Recent advancements in microwave technology have produced a reliable method to inspect non-conductive materials such as polyethylene piping and fiberglass reinforcement patches. Dielectric materials, such as these, are in wide spread use, in the refining and petrochemical industry, to replace steel components, due to their high corrosion resistance and strength to weight properties. Previously, inspection of these materials was limited to the detection of foreign objects or separated areas of delamination. Microwave inspection is the only technology which can reliably detect defects, such as a poor adhesive bond or a "stuck" thermal weld, structural defects which may cause component failure, over time.

The Technology: Microwave inspection can now inspect components that, previously, could only be externally inspected visually. The inspection system consists of a laptop computer, a small instrument box, an umbilical cable, a scanning device and the microwave transducer. Inspection scans are performed from one side of the component being tested, much like conventional ultrasonic testing. The transducer produces the microwaves and projects them past sensors, which record baseline amplitude. The microwaves penetrate the test piece and at each interface and area, where discontinuities are present, energy is reflected and refracted. Energy reflected back to the probe is mixed with the baseline amplitude signal to create difference amplitudes, with these signals being measured, in volts, by the probe. The data are then processed and digital images of amplitude v. position are produced. This plot is then analyzed by an experienced operator to ascertain the nature of the inspected volume. The data can be used as baseline data for repeated inspection as part of an ongoing maintenance program or can stand alone. Many dielectric components have been successfully inspected including wood, ceramics, composite aircraft components, poly-urea coatings, spay-on foam insulation and rubber piping expansion joints. The system can detect abnormalities such as delaminations, disbonds, foreign material inclusion, voids, changes in thickness, moisture and other liquid contamination, mechanical damage and physical changes due to chemical attack.

Polyethylene Piping: Polyethylene piping is becoming more prevalent in the refining and petrochemical industry for various services, including harsh environment services, due to its ability to withstand highly corrosive environments and its low cost, versus steel. Many types of polyethylene piping systems are currently in use, such as high-density polyethylene (HDPE) for firewater service, and low-density polyethylene (LDPE) for gas transfer service. These piping systems are usually joined at the seams by way of thermal welding, mechanical coupling, and glue-bonded couplings. Where thermal welding and glue-bonded couplings are used, microwave inspection of the areas has successfully located discontinuities and areas of insufficient bonding or leaking. Figure 2 contains data samples of polyethylene welds with different defects.

Fiberglass: Fiberglass has also been widely used in the refining and petrochemical industry. Fiberglass patches, joints, and piping are common where highly corrosive fluids are found. Since the fiberglass joints are typically glued together, a common defect is an

inadequate or missing glue layer. Poor adhesion in these areas can lead to joint instability due to thermal cycling or other mechanical loading. Microwave inspection of these components offers a reliable and effective method of detecting failure sites and provides data to support the decision to repair or replace these defective joints.