# Presentation: 161383

## Todd KedzieEl Paso Corporation Manager of Laboratory Services

**Bell Hole Inspection Techniques for Assessing SCC Severity**December 2, 2003

## Introduction

- Magnetic Particle Inspection (MPI) Techniques
- SCC Depth Measurement by Grinding
- SCC Depth Measurement Technology Research

## Magnetic Particle Inspection (MPI)

- MPI is an NDE method of inspection that uses fine magnetic particles (iron) that are applied to the part, and are attracted to any magnetic-leakage field created by an imperfection, such as SCC
- Magnetic yokes are commonly used for bell hole MPI of pipelines
- Each MPI method discussed is capable of detecting SCC, depending on field and pipeline operating conditions
- No single MPI method is effective in all situations, therefore several methods must be available to choose from
- MPI can be performed at all clock positions

## Dry MPI

**Description: Dry MPI uses fine iron particles that are not suspended in a liquid. The iron particles are blown onto the pipe surface using a bulb or powder blower applicator. Iron particles are available in a variety of colors to obtain contrast with the pipe surface**

## Dry MPI

- Limitations
- Dry MPI method is not suitable for use when the pipe surface is wet (sweating, rain, etc.)
- Least sensitive method of MPI

## Wet Fluorescent MPI

**Description: Wet Fluorescent MPI uses fine iron particles that are suspended in a liquid (water or hydrocarbon). The iron particle  suspension liquid is sprayed onto the pipe surface. The iron particles fluoresce in the dark when illuminated with a black light  **

## Wet Fluorescent MPI

- Limitations
- Hydrocarbon suspension can result in a cloudy fluorescent background that can reduce the contrast between the indications and the background when inspecting coal tar coated pipelines
- Requires dark background often provided by a tarp or tent for black light use

## Wet Visible MPI

- Description: Wet visible MPI uses fine iron particles that are suspended in a liquid (water or hydrocarbon). The iron particle  suspension liquid is sprayed onto the pipe surface. The iron particles are visible, and do not require black light illumination
- Limitations
- Limited variety of colors for contrast

## Black and White Contrast MPI

- Description: Contrast MPI uses fine iron particles that are suspended in a liquid (hydrocarbon) that is sprayed onto the pipe surface. The surface of the pipe is painted prior to application of MPI in order to provide contrast with the visible iron particles
- Limitations
- Greater surface cleanliness required for white paint application
- Contrast paint may increase the clean up time

## Grinding Method to DetermineSCC Depth

- Description: The population of SCC indications are assessed, and grinding is performed on selected indications. MPI is performed, and the depth of the SCC is measured when the indication has been removed
- Limitations
- Depth is only determinedfor those indications chosenfor examination
- Grinding on loaded lines mustbe performed cautiously(see PRCI Pipeline RepairManual for additionalinformation)

## SCC Depth Measurement Research

- Description: Technologies from 16 companies were evaluated for SCC depth measurement
- Technical Challenge: Accurately measuring the deepest crack within a colony using NDE from the same side as the cracking
- 3 general types of technologies were studied
- Ultrasonic based methods
- Electromagnetic methods
- Electromagnetic acoustic transducer methods

**PR-003-9718**

## SCC Depth Measurement Research

- Techniques were evaluated with the following criteria:
- Accurate depth measurement for near-critical flaws
- Accurate depth measurement for sub-critical flaws
- Accurate discrimination of inconsequential cracks from cracks that may grow to failure though fatigue mechanism

**PR-003-9718**

## SCC Depth Measurement Research

- Results of research:
- None of the techniques completely met the goal of a simple, low cost, operator independent sizing technique
- Ultrasonic techniques were found to have the greatest potential for sizing SCC
- Most successful techniques were:
- Ultrasonic Time of Flight Diffraction (TOFD)
- Ultrasonic Phased Array. Note: This method provided a 3-dimensional examination of the cracks
- Electromagnetic methods were found to consistently under estimate the crack depths.  Improved technology, calibration methods, and cleaning procedures will be required for this method to become useful

**PR-003-9718**

## Current SCC Depth Measurement Research

- Research program:
- Application of phased array UT characterization in the field

**GRI 8122**

## Concluding Remarks

- Current bell hole inspection techniques utilize MPI and grinding to determine SCC depth, length, orientation, and clock position
- More advanced inspection methods have been evaluated, but none of these methods have proven to be capable of accurately measuring SCC depth
- Most promising technologies (phased array UT characterization) are currently being evaluated

## Todd KedzieEl Paso Corporation Manager of Laboratory Services

**Bell Hole Inspection Techniques for Assessing SCC Severity**December 2, 2003

## Slide 17