Corrosion Problems and their Solutions in the Oil Refining Industry.

Alec Groysman

Oil Refineries Ltd., POBox 4, Haifa,31000, Israel E-mail: [email protected] Phone: 972-4-8788623; Fax: 972-4-8788371

Abstract. Many corrosion problems have occurred with related ecological damage, during the 90 years of the existence of the oil refining industry. Many corrosion problems have been solved. Some of them have not. Why? Sometimes corrosion damages occur at certain facilities, but nor at others. There are many corrosion experts, institutes and laboratories, corrosion magazines, books, standards, and conferences, etc. A lot of companies manufacture different materials and equipment for corrosion control. In spite of this, corrosion problems remain the main danger to the oil refining industry and to ecology. The aim of this work is to survey the corrosion situation at Oil Refineries LTD. Israel, during the past three years, in order to estimate cost of corrosion; to define the reasons for corrosion problems and to find effective measures to solve them, and, as a result, to improve reliability, availability and profitability at the refinery facilities. Every industry, even every plant, has its own distribution of corrosion phenomena that occur with different frequency. Even this distribution changes every year. The present corrosion survey gives estimation of direct corrosion loss at the facilities at Oil Refineries. Real examples of distribution of corrosion damages that occurred during the last three years as well as the solutions of their prevention in the future are given. Corrosion cases are classified according to corrosion forms. The distribution of corrosion forms changes every year. About 75% of all corrosion failures happened because of insufficient information and knowledge, as well as inadequate interaction among different groups responsible for the acceptance and approval of anti-corrosion decisions. The human factor was the main reason of corrosion failures. Corrosion management must be designed in such a manner that will increase human potential in performance of correct decisions. Examples of wrong use of corrosion control measures, such as corrosion inhibitors` type and their concentrations, alloys, coats, and technological regimes are given. Insufficient, or sometimes lack of use of corrosion monitoring methods result in a non-controlling corrosion situation. Indirect cost of corrosion is connected with the ecological impact on the environment, loss of expensive chemicals, a contamination of technological streams by corrosion products, loss of efficiency, overdesign and shutdowns. The corrosion risk is connected with environmental pollution by hazardous chemicals, fuels, and gases, resulting in possible fires and explosions, damage to people, animals, plants, air, soil and water. The causes of corrosion damage of aboveground storage tanks, pipes, heat exchangers, and other equipment, as well as preventative measures are analyzed. Most of the corrosion cost can be saved by means of correct use of existent corrosion control measures, dissemination of information and knowledge, and wide use of corrosion monitoring techniques. A model of interconnections of all groups at the Oil Refineries with the aim to diminish corrosion risk was suggested.

Keywords: corrosion problems, control, monitoring, anti-corrosion management.

1 Introduction.

The Oil Refining industry exists for about 90 years. All types of corrosion phenomena known to corrosion experts, plus some specific problems (such as naphthenic acid corrosion), were found at the Units of the Oil Refineries. Many corrosion problems have been solved [1]. Some of them have not. Why? Sometimes corrosion damages occur at certain facilities, but not at others. There are many corrosion experts, institutes and laboratories, corrosion magazines, books, standards, and conferences, such as ours, etc. A lot of companies manufacture different materials and equipment for corrosion control. In spite of this, corrosion problems remain the main danger to the oil refining industry and to ecology. The aim of this work is to survey the corrosion situation at two Oil Refineries in Israel, during the past three years, in order to estimate the cost of corrosion; to define the reasons for corrosion problems and to find effective measures to solve them, and, as a result, to improve reliability, availability and profitability at the refinery facilities. Analysis of corrosion cases. Corrosion cases registered during the last three years showed that they occurred about once a week (Table 1). Table 1. Corrosion cases in the Oil Refineries in 2001 – 2003.

Year Number of Cases 2001 52 2002 41 2003 46 How do we define a corrosion case? It is any failure that occurred because one of the following corrosion phenomena: general corrosion, pitting, crevice, galvanic, under deposit corrosion, intergranular, SCC (stress corrosion cracking), MIC (microbiologically induced corrosion), dezincification, erosion-corrosion, cavitation, caustic embrittlement, corrosion fatigue, stray current corrosion, overheating, corrosion under thermal insulation, and dew point corrosion. Failure of one of the corrosion control measures such as incorrect use of protective coatings or corrosion inhibitors, is also considered corrosion case. Estimation of the direct corrosion cost gave the value of about 1 million dollars per year. We analyzed the reasons in every corrosion case (Table 2).

Table 2. Human factor in corrosion failures in 2001 - 2003.

Factor 2001 20022003 Number of cases 52 41 46 Human factor (general) 44 30 33 Lack of awareness and knowledge 13 2 15 Lack of control and supervision 10 14 8 Unwillingness to improve 13 8 6 Incorrect operation 4 2 3 Incorrect design 4 3 1 Human error 1 Un-known 2 2

2 About 75% of all corrosion failures happened because of insufficient information and knowledge. So, the human factor was the main reason for corrosion failures. The human factor was divided into the lack of awareness and knowledge, insufficient control and supervision, unwillingness to improve the situation, wrong operation and design. Corrosion management must be designed in such a manner that it will increase the human potential in performance of correct decisions. Every industry, every plant, has its own distribution of corrosion phenomena that occur with different frequency. This distribution changes every year at one enterprise. We classified real corrosion cases occurring during the last three years according to corrosion forms (Table 3).

Table 3. Different types of corrosion in the Oil Refineries.

2001 2002 2003 Type of Corrosion Number % Number % Number % General Corrosion 4 7.7 14 34.1 14 30.4 Pitting Corrosion 13 25 10 24.4 6 13.0 Erosion - Cavitation 3 5.8 5 12.2 5 10.9 Failure of Coatings and Polymers 4 7.7 3 7.3 5 10.9 Stress Corrosion Cracking 4 7.7 0 0 4 8.7 Plugging (Formation of Deposits) 0 0 0 0 4 8.7 Un-known Failures 7 13.5 2 4.9 2 4.3 Dezincification 0 0 0 0 2 4.3 Caustic Embrittlement 1 1.9 0 0 1 2.2 Under Deposit Corrosion 2 3.8 1 2.4 1 2.2 Dew Point Corrosion 2 3.8 0 0 1 2.2 Microbiologically Induced Corrosion 2 3.8 0 0 1 2.2 Mechanical Failures 3 5.8 1 2.4 0 0 Galvanic Corrosion 1 1.9 2 4.9 0 0 Corrosion because of Water Stagnation 0 0 2 4.9 0 0 Over - Heating Corrosion 0 0 1 2.4 0 0 Corrosion Fatigue 3 5.8 0 0 0 0 Stray Current Corrosion 2 3.8 0 0 0 0 Chemical Cleaning Corrosion 1 1.9 0 0 0 0 Total 52 100 41 100 46 100

The distribution of corrosion forms changes every year. The first three forms of corrosion failures, namely, general corrosion, pitting, and erosion – cavitation constitute about 60% of the 50 cases reported. We can emphasize that the frequency of general corrosion (30%) and pitting (13 to 25%) is indicative of most industries in general (for example, the chemical industry [2]) and is not limited to the Oil Refining industry alone. I have to mention the failures of coatings and polymers (about 11% of cases) and stress corrosion cracking (8%). Many structures at the Oil Refineries are coated, and polymers are used in the aboveground storage tanks with different media: petroleum distillates, aromatic solvents and oxygenates (MTBE –Methyl-Tert-Butyl-Ether). There is no ideal polymer which is resistant to all media. Stress corrosion cracking relates to the usage of austenitic stainless steels as a material of construction for many highly corrosive applications in the Oil Refining industry [3].

3 Examples of corrosion failures.

Here are several examples of correct and incorrect use of corrosion control measures, such as use of alloys, coating systems, and technological regime. 1. General corrosion of the bed for the catalyst and pipe in the stripper column at the Continuous Catalytic Reforming Unit (Figire 1).

Figure 1. The carbon steel bed for the catalyst and pipe in the stripper column at the Continuous Catalytic Reforming Unit

The medium was the 1% aqueous soda solution containing 1000 ppm of chlorides and 6 ppm of iron. Severe corrosion of carbon steel internals occurred after 8 years of operation. Laboratory examination of corrosiveness of this medium showed corrosion rate of 1 mm/year for carbon steel. It was found that some kinds of Duplex steels, high molybdenum stainless steel and Monel, were resistant to the corrosive medium in the stripper. The human factor was responsible in this case, because carbon steel was wrongly chosen as the material of construction at the project stage. 2. General corrosion and incorrect use of material – corrosion of heat exchanger tubes made of carbon steel after 8 years of operation (Figure 2).

Figure 2. Heat exchanger tubes. Inside of tubes – FeS.

Inside of the tubes there was crude oil, outside – vacuum bottom. The temperature varied from 280 to 320oC. Sulfur content in crude oil varied from 4.3 to 5.6%. It is well known that carbon steel is not resistant to high sulfur (above 1% weight) crude oil and vacuum bottom at temperatures above 290oC. Insufficient control (that is, the human factor) at the stage of the manufacture of carbon steel heat exchanger tubes was the reason for this corrosion failure. The correct decision is to use a low alloy steel containing 5% Cr. 3. The wrong design of the condenser made of the Admiralty brass at the Hydrodesulfurizer unit (Figure 3). This condenser was intended for cooling of gasoline at 160oC to a lower

4 temperature using water at 30oC. Water boiled in the tubes in the area of the contact with hot gasoline at 160oC and resulted in two phenomena: dezincification and erosion – cavitation of the Admiralty brass tubes. The correct way is to install an air cooler before the condenser for cooling of gasoline from 160oC to 80oC.

Figure 3. Admiralty brass (CDA 443) tubes after failure.

Corrosion monitoring methods at the Oil Refineries Units. Many problems of correct use of corrosion control measures (for example, injection of chemicals such as inhibitors, neutralizers, biocides and others) may be solved by means of corrosion monitoring methods [4 – 6]. Here are two examples, how we use corrosion monitoring at the process units and in the cooling water system. Figure 4 shows the atmospheric distillation column with air cooler and condensers (overhead).

Figure 4. Corrosion monitoring at the overhead of the atmospheric distillation column. Schematic of setting of corrosion probes.

Hydrocarbons containing water vapors, hydrogen chloride and hydrogen sulfide, leave the distillation column at 130oC. This mixture becomes very corrosive when cooled below the dew point temperature of 100oC. In order to prevent high acidic corrosion in air cooler and condensers, neutralizers and corrosion inhibitor are injected in the overhead of the distillation

5 column. Weight loss coupons and electrical resistance (ER) probes are installed in many places and OM –On-line Monitoring by means of ER-probes. They are also installed in the naphtha pump-around and kero pump-around lines. The electrical resistance probes show the corrosion situation continuously. We change the weight loss coupons every several months, in order to compare with the results of the ER-probes and to examine the danger of chloride attack (pitting corrosion). This is very important, and the more points in the unit that are included for corrosion monitoring, the fuller is the corrosion coverage we receive. Figure 5 shows typical on-line data – dial reading of the ER-probes with time in one of the condensers in the overhead of the distillation column.

Figure 5. Dial Reading ER-probe vs Time.

Every engineer can receive such a picture on the screen of his computer. The sudden rise of corrosion rate of carbon steel is analyzed for every period. The acceptable corrosion rate of 5 mpy (0.11 mm/year) for carbon steel is defined for our units. Therefore any increase above 5 mpy is analyzed and the causes are determined. There were two short periods when the corrosion rate increased above 5 mpy. Insufficient injection of neutralizer was the reason of a sudden increase of corrosion rate of carbon steel. So, we can monitor the anti-corrosion program and as a result the corrosion situation in the overhead of the distillation column. The average corrosion rate for any period can be compared with the results received by means of the weight loss coupons (Figure 6). Usually we receive good correlation between these two methods.

Figure 6. Average corrosion rate with ER-probe (0.037 mm/year) and weight loss coupons (0.025 mm/year).

6 Corrosion and deposit monitoring in the cooling water system.

Three main problems exist in every cooling water system in the Oil Refining Industry: corrosion, inorganic deposits containing carbonate scale, corrosion products of iron, phosphates, silicates and some others, and biofouling. Two on-line corrosion and deposit monitoring systems are used in cooling water at our Refinery. Such systems allow monitoring the general corrosion of carbon steel (or any other alloy) at ambient temperature (non-heated steel surface) and at the drop temperature in the heat exchanger (heated steel surface), pitting tendency also for heated and non-heated surface, and heat transfer resistance – the quantitative value of inorganic and organic deposits (fouling). General corrosion rate is defined by means of the LPR (Linear Polarization Resistance) method, and the pitting tendency is based on the Electrochemical Noise Measurements (ENM). The typical change of Heat Transfer Resistance versus Time is presentedat Figure 7. One can calculate the cleaning factor according to these data. The drawback of these data is that general fouling is measured: total sum of inorganic and organic deposits.

Heat Transfer Resistance vs Time DATS data

0.4 0.38 0.36 0.34 /KW 2 0.32

Cm 0.3 o 0.28 0.26 x1000, 0.24

Heat Transfer Resistance, Resistance, Transfer Heat 0.22 0.2 27/09/99 17/10/99 06/11/99 26/11/99 16/12/99 05/01/00 25/01/00 14/02/00

Figure 7. Heat Transfer Resitance vs Time (DATS – Deposit Accumulation System data).

Fugure 8 presents the dial reading data of general corrosion by LPR corrosometers and pitting tendency by ENM. So, on-line corrosion information is received continuously.

On-line Corrosion Rate of Mild Steel vs Time

0.3 0.25 0.2 0.15 0.1 0.05 Corr. Rate, mpy Rate, Corr. 0 27/09/99 17/10/99 06/11/99 26/11/99 16/12/99 05/01/00 25/01/00 14/02/00

Heat Surface Corr. Rate Nonheat Surface Corr. Rate Heat Surface Pitting Tendency Nonheat Surface Pitting Tendency Linear (Nonheat Surface Corr. Rate) Linear (Nonheat Surface Pitting Tende Linear (Heat Surface Pitting Tendency) Linear (Heat Surface Corr. Rate)

Figure 8. On-line corrosion rate of mild steel (general corrosion and pitting tendency) in cooling water vs Time.

7 Anti-corrosion management at the Oil Refineries.

We suggest the foolowing scheme of anti-corrosion management at the Oil Refineries (Figure 9).

Supervision at the Economical Benefit of

design stage for estimation of usage of

suitability of material corrosion losses corrosion

choice, protective supervision

measures and methods s corrosion control

Direct Indirect

Avoidable Unavoidable

Developing of Protection Material

procedures, of control

specifications, equipment during

standards for during purchasing.

corrosion storage.

prevention,

control and Insurance in corrosion supervision: damage.

1. Standard for coatings. 2. Cathodic protection. 3. Corrosion under thermal insulation.

Criteria search for penalty and prize for anti-corrosive management.

Computerized library Dissemination

of corrosion failures of information

with analysis and and

solutions. knowledge.

Figure 9. Anti-Corrosion Management.

Such scheme is useful for all industries. Supervision at the design stage for suitability of material choice, protective measures and corrosion control must be carried out. We have to estimate the cost of corrosion in every case, in every corrosion event. Corrosion losses are included in the price of petroleum distillates and all fuels. We have to differentiate and to analyse direct and indirect, avoidable and unavoidable corrosion losses. We developed and continue to develop the procedures, specifications and standards for corrosion prevention, control and supervision. Some of them were introduced into practice. For example, a standard of coating systems for the protection of structures and equipment at the Oil Refineries.

8 Every two years we revise these systems after analysis of experience and new data of study of resistance of coating systems under different conditions at the Oil Refineries. Another example: cathodic protection of underground structures. This document was introduced into practice for all industrial enterprises in the Haifa area 12 years ago. Protection of equipment during storage and material control during purchasing are a very important part of anti-corrosion management. Some equipment (heat exchangers, bundles, elbows) is not used immediately after purchasing. Therefore, anticorrosion measures must be carried out for the temporary protection. We have to find criteria for penalty and prize for anti-corrosive management, computerize the library of corrosion cases, and disseminate information and knowledge. Conclusion. 1. The Chinese Taoist philosopher Lao Tzu who lived more than 2600 years ago, said: “Stop thinking, and end your problems”. We saw that human factor was responsible in 75% of corrosion failures. By the human factor we mean: the absense of awareness and knowledge, of control and supervision, wrong operation and design, and lack of a wish to improve the corrosion situation. 2. The previous French president George Pompidou said: “The problems are not solved. We live with the problems”. We live with old problems of general and pitting corrosion, erosion – cavitation, coatings failure and SCC (stress corrosion cracking). We know them well and can avoid … if we would emphasize the role of a human factor and corrosion monitoring. 3. Insufficient, or sometimes lack of use of corrosion monitoring methods result in a non- controlling corrosion situation. Periodical and on-line corrosion monitoring in the overhead of crude distillation columns and cooling water systems proved its high efficiency. Corrosion failures diminished drastically in these places. Corrosion monitoring methods are universal as they can be used in all industries. The main our task is to install corrosion monitoring systems in all critical places, in order to avoid sudden failures and to reach high reliability, availability and profitability.

References.

1. A. Groysman, Corrosion Cases, Their Analysis and Solutions in the Oil Refinery, Paper No. 335, CORROSION/95, Orlando, USA, 1995, 12 p. 2. R. J. Landrum, Fundamentals of Designing for Corrosion Control, NACE, Houston, USA1989, 352 p. 3. R. A. White, E. F. Ehmke, Materials Selection for Refineries and Associated Facilities, NACE, USA, 1991. 183 p. 4. A. Groysman, Corrosion Monitoring and Control in Refinery Process Units. Paper No. 512, CORROSION/97, New Orleans, USA, 1997, 25 p. 5. A. Groysman, Corrosion Monitoring in the Oil Refinery, Proceedings of the 13th International Corrosion Congress, 25-29 November 1996, Melbourne, Australia. 6. A. Groysman, Corrosion Monitoring in the Oil Refinery, International Conference “Corrosion in natural and industrial environments: problems and solutions” (Italy), Paper No.07, 23-25 May 1995.

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