Materials and Fabrication of 2 1/4Cr-1Mo, 2 1/4Cr-1Mo-1/4V,

3Cr-1Mo, and 3Cr-1Mo-1/4V Steel Heavy Wall Pressure

Vessels for High-temperature, High-pressure Hydrogen Service

API RECOMMENDED PRACTICE 934-A SECOND EDITION, MAY 2008

ADDENDUM 1, FEBRUARY 2010

ADDENDUM 2, MARCH 2012

Materials and Fabrication of 2 1/4Cr-1Mo, 2 1/4Cr-1Mo-1/4V,

3Cr-1Mo, and 3Cr-1Mo-1/4V Steel Heavy Wall Pressure Vessels for High-temperature,

High-pressure Hydrogen Service

Downstream Segment

API RECOMMENDED PRACTICE 934-A SECOND EDITION, MAY 2008

ADDENDUM 1, FEBRUARY 2010

ADDENDUM 2, MARCH 2012

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Copyright © 2008 American Petroleum Institute

Foreword

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Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, D.C. 20005, standards@api.org.

iii

Contents

Page

1. Scope 1

2. References 1

3. Terms, Definitions, and Acronyms 2

   1. Terms and Definitions 2

   2. Acronyms 4

4. Design 4

5. Base Metal Requirements 5

   1. Material Specifications 5

   2. Steel Making Practice 6

   3. Chemical Composition Limits 6

   4. Heat Treatment 6

   5. Mechanical Properties 6

6. Welding Consumable Requirements 8

   1. Material Requirements 8

   2. Mechanical Properties 8

7. Welding, Heat Treatment and Production Testing 9

   1. General Welding Requirements 9

   2. Welding Procedure Qualification 10

   3. Preheat and Heat Treatments During Base Metal Welding 11

   4. Production Testing of Base Metal Welds 12

   5. Weld Overlay 13

   6. Final Postweld Heat Treatment (PWHT) 15

8. Nondestructive Examinations (NDE) 16

   1. General 16

   2. NDE Prior to Fabrication 16

   3. NDE During Fabrication 16

   4. NDE After Fabrication and Prior to Final PWHT 17

   5. NDE After Final PWHT 17

   6. Positive Material Identification 17

9. Hydrostatic Testing 17

10. Preparations for Shipping 18

11. Documentation 18

Annex A (informative) Guidance for Inspection for Transverse Reheat Cracking 19

Annex B (informative) Weld Metal/Flux Screening Test for Reheat Cracking Susceptibility 30

Bibliography 43

Figures

1 Location of Vickers Hardness Indentations 11

1. Schematic Showing of Reheat Cracking Locations 25

2. B-scan for Detecting Transverse Defects with TOFD 26

3. Alternate Probe Setup with Offset for Detecting Transverse Defects 27

4. TOFD Sensitivity Demonstration Block 28

5. Characterization of Reheat Cracks Using Pulse-echo UT 29

v

Contents

Page

1. Example of a Gripping Device Devoted to Threaded-end Specimens 33

2. Geometry of the Weld Joint to be Used for the Screening Test Coupon 36

3. Welding Sequence to be Used for the Screening Test 36

4. Example of Strongbacks Used to Minimize Coupon Distortion. 36

5. Position of Pre-forms Inside the Welded Zone—Macrographic View 37

6. Position of Pre-forms Inside the Welded Zone—Schematic View 37

7. Detailed Geometry of RHC Standard Specimen. 38

8. Location of the Thermocouples on the RHC Standard Specimen 39

9. Illustration of Heating Requirements on Test Specimens 40

Tables

1. Base Metal Specifications 5

2. Heat Treatment of Test Specimens 7

3. Maximum Operation Conditions Correlated to Testing Conditions at 450 °C (842 °F) 14

4. Test Conditions Domains 14

5. PWHT Holding Temperature and Time 16

1. TOFD Guideline for Identifying Transverse Reheat Cracks 23

2. Manual Pulse-echo Shear Wave Guideline for Identifying Transverse Reheat Cracks 24

1. Welding Parameters to be Used for Welding of Screening Test Coupons 35

2. Sample Test Certificate 42

Introduction

This recommended practice applies to new heavy wall pressure vessels in petroleum refining, petrochemical, and chemical facilities in which hydrogen or hydrogen-containing fluids are processed at elevated temperature and pressure. It is based on decades of industry operating experience and the results of experimentation and testing conducted by independent manufacturers and purchasers of heavy wall pressure vessels for this service.

Licensors and owners of process units in which these heavy wall pressure vessels are to be used may modify and/or supplement this recommended practice with additional proprietary requirements.

Materials and Fabrication of 2 1/4Cr-1Mo, 2 1/4Cr-1Mo-1/4V, 3Cr-1Mo, and 3Cr-1Mo-1/4V Steel Heavy Wall Pressure Vessels for High-temperature, High-pressure Hydrogen Service

1. Scope

   This recommended practice presents materials and fabrication requirements for new 2 1/4Cr and 3Cr steel heavy wall pressure vessels for high-temperature, high-pressure hydrogen service. It applies to vessels that are designed, fabricated, certified, and documented in accordance with ASME BPVC, Section VIII, Division 2, including Section 3.4, Supplemental Requirements for Cr-Mo Steels and ASME Code Case 2151, as applicable. This document may also be used as a resource when planning to modify an existing heavy wall pressure vessel.

   
   

   A newer ASME BPVC, Section VIII, Division 3, is available and has higher design allowables, however it has much stricter design rules (e.g. fatigue and fracture mechanics analyses required) and material testing requirements. It is outside the scope of this document.

   
   

   Materials covered by this recommended practice are conventional steels including standard 2-1/4Cr-1Mo and 3Cr-1Mo steels, and advanced steels which include 2 1/4Cr-1Mo-1/4V, 3Cr-1Mo-1/4V-Ti-B, and 3Cr-1Mo-1/4V-Nb-Ca steels. This document may be used as a reference document for the fabrication of vessels made of enhanced steels (steels with mechanical properties increased by special heat treatments) at purchaser discretion. However, no attempt has been made to cover specific requirements for the enhanced steels.

   
   

   The interior surfaces of these heavy wall pressure vessels may have an austenitic stainless steel weld overlay lining to provide additional corrosion resistance. A stainless clad lining using a roll-bonded or explosion-bonded layer on Cr- Mo base metal may be acceptable, but is outside the scope of this document.

   
   

2. References

The following referenced documents are cited in 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 RP 582, Welding Guidelines for the Chemical, Oil, and Gas Industries

ASME1 Boiler and Pressure Vessel Code, Section II—Materials; Part A—Ferrous Material Specifications; Part C—

Specifications for Welding Rods, Electrodes and Filler Metals; Part D—Properties ASME Boiler and Pressure Vessel Code, Section V—Nondestructive Examination

ASME Boiler and Pressure Vessel Code, Section VIII—Rules for Construction of Pressure Vessels, Division 1

ASME Boiler and Pressure Vessel Code, Section VIII—Rules for Construction of Pressure Vessels, Division 2—Alternative Rules

ASME Boiler and Pressure Vessel Code, Section IX—Welding and Brazing Qualifications

ASME Code Case 2151-1, 3 Chromium-1 Molybdenum-1/4 Vanadium-Columbium-Calcium Alloy Steel Plates and Forgings

ASME SA-20, Standard Specification for General Requirements for Steel Plates for Pressure Vessels

1ASME International, 3 Park Avenue, New York, New York 10016, www.asme.org.

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