Prepared for
JOINT INDUSTRY SPONSORSHIP

Prepared by:
Dr. Russell D. Kane
Dr. Michael S. Cayard
InterCorr International, Inc.

Project No.: P004260TK
Date: MARCH 13, 2002
Revised: MAY 20, 2003

Executive Summary | Introduction | Problem | Background | Solution | Benefits
Technical Approach | Experimental Program | Program Management | Relevant Experience
Administration, Schedule, Cost and Reporting | InterCorr
Action | References| Sponsorship Fee

Executive Summary

Presented herein is a proposal prepared by InterCorr International, Inc. for a Phase II +technical investigation on "Prediction and Assessment of Ammonium Bisulfide Corrosion under Refinery Sour Water Service Conditions". This proposal has been developed in association with Shell Global Solutions (US) Inc. to address important technical needs of the petroleum refining industry which substantially impact process unit safety and reliability issues.

Many studies have been conducted that have focused mainly on empirical findings heavily relying on evaluations of operational experience. The Phase I program showed the value of more precise and quantitative data on ammonium bisulfide corrosion, and an expansion of this engineering database is proposed. These data are needed as a technical basis for improved prediction of ammonium bisulfide corrosion for use in materials selection, control of process unit operation, and assessment of chemical treatments for both sour water strippers and hydroprocessing unit applications. Furthermore, there is a major economic impact of sour water corrosion for these applications that more than justifies the sponsorship commitment and the level of funding proposed for this Phase II effort.

The Phase II program involves the following tasks:

Subtask 2.1.1 - Parametric Effects of Ammonia Partial Pressure

Subtask 2.1.2 - Parametric Effects of Temperature

Subtask 2.1.3 - Parametric Effects of Cyanide

·         Task 2.2 - Performance of Chemical Treatments in Sour Water Systems

Subtask 2.2.1 - Additional tests in ammonia-dominated environments

·         Task 2.3 - Expanded Predict-SW (Predictive software corrosion model)

This program focuses on developing corrosion data in ammonium bisulfide environments using a laboratory flow loop run under simulated service conditions focusing on the effects of velocity (flow-induced wall shear stress) on corrosion and the performance of commonly used alloys. This approach has already been shown to have substantial success in Phase I in terms of being able to simulate ammonium bisulfide environments common to sour water effluent streams. The results from Phase I are nearly complete and have already been utilized to evaluate and improve plant operations by the original sponsors. New data will be developed and the Predict-SW corrosion model extended for sponsors of the Phase II effort.

As a result of joint industry sponsorship of this program, sponsor companies will be required to pay only a small portion (<10 percent) of the total program cost. Maximum benefit is being given to the Original Sponsors that join at the start of the program. Furthermore, the results and the associated software from this program will be held in confidence among the sponsoring companies for a period of at least two years from their release to the program sponsors.

Introduction

Presented herein is a proposal prepared by InterCorr International, Inc. for a Phase II technical investigation on "Prediction and Assessment of Ammonium Bisulfide Corrosion under Refinery Sour Water Service Conditions". This proposal has been developed in association with Shell Global Solutions (US) Inc. to extend the engineering data base and corrosion model developed in the Phase I program. This work addresses important technical needs of the petroleum refining industry which substantially impact process unit safety and reliability issues.

By and large, the feedback from the sponsors of Phase I has been resoundingly positive during this program. The data development and modeling efforts in this program have provided important insights and better defined operating envelopes for refinery sour water services. InterCorr reviewed several potential topics for inclusion into the Phase II program. This revised proposal was developed based on the feedback received from the Phase I sponsor representatives.  The proposed program now includes:

·        Expansion of the database into ammonia-dominated sour water system typical of sour water strippers and some hydrotreaters,

·        Additional parametric studies on important sour water variables such as ammonia partial pressure, temperature, cyanides, and inhibition.

·        Expansion of the Predict-SW corrosion model into ammonia-dominated systems and additional functionality requested by the program sponsors.

Background

Previous Investigations

In the Phase I proposal, three major studies were cited from the literature as the basis of the initial effort. These studies are the work of Piehl [1], Damin and McCoy [2], and Scherrer et. al. [3], which helped to document the problems associated with ammonium bisulfide corrosion, limits of use (concentration and velocity) based on primarily experiential plant findings and only very limited controlled laboratory tests.

This Phase II program builds on these studies along with the pioneering Phase I investigation that rigorously simulated the chemical and flow effects intimately involved in the ammonium bisulfide corrosion mechanism found in H₂S-dominated refinery process services. The Phase I results indicated conclusively that the innovative laboratory test methodologies used to simulate sour water corrosion developed for this program are valid. This is a significant finding since, as mentioned above, there have only been very limited laboratory test data available from which to predict service experience. As a result of this situation, most of the design and corrosion control guidelines currently in use for refinery sour water systems are limited to experiential information, which is usually qualitative at best, and does not allow for inclusion of all critical parameters for optimum predictability and control.

Another import aspect of the Phase I program is that it was the first significant effort to include a major emphasis on fluid flow as a critical parameter and its representation in terms of a "wall shear stress" parameter. This parameter reflects the mechanical force produced on the inner pipe surface by the flowing media. This approach allows linkage between the laboratory conditions from the program and actual multiphase flow conditions in real sour water services irrespective of the pipe size and flow regime. The Phase I program also helped in defining the effectiveness of ammonium polysulfide and imidazoline-based inhibitors in H2S dominated sour water systems which may be of benefit in some operation cases.

Most importantly, the data from the Phase I program have identified a new parameter, not previously utilized in the generally accepted guidelines for sour water corrosion. This parameter suggests that some of the units may have gone from non-corrosive to corrosive through "process creep". This term refers to units in which the process conditions have slowly changed with time without serious consideration given to the overall magnitude of the change made and its effect on critical system parameters that impact corrosion, which can lead to unforeseen operational problems and even catastrophic failure.

Problem

As reviewed in detail in the Phase I proposal, the subject of alkaline sour water (ammonium bisulfide) corrosion in petroleum refineries over the past 25 years has been addressed in the literature [4]. However, due to the limited experimental studies in this area, there was still a need for more precise and quantitative data on ammonium bisulfide corrosion for a variety of materials under simulated service conditions. The Phase I data have now proven the ability to simulate the service environments involving H₂S-dominated conditions (pH 7 to 9) and flow characteristics found in many refinery sour water systems.

Based on sponsor review of the data and comparison with many case studies, this new information has shown to dramatically extend the knowledge base on sour water corrosion and provides a basis for optimizing service performance and reducing costs, improving safety and reducing unscheduled unit downtime. This has come from the a sound technical basis for improved prediction of ammonium bisulfide corrosion for use in materials selection, control of process unit operation, and assessment of chemical treatments, using the Phase I data.

The information gained in Phase I generally showed a trend of decreasing corrosion rate with increasing pH over the range pH 7 to 9 with other key variables held constant. This is likely due to the dominance of H₂S on the ammonium bisulfide corrosion reaction over this range of pH. However, there are some concerns that this trend could be reversed when going to still higher pH (pH 9 to 11 or higher) due to the dominance of ammonia and its influence on sulfide corrosion product complexation in these environments, as postulated by Damin and McCoy [2].  In fact, several sponsor representatives have presented case histories of severe corrosion of alloy materials in these high pH environments that could not be predicted by Phase I data in H₂S dominated environments. Therefore, there is a need to extend the Phase I database to higher pH (shown schematically in Figure 1) to cover the full range of refinery sour water system.

Figure 1 - Schematic diagram showing possible regimes of sour water corrosion; H₂Sdominated region examined in Phase I program (left); anticipated trend in ammonia-dominated region (right).

Another factor that influenced the Phase II work scope was the consolidation in the oil industry. Due to this situation some of the work proposed to be conducted in Phase I could not be performed with the available funding allocation. Additionally, there is a need to extend the sour water corrosion database into higher pH, ammonia-dominated systems found in sour water strippers and even in some hydroprocessing units where low sulfur refined products are being produced. The need to develop new data to maintain safe operations is the major driving force especially in relation to hydroprocessing operations. In the case of sour water strippers, there is an additional need for this new data that arises from the requirements to minimize unexpected unit outages that can reduce refinery throughput. In some cases, over capacity can be built-in to reduce this impact. But, in many cases, the ability to minimize excess stripping capacity by increasing throughput on demand is an equally important consideration to which this new data can be brought to bear.

Solution

InterCorr International, Inc., in collaboration with Shell Global Solution (US) Inc. proposes a Phase II joint industry sponsored program.  This program has been specifically designed to expand the Phase I engineering database into ammonia-dominated systems covering additional parametric effects while completing the Phase I task on performance of chemical treatments in sour water systems. This information will be used to expand the Predict-SW corrosion model and provide a wider basis for the assessment and control of ammonium bisulfide corrosion of a wide range of materials of construction to help attain safe and reliable operation of process units handling ammonium bisulfide environments.

Benefits

As a result of joint industry sponsorship of this program, each participating sponsor company will be required to pay only a small portion (£10 percent) of the total program cost. Furthermore, the results and the associated software from this program will be held in confidence among the sponsoring companies for a period of at least two years from their release to the program sponsors. Non-sponsor companies desiring to obtain the program results and software during this confidentiality period will have to pay a fee 50 percent higher than that paid by the Original Sponsors. This arrangement gives program sponsors maximum leveraging of their sponsorship fee. An important benefit to joining sponsors will be the immediate continuation of the work from the Phase I program without loss of continuity.

Technical Approach

The Phase II program will utilize the same experimental and analytical techniques originally developed by Shell Global Solutions (US) Inc. and extended into multiphase and inhibited system in the Phase I program. This experimental method is to define sets of test conditions that are relevant to refinery operations. Once baseline data are established, subsequent tests are used to explore the role of a specific variable in a separate set of tests. The single variable approach is being employed in this study to define the specific regions of corrosion performance for each alloy while paying close attention to conditions where large incremental changes in corrosion rate are occurring (i.e. threshold conditions).

Phase II Experimental Program

The present study will involve a series of tasks containing sets of tests developed to address specific questions related to ammonium bisulfide corrosion. A series of tasks and subtasks have been outlined below that will accomplish a planned expansion of the Phase I database.

·        Task 2.1 - Ammonia-Dominated Alkaline Sour Water Systems

Subtask 2.1.1 - Parametric Effects of Ammonia Partial Pressure

Subtask 2.1.2 - Parametric Effects of Temperature

Subtask 2.1.3 - Parametric Effects of Cyanides

·        Task 2.2 - Performance of Chemical Treatments in Sour Water Systems

Subtask 2.2.1 - Additional tests in ammonia-dominated environments

·        Task 2.3 - Expanded Predict-SW (Predictive software corrosion model)

Phase II Program - Engineering Data Development

Task 2.1 - Ammonia-Dominated Alkaline Sour Water Systems

The evaluation of NH₃-dominated alkaline sour water systems will focus on environments with moderate to high solution pH (9 to 11). These conditions are common in sour water stripper overhead applications and may also be found in some hydroprocessing units handling low sulfur hydrocarbon streams.

Subtask 2.1.1 - Parametric Effects of Ammonia Partial Pressure.  These tests will examine corrosion rates of selected alloys in NH₃‑dominated systems that have generally higher pH and much higher NH₃ partial pressure than those examined in Phase I. Conditions will range from approximately P_NH3 = 5 to 20 psia, pH = 9 to 11 and temperature of 130 F (55 C). [Note: Actual test conditions will be based on ionic modeling used so successfully in Phase I.] A total of 27 tests are anticipated involving 3 concentrations of NH₄HS and 3 velocities and 3 levels of ammonia partial pressure.  These conditions will be selected to tie into the existing Phase I data and provide maximum use of the information. Alloys to be included are carbon steel, AISI 304 or AISI 316 (based on the Phase I results), duplex alloys 2205 and 2507, AL6XN, alloy 825, alloy 625, alloy C-276 and titanium. [others possible] Actual alloys tested will be selected based on the anticipated severity of the particular conditions in each test. The higher alloy materials will be selected for evaluation in the more severe environments.

Subtask 2.1.2 - Parametric Effects of Temperature. This subtask will examine the influence of solution temperature on the corrosion rate of selected materials in combination with velocity and NH₄HS concentration in ammonia-dominated sour water systems. A total of 9 tests are estimated based on 3 NH₄HS concentrations, 3 velocities and 1 additional temperature over the 130 F used in Subtask 2.1.1. The proposed temperature to be used in Subtask 2.1.2 is 190 F. The specific alloys to be evaluated in these tests and the exact test conditions will be selected based on the initial experimental results obtained in Task 2.1.1. A total of at least six alloys will be evaluated under each test condition.

Subtask 2.1.3 - Parametric Effects of Cyanides. This subtask will examine the influence of cyanide on the corrosion rate of selected materials in combination with velocity and NH₄HS concentration. A total of 22 tests are estimated based on 2 cyanide concentrations (in addition to the base case of 0 ppm from Subtask 2.1.1), 3 NH₄HS concentrations, and 3 velocities, with an additional four  "wild card" tests to explore other effects as maybe required to fully characterize the influence of cyanide. For example, these extra tests may be used to examine the influence of temperature on corrosion in cyanide containing environments. The proposed test sequence will be to start the testing on the cyanide effects at a concentration of 50 to 100 ppm - depending on how easily this variable can be controlled. Data for zero cyanide will already be available from the previous tasks. The other cyanide level will be 500 ppm, but may be changed depending on the results from the tests performed at 100 ppm. The specific alloys to be evaluated in these tests and the exact test conditions will be selected based on the initial experimental results obtained in Task 2.1.1 A total of at least six alloys will be evaluated under each test condition.

Task 2.2 - Performance of Chemical Treatments in Sour Water Environments

Subtask 2.2.1 - Inhibition of Corrosion in Ammonia-Dominated Systems. A total of about 12 tests are anticipated based on 2 NH₄HS concentrations, 2 dosages, 3 velocities and only 1 chemical treatment (APS). The specific chemical treatment will be selected based on the requirements of the program as defined by the sponsoring companies.

Task 2.3 - Expansion of Predict-SW

The data from the Phase I program have been used to develop a sour water corrosion prediction model - Predict^®-SW.  This software tool provides quick access to data for a wide range of alloys for specific service conditions. It includes selected chemical variables relevant to sour water systems that were found to influence corrosion rates and interpolates between test conditions used in the Phase I program for matching specific plant conditions.  It also provides flow modeling capabilities so that the linear velocities used in the experimental flow loop studies can be easily related to plant flow conditions that involve single or multiphase flow regimes.

The Predict^®-SW software will be updated to incorporate the data obtained in the Phase II effort, including theprediction of corrosion rate in NH₃-dominated systems. It will also address the influence of cyanide, temperature and chemical treatments as evaluated in the context of this program.

During the development, the sponsors will review the technical basis of the software and have access to a Beta-version of the program for review and comment. At the conclusion of the Phase II program, sponsors will obtain a single user license for the Predict-SW software.

Program Management

The technical effort described in this Phase II program proposal will involve testing capabilities and technical specialists available from InterCorr International, Inc. and Shell Global Solutions (US) Inc. They will provide all experimental capabilities, technical expertise and important business functions that will include responsibilities for overall program management, contractual matters and development of and liaison with the sponsoring group.

The Program Manager for the Phase II effort will be Dr. Michael S. Cayard, President of InterCorr International, Inc. Dr. Cayard has over 13 years of experience in materials and corrosion engineering and research activities. Specifically, he has led numerous contract efforts for client companies and has served as Program Manager and/or Principal Investigator to several major joint industry sponsored programs including those in the areas of wet H₂S cracking and API funded research efforts in large-scale evaluation of these phenomena. He will be assisted by Mr. Sridhar Srinivasan, Manager of the InterCorr Software and Internet Services Division, for software programming expertise and Dr. Russell D. Kane, Founder and Senior Consultant of InterCorr, as technical advisor in the areas of corrosion simulation, testing and corrosion modeling in sour water environments. Shell has designated Mr. Richard J. Horvath, a recognized corrosion specialist in sour water corrosion who has been associated with these studies for several years as Co‑Principal Investigator for the program.

Relevant Experience

InterCorr International Inc. will conduct the experimental program described herein in association with Shell Global Solutions U.S. Combined, both companies have the unique technical expertise and the specialized laboratory and computer programming capabilities vital to the success of this multidisciplinary program.

InterCorr International, Inc.

InterCorr has a track record of successful completion of major joint industry sponsored research and engineering data development programs with specific emphasis on the needs of the petroleum industry. This includes work in the areas of wet H₂S cracking, high temperature naphthenic acid and sulfidic corrosion, and sour water corrosion. InterCorr has developed and operated sophisticated flow loop systems for simulation of petroleum service environments under conditions of high pressure, high temperature and high flow rate also involving exposure to H₂S, CO₂, crude oil and a variety of aqueous solutions.

Capabilities of Shell Global Solutions (US) Inc.

InterCorr has negotiated with Shell Global Solutions (US) Inc., which has extensive experience in ammonium bisulfide corrosion to collaborate in this program. This company has unique capabilities and technical expertise important to this program in the areas of ammonium bisulfide corrosion from the standpoint of NH₄HS chemistry, corrosion characteristics and practical plant experience. It has the necessary analytical capabilities to assess ionic equilibria using computer simulation techniques that provide the link for determining exact test loading conditions that simulate specific plant operating conditions. Their specialists have demonstrated the ability to conduct tests under sour water conditions using the required combination of analytical methods, anaerobic conditions, and range of velocities required for the program.

Program Administration, Schedule, Cost and Reporting

The program presented herein will be funded by joint industry support. Each participating sponsor company will be required to pay only a small portion (£10 percent) of the total program cost. This benefit provides substantial cost savings and leveraging of valuable corporate funds while providing access to the results from a major technical effort in sour water corrosion.

Administration

To qualify as a sponsor of the program, each company must sign a participation agreement and make timely payments of the program sponsorship fee. The greatest economic leveraging will be given to the Original Sponsors of the program that establish their participation at the beginning of the Phase II program. Sponsors that join later will be classified as Late Sponsors and will incur an additional late fee of 25 percent after the first three months of the program. This late fee will be increased to 40 percent for those Late Sponsors that join after the first 12 months of the effort.

Furthermore, the results and the associated software from this program will be held in confidence among the sponsoring companies for a period of at least two years from its release to the program sponsors. Non-sponsor companies desiring to obtain the program results and software during this confidentiality period will have to pay a fee 50 percent higher than that paid by the Original Sponsors. This arrangement gives program sponsors maximum leveraging of their sponsorship fee.

Schedule

The Phase II program is anticipated to run over a period of approximately thirty months (30)  months. This time period was selected to limit the annualized cost of the program to sponsor companies to what was believed to be an acceptable level of funding while weighing the immediate benefits of the program.

The program will be initiated when five (5) companies agree to participate. At this level Task 2.1.1 (effect of ammonia partial pressure) and 2.1.2 (temperature effects) will be completed and initial work on Task 2.3 (Predict-SW expansion) will be completed. When a total of eight (8) companies join, Tasks 2.1.3 (cyanide) will be completed along with a further update in Task 2.3 (Predict-SW). When a total of ten (10) companies join the program, the balance of the work including Task 2.2.1 (inhibitor effects) will be completed, the Predict-SW software finalized and a final report provided.

Sponsorship Fee

Please contact Dr. R.D. Kane for current participation fee structure at rkane@intercorr.com or tele: 281-444-2282

Reporting

Short quarterly status reports will be provided which describe the progress of each active subtask, highlight important results and their completion status. At the completion of each task, the data will be organized into a topical report and supporting database summarizing the results and major findings. These reports will include analysis of the data and interpretation relative to important aspects of the results. These data will be provided in both tabular and graphic form. Where possible, plots will be made showing regions of corrosion behavior using isocorrosion lines for the alloys evaluated to the extent possible from data obtained in the various tests. All program report documents will be password protected and archived on the program web site to be maintained by InterCorr for at least the duration of the program. This feature will provide ease of access to the program results to authorized sponsor company representatives.

InterCorr International, Inc.

InterCorr International, Inc., (located in Houston, Texas; formerly CLI International, Inc.) is an independent technology company that specializes in the technology needs of industry in the area of materials and corrosion research and engineering. It has three operating divisions that provide

·        Technical and research support services

·        Specialty equipment design, manufacturing and marketing

·        Corrosion and flow modeling, software development and Internet-based information services

InterCorr has over 20 years of commercial history in materials research and corrosion engineering including materials selection, evaluation of materials, coatings and treatment chemicals, corrosion, fracture and fatigue testing, failure analysis and technical consulting. It has worked with over 850 clients in 32 countries worldwide and has participated in and developed over 18 joint industry sponsored programs.

Action

We look forward to your company's participation in this exciting, new technical program that is in support of the research and engineering needs of the petroleum refining industry. If you would like to receive agreements to establish your company's sponsorship or if you would like further information, please contact the following:

Dr. Michael S. Cayard
Dr. Russell D. Kane

InterCorr International, Inc.
14503 Bammel North Houston Road, Suite 300
Houston, Texas USA 77014
 

Tele: 281-444-2282
Fax:  281-444-0246
Email: inquiries@intercorr.com

References

1.      R.L. Piehl, "Survey of Corrosion in Hydrocracker Effluent Air Coolers", Materials Performance, Vol 15 (1), January 1976, pp 15-20.

2.      D.G. Damin and J. D. McCoy, "Prevention of Corrosion in Hydrodesulfurizer Air Coolers and Condensers", Materials Performance, Vol 17 (12), December 1978, pp 23-26 (see also NACE Corrosion/78, paper # 131).

3.      C. Scherrer, M. Durrieu, and G. Jarno, "Distillate and Resid Hydroprocessing: Coping with High Concentrations of Ammonium Bisulfide in the Process Water", Materials Performance, Vol 19 (11), November 1980, pp 25-31 (see also NACE Corrosion/79, paper # 27).

4.  ASM Handbook, Volume 13, Corrosion, ASM International.