Safe Operation of Hydrofluoric Acid Alkylation Units

API RECOMMENDED PRACTICE 751 FIFTH EDITION, AUGUST 2021

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Copyright © 2021 American Petroleum Institute

Foreword

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Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the standard.

Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in order to conform to the standard.

May: As used in a standard, “may” denotes a course of action permissible within the limits of a standard. Can: As used in a standard, “can” denotes a statement of possibility or capability.

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Contents

Page

1. Scope and Purpose 1

2. Normative References 1

3. Terms, Definitions, Acronyms, Abbreviations, and Symbols 1

   1. Terms and Definitions 1

   2. Acronyms, Abbreviations, and Symbols 12

4. Hazards Management 16

   1. Process Hazards Management Plan 16

   2. API 751 Audits 21

   3. Environmental Impact 22

   4. Lifting Over In-service Equipment 22

   5. Incident Review 22

   6. Security 23

   7. Safety Systems 23

5. Operating Procedures and Worker Protection 24

   1. General 24

   2. Health Hazard Information 24

   3. Plant Operations 25

   4. Laboratory Safety 30

   5. Training 31

   6. PPE and Clothing 32

   7. Safety Showers and Eyewash Stations 35

   8. Controlled Access to the HF Alkylation Unit 35

   9. Medical Response to HF Exposure 35

6. Materials, Fabrication, Inspection, and Maintenance Practices 36

   1. Common Discussion about Section 6 36

   2. Materials of Construction 39

   3. Specifications, Fabrication, and Repair 45

   4. Inspection Programs 50

   5. HF Service Equipment and Components 57

   6. Maintenance and Related Work Practices 73

7. Transportation and Inventory Control 76

   1. Refiner/Shipper Cooperation 76

   2. HF Unloading 78

8. Pressure-relief, Product Treatment, and Utility Systems 79

   1. Pressure-relief and Flare Systems 79

   2. Product Treatment and Neutralization of Byproducts 80

   3. Utility Systems 82

9. Risk Mitigation-Options and Techniques 83

   1. Background 83

   2. Mitigation Systems 84

   3. Risk Assessment Approach, Scenario Selection, and Evaluation 84

   4. Detection Systems 86

   5. Water Mitigation Systems 87

   6. Mitigation Systems that Limit Event Duration 88

   7. Passive Mitigation Systems 89

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Contents

Page

Annex A (informative) PHA Scenarios for Consideration 90

Annex B (informative) An Approach for Toxic Refuge Facility Siting 99

Annex C (informative) Elements of a Comprehensive Audit 105

Annex D (informative) HF Exposure Limitations and Guidance Criteria 108

Annex E (informative) An Approach for HF Leak Tracking and Management 112

Annex F (informative) Examples of Tasks for Each Clothing Class 118

Annex G (informative) Corrosion and Materials Considerations Specific to HF Alkylation 119

Annex H (informative) Inspection Considerations Specific to HF Alkylation 147

Annex I (informative) Procedures for Unloading HF Acid Tank Trucks 150

Annex J (informative) LPG Treater Systems—Safety Interlocks 153

Annex K (informative) Design Considerations for Assessment and Mitigation Options 156

Bibliography 171

Figures

1. Facility Siting Concepts 99

2. Center Line Concentration and Toxic Refuge Protection 100

3. Potential Hazard Zone 100

1. Examples of Category 1 Leaks 113

2. Example of Category 2 Leak 114

3. Example of Category 3 Leak 115

G.1 Corrosion Zone Diagram 146

1. Field HF Water Spray Study Base Case Downflow 162

2. Example Water Curtain 164

3. Example Water Wall 165

4. Example Aim-and-Shoot Water Mitigation System 166

5. Example Equipment Deluge System 167

Tables

1. Minimum Requirements of the Four Classes of PPE for Planned Work Activity 33

2. Types of Testing Typically Recommended for Cast Valves 42

3. Piping and Pressure Vessel Maximum Inspection Intervals 54

A.1 PHA Scenarios for Consideration 90

1. Occupational Exposure Limitation 108

2. AIHA™ Emergency Response Planning Guidelines (ERPG™) in ppma 109

3. Acute Exposure Guideline Levels (AEGLs) for HF, in ppma 109

4. Probit Constants 111

G.1 Typical IOW Parameters for HF Alkylation Units 140

K.1 Considerations for HF Sensors in Wide Use as of This Publication 159

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Safe Operation of Hydrofluoric Acid Alkylation Units

Scope and Purpose

API 751 provides requirements (shall) and recommendations (should) for practices and procedures related to safety, operations, design, inspection, and maintenance to support the safe and reliable operation of Hydrofluoric acid (HF) alkylation units. Topics include hazard management; operating procedures and worker protection; materials, construction, inspection, and work practices; transportation and inventory control; pressure-relief, product treatment, and utility systems; and risk mitigation. This document contains requirements and recommendations that have been found effective based on broad industry acceptance, proven effective industry practices, testing, and regulatory requirements.

Normative References

The following documents are referred to in the text in such a way that some or all of their content constitutes the requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

API 510, Pressure Vessel Inspection Code: In-Service Rating, Repair, and Alteration

API 570, Piping Inspection Code: In-service Inspection, Rating, Repair, and Alteration of Piping Systems

API Standard 653, Tank Inspection, Repair, Alteration, and Reconstruction

NOTE Whenever API standards are referenced, where equivalent national standards exist, they may be used in accordance with other applicable regulations for non-U.S. jurisdictions.

Terms, Definitions, Acronyms, Abbreviations, and Symbols

3.1 Terms and Definitions

For the purposes of this document, the following definitions apply.

3.1.1

acid detecting paint

Acid detecting paint is a durable, industrial coating with a unique acid-sensitive component, which changes color (e.g. golden yellow to brilliant red) when exposed to an acid or acid vapor of pH 3 or lower. (Also known as “acid indicating paint.”)

3.1.2

acid relief neutralizer ARN

This system is where the flow from acid-containing relief valves is routed to allow the acid to be neutralized before being routed to the non-acid flare system. Vapor flow is typically routed to the general refinery flare header once neutralized. This can refer to a flare gas scrubber (FGS), a relief gas scrubber (RGS), or an acid relief neutralizer (ARN).

3.1.3

acid soluble oil ASO

Typically seen as the waste stream created by secondary or side reactions in the presence of feed contaminants or unfavorable reaction conditions. Ranges from light to heavy material and will vary depending upon reaction conditions. This byproduct may be referred to as polymer.

1