NDE Methods for Detecting In-Service FRP Damage

Introduction

Fiber-reinforced thermosetting polymer (FRP) has been used successfully in many applications of pressure vessels, tankage, and piping. The ability of FRP to handle fluids and substances that are highly corrosive and potentially dangerous to personnel and the environment is undisputed. In some cases, service life exceeding 65 years has been documented.

There is considerable uncertainty about the capability of aging pressure vessels, piping, and tankage that is made from FRP to continue in service. Practices for how to detect and assess flaws and damage have not been consistent nor well-understood and accepted, and have often relied on subjective opinions that impose the expected behavior of metallics onto these materials. Damage to FRP from service conditions and material properties is usually completely different from damage that will occur to metal alloys, so using techniques and procedures developed for metals will produce unsatisfactory results.

When the fitness-for-service (FFS) is assessed using a Code such as API 579-1/ASME FFS-1, the engineer completing the assessment requires information on the type of material and the damage or flaw being assessed, along with the size or magnitude of the damage and the extent of the damage. The inspection data must come in a form that can be used for engineering analysis. This information is required so that the engineer can complete calculations to determine:

1. Is the equipment fit for service?
2. Is damage localized, or does it apply to the entire structure?
3. If the equipment is not fit for service, can it be re-rated?
4. Can repairs be made to address the damage?

For equipment made with metal alloys, the inspection techniques to be used for this are generally defined by codes such as ASME BPVC.V or other standards.

This article will explore the dominant damage mechanisms experienced by FRP during service. The article will then describe several detection methods and how they can be used to provide information on the size, magnitude, and extent of damage to FRP. The result of this article is to identify inspection information that is required to allow FFS assessment of equipment made from FRP.