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
Key Words: Corrosion
monitoring, new, rapid technique, LPR, ER, field trial results, corrosion rate
measurement, corrosion probe, high velocity, corrosion inhibitor, chemical
inhibitor, high shear, flow loop, multiphase, jet impingement, rotating
cylinder electrode, oilfield, pipeline, pipeline integrity, rotating cylinder
autoclave, system’s design, wet gas
INTRODUCTION
This paper is
intended to update the knowledgeable reader, as well as inform the uninitiated
with a basic overview of modern corrosion testing laboratory equipment and
field instrumentation. It is only intended as a starting point and is in no way
to be construed as comprehensive.
Perusing
Internet advertising is not a substitute for rigorous investigation of
corrosion measurement equipment suppliers. Manufacturers must also be involved
in day to day scientific corrosion studies, as well as R&D toward new
products and faster results.
A catalog “bomb”
may allow an end user results found similar to those in 1939, but today’s
competitive global marketplace for produced finished products requires
real-time corrosion monitoring and control, all the way from the geological
formation up to and past the point of custody transfer.
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. Trade
named MICROCOR*, 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/Microcor 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.
Corrosion Modeling
Multiphase
Flow Regimes Simulation studies became more important around the 1960’s and
evolved (1980s to 1990s) into modern laboratory test equipment assemblies. As
example, Corrosion in Multiphase Systems Center
(Ohio University)
and Multiphase Interactive Systems & Technologies, Inc., Orlando, Florida,
built full-scale loops and tilt-up sections were brought on-line around 1993.
NACE 2000 Paper #00070 Corrosion Inhibition of Wet Gas Pipelines Under High
Gas & Liquid Velocities is a good representative case study of the use
of such systems as supported through consulting contracts, which were client
sponsored by global operators and producers.
Recently
several Universities and industry corrosion laboratories have built large scale
Multiphase Flow Loops. As example, NACE 2002 Paper No. 02502 The Design
& Development of a Large Scale, Multiphase Flow Loop for the Study of
Corrosion in Sour Gas Environments and the 9th Middle East
Corrosion Conference proceeding’s papers, including Modeling the Effects of
Multiphase Flow on Corrosion in Oil & Gas Production by Prof. P.
Jepson, bring focus to the necessity of state-of-the-art laboratory testing
equipment and components to make fast and reliable decisions and predictions
about corrosion control in multiphase operations.
Pipeline
Integrity
Another
paper presented by CC Technologies titled “Engineering Challenge of Pipeline
Integrity Management” emphasizes the importance of 1. Preserve Pipeline
Infrastructure and 2. Pipeline Integrity Management Program. In the
CCT summary is the key statement, “to maximize the cost benefit, pipeline
integrity management programs must be established that optimize monitoring and
inspection on specific pipeline conditions, which are integrated into risk
models.”
An
interesting reference work from CCT, sponsored by
U.S. D.O.T./FHA should also be
consulted, which can be easily accessed on the Internet at
www.corrosioncost.com. The 733 page
compendium,
Corrosion Cost and Preventative Strategies in the United States
presents a partial view of the global expense due to corrosion, as well as
other associated expenses which are not direct corrosion costs, but instead
management/measurement and remediation long term higher costs.
NACE
2000 Paper #00068 Oilfield Corrosion Inhibitor Under Extremely High Shear Conditions
by Nalco/Exxon Energy Chemicals emphasizes the importance of “high shear
conditions, which must be carefully modeled in lab simulations using a new Jet
Impingement test technique supported by a flow loop for accurate
experimental control.
With
the above developments came faster and easier development and evaluation of
anti-corrosion inhibitor chemicals and drag reducing agents. Other lab test
methods, such as Rotating Cylinder Electrode (RCE) as found in example NACE 2002 Papers #02286 Corrosion
Inhibitor Film Life Studies Using RCE Flow-Through Test and #02497 Reproducibility
in Rotating Cylinder Autoclave Testing of Corrosion Inhibitors also make
important points about accurate modeling and simulation of field application
operating conditions.
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 (Microcor) 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.
