The prevention and early detection of corrosion is far more cost-effective than conducting repairs after the damage is done. Corrosion monitoring sensors and non-destructive testing (NDT) technologies simplify the process of combating corrosive conditions. Selecting corrosion-resistant materials further minimizes the risks and costs.
Online, real-time visibility into general corrosion, localized (pitting) corrosion, and conductivity allows for better planning of maintenance and process changes than traditional, coupon-based corrosion monitoring, which establishes an average corrosion rate over time. The CorrTran MV corrosion monitor from Pepperl+Fuchs measures general and localized corrosion rates in real time using enhanced linear polarization resistance (LPR) and electrochemical noise (ECN) techniques.
“LPR and ECN measurements allow the corrosion engineer to optimize additions of corrosion inhibitors in the water treatment system,” says Michael McElroy, corrosion technology manager for Pepperl+Fuchs (www.pepperl-fuchs.us). “Typically, inhibitors are added to keep the general corrosion rates in the range of 2-4 MPY and pitting index less than 0.2 for carbon steel pipes and vessels.”
Southwest Research Institute offers a sensor that monitors corrosion under insulation (CUI) using a potentiometric technique. “CUI accounts for 40% to 60% of piping maintenance costs and significant plant downtime,” says James F. Dante, manager of the environmental performance of materials for Southwest Research Institute (www.swri.org). “We have developed a low-power, wireless Wi-Fi sensor to monitor wetness and corrosivity under insulation that can replace tedious manual inspections and find corrosion before leaks occur.”
A new pipeline corrosion sensor developed by Southwest Research Institute is currently being tested. The Mobile Sensor is a small, durable sphere that rolls down a pipeline with the fluid stream, and along the way it monitors various operating characteristics and identifies potential corrosion conditions. The Institute is currently in a joint development venture to bring this sensor to market.
Assessment and testing
Corrosion inspection service providers rely on a range of assessment techniques. Corrosion Monitoring Services (http://cmsinc.us/) relies on air testing, acoustic eye testing, and visual inspection methods to identify damage caused by corrosion in tubular air heaters. The result is a cross-sectional picture of the entire air heater, with all areas of tube damage pinpointed.
Based on acoustic pulse reflectometry (APR) technology, the acoustic eye is a non-invasive virtual probe that can test a tube in seconds from a single point outside the tube. “The acoustic eye testing method allows CMS to inspect the inside of a tube to identify flaws that could ruin the efficiency of the unit,” says Ronald Preston, executive vice president for CMS.
SGS PfiNDE (http://pfinde.us/) uses non-destructive evaluation (NDE) methods in its pipeline integrity inspections. More than 80% of its in-trench assessments of anomalies at pipeline integrity digs involve outside diameter (OD) corrosion, explains Mike Redmond, director of industrial services for SGS PfiNDE.
“We constantly assess new technologies and have been looking for a fast, accurate, and repeatable inspection technology for OD corrosion and dents. We have determined that the Creaform (www.creaform3d.com) Pipecheck solution with the Handyscan3D scanner offers all of this, plus an order of magnitude reduction in assessment time. We feel it is a replacement technology for traditional pit gauging and mechanical measurement,” says Redmond.
Creaform’s code-compliant Pipecheck solution is an NDT method for conducting external corrosion and mechanical damage analysis on pipelines. It is comprised of a Handyscan 3D portable laser scanner, which is self-positioned to the pipe, and Pipecheck data acquisition/analysis software, which generates real-time, on-site findings.
“The 3D laser scanner can easily be deployed to acquire 100% of the damaged area with accuracy up to 0.0016 in. The software allows a quick and complete analysis in-situ to accelerate decision making on repairs,” says Pierre-Hugues Allard, engineer for Creaform.
Combating corrosion during the engineering design phase involves choosing the right materials for the application. ATI Wah Chang (www.atimetals.com) researches and manufactures corrosion-resistant specialty metals, both reactive and refractory, for a range of industries. For example, ATI OmegaBond Tubing uses a metallurgical bond to prevent corrosive solutions from leaking between its zirconium inner tube and titanium outer tube layers. This tubing is suitable for several chemical processing applications.
“While corrosion monitoring enables you to detect metal degradation early enough to avoid unscheduled downtime or unforeseen equipment failure, choosing the optimum corrosion-resistant alloys initially can minimize or eliminate the occurrence of corrosion itself,” says Richard Sutherlin, a manager of technical services at ATI.