Design, Fabrication, Operational Effects, Inspection, Assessment, and Repair of Coke Drums and Peripheral Components in Delayed Coking Units

API TECHNICAL REPORT 934-G FIRST EDITION, APRIL 2016

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Foreword

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Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, and Acronyms 1

   1. Terms and Definitions 1

   2. Acronyms 3

4. Background 3

   1. General Information 3

   2. API Survey of Experience 4

   3. Degradation Mechanism(s) 8

5. Design 18

   1. General 18

   2. Design Approaches 18

   3. Materials Selection Including Plate Material, Welding Consumables, and Cladding 19

   4. Thickness Considerations 22

   5. Fatigue Design Considerations 22

   6. Skirt and Vessel Support Details 23

   7. Insulation Details (including Hot Box details) 27

   8. Tolerances for New Coke Drums 31

6. Fabrication 34

   1. General 34

   2. Weld Joint Design Details, Including Finishing 34

   3. Clad Restoration Welds 35

   4. Weld Property Requirements 35

   5. PWHT Requirements 36

   6. QA and QC Requirements 38

7. Effects of Operating Practices on Drum Reliability 40

   1. General 40

   2. Effect of Drum Cycle Time 40

   3. Quench Portion of the Operating Cycle 40

   4. Feed Injection Portion of the Operating Cycle 40

   5. Drum Preheat 41

   6. Manufacture of Fuel Grade Shot Coke 41

   7. Analyzing the Effect of Changes in Operating Practices on Drum Reliability 41

8. Inspection and Monitoring 43

   1. General Inspection Considerations 43

   2. Bulging Inspection Method 43

   3. Cracking Inspection Methods 43

   4. Frequency of Inspection 44

   5. Use of Strain Gages and Shell Temperature Measurements to Monitor Drum Damage 46

   6. Monitoring for Drum Bowing or Tilting 46

9. Condition Assessment 47

10. Repairs 47

    1. General 47

    2. Types of Coke Drum Repairs 47

       Contents

       Page

    3. Minor Shell Replacements in Coke Drums 50

    4. Major Replacements in Coke Drums 51

    5. PWHT Versus Temper Bead Welding 51

11. Peripheral Equipment 52

    1. General 52

    2. Feed Nozzle Location/Details 53

    3. Top and Bottom Unheading Design 53

    4. Foundation Bolting 55

Bibliography 56

Figures

1. Typical Drum Heating and Cooling Cycle 4

2. Correlation Between Drum Shell Thickness and D/t Ratio and Time to Bulging 7

3. Overview of Coke Drum Thermal Cycling Damage 9

4. Early 1960s Photo Showing Typical Bulging Observed in Drums Used in Delayed Coking Units 11

5. Circumferential Weld Crack Between the Nickel-based Restoration Weld and 12Cr Cladding 12

6. Typical Cracking Observed at Skirt-to-Bottom Head Weld 12

7. Keyhole Skirt-to-Bottom Head Weld Cracks 13

8. Coke Drum Bottom Cone Cracks 13

9a Internal Surface Bulge Cracks 14

9b External Surface Bulge Cracks 14

1. Bowed Drum in a Delayed Coking Unit 15

2. Corrosion of 12Cr Cladding in a Coke Drum Upper Section 17

3. A Typical Sectional Plate Layout Used to Minimize Plate Strength and Thickness Mismatch 20

4. Typical Skirt-to-Shell Fillet Weld Detail Used in Earlier Drum Construction 24

5. Skirt-to-Shell Detail of a Modified Fillet Weld with an Internal

   Weld Crotch Radius to Reduce Stress at the Weld 24

6. Forged Skirt-to-Shell Attachment Detail Removes Welds from High Stress Areas 25

7. Skirt-to-Shell Attachment Weld is Moved Up On the Shell From the Tangent Line to Remove

   the Weld From the High Stress Area 25

8. Typical Details for Coke Drum Skirt Keyholes 26

9. General Details for the Insulation System on Drums in Coking Units 28

10. Insulation Support System with Pins/studs Welded to the Shell, Heads, and Cones 29

11. Insulation Support System with Clips Welded to the Shell With Segmented Rings Connected

    to the Clips by Bolts 29

12. Insulation Support System with Clips Welded to the Shell Supporting Floating Rings 30

13. Insulation Support System with Bird Cage Type Supports with a Floating Ring 31

14. Typical “Hot Box” Insulation Details at the Shell-to-Skirt Connection 32

15. Typical Tolerances Specified for Drums in Coking Units 33

16. WRC Bulletin PWHT Heating and Insulating Details 38

Tables

1. Factors Used in Evaluating the Change in a Coke Drum Operating Cycle Time 42

2. Typical Onstream and Downtime Inspection Techniques

and Frequencies for Coke Drums 45

Design, Fabrication, Operational Effects, Inspection, Assessment, and Repair of Coke Drums and Peripheral Components in Delayed Coking Units

1. Scope

   This technical report includes information and guidance on the practices used by industry practitioners on the design, fabrication, operation, inspection, assessment and repair of coke drums and peripheral components in delayed coking units. The guidance is general and does not reflect specific details associated with a design offered by licensors of delayed coking technology, or inspection tools, operating devices/components, repairs techniques, and/or engineering assessments offered by contractors. For details associated with the design offered by a licensor or services provided by contractors, the licensor or contractor should be consulted for guidance and recommendations for their design details and operating guidance. This document is a technical report and as such, provides generally used practices in industry and is not an API Recommended Practice for coke drums in delayed coking units.

   
   

2. Normative References

   No other document is identified as indispensable or required for the application of this technical report. A list of documents associated with API 934-G are included in the bibliography.

   
   

3. Terms, Definitions, and Acronyms

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

3.1 Terms and Definitions

For the purpose of this technical report, the following definitions apply.

3.1.1

ASME Code

ASME Boiler and Pressure Vessel Code, Section II, Parts A though D, Section V, Section VIII, Division 1 and Division 2, and Section IX, including applicable addenda and Code Cases.

3.1.2

final PWHT

The last post weld heat treatment (PWHT) after fabrication of the vessel and prior to placing the vessel in service.

3.1.3

fracture ductility

The term used to define the limiting ductility before fracture occurs as a result of low cycle fatigue as modeled using the Coffin-Manson equation. It is typically defined as follows:

fracture ductility = ln(100/(100 – RA)

where

RA is reduction in area during a tensile test.

1