Introduction

The power generation industry has a wide variety of inspection problems. Many of which can be solved using ACFM inspection techniques.

Power station corrosion

U19 AMIGO instrument   

Standard ACFM weld probe

Micro ACFM weld probe   

ACFM mini probe

Encoder weld Probe

Flat array Probe 45KHz

ACFM was used to investigate corrosion. (Visually this is not unlike crazed cracking with multiple branching cracks covering large areas of a weld). The probes used for this inspection were standard manual probes predominantly used for detecting and sizing fatigue cracks in weld toes and caps. When inspecting for environmental cracking, such as corrosion cracking or hydrogen induced cracking, it has been found that the more advanced array probes are more appropriate for defining and categorizing this type of defect.  

Array probes contain multiple sensors which cover a wider area and are particularly useful in assessing cracks that branch and extend laterally on the surface. An array probe was available, though this is an optically encoded, flat probe, optimized for the inspection of smooth, flat surfaces – it was not suitable for the surface conditions encountered on this inspection. TSC are able to produce array probes to fit most profiles and geometries, fitted with wheeled encoders that are more suited to rough or uneven surface conditions.

U19 AMIGO instrument

Standard ACFM weld probe 45KHz

Micro ACFM weld probe 45KHz

Custom build contoured probe 45KHz       

TSC Inspection Systems have provided a solution to the power generation industry for the rapid detection of transverse surface breaking cracks on the internal waterwalls of boilers - commonly occurring on the tube fins.

This has resulted in clients being able to rapidly assess the condition of the walls during the limited time available during a shutdown and repair or replace tubes with confidence.

The TSC Waterwall array probe uses a contoured face that is customized for the specific tube external diameter. The scanner is manually moved along the tube wall to scan for defects.

The tubes are not required to be cleaned to the level necessary for ultrasonic or magnetic particle inspection. A modest uniform scale will still produce excellent results.

The Waterwall array probe uses no couplant and can detect small defects and defect areas that can be difficult to identify with other inspection methods.

Power station re-heater pipes

U9 AMIGO instrument

Standard ACFM weld probe 5KHz

Straight mini probe 45KHz

Right angle mini probe 5KHz

Right angle transverse mini probe 45KHz         

During a routine annual shutdown, ACFM inspection was carried out on pre-selected circumferential pipe welds and pipe attachment welds on main steam piping and hot reheater piping.

U19 AMIGO instrument

Standard ACFM weld probe

Micro ACFM weld probe            

ACFM Pencil probe         

Alternating Current Field Measurement (ACFM) inspection was carried out on selected internal welds in spiral casings at an ESB pump/storage power station.

Usually units are cleaned and repainted. Two units had not been prepared and had the previous paint coating and had not been cleaned. The paint coating was approximately 1mm thick. This made visual examination impossible. Due to stringent time constraints, there was no time to remove paint, inspect and reinstate, and ACFM was used to quickly assess and report on any defects under the coating. Normal inspection would be planned for a week. All work was completed with ACFM in 2 days.