Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems

API RECOMMENDED PRACTICE 932-B SECOND EDITION, MARCH 2012

ERRATA, JANUARY 2014

Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems

Downstream Segment

API RECOMMENDED PRACTICE 932-B SECOND EDITION, MARCH 2012

ERRATA, JANUARY 2014

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Copyright © 2012 American Petroleum Institute

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iii

Contents

Page

1. Scope 1

2. Normative References 2

   1. Codes and Standards 2

   2. Other References 3

3. Terms, Definitions, and Acronyms 4

   1. Terms and Definitions 4

   2. Acronyms 5

4. Background of REAC Corrosion 5

   1. History of Reactor Effluent System Corrosion Surveys 5

   2. Typical Hydroprocessing Units 6

   3. Effluent Separation Designs 8

   4. REAC System Corrosion 8

5. Strategies to Promote System Reliability 11

   1. General 11

   2. Material Selection and Design 12

   3. Establishing an Operating Envelope (Integrity Operating Window) 12

   4. Inspection Plans 13

6. Process Variables Affecting Corrosion 13

   1. Ammonium Bisulfide Concentration 13

   2. Process Conditions at the Water Dew Point 13

   3. Fluid Velocities 14

   4. Hydrogen Sulfide (H2S) Partial Pressure 15

   5. Flow Regime 16

   6. Chlorides 16

   7. Other Process Variables 17

   8. Wash Water 17

   9. Corrosion Inhibitors 20

   10. Air Cooler Fan Operations 20

   11. Process Monitoring 20

7. Materials of Construction 21

   1. General 21

   2. Material Selection Criteria 22

8. Equipment Specific Design Considerations 25

   1. Fin Fan Air Coolers 25

   2. Shell-and-Tube Trim Coolers 27

   3. Cold High-Pressure Separator (CHPS) 27

   4. Heat Exchanger or Air Cooler Upstream of REAC 28

   5. Piping & Valves 28

9. Inspection of the REAC System 32

   1. General 32

   2. Reactor Effluent Air Coolers 32

   3. Piping 35

   4. Pressure Vessels—Separators, Heat Exchanger Shells 36

10. Limitations and Recent Improvements in the Industry Knowledge Base 36

    v

    Page

    1. Experience 36

    2. Recent Joint Industry Research 37

Annex A (normative) Process Calculations and Estimates 39

Bibliography 43

Figures

1. Example Hydrotreating Unit Process Flow Diagram 7

2. Example Hydrocracking Unit Process Flow Diagram 7

3. Example Process Scheme with a CHPS 9

4. Example Process Scheme with a CHPS and CLPS 9

5. Example Process Scheme with Two Separators, a HHPS and CHPS 10

6. Example Process Scheme with Four Separators 10

7. Isocorrosion Curves for Carbon Steel at Various NH4HS Concentrations and Velocities

   through Small Orifice (0.15 in.) Coupons 14

8. Curves Showing Effect of H2S Partial Pressure on Corrosion of Carbon Steel 15

9. Relative Alloy Performance in Aqueous NH4HS Service 25

10. Illustration of a Balanced and Unbalanced Inlet Piping Configuration 31

11. Cross Section of Internal Surface of Failed REAC Outlet Nozzle 33

12. Erosion-Corrosion of Carbon Steel Piping Elbow 35

1. Estimating NH4HS Deposition Temperature from Process Stream Composition 40

2. Estimating NH4CI Deposition Temperature from Process Stream Composition 41

Tables

1. Keys to REAC Systems 2

2. Quality Parameters of Injected Wash Water 18

3. Guidelines for Monitoring Process Variables 21

4. Referenced Material Compositions 23

A.1 FC Value 42

vi

Design, Materials, Fabrication, Operation, and Inspection Guidelines for Corrosion Control in Hydroprocessing Reactor Effluent Air Cooler (REAC) Systems

1 Scope

This recommended practice (RP) provides guidance to engineering and plant personnel on equipment and piping design, material selection, fabrication, operation, and inspection practices to manage corrosion and fouling in the wet sections of hydroprocessing reactor effluent systems. The reactor effluent system includes all equipment and piping between the exchanger upstream of the wash water injection point and the cold, low-pressure separator (CLPS). The majority of these systems have an air cooler, however, some systems utilize only shell and tube heat exchangers. Reactor effluent systems are prone to fouling and corrosion by ammonium bisulfide (NH4HS) and ammonium chloride (NH4Cl) salts.

An understanding of all variables impacting corrosion and fouling in these systems is necessary to improve the reliability, safety, and environmental impact associated with them. Past attempts to define generic optimum equipment design and acceptable operating variables to minimize fouling and corrosion have had limited success due to the interdependence of the variables. Corrosion can occur at high rates and be extremely localized, making it difficult to inspect for deterioration and to accurately predict remaining life of equipment and piping. Within the refining industry, continuing equipment replacements, unplanned outages, and catastrophic incidents illustrate the current need to better understand the corrosion characteristics and provide guidance on all factors that can impact fouling and corrosion.

This RP is applicable to process streams in which NH4Cl and NH4HS salts can form and deposit in equipment and piping or dissolve in water to form aqueous solutions of these salts. Included in this practice are:

• details of deterioration mechanisms;

  
  

• methods to assess and monitor the corrosivity of systems;

  
  

• details on materials selection, design and fabrication of equipment for new and revamped processes;

  
  

• considerations in equipment repairs; and

  
  

• details of an inspection plan.

Table 1 lists key issues to REAC system performance and section reference for more detail.

Materials and corrosion specialists should be consulted for additional unit-specific interpretation and application of this document. This is especially important since new proprietary research is underway which challenges several previously held beliefs about NH4HS corrosion in the reactor effluent system. Each facility needs to establish its own safe operating envelope to assure satisfactory service. This RP helps to identify key variables necessary for monitoring and establishing the operating envelope.

Other equipment downstream of the REAC can also deteriorate from these ammonium salts. These include the recycle gas, sour gas and the H2S stripper and product fractionator overhead systems. Although these are beyond the scope of this document, plant personnel should be alert to these other locations where ammonium salt fouling and corrosion can occur.

Since the first edition of API 932-B was published in July 2004, findings from a recent joint industry sponsored research program contributed important new data on NH4HS corrosion relevant to these systems. While not all the data are in the public domain, recent publications have highlighted key data which are incorporated into this current edition of API 932-B.

1