Speight Oil and Gas Corrosion Prevention

From Surface Facilities to Refineries
1. Auflage 2014
ISBN: 978-0-12-800415-9
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 150 Seiten

According to NACE (National Association of Corrosion Engineers), the total annual cost of corrosion in petroleum refining takes up $3.7 billion in the US alone. Corrosion control is always a challenge for the downstream industry, but as the quality of feedstock is declining due to refineries accepting more of the heavy and shale gas and oil resources that are more readily available today, refinery managers, petroleum and natural gas engineers are unprepared for the new set of corrosion problems that are showing up in their equipment and processing units. Oil and Gas Corrosion Prevention: From Surface Facilities to Refineries quickly gets the engineer and manager up to speed on the latest types of corrosion common for these lower grade crude oils and gases as well as the best prevention methods for all of the major sections of the refinery, especially desalting and sulfur recovery units, which are the most common problem areas for unconventional feedstocks. Also covering the unique midstream sections, or point of entry to the refinery, as well as the major critical refinery equipment, Oil and Gas Corrosion Prevention: From Surface Facilities to Refineries offers the perfect quick cross-reference for the oil and gas community. - Gets engineers and managers up to speed on the latest types of corrosion common for lower grade crude oils and gases - Provides the best prevention methods for all of the major sections of the refinery, especially desalting and sulfur recovery units - Covers additional topics such as unique midstream sections, or point of entry to the refinery, as well as major critical refinery equipment

Dr. Speight is currently editor of the journal Petroleum Science and Technology (formerly Fuel Science and Technology International) and editor of the journal EnergySources. He is recognized as a world leader in the areas of fuels characterization and development. Dr. Speight is also Adjunct Professor of Chemical and Fuels Engineering at the University of Utah.James Speight is also a Consultant, Author and Lecturer on energy and environmental issues. He has a B.Sc. degree in Chemistry and a Ph.D. in Organic Chemistry, both from University of Manchester. James has worked for various corporations and research facilities including Exxon, Alberta Research Council and the University of Manchester. With more than 45 years of experience, he has authored more than 400 publications--including over 50 books--reports and presentations, taught more than 70 courses, and is the Editor on many journals including the Founding Editor of Petroleum Science and Technology.

Autoren/Hrsg.

Speight, James G.

Leseproben

Chapter 2

Materials of Construction for Refinery Units

Metallic materials used in the manufacture of equipment for the petroleum refining industry are subjected to a wide variety of potential damage mechanisms, the most common being corrosion and environmental stress corrosion cracking. Stress corrosion cracking mechanisms are associated with wet corrosion processes, and the most common ones, affecting metals and alloys used in oil refineries, are described. Dry corrosion affects large areas of refineries and (as the name implies) does not require the presence of water. The dry corrosion process also includes oxidation, carburization, and metal dusting, but the most relevant for oil refining is attributed to the presence of sulfur, naphthenic acids, or both.

This chapter presents the issues involved in selecting the proper material for construction of refinery units that will assist in corrosion control.

Keywords

Materials selection; metals and alloys; ferritic alloys; ferrous alloys; pipes; pipelines

2.1 Introduction

To accomplish the conversion of crude oil feedstock to saleable products, a refinery is a large industrial complex with extensive piping to transport different fluids between large reactor units (Speight and Ozum, 2002; Hsu and Robinson, 2006; Gary et al., 2007; Speight, 2014). The complexity of refineries depends on the type of crude oil being processed and the type of products being manufactured. Oil refineries typically process between 100,000 and 2,000,000 barrels of crude oil per day into saleable petroleum products. Because of this high-throughput capacity, most refinery processing units are operated continuously, which makes process optimization and process control very desirable.

The relative complexity of a refinery is determined by the number and nature of the process units. Refining begins with the desalting/dewatering of the petroleum feedstock(s) followed by fractionation (distillation) into separate boiling-range fractions: the resultant products are directly related to the properties of the crude oil. Beyond the desalting operation, refineries are classified into (1) simple refineries, which include distillation, catalytic cracking, and distillate hydrotreating units, (2) complex refineries, which—in addition to the units at simple refineries—include catalytic reforming, alkylation or polymerization units, and gas processing operations, and (3) very complex refineries, which—in addition to the units found in complex refineries—include a hydrocracking unit, a coking unit, an asphalt plant, and—often—a petrochemical plant (Speight and Ozum, 2002; Hsu and Robinson, 2006; Gary et al., 2007; Speight, 2014). Each unit in the refinery is subject to common corrosion problems (Table 2.1). From the refinery, the products are transported to product distribution centers or terminals. Pipelines are used to transport petroleum to the refinery and also to transport petroleum products to the various distribution centers.

Table 2.1

Typical Refinery Units, Materials of Construction, and Operating Conditions

Desalter

Carbon steel

50

50

200

Localized pitting corrosion

Salt

Atmospheric distillation

Carbon steel, CrMo steels, 12Cr, 316 stainless steel, Monel, and 70-30 copper/nickel alloy

371

50

315

Localized pitting corrosion, and flow-induced localized corrosion

Naphthenic acid and sulfur, HCl in overhead

Vacuum distillation

Carbon steel, 9Cr1Mo steel, and austenitic stainless steel

400

10

~417

Localized pitting corrosion

Naphthenic acid, sulfur, HCl in overhead

Catalytic cracking

Carbon steel and stainless steel with refractory lining, Inconel 625, alloy 800

600

100

Intergranular SCC, graphitization, erosion

Hydrotreating

Carbon steel, CrMo steels, alloy 825, 321 stainless steel, 347 stainless steel, alloy 800, alloy 800H

670

2000

~137

SSC, SCC, hydrogen flaking, pitting corrosion

H2S, polythionic acid, and ammonium salts

Hydrodesulfurization

Carbon steel, 316L stainless steel, 405 stainless steel, alloy 825, 9CrAl, and graphitized SA 268

593

750

383

Intergranular cracking, localized pitting corrosion

H2S

Catalytic reforming

Carbon steel and 2.25Cr 1Mo steel

650

360

48

Metal dusting, carburization, and localized pitting corrosion

Chloride, ammonia, caustic

Visbreaker

Carbon steel

220

16

Coker

Carbon steel

300

20

High-temperature oxidation and sulfidation

H2S

Alkylation

Carbon steel, alloy 400, and Monel 400

188

60

100

Localized pitting corrosion

SO2 and acid (sulfuric and hydrofluoric acid)

Gas treating

Carbon steel

128

1250

10

Localized pitting corrosion

H2S, CO2, amine

Sour water stripper

Carbon steel, 316L stainless steel, alloy 825, Nialloy C-276, alloy 2205, alloy 2507 and grade 2 titanium

245

100

85

Localized pitting corrosion, erosion-corrosion

H2S, flow, and chloride

Sulfur recovery

Carbon steel, 304L stainless steel, refractory

121

16

Localized pitting corrosion

H2S

SCC, stress corrosion cracking.

Metallic materials used to manufacture equipment for the refining and gas processing industries are subjected to a wide variety of potential damage mechanisms, the most common being corrosion (Chapter 1). Safe operation of a refinery or gas processing plant depends on understanding these corrosion degradation mechanisms, making the proper material selection, devising corrosion control, creating inspection programs for early detection of problems, and monitoring material performance.

2.2 Metals and Alloys

There are many diverse applications for the stainless and heat-resistant alloys throughout the range of temperatures encountered in the refining, petrochemical, and gas processing industries (Tillack and Guthrie, 1998). A wide variety of iron- and nickel-based materials are used for pressure vessels, piping, fittings, valves, and other equipment in refineries and petrochemical plants. The most common of these is carbon steel in which the main interstitial constituent is carbon in the range of 0.12–2.0% w/w. The term may also be used in reference to steel that is not stainless steel. As the percentage of carbon increases, steel has the ability to become harder and stronger through heat treating, but this is accompanied by a lowering of the ductility along with a lower melting point and lower weldability.

Furthermore, drilling for crude oil and natural gas, as well as the production, refining, storage, and transportation inflicts corrosion on the equipment. For example, acid-bearing fluids used during drilling operations can corrode the tubing through which they flow. The presence of hydrogen sulfide, other sulfur compounds, and mineral matter can induce corrosion in pipelines either chemically or through attrition—problems that have affected many pipelines transporting crude oil and natural gas from the wellhead to refineries.

2.2.1 Metals

Metals used for unit constriction should be durable and corrosion resistant. Most refining and petrochemical processing equipment—as well as gas processing equipment—is designed and fabricated to the requirements of the American Society of Mechanical Engineers (ASME) or equivalent pressure vessel and piping codes of other countries. These codes establish the basis for and the setting of allowable stresses. Thus, the mechanical properties of a material are usually the first criteria used in the selection process. This is especially important for applications at temperatures in the creep range in which a minor difference in operating temperature can significantly affect the load-carrying ability of the material.

Without adequate corrosion resistance (or corrosion allowance), the component will fall short of the minimum design life desired. In the refining and petrochemical industries, this is typically set at 10 years or more. The additional cost usually associated with choosing increased corrosion resistance during the selection process is invariably less than that due to product contamination or lost production and high maintenance costs due to premature failure.

However, unlike mechanical properties, there are very few, if any, codes governing corrosion properties of metals. For some applications or services, recommended practices have been published by organizations such as the American Petroleum Institute and NACE International. Small variations in the composition of a process stream or in operating conditions can cause very different corrosion rates. Therefore,...