Detection and Sizing of Corrosion under Fireproofing (CUF) with Welded Wire Mesh Using MR-MWM-Array

摘要

This presentation describes a new capability for imaging of external and internal corrosion under fireproofing (CUF) in refinery vessels (and other structures such as the legs of LPG spheres and I-beam structures) without removal of fireproofing. These methods allow for inspection during normal plant operation from outside of vessels, skirts, and other structures. This presentation focusses specifically on a demonstration performed at a Saudi Aramco facility in July 2013 for the skirt region of a drum with fireproofing and wire mesh with welded vertical and horizontal segments. This welded wire mesh presents a different challenge to magnetic field based inspection technologies than non-welded wire mesh. The welded mesh is typically comprised of horizontal and vertical wire segments with spacing ranging from 4-8 inches (10-20 cm) and with welds at each of the wire segment crossing nodes. These welds create a pathway for induced eddy currents to circulate, producing a substantial contribution to the sensor response that must be removed to enable reliable corrosion (skirt wall thickness) imaging.The MR-MWM®-Array uses a novel linear drive winding construct with a linear array of solid state Magneto-Resistive (MR) sensing elements. Data is acquired simultaneously on multiple channels with the fully parallel GridStation® impedance instrument and rapidly converted into corrosion images using a HyperLattice™ based multivariate inverse method (MIM) that also removes the contribution from the wire mesh. The Hyperlattice MIM uses pre-computed databases of sensor responses to rapidly convert two dimensional maps of sensor impedance over large surface areas into skirt wall thickness and magnetic permeability images (where the remaining wall thickness provides the quantitative corrosion image and the permeability is correlated with relative stress variations in the steel). A vertical scanner was used to allow relatively rapid coverage of large surfaces. The demonstration unit provided a 9 inch (23 cm) scan path width using an 18 channel system. Systems with up to 119 channels can be configured with the new GridStation® 8200 family of fully parallel impedance instruments. This paper describes the underlying technology and the results of the field demonstrations at a Saudi Aramco facility in the Kingdom of Saudi Arabia.