Flange Face Corrosion

Flange Face Corrosion Detection Using Phased Array Technology

 

This technique has been developed by Mechanical Integrity, as a way to detect and measure different corrosion geometries of raised face flanges. A series of tests were performed to determine the accuracy of Phased Array ultrasonics in locating corroded areas and measuring the remaining sealing surface of raised face flanges. A blind test was performed on two flanges bolted together courtesy of Rick Jancleas of ExxonMobil. The results can be seen in below.

Recent software developments enable the corrosion to be measured directly on the data screen. The results of the tests conclude that the Phased Array approach works well for smooth flange face corrosion detection and measurement.

The system consists of computerized scanning instrument based on a laptop computer, a small scan controller, the umbilical cable and a scanner.

The TD Focus- Scan Multi-Channel Automated Inspection System provides the operator with an opportunity to scan a component or area with a phased array element or one to eight channels simultaneously.

The operating system is based on Windows-XP Software. This makes the operating system stable and immediately familiar to engineers that use computers in their daily function. The training requirement then becomes one of Ultrasonics and the application of multiple ultrasonic transducers. The phased array transducer sits on the external side or top face of the flange. This face is parallel and opposite to the sealing surface face. The transducer is placed between the boltholes, bolts, nuts, and washers.

A single, 5 MHz transducer housing and using 32 total elements is calibrated for linearity on an IIW block. The beam index increments were set from 20 deg. to 65 deg. at 0.5 degree increments, for a total of ninety (90) different beam angles introduced into the test material. The greater number of beam angles allows for better signal and image resolution.

Coverage: Having an index from 20 deg. to 65 deg. allows for sound coverage of the entire raised face of the flange, from the transition or OD diameter of the raised face, to the inside corner or ID diameter of the raised face. Different size flanges may require a variance (± 10 deg.) in these settings due to different thicknesses and surface distances required to allow beam coverage of the entire raised face area.

Sensitivity: Sensitivity is set on reflected signal amplitude criteria. The ID diameter of the raised face (ID flange corner) signal is taken to at least 50% full screen height for initial testing. The image is evaluated and more decibels may be introduced to better rectify the raised face surface of the flange. This is recommended when evaluation of the reflected signals is difficult due to complex geometries of the corroded areas.

After an image has been captured, analysis is completed by utilizing cursors in the software to measure the remaining sealing surface. Two flanges were bolted together with a gasket and sent to Mechanical Integrity for evaluation. The flanges were numbered for identification and examined using the phased array technique. Each flange was inspected between each bolt hole location (16 areas in all). The minimum depth amount of loss or corrosion that could be detected was approx. 0.020”. The results for each flange are as follows:

Flange #	Section #	PA Measurement	Actual Meas.	Difference
1	1	0.492"	0.410"	0.082"
1	2	0.457"
1	3	0.445"	0.440"	0.005"
1	4	0.518"
1	5	0.488"	0.480"	0.008"
1	6	0.528"
1	7	0.457"	0.468"	0.011"
1	8	0.417"
Flange # 1	Avg. Remaining Surface	0.475"
2	1	0.556"	0.490"	0.066"
2	2	0.461"
2	3	0.380"	0.428"	0.048"
2	4	0.481"
2	5	0.417"	0.398"	0.019"
2	6	0.397"
2	7	0.516"	0.473"	0.043"
2	8	0.540"
Flange # 2	Avg. Remaining Surface	0.468"	AVG. Diff.	0.035"