Materials, Fabrication, and Repair Considerations for Hydrogen Reformer Furnace Outlet Pigtails and Manifolds

API TECHNICAL REPORT 942-A FIRST EDITION, JUNE 2014

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Foreword

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1. Scope 1

2. Technical Approach 1

3. Results of Literature Survey. 2

   1. General 2

   2. Materials Selection 2

   3. Welding Consumable Selection 7

   4. Welding and Repair Practices 8

   5. Mechanical Design 9

   6. Case Studies 14

4. Results of Industry Survey 18

   1. General 18

   2. Designers of Reformers 19

   3. Location of Outlet Manifold and Pigtails Relative to Firebox 19

   4. Age Distribution of Reformers 20

   5. Operating Conditions: Temperature, Pressure, and Cyclic Operation 20

   6. Manifold System Alloys 21

   7. Pigtail Alloys and Problems 22

   8. Inspection Programs 23

   9. Repairs, Modifications, or Upgrades 23

   10. Stress-rupture Behavior of Alloys and Welds 23

5. Industry Case Studies 28

   1. General 28

   2. Case 1: Creep Cracking of Bull Tee to Header Welds 28

   3. Case 2: Creep Failure of Outlet Header 32

   4. Case 3: Pigtail Ruptures 35

   5. Case 4: Stress Relaxation Cracking of Alloy 800HT Pigtail Section 35

   6. Case 5: Weldability Issues with Cast 20Cr-32Ni-Nb 35

   7. Case 6: Repair and Mitigation of Cast 20Cr-32Ni-Nb Tees 39

   8. Case 7: Cracking at Weld Between an Alloy 800HT Forged Fitting and an Alloy 800HT Outlet

      Transfer Line 42

6. Conclusions 43

7. Acknowledgments 44

Annex A (informative) Analysis of Stress-rupture Data Using Larson-Miller Parameter 45

Bibliography 46

Figures

1. Example of HAZ Liquation Cracking in Aged 20Cr-32Ni-Nb Casting 11

2. Example of Reheat Cracking in Aged 20Cr-32Ni-Nb Casting 12

3. Location of Cracking in Aged 20Cr-32Ni-Nb Cast Tee Piece after Welding a New Cone Piece to it 12

4. Example of Cracking at Subheader to Tee Weld; Both Are 20Cr-32Ni-Nb Castings 13

5. Typical Pressure and Temperature Ranges for Steam-Methane Reforming 13

6. Typical Designs of Outlet Manifold Systems 15

7. Typical Designs of Outlet Pigtail Systems 16

8. Distribution of Reformer Designers in Survey 19

9. Age Distribution of Reformers in Survey 20

   
   

10. Ranges of Operating Temperature for Reformers in Survey 21

11. Ranges of Operating Pressure for Reformers in Survey 22

12. Stress-rupture Curves for the 20Cr 32Ni Nb Alloy 24

13. Comparison of Stress-rupture Behavior of Hot-manifold Alloys and Weldments at 816 °C (1500 °F) . . 27

14. Comparison of Stress-rupture Behavior of Hot-Manifold Alloys and Weldments at 871 °C (1600 °F) . . 28

15. Comparison of Stress-rupture Behavior of Hot-manifold Alloys and Weldments at 927 °C (1700 °F) . . 29

16. Comparison of Stress-rupture Behavior of 2133 Mn and 21/33 So Welds with That of 21Cr-32Ni-Nb

    Alloy Base Metal 30

17. Drawing of Central Portion of Outlet Manifold Showing Central Portion of Header, Bull Tee, and Increaser Cone 30

18. Photograph of Bull Tee Showing Areas Where Cracking of Welds Was Observed 31

19. Results of Finite-element Stress Analysis of Outlet Manifold for Internal Pressure Loading of

    1862 kPa (270 psig) 31

20. Photomicrograph of Creep Cracking and Voids Observed in Bull Tee Weld 32

21. Photograph of Cracking Observed in Ring Section from Outlet Header 33

22. Photomicrograph of Creep Cracking at Crack Location Shown in Figure 21 (As-polished) 33

23. Photomicrograph of Aligned Creep Voids Near Outer Surface on Side Opposite Cracking of Header Ring Section Shown in Figure 21 and Figure 22 (As-polished) 34

24. Photomicrograph of Creep Cracking on Surface of Header as Seen on Metallographic Replica 34

25. Photograph of Alloy 800HT Inlet Pigtail and Attachment Fitting 36

26. Photograph of Cracking of Alloy 800HT Inlet Pigtail Shown in Figure 25 36

27. Photomicrograph of Crack in Alloy 800HT Inlet Pigtail Showing Evidence of Stress Relaxation

    Cracking 37

28. Photomicrograph of Showing Typical Aged Microstructure of 20Cr-32Ni-Nb Cone Material 38

29. Photomicrograph Showing Evidence of Liquation Cracking in Weldability Test Sample of Aged

    20Cr-32Ni-Nb Cone Material 38

30. Photomicrograph Showing Evidence of Reheat Cracking in Weldability Test Sample of Aged

    20Cr-32Ni-Nb Cone Material 39

31. Photograph of Showing Locations of Old Tee and New Reducer Cone in 20Cr-32Ni-Nb

    Outlet Manifold 40

32. Photograph of Showing Location of Cracking That Occurred When New Centrifugally Cast

    20Cr-32Ni-Nb Reducer Cone Was Welded to Old 20Cr-32Ni-Nb Statically Cast Tee 40

33. Photograph Showing Cracking That Was Found in Base Metal of Old 20Cr-32Ni-Nb Statically

    Cast Tee after Welding 41

34. Cracking at the Weld Joint Between an Alloy 800HT Forged Fitting, and an Alloy 800HT Outlet

Transfer Line 43

Tables

1. Chemical Composition and Grain Size Requirements for the Variants of Alloy 800 3

2. Specifications of Typical Welding Consumables for Hydrogen Reformer Outlet Manifolds

   and Pigtails 10

3. Chemical Compositions of Weld Metals Used in Hydrogen Reformer Outlet Manifolds and Pigtails . . 11

4. Typical Chemical Compositions of the 20Cr-32Ni-Nb Alloy and Chemical Composition of a

Modified HT Alloy 24

Materials, Fabrication, and Repair Considerations for Hydrogen Reformer Furnace Outlet Pigtails and Manifolds

1. Scope

   
   

   The American Petroleum Institute (API) Committee on Refinery Equipment, Subcommittee on Corrosion and Materials undertook a project to develop this technical report on materials, fabrication, and repair issues related to hydrogen and syngas reformer furnace outlet pigtails and manifolds. High reliability of outlet pigtails and manifold components, such as headers, tees, and fittings, is important to the successful long- term operation of hydrogen and syngas reformer furnaces. These components typically operate at high temperatures in the range of 750 °C to 950 °C (1382 °F to 1742 °F) where they are potentially subject to high-temperature creep, stress relaxation, hot corrosion, and thermal fatigue damage.

   
   

   In recent years a number of reformer furnace operators have encountered problems of in-service degradation and cracking of outlet pigtails and manifold components, while others have had little or no problems of this type. Both direct experience in addressing specific cases of outlet pigtail and manifold cracking problems and indirect experience gained from surveying industry with regard to these problems were used in preparing this report.

   
   

   The objective of the project was to develop an understanding, based on published literature and industry experience, of why some reformer furnaces have had problems with embrittlement and cracking of outlet pigtails and manifold components in service, while others have not had such problems.

   
   

2. Technical Approach

The project objective was achieved by reviewing relevant published literature and industry experience and then documenting the results of that review in this report. The published technical literature was reviewed using the following four databases:

• ScienceDirect (https://www.sciencedirect.com/),

  
  

• Engineering Village 2 (https://www.engineeringvillage2.org/),

  
  

• CSA Materials Research Database with METADEX (https://www.csa.com/),

  
  

• REFIN*COR 8.0 database (https://www.nace.org/).

The first two databases were available through a library service. The third database was available through The Welding Institute (TWI), while the fourth one was available through NACE International. The

proceedings of AIChE Ammonia Plants & Related Facilities Symposia [1-4] were also searched because they

were known to contain a number of relevant technical papers. These symposia proceedings are published as searchable CDs, which facilitated identification and review of relevant papers. In addition, literature was obtained through personal contacts with members of the API Subcommittee of Corrosion and Materials and records of roundtable presentations at past API meetings.

Industry was surveyed by sending a questionnaire to key contacts at companies who operate reformer furnaces or provide materials used in outlet pigtails and manifold components. A draft questionnaire was prepared and submitted to the API project committee for review and comment. Recommendations from that review then were incorporated into the final questionnaire. The survey was distributed in two ways. First, API sent it to select members deemed to have an interest in the topic. Second, it was sent to individuals in companies that operate reformer furnaces in other industries or in international refining companies not affiliated with API.

Section 6 of this report lists references to the published literature that is cited herein. The sources of industry comments have been kept anonymous; each respondent is simply identified by a code. The information and

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