do. Calculations rely on information that can be readily obtained — on the nameplate and/or in equipment documentation — to show whether the equipment aligns with construction codes.
Non-destructive evaluation methods including acoustic emission (AE), acousto-ultrasonic (AU) and attenuation-based ultrasonic (UAX) can be used to determine factors such as:
- FRP thickness
- Corrosion barrier thickness
- Polymer damage status (PDS)
This information is needed to calculate Remaining Strength Factor (RSF) and Remaining Life. Note that while AE is a widely used NDE method, it cannot provide the information needed to determine Remaining Life of an asset.
If a piece of equipment passes Level 1, then you can feel pretty confident that it can continue in service.
If it fails, a decision needs to be made whether to:
- Repair or replace the asset
- Re-rate it to meet the requirements of Level 1, or
- Conduct a more in-depth Level 2 assessment.
Level 2 FRP Assessment
Level 2 assessment is intended to provide a more detailed evaluation for results that are more precise than Level 1.
Level 2 assessment can be undertaken when:
- FRP being tested has failed a Level 1
- Applied loads and operating pressures are unknown, or
- Measurable crack-like flaws have been detected.
It provides the steps needed to examine the asset in more detail, including:
- The structure of the FRP
- How it was constructed
- Operating conditions and other factors.
Many of the same calculations are performed as in Level 1 but the factors included in the calculations change as more refined data is collected.
Often as the data becomes more precise, RSF increases and an FRP asset that failed Level 1 could pass a Level 2 assessment and be declared fit for service.
Level 3 FRP Assessment
While Level 1 assessments don’t necessarily require a high level of engineering expertise, Level 3 requires the knowledge and skills of an FRP subject matter expert.
Level 3 provides a more detailed look at the FRP structure, including in-depth analysis of ultrasonic data to identify zones where the FRP appears to be undamaged. In such cases, it’s likely that the equipment may be in better condition than could be determined from a Level 1 or Level 2 assessment.
A rational basis for FRP repairs and replacement
Part 16 includes a theoretical example where inspectors determined that a piece of equipment had a Remaining Life of less than a year based on a Level 1 assessment.
In fact, if some of the values had been only slightly lower, the equipment would have failed a Level 1 – it would not be Fit For Service. In the real world, owners of that asset would have to repair or replace it.
At Level 2, a little more engineering expertise is applied. Some factors in the equations change as the inspector gathers more information including details about how the PDS of the material affects the Young’s Modulus (elongation under stress). This in turn affects the equation for RSF.
The result: a Level 2 assessment projected a Remaining Life of six years, compared to less than one year at Level 1.
This gives the asset owner or plant manager a lot more time to plan and act on replacing or repairing the equipment.
Invest in longer life for your FRP assets
Like steel, most FRP equipment can continue in service despite minor flaws or damage. Learn more about FRP damage mechanisms.
The question is, for how long.
Fitness For Service assessment provides a rational basis for distinguishing between acceptable and unacceptable damage, and for determining RSF and Remaining Life.
For asset owners, each level of assessment is likely to increase the overall cost of their maintenance and inspection program.
However, investing in accurate, reliable Fitness For Service assessment is essential for maximizing the lifespan and performance of your FRP equipment.
It provides the tools to identify and remediate damage today in order to avoid bigger, more expensive and possibly disastrous problems in the future.