Inspection of Fired Boilers and Heaters

API RECOMMENDED PRACTICE 573 FOURTH EDITION, JANUARY 2021

Special Notes

API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed. The use of API publications is voluntary. In some cases, third parties or authorities having jurisdiction may choose to incorporate API standards by reference and may mandate compliance.

Neither API nor any of API's employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API’s employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.

API publications are published to facilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices.

Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.

All rights reserved. No part of this work may be reproduced, translated, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 200 Massachusetts Avenue, NW, Suite 1100, Washington, DC 20001.

Copyright © 2020 American Petroleum Institute

Foreword

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

The verbal forms used to express the provisions in this document are as follows.

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.

This document was produced under API standardization procedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures under which this publication was developed should be directed in writing to the Director of Standards, American Petroleum Institute, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001.

Suggested revisions are invited and should be submitted to the Standards Department, API, 200 Massachusetts Avenue, Suite 1100, Washington, DC 20001, standards@api.org.

iii

Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, and Acronyms 2

   1. Terms and Definitions 2

   2. Acronyms 8

4. Common Heater and Boiler Designs 8

   1. Types of Heaters 8

   2. Types of Boilers 13

5. Heater, Furnace, and Boiler Mechanical Reliability 19

   1. Integrity Reliability Programs 19

   2. Potential Consequences of a Tube Rupture 21

   3. Purpose of Inspection 21

   4. Inspection of Fired Boilers 21

   5. Inspection of Fired Heaters and Furnaces 22

   6. Inspector Qualifications 22

   7. Corrosion Control Documents (CCDs) 22

6. Damage Mechanisms 23

   1. Deterioration of Tubes 23

   2. Deterioration of Boiler Tubes 33

   3. Damage Mechanisms of Other Components 37

7. Frequency and Timing of Inspections. 43

   1. General 43

   2. Boiler Inspection Frequency 43

   3. Heater Inspection Frequency 43

8. Safety Precautions, Preparatory Work, and Cleaning 43

   1. Safety 43

   2. General Preparatory Work 44

   3. Precautions to Avoid PTA SCC in Stainless Steel Tubes 45

   4. Cleaning 45

9. Outage Inspection Programs 46

   1. General 46

   2. Visual Inspection of Heating Coils 46

   3. Wall Thickness Measurements 54

      v

      Contents

      Page

   4. Tube Diameter, Circumference, Sag, and Bow Measurements 55

   5. Pit Depth Measurements 58

   6. Intelligent Pigs and In-line Inspection Devices 58

   7. Radiographic Examination 60

   8. Borescope and Videoprobe 60

   9. Hardness Measurements 61

   10. Dye Penetrant and Magnetic Particle Examination 61

   11. In Situ Metallography and Replication 62

   12. Detailed Examination and Destructive Testing of Tube Samples 62

   13. Testing of Tubeskin Thermocouples. 62

   14. Magnetic Test for Carburization 63

   15. Hammer Testing 64

   16. Inspection of Steam-Methane Reformer Tubes 64

   17. Inspection of Pigtails 66

10. Boiler Outage Inspection 66

    1. General 66

    2. Piping 67

    3. Drums 67

    4. Water Headers 69

    5. Superheater Header 69

    6. Tubes 70

11. Onstream Inspection Programs 72

    1. General 72

    2. Typical Inspection Activities 72

    3. External Tube Cleaning 75

    4. Pre-shutdown Inspection 75

12. Tube Reliability Assessment 76

    1. General 76

    2. Minimum Thickness and Stress Rupture 76

    3. Creep Rupture Life 78

13. Method of Inspection for Foundations, Settings, and Other Appurtenances 78

    1. Foundations 78

    2. Structural Supports 79

       vi

       Contents

       Page

    3. Setting, Exterior, and Casing 80

    4. Refractory Linings and Insulation 80

    5. Tube Supports 82

    6. Visual Inspection of Auxiliary Equipment. 83

    7. Stacks 88

14. Repairs 91

    1. Heaters and Furnaces 91

    2. Boilers 92

    3. Materials Verification 92

15. Records and Reports 92

    1. Retention 92

    2. Contents 92

Annex A (informative) Sample Inspection Checklists for Heaters and Boilers 93

Annex B (informative) Sample Heater Inspection Records 101

Annex C (informative) Sample Stack Inspection Record 111

Annex D (informative) Parameters for Integrity Operating Windows in Fired Heaters 112

Annex E (informative) Cleaning Methods 114

Bibliography 117

Figures

1. Typical Heater Types 9

2. Box-type Heater with Horizontal Tube Coil Showing Main Components 11

3. One Type of Steam-Methane Reforming Furnace 12

4. Typical Vertical Oil or Gas-fired Water Tube Boiler 14

5. Another Variation of a Two-drum Bent Tube Boiler 15

6. Typical Carbon Monoxide Boiler 16

7. Tubular and Plate Air Preheaters 17

8. Types of Regenerative Air Preheaters 18

9. Inside Diameter (ID) of Fireside Portion of Tube Showing Severe Corrosion 25

10. Convective Tube Failure from Internal, High-temperature Sulfidic Corrosion 26

11. General Metal Loss and Pitting of Tubes Exposed to Moisture and Corrosive Deposits

    During Idle Periods 27

12. Roof Tubes Sagged as a Result of Failed Tube Hangers 28

13. Changes in Magnetic Permeability Caused by Chromium Depletion 31

14. Localized Tubing Wall Loss Caused by Caustic Gouging 34

15. Boiler Tube Showing Penetration of the Tube Wall by a Localized Oxygen Pit 35

16. Short-term Boiler Tube Failure Caused by Waterside Deposits, Subsequent Overheating,

    and Final Bulging of the Tube Wall 36

17. Longer-term Boiler Tube Failure Caused by Poor Circulation and Subsequent Overheating,

    Oxidation, and Final Failure by Stress Rupture 36

    Contents

    Page

18. Dew Point Corrosion from Flue Gas Corrosion on Radiant Section Header Box 39

19. Bulged Tube 48

20. Bulged and Split Tube 49

21. Scaled Tube 49

22. Oxidized Tube 50

23. Split Tube 50

24. External Corrosion 51

25. Fitting and Tube that Have Leaked in the Roll 51

26. Corrosion/Erosion of the Annular Space in a Streamlined Fitting 52

27. Corrosion of U-bends 53

28. Spreading and Poor Fit of a Horseshoe Holding Section 53

29. Tube Damage Caused by Mechanical Cleaning Equipment 57

30. Eccentric Corrosion of a Tube 58

31. Intelligent Pig Positioned in Short Radius 1D  180° Return Bend 59

32. Spot-type and Pit-type Corrosion 61

33. Various Magnetic Measurement Devices 63

34. Laser Profilometry Results 65

35. Interior Surface of a Tube Damaged by Operating a Tube Cleaner Too Long in One Place 71

36. Infrared Thermography Identifying a Local Hot Spot on Tubes 74

37. Infrared Thermography Identifying a Hot Coil 74

38. Sample Locations for Tell-tale Holes on Heater Tubes 75

39. Plug-type Tube Fittings 77

40. Yielding and Creep of a Tube Support Connection 82

41. Corrosion Products from Acid Condensation Plug Tubes in Air Preheater 85

42. Improper Burner Tile Installation Leads to Poor Flame Pattern 87

43. Self-supporting Steel Stack 90

1. Sample of Tube Layout Drawing 102

2. Sample of Tube Inspection History 103

3. Sample of Tube Inspection Record (Tubes Calipered) 105

4. Sample of Tube Inspection Record (Instrument Calipered) 106

5. Sample of Tube Renewal Record 108

6. Sample of Field Work and Record Sheet (Tube Rolling) 109

7. Sample Record of Heater Fitting Inspection and Replacement 110

E.1 Mechanical Decoking Pig 115

Tables

1. Common Heater Tube Metallurgies 13

2. Tube Damage Mechanisms Common to Specific Services. 23

3. Recommended Inspection and Acceptance Criteria for Damage Mechanisms 47

4. Tube Support Materials Specifications Maximum Design Temperature 83

1. Fired Heater Internal and External Inspection Checklist 94

2. Water Tube Boiler Inspection Checklist 96

3. Fire Tube Boiler Inspection Checklist 98

A.4a Fired Heater Operator Rounds Checklist (Checklist I) 99

A.4b Fired Heater Operator Rounds Checklist (Checklist II) 100

Inspection of Fired Boilers and Heaters

Scope

This recommended practice (RP) covers the inspection practices for fired boilers, process heaters, and furnaces used in petroleum refineries and petrochemical plants. The practices described in this document are focused to improve equipment reliability and plant safety. The intent is to provide inspection practices that accurately capture appropriate data, both onstream and off-stream, to assess current and future performance of the equipment.

Normative References

The following referenced documents are indispensable for the application 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 Standard 530, Calculation of Heater-tube Thickness in Petroleum Refineries

API Recommended Practice 538, Industrial Fired Boilers for General Refinery and Petrochemical Service

API Standard 560, Fired Heaters for General Refinery Services

API Recommended Practice 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry

API Recommended Practice 572, Inspection Practices for Pressure Vessels

API Recommended Practice 578, Guidelines for a Material Verification Program (MVP) for New and Existing Assets

API Standard 579-1/ASME 1 FFS-1, Fitness-For-Service

API Recommended Practice 580, Risk-Based Inspection

API Recommended Practice 584, Integrity Operating Windows

API Recommended Practice 585, Pressure Equipment Integrity Incident Investigation

API Recommended Practice 936, Refractory Installation Quality Control—Inspection and Testing Monolithic Refractory Linings and Materials

API Recommended Practice 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants

API Recommended Practice 970, Corrosion Control Documents

API Recommended Practice 939-C, Guidelines for Avoiding Sulfidation (Sulfidic) Corrosion Failures in Oil Refineries

AISC M015L 2, Manual of Steel Construction, Load and Resistance Factor Design

1

American Society of Mechanical Engineers International, Two Park Avenue, New York, New York 10016-5990,

www.asme.org.

2

American Institute of Steel Construction, 130 East Randolph, Suite 2000, Chicago, Illinois, 60601, www.aisc.org.

1