Guidelines and Methods for Inspection of Existing Atmospheric and Low-pressure Storage Tanks

API RECOMMENDED PRACTICE 575 SECOND EDITION, MAY 2005

Guidelines and Methods for Inspection of Existing Atmospheric and Low-pressure Storage Tanks

Downstream Segment

API RECOMMENDED PRACTICE 575 SECOND EDITION, MAY 2005

SPECIAL NOTES

API publications necessarily address problems of a general nature. With respect to partic- ular circumstances, local, state, and federal laws and regulations should be reviewed.

API is not undertaking to meet the duties of employers, manufacturers, or suppliers to warn and properly train and equip their employees, and others exposed, concerning health and safety risks and precautions, nor undertaking their obligations under local, state, or fed- eral laws.

Information concerning safety and health risks and proper precautions with respect to par- ticular materials and conditions should be obtained from the employer, the manufacturer or supplier of that material, or the material safety data sheet.

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 prod- uct covered by letters patent. Neither should anything contained in the publication be con- strued as insuring anyone against liability for infringement of letters patent.

Generally, API standards are reviewed and revised, reaf?rmed, or withdrawn at least every

?ve years. Sometimes a one-time extension of up to two years will be added to this review cycle. This publication will no longer be in effect ?ve years after its publication date as an operative API standard or, where an extension has been granted, upon republication. Status of the publication can be ascertained from the API Standards department telephone (202) 682-8000. A catalog of API publications, programs and services is published annually and updated biannually by API, and available through Global Engineering Documents, 15 Inv- erness Way East, M/S C303B, Englewood, CO 80112-5776.

This document was produced under API standardization procedures that ensure appropri- ate noti?cation and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this standard or com- ments and questions concerning the procedures under which this standard was developed should be directed in writing to the Director of the Standards department, American Petro- leum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should be addressed to the Director, Business Services.

API standards are published to facilitate the broad availability of proven, sound engineer- ing and operating practices. These standards are not intended to obviate the need for apply- ing sound engineering judgment regarding when and where these standards should be utilized. The formulation and publication of API standards 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 prod- ucts do in fact conform to the applicable API standard.

All rights reserved. No part of this work may be reproduced, 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, 1220 L Street, N.W., Washington, D.C. 20005.

Copyright ? 2005 American Petroleum Institute

FOREWORD

This recommended practice is based on the accumulated knowledge and experience of engineers and inspectors in the petroleum and chemical industries.

Some of the information contained in this publication was previously presented as Chap- ter XIII of the API Guide for Inspection of Refinery Equipment, which is being reorganized as an individual recommended practice. The information in this recommended practice does not constitute and should not be construed as a code of rules, regulations, or minimum safe practices. The practices described in this publication are not intended to supplant other prac- tices that have proven satisfactory, nor is this publication intended to discourage innovation and originality in inspection. Users of this recommended practice are reminded that no book or manual is a substitute for the judgment of a responsible, quali?ed person.

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 federal, state, or municipal regulation with which this publication may con?ict.

Suggested revisions are invited and should be submitted to the standardization manager, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005, stan- dards@api.org.

IMPORTANT INFORMATION CONCERNING USE OF ASBESTOS OR ALTERNATIVE MATERIALS

Asbestos is speci?ed or referenced for certain components of the equipment described in some API standards. It has been of extreme usefulness in minimizing ?re hazards associated with petroleum processing. It has also been a universal sealing material, compatible with most re?ning ?uid services.

Certain serious adverse health effects are associated with asbestos, among them the serious and often fatal diseases of lung cancer, asbestosis, and mesothelioma (a cancer of the chest and abdominal linings). The degree of exposure to asbestos varies with the prod- uct and the work practices involved.

Consult the most recent edition of the Occupational Safety and Health Administration (OSHA), U.S. Department of Labor, Occupational Safety and Health Standard for Asbestos, Tremolite, Anthophyllite, and Actinolite, 29 Code of Federal Regulations Section 1910.1001; the U.S. Environmental Protection Agency, National Emission Standard for Asbestos, 40 Code of Federal Regulations Sections 61.140 through 61.156; and the U.S. Environmental Protection Agency (EPA) rule on labeling requirements and phased banning of asbestos products (Sections 763.160-179).

There are currently in use and under development a number of substitute materials to replace asbestos in certain applications. Manufacturers and users are encouraged to develop and use effective substitute materials that can meet the speci?cations for, and operating requirements of, the equipment to which they would apply.

SAFETY AND HEALTH INFORMATION WITH RESPECT TO PARTICULAR PRODUCTS OR MATERIALS CAN BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER OR SUPPLIER OF THAT PRODUCT OR MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.

APPENDIX A SELECTED NON-DESTRUCTIVE EXAMINATION (NDE) METHODS 61

APPENDIX B SIMILAR SERVICE EVALUATION TABLES 63

APPENDIX C SELECTED BIBLIOGRAPHY 67

Figures

1. Cone Roof Tank 5

2. Umbrella Roof Tank 5

3. Geodesic Dome Roof Tank 5

4. Self-supporting Dome Roof 6

5. Pan-type Floating-roof Tank 6

6. Annular-pontoon Floating-roof Tank 6

7. Double-deck Floating-roof Tank 6

8. Cross-section Sketches of Floating-roof Tanks Showing the Most

   Important Features 7

9. Floating-roof Shoe Seal 8

10. Floating-roof Foam Log Seal 8

11. Floating Roof Using Counterweights to Maintain Seal 9

12. Floating Roof Using Resilient Tube-type Seal 9

13. Typical Internal Floating-roof Components 10

14. Typical Arrangement for Metallic Float Internal Floating-roof Seals 11

15. Plain Breather Roof Tanks 12

16. Balloon Roof Tank 12

17. Tank with Vapor Dome Roof 13

18. Cutaway View of Vapor Dome Roof 13

19. Welded Horizontal Tank Supported on Saddles 14

20. Plain Hemispheroids 14

21. Noded Hemispheroids 14

22. Drawing of Hemispheroid 15

23. Plain Hemispheroid with Knuckle Radius 15

24. Plain Spheroid 15

25. Noded Spheroid 15

26. Drawing of Noded Spheroid 16

27. Foundation Seal 16

28. Extensive Destruction from Instantaneous Failure 18

29. Cracks in Tank Shell Plate 19

30. Cracks in Bottom Plate Welds Near the Shell-to-Bottom Joint 19

31. Cracks in Tank at Riveted Lap Joint to Tank Shell 20

32. Hypothetical Corrosion Rate Curves for Top Course of Storage Tank 23

33. Failure of Concrete Ringwall 27

34. Anchor Bolt 27

35. Corrosion of Anchor Bolts 27

36. Corrosion under Insulation 29

37. Close-up of Corrosion under Insulation 30

38. Corrosion (External) at Grade 31

39. Caustic Stress Corrosion Cracks 32

40. Small Hydrogen Blisters on Shell Interior 32

41. Large Hydrogen Blisters on Shell Interior 32

42. Tank Failure Caused by Inadequate Vacuum Venting 33

43. Roof Overpressure 34

44. Example of Severe Corrosion of Tank Roof 36

45. Deterioration of Floating-roof Seal 37

46. Collapse of Pan-type Roof from Excessive Weight of Water While the

    Roof was Resting on its Supports 38

47. Pontoon Floating-roof Failure 39

48. Tank Buggy Used for Inspection and Repairs Inside of Tank 40

49. Remote-control Automated Crawler 41

50. Example of Vapor-liquid Line Corrosion 41

51. Corrosion behind Floating-roof Seal 42

52. Localized Corrosion-erosion at Riveted Seam in a Tank Bottom 43

53. Example of Extensive Corrosion of a Tank Bottom 44

54. Shell-to-Bottom Weld Corrosion 45

55. External View of Corrosion-erosion Completely Through a Tank Shell 45

56. Deterioration of Lining on Roof of Tank Caused by Leaks in Lining 46

57. Internal Corrosion on Rafters and Roof Plates 46

58. Failure of Roof Supports 46

59. Fin-tube Type of Heaters Commonly Used in Storage Tanks 46

60. Example of Corrosion of Steam Heating Coil 47

61. Hydraulic Integrity Test Procedures 49

62. Vacuum Box Used for Testing Leaks 51

63. Vacuum Test Box Arrangement for Detection of Leaks in Vacuum Seals 51

64. Helium Tester 52

65. Method of Repairing Tank Bottoms 57

66. Temporary ?Soft Patch? over Leak in Tank Roof 58

67. Mastic Roof Coating 58

68. Tank Jacked Up for Repairing Pad 58

1. Automatic UT 62

2. MFL Scanner 62

3. UT Scrub 62

4. Robotic Inspection Tool 62

Tables

1. Tools for Tank Inspection 25

2. Tools to Be Available in Case Needed for Tank Inspection 26

1. Selected Factors for Using Similar Service Principles in Estimating

   Corrosion Rates for Tank Bottoms 64

2. Similar Service Example for Product-side Corrosion 66

vii

Guidelines and Methods for Inspection of Existing Atmospheric and Low-pressure Storage Tanks

1. Scope

   This document provides useful information and recom- mended practices for the maintenance and inspection of atmospheric and low-pressure storage tanks. While some of these guidelines may apply to other types of tanks, these practices are intended primarily for existing tanks that were constructed to API Spec 12A or API Spec 12C, and API Std 620 or API Std 650. This recommended practice includes:

   1. Descriptions of the various types of storage tanks.

   2. Construction standards.

   3. Maintenance practices.

   4. Reasons for inspection.

   5. Causes of deterioration.

   6. Frequency of inspection.

   7. Methods of inspection.

   8. Inspection of repairs.

   9. Preparation of records and reports.

   10. Safe and ef?cient operations.

   11. Leak prevention methods.

   
   

   This recommended practice is intended to supplement API Std 653, which provides minimum requirements for main- taining the integrity of storage tanks after they have been placed in service.

   
   

2. References

2.1 CODES, STANDARDS, AND RELATED PUBLICATIONS

The following standards, codes, publications, and speci?- cations are cited in this recommended practice. The latest edi-

RP 12R1 Recommended Practice for Setting, Main- tenance, Inspection, Operation and Repair of Tanks in Production Service

Publ 306 An Engineering Assessment of Volumetric Methods of Leak Detection In Above- ground Storage Tanks

Publ 307 An Engineering Assessment of Acoustic Methods of Leak Detection In Above- ground Storage Tanks

Publ 315 Assessment of Tankfield Dike Lining Mate- rials and Methods

Publ 322 An Engineering Evaluation of Acoustic Methods of Leak Detection In Above- ground Storage Tanks

Publ 323 An Engineering Evaluation of Volumetric Methods of Leak Detection In Above- ground Storage Tanks

Publ 325 An Evaluation of a Methodology for the Detection of Leaks in Aboveground Stor- age Tanks

Publ 334 A Guide to Leak Detection for Above- ground Storage Tanks

Publ 340 Liquid Release Prevention and Detection Measures for Aboveground Storage Facilities

Publ 341 A Survey of Diked-Area Liner Use at Aboveground Storage Tank Facilities

API 570 Inspection, Repair, Alteration, and Rerat- ing of In-Service Piping Systems

RP 571 Damage Mechanisms Affecting Fixed Equipment in the Refining Industry