Traditional HPHT Autoclave designs have been enhanced by the introduction of real-time corrosion measurement instruments and probes, to accurately reproduce the multiphase flowing field conditions of operating pipelines and industrial environments.
Corrosion Measurement - Early Practices
Shear Stress Measurement- Effect of Velocity on Corrosion- Laminar Flow Studies
Corrosion Modeling- Multiphase Studies Accelerated Pipeline Integrity
Automated Inhibitor Injection (A.I.I.)- “Feedback” Chemical Pump Control
Corrosion Measurement
For many decades’ production and pipeline operators used simple corrosion coupons as an intermittent corrosion weight loss measurement. NACE, ASTM and others made exhaustive attempts to upgrade the method, Conducting Corrosion Coupon Tests in Plant Equipment, ASTM G4-84 originating (A224-39) in 1939.
Additional test methods were developed by NACE and others, as example TM01-77-96, Laboratory Testing of Metals for Resistance to Sulfide Stress Corrosion Cracking in H2S Environments. The standard addressed “the testing of metals for resistance to cracking failure under combined action of tensile stress and corrosion in aqueous environments containing Hydrogen Sulfide (H2S)”.
Shear Stress Measurement
The 1995 NACE Publication 5A195 State Of-The-Art on Controlled Flow Laboratory Corrosion Tests was a “compilation of experimental techniques intended to provide the most up to date information available at the time on evaluating the effect of velocity on corrosion”, called Shear Stress. Included in NACE #5A195 (but not limited to) were the contents:
Interpretation of Lab Measurements
Philosophy Behind Experimental Design
Experimental Systems
References
Appendix B Governing Equations:
Rotating Disk
Rotating Cylinder
Impingement Jet
Flow-Loop System
In 1996 NACE Publication #1D196 Laboratory Test Methods for Evaluating Oilfield Corrosion Inhibitors, coupled the above NACE #5A195 with the effects of chemical inhibitor applications under multiphase flow controlled test equipment for lab simulations.
During recent decades, ER/LPR became viable techniques adapted from lab studies and applied in the form of probes and instruments developed for long-term field studies.
Modern electronic components and high speed data acquisition evolution allowed a more rapid response corrosion rate measurement to be made in real time. The new probe/instrument system could be used to make measurements not only in electrolytic, but in non-conductive gas environments as well. The rapid response Systems have been readily accepted by the corrosion community as touted in NACE Papers 1997 #288 A Critical Comparison of Corrosion Monitoring Techniques in Industrial Applications, and later in NACE 2000 #00090 Field Trial Results of a New Rapid Corrosion Monitoring System
Automated Inhibitor Injection
Complimenting the high shear and impingement measurements, new Automated Inhibitor Injection (A.I.I.) systems are in operation since 1998 using the rapid response corrosion rate output signal to determine and control the optimum inhibitor chemical dose rate using variable flow rate inhibitor chemical injection pumps.
CONCLUSION
Cost of corrosion and its associated long terms costs can be significantly reduced with properly configured laboratory HPHT simulation systems, in combination with the newest state-of-the-art A.I.I. skid installations. The initial cost of these systems is quite small compared to the potential savings in material assets, non-productive downtime, the global environment and personnel safety.
G. W. Mazurk Sr. Vice President Cortest, Inc.
www. cortest.com
