Materials and Fabrication of

11/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High-pressure Hydrogen Service Operating at or Below 825 °F (440 °C)

RECOMMENDED PRACTICE 934-C SECOND EDITION, FEBRUARY 2019

Special Notes

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Classified areas may vary depending on the location, conditions, equipment, and substances involved in any given situation. Users of this recommended practice should consult with the appropriate authorities having jurisdiction.

Users of this recommended practice should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein.

Where applicable, authorities having jurisdiction should be consulted.

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Copyright © 2019 American Petroleum Institute

Foreword

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The verbal forms used to express the provisions in this specification are as follows:

• the term “shall” denotes a minimum requirement in order to conform to the standard;

  
  

• the term “should” denotes a recommendation or that which is advised but not required in order to conform to the standard;

  
  

• the term “may” is used to express permission or a provision that is optional;

  
  

• the term “can” is used to express possibility or capability.

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Contents

Page

1. Scope 1

2. Normative References. 1

3. Terms, Definitions, and Abbreviations 3

   1. Terms and Definitions 3

   2. Abbreviations 4

4. Design 4

5. Base Metal Requirements 5

   1. Material Specifications 5

   2. Steel Making Practice 5

   3. Chemical Composition Limits 6

   4. Heat Treatment 6

   5. Mechanical Properties 6

6. Welding Consumable Requirements 7

   1. Material Requirements 7

   2. Mechanical Requirements 8

7. Welding, Heat Treatment, and Production Testing 8

   1. General Welding Requirements 8

   2. Welding Procedure Qualification 9

   3. Preheat and Dehydrogenation Heat Treatment (DHT) 10

   4. Production Testing of Base Metal Welds 10

   5. Weld Overlay or Integral Clad 11

   6. Final Postweld Heat Treatment (PWHT) 12

8. Nondestructive Testing (NDE) 12

   1. General 12

   2. NDE Prior to Fabrication 13

   3. NDE During Fabrication 13

   4. NDE After Fabrication and Prior to Final PWHT 13

   5. NDE After Final PWHT 14

   6. Positive Material Identification 14

9. Hydrostatic Testing 14

10. Preparation for Shipping 14

11. Documentation 15

12. Summary Material Examination and NDE Requirements 15

Figures

1 Location of Vickers Hardness Indentations 5

Tables

1. Base Metal Specifications 9

2. Summary of API RP 934-C Material Examination and NDE Requirements 16

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Introduction

This recommended practice (RP) applies to new fabrication of 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, fabricators, 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.

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Materials and Fabrication of 1 1/4Cr-1/2 Mo Steel Heavy Wall Pressure Vessels for High-pressure Hydrogen Service Operating at or Below 825 °F (440 °C)

1. Scope

   This recommended practice (RP) covers materials and fabrication requirements for new 11/4Cr-1/2Mo steel heavy wall pressure vessels and heat exchangers for high-temperature, high-pressure hydrogen service. It applies to vessels that are designed, fabricated, certified, and documented in accordance with ASME Section VIII, Division 1 or Division 2. This document may also be used as a resource for equipment fabricated of 1Cr-1/2Mo Steel.

   
   

   This document may also be used as a resource when planning to modify an existing heavy wall pressure vessel.

   
   

   The interior surfaces of these heavy wall pressure vessels may have an austenitic stainless steel or ferritic stainless steel weld overlay or cladding to provide additional corrosion resistance.

   
   

   For this recommended practice, “heavy wall” is defined as a shell thickness 2 in. (50 mm) or greater, but less than or equal to 4 in. (100 mm) at the time of mill heat treatment. At shell or head thicknesses greater than 4 in. (100 mm), 11/4Cr-1/2Mo plates and forgings have been shown to have difficulty meeting the toughness requirements given in this document. Thick 11/4Cr-1/2Mo forgings, such as integrally reinforced nozzles, flanges, tube sheets, channel covers, etc., can especially have difficulty meeting specified properties. 21/4Cr-1Mo plates and forgings can be used as an alternative to ensure properties are met. Although outside of its scope, this document can be used as a resource for vessels down to 1 in. (25 mm) or lower in shell thickness, with changes defined by the purchaser.

   
   

   Multilayer vessels are outside the scope of this document.

   
   

   This recommended practice is not intended for use for equipment operating above 825 °F (440 °C) or in the creep range. API RP 934-E covers these higher-temperature applications.

   
   

2. Normative References

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any addenda) applies.

API Recommended Practice 582, Welding Guidelines for the Chemical, Oil, and Gas Industries

API Recommended Practice 934-A, Materials and Fabrication of 21/4Cr-1Mo, 21/4Cr-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-E, Recommended Practice for Materials and Fabrication of 11/4Cr-1/2Mo Steel Pressure Vessels for Service above 825 °F (440 °C)

ASME 1 Boiler and Pressure Vessel Code, Section II-Materials; Part A-Ferrous Material Specifications; Part C, Specification 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

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

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