Identification, Repair, and Mitigation of Cracking of Steel Equipment in Fuel Ethanol Service

API BULLETIN 939-E

SECOND EDITION, AUGUST 2013

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Contents

Page

1. Scope 1

2. Normative References 1

3. Terms, Definitions, Acronyms, and Abbreviations 3

   1. Terms and Definitions 3

   2. Acronyms and Abbreviations 4

4. Background on SCC in Fuel Ethanol 5

   1. Description of Fuel Ethanol 5

   2. Relevant Standards for Fuel Ethanol 5

   3. Supply Chain for Fuel Ethanol 6

   4. Significance of SCC in Fuel Ethanol 7

   5. Factors Related to SCC. 10

5. Guidelines for Fabrication of Equipment 13

   1. Materials of Construction 13

   2. Tank Foundations 15

   3. Fabrication of Tanks 15

   4. Fabrication Guidelines to Minimize SCC 16

   5. Specific Guidelines for Minimizing SCC in Various Components 16

   6. Guidelines for PWHT 17

   7. Organic Coatings for Internal Protection of Tanks 18

6. Inspection of Existing Equipment 19

   1. General 19

   2. Inspection Intervals 19

   3. Inspection After Leakage Caused by SCC 20

   4. Initial Inspection Without Leakage 20

   5. Examination Procedures for Identification of SCC 20

7. Repair of SCC Damaged Equipment 23

   1. General 23

   2. Assessment of Fitness-for-service and Risk 23

   3. Temporary Repair by Clamps and Patches 23

   4. Crack Repair 24

   5. Stress Relief Heat Treatment Applied to Piping and Components 24

   6. Coatings 25

8. Monitoring of Fuel Ethanol 25

   1. Sampling and Analysis of Fuel Ethanol 25

   2. Methods for Monitoring and Testing for Corrosion and SCC 25

Annex A (informative) Listing of Reported Cases of SCC in Fuel Ethanol and Remedial Measures 26

Annex B (informative) Form to Submit New Information on SCC in Fuel Ethanol Systems 32

Annex C (informative) Examples of Typical SCC in Fuel Ethanol 34

Bibliography 42

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Contents

Figures

Page

1. SCC in Steel Tank Bottom 34

2. SCC in Steel Air Eliminator Vessel 35

3. Leak in Piping Resulting from a Crack Adjacent to the Weld 36

4. Characteristics of SCC in Steel Exposed to Fuel Ethanol, Showing Multiple Crack

   Initiations and Through-thickness Propagation in Piping 36

5. SCC in Steel Tank Bottom Showing Highly Branched, Intergranular Cracks at 100X 37

6. SCC in Steel Metallographically Prepared with Grain Boundary Etch at 500X 37

7. SCC in Steel Pipe from a Loading Rack Supply Line 38

8. Cracking of Another Pipe Sample from Same Situation as Noted in the Previous Figure 39

9. SCC of Steel Piping in a Fuel Ethanol System Return Line/Tank Transfer Line 40

10. Same SCC Incidence Shown in Previous Figure 41

Tables

1. Quality Specification for Fuel Ethanol per ASTM D4806 6

2. Generally Compatible and Incompatible Polymeric Materials 15

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Identification, Repair, and Mitigation of Cracking of Steel Equipment in Fuel Ethanol Service

1. Scope

   Usage of fuel ethanol as an oxygenate additive in gasoline blends is increasing both in the United States and internationally. This document discusses stress corrosion cracking (SCC) of carbon steel tanks, piping, and equipment exposed to fuel ethanol as a consequence of being in the distribution system, at ethanol distribution facilities, or end user (EU) facilities where the fuel ethanol is eventually added to gasoline. Such equipment includes but is not limited to:

   
   

   • storage tanks,

     
     

   • piping and related handling equipment, and

     
     

   • pipelines

   
   

   that are used in distribution, handling, storage, and blending of fuel ethanol. However, data for pipelines in ethanol service is limited and caution should be used when applying guidelines from this document that have been derived mainly from applications involving piping and tanks in ethanol storage and blending facilities. SCC of other metals and alloys is beyond the scope of this document, as is the corrosion of steel in this service.

   
   

   It is realized that SCC of steel in fuel ethanol is a topic where knowledge of the subject is actively growing through documentation of recent experience and through research in progress. This document deals with handling of cracks in existing equipment and reduction of SCC occurrence in new equipment as a result of exposure to fuel ethanol per ASTM D4806 (or other international specifications), ethanol fuel blends, and pipeline transmixes involving fuel ethanol and conventional hydrocarbon fuels (gasoline, diesel, or jet fuel). It includes guidelines for carbon steel construction materials, including their fabrication, inspection, and repair to help assure safe and reliable operations.

   
   

   This document is based on current engineering practices and insights from recent industrial experience and research. Older equipment may not conform exactly to the information contained herein, but this does not imply that such equipment is being operated in an unsafe or unreliable manner. It is also recognized that facilities may vary and may need to be modified depending on specific operating conditions, inspection, and maintenance experience. Each user company is ultimately responsible for its own safe and reliable operations.

   
   

   The steels referred to in this document are defined by the ASTM or API designation systems or equivalent steel grades contained in other recognized codes or standards. Welded construction is considered the primary method of fabrication in equipment exposed to fuel ethanol.

   
   

   Terminology used herein is given in Section 3.

   
   

2. 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 Specification 5L, Specification for Line Pipe

API Publication 327, Aboveground Storage Tank Standards: A Tutorial

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

API Recommended Practice 574, Inspection Practices for Piping System Components

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