NACE_SP0472-2010

Standard Practice Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments This NACE International standard represents a consensus of those individual members who have reviewed this document, its scope, and provisions. Its acceptance does not in any respect preclude anyone, whether he or she has adopted the standard or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformance with this standard. Nothing contained in this NACE International standard is to be construed as granting any right, by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or product covered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This standard represents minimum requirements and should in no way be interpreted as a restriction on the use of better procedures or materials. Neither is this standard intended to apply in all cases relating to the subject. Unpredictable circumstances may negate the usefulness of this standard in specific instances. NACE International assumes no responsibility for the interpretation or use of this standard by other parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE International standard are responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropriate regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with NACE technical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edition. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International FirstService Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone +1 281-228-6200). Revised 2010-03-13 Revised 2008-11-07 Revised 2005-12-02 Reaffirmed 2000-09-13 Revised October 1995 NACE International 1440 South Creek Dr. Houston, Texas 77084-4906 +1 281/228-6200 ISBN 1-57590-114-5 © 2010, NACE International NACE SP0472-2010 (formerly RP0472) Item No. 21006 Revised 2010-03-13 Revised 2008-11-07 Revised 2005-12-02 Reaffirmed 2000-09-13 Revised October 1995 Revised March 1987 Reaffirmed 1974 Approved April 1972 NACE International 1440 South Creek Dr. Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-114-5 © 2010, NACE International Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS - - ` , , ` ` ` , , , , ` ` ` ` - ` - ` , , ` , , ` , ` , , ` - - - Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS - - ` , , ` ` ` , , , , ` ` ` ` - ` - ` , , ` , , ` , ` , , ` - - - SP0472-2010 NACE International i ________________________________________________________________________ Foreword This NACE standard defines standard practices for producing weldments in P-No. 1 steels resistant to environmental cracking in corrosive petroleum refining environments. It is intended to be used by refiners, equipment manufacturers, engineering contractors, and construction contractors. Most petroleum refining equipment are constructed from carbon steel having a minimum specified tensile strength of 480 MPa (70,000 psi) or less, and in almost every case, the equipment is fabricated by welding. The welds for refinery equipment are made to conform to various codes and standards, including the ASME(1) Boiler and Pressure Vessel Code, Section VIII1 for pressure vessels, ASME/ANSI(2) B31.32 for process piping, or API(3) Standards 6203 and 6504 for tanks. According to these codes and standards, these carbon steels are classified as P-No. 1, Group 1 or 2, and in this standard, they are referred to as P-No. 1 steels. Petroleum refineries as well as oil- and gas-processing plants have predominantly used P-No. 1 steels for services containing wet hydrogen sulfide (H2S), or sour services. They are the basic materials of construction for pressure vessels, heat exchangers, storage tanks, and piping. Decades of successful service have shown them to be generally resistant to a form of hydrogen stress cracking (HSC) called sulfide stress cracking (SSC). HSC occurs in high-strength materials or zones of a hard or high-strength microstructure in an otherwise soft material. With commonly used fabrication methods, P-No. 1 steels should be below the strength threshold for this cracking. NACE Standard MR01035 provides guidance for materials in sour oil and gas environments in refinery services, including limiting the hardness of P-No. 1 steels and reducing the likelihood of SSC. NACE MR0175/ISO(4) 151566 provides additional guidance for materials in sour oil and gas environments in production services. In the late 1960s, a number of SSC failures occurred in hard weld deposits in P-No. 1 steel refinery equipment. To detect hard weld deposits caused by improper welding filler metals or procedures, the petroleum refining industry began requiring hardness testing of production weld deposits under certain conditions and applied a criterion of 200 Brinell hardness (HBW) maximum. These requirements were given in previous editions of this standard and in API RP 942.7 In the late 1980s, instances of heat-affected zone (HAZ) cracking were reported in P-No. 1 steel equipment that met the 200 HBW weld deposit hardness limit. Some cases were determined to be SSC that was caused by high hardness in the HAZ. Some were (1) ASME International (ASME), Three Park Avenue, New York, NY 10016-5990. (2) American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036. (3) American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070. (4) International Organization for Standardization (ISO), 1 ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland. __________________________________________ (1) ASME International (ASME), Three Park Avenue, New York, NY 10016-5990. (2) American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036. (3) American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070. (4) International Organization for Standardization (ISO), 1 ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland. Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS - - ` , , ` ` ` , , , , ` ` ` ` - ` - ` , , ` , , ` , ` , , ` - - - SP0472-2010 ii NACE International identified as another form of hydrogen damage called stress-oriented hydrogen-induced cracking (SOHIC).8 These cracks propagated primarily in the HAZs of weldments and were found in both high- and low-hardness HAZs. Other HAZ cracking instances in specific corrosive refinery process environments were attributed to alkaline stress corrosion cracking (ASCC), which can occur as a result of high residual stress levels. HAZ hardness controls and reduction of residual stresses in weldments were outside the scope of early editions of this standard, which covered only weld deposit hardness limits. The 1995 revision of this standard was expanded to cover the entire weldment and the various in-service cracking mechanisms (HSC in the weld deposit, HSC in the weld HAZ, and ASCC) that can occur in corrosive petroleum refining environments. This standard was originally prepared in 1972 by NACE Task Group (TG) T-8-7, which was composed of corrosion consultants, corrosion engineers, and other specialists associated with the petroleum refining industry. It was reaffirmed in 1974, and revised in 1987 and 1995. It was reaffirmed in 2000 by Specific Technology Group (STG) 34, “Petroleum Refining and Gas Processing,” and revised in 2005, 2008, and 2010 by TG 326, “Weldments, Carbon Steel: Prevention of Environmental Cracking in Refining Environments.” API previously published a standard, API RP 942, with similar objectives. The API standard has been discontinued with the intention of recognizing this NACE standard as the industry consensus standard. This standard is issued by NACE International under the auspices of STG 34. In NACE standards, the terms shall, must, should, and may are used in accordance with the definitions of these terms in the NACE Publications Style Manual. The terms shall and must are used to state a requirement, and are considered mandatory. The term should is used to state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional. ________________________________________________________________________ Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS --`,,```,,,,````-`-`,,`,,`,`,,`--- SP0472-2010 NACE International iii ________________________________________________________________________ NACE International Standard Practice Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments Contents 1. General ......................................................................................................................... 1 2. Prevention of Hydrogen Stress Cracking ..................................................................... 5 3. Prevention of Alkaline Stress Corrosion Cracking ..................................................... 14 References ........................................................................................................................ 15 Bibliography ...................................................................................................................... 17 Appendix A: Rationale for Guidelines for Prevention of Hydrogen Stress Cracking ........ 18 Appendix B: Rationale for Guidelines for Prevention of Alkaline Stress Corrosion Cracking ........................................................................................................... 26 Appendix C: Summary of Cooling Time (t8/5) Concept ..................................................... 27 FIGURES Figure 1: Interrelationships of the various cracking mechanisms. ...................................... 2 Figure 2: Hardness test locations.. .................................................................................. 10 Figure 3: Hardness test details.. ...................................................................................... 11 Figure C1: Types of heat flow during welding.. ................................................................ 27 Figure C2: Transition plate thickness (dt) from three-dimensional to two-dimensional heat flow as a function of heat input (Q) for different preheat temperatures (Tp). ............ 28 Figure C3: Cooling time (t8/5) for three-dimensional heat flow as a function of heat input (Q) for different preheat temperatures (Tp). ...................................................................... 31 Figure C4: Cooling time (t8/5) for two-dimensional heat flow as a function of heat input (Q) for different preheat temperatures (Tp) and plate thicknesses (d). ............................. 32 TABLES Table 1: “Road Map” for SP0472 ....................................................................................... 4 Table 2: Welding Process/Filler Metal Combinations Exempt from Weld Deposit Hardness Testing ................................................................................................................ 5 Table A1: Level of Base Metal Chemistry Control as a Function of Butt Weld Joint Configurations and HAZ Hardness Control Method Used ................................................ 21 Table C1: Shape Factors for Influence of the Form of Weld on t8/5 ................................................... 30 ________________________________________________________________________ Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS - - ` , , ` ` ` , , , , ` ` ` ` - ` - ` , , ` , , ` , ` , , ` - - - Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS --`,,```,,,,````-`-`,,`,,`,`,,`--- SP0472-2010 NACE International 1 ________________________________________________________________________ Section 1: General 1.1 This standard establishes guidelines to prevent most forms of environmental cracking of weldments in carbon steel refinery equipment, including pressure vessels, heat exchangers, piping, valve bodies, and pump and compressor cases. Weldments are defined to include the weld deposit, base metal HAZ, and adjacent base metal zones subject to residual stresses from welding. 1.2 This standard covers only carbon steels classified as P-No. 1, Group 1 or 2. These classifications can be found in the ASME Boiler and Pressure Vessel Code, Section IX9 for pressure vessels, ASME/ANSI B31.3 for process piping, or API Standards 620 and 650 for tanks. It excludes steels with greater than 480 MPa (70,000 psi) minimum specified tensile strength. Other materials may be vulnerable to cracking, but these materials are outside the scope of this standard. 1.3 The types of equipment covered by this standard include pressure vessels, heat exchangers, piping, valve bodies, and pump and compressor cases. All pressure-containing weldments or internal attachment weldments to the pressure boundary are included. External attachment weldments are sometimes included as discussed in Paragraph 3.5.1. In addition, this standard may be applied to weldments in some non-pressure-containing equipment, such as atmospheric storage tanks. 1.4 Both new fabrication and repair welds are within the scope of this standard. The practices included herein are intended to prevent in-service cracking and are not intended to address cracking that can occur during fabrication, such as delayed hydrogen cracking. In most cases, however, these practices are also helpful in minimizing these fabrication problems. Useful information for preventing delayed hydrogen cracking is provided by F.R. Coe, et al.10 1.5 Welding processes covered by this standard include shielded metal arc welding (SMAW); gas metal arc welding (GMAW); flux-cored arc welding (FCAW); gas tungsten arc welding (GTAW); and submerged arc welding (SAW). Almost all types of weld configurations are included. For specific exceptions, such as hot taps, hardness limits and postweld heat treatment (PWHT) requirements should be reviewed on a case-by-case basis. 1.6 Corrosive refinery process environments covered by this standard can be divided into two general categories: services that could cause cracking as a result of hydrogen charging, and services that could cause ASCC. However, identification of the specific environments to which the guidelines set forth in this standard are to be applied to prevent various forms of in-service environmental cracking is the responsibility of the user. Figure 1 is a simplified schematic showing the interrelationships of the various cracking mechanisms discussed in this standard. Copyright NACE International Provided by IHS under license with NACE Not for ResaleNo reproduction or networking permitted without license from IHS --`,,```,,,,````-`-`,,`,,`,`,,`--- SP0472-2010 2 NACE International _______________________________ (A) Refer to the NACE Glossary of Corrosion-Related Terms11 for definitions (including stress corrosion cracking). (B) The forms of environmental cracking included within the double lines are commonly referred to as wet H2S cracking when they occur in wet H2S environments. (C) This form of environmental cracking can also occur in nonsulfide environments such as hydrofluoric acid. Figure 1: Interrelationships of the various cracking mechanisms. 1.6.1 Services that could cause cracking as a result of hydrogen charging: 1.6.1.1 In these services, the environment or corrosion reactions result in diffusion of atomic hydrogen into the base metal and weldment. In high-strength or high-hardness areas, this hydrogen can result in HSC. In petroleum refining processes, the primary manifestation of HSC is SSC of hard weldments in process environments containing wet H2S. Information regarding the definition of wet H2S refinery services is given in NACE Standard MR0103. However, other processes that promote aqueous corrosion of steel and promote hydrogen charging (such as hydrofluoric acid) can also cause HSC. Controlling both the weld deposit and HAZ hardness using the guidelines in Section 2 prevents HSC in most cases. 1.6.1.2 SOHIC can also occur in the services described above, but it does not require high strengths or high hardnesses. Hence, limiting weldment hardness does not prevent this form of cracking. Reducing weldment hardness and residual stress is believed to reduce the likelihood of this cracking, so the guidelines in Sections 2 and 3 may still be helpful. However, additional steps, such as the use of special clean steels, water washing, corrosion inhibitors, or corrosion-resistant liners, may be needed for some services. An overview of the materials selection, fabrication, PWHT, and testing practices that have been applied to new pressure vessels for preventing SOHIC is in NACE Publication 8X194.12 1.6.1.3 Cases of cracking of hard welds have occurred as a result of short-term upset, start-up, or transient conditions in non-stress-relieved P-No. 1 steel refinery equipment in which hydrogen sulfide is not normally present. HYDROGEN-INDUCED CRACKING (HSC)(A,C) CRACKING AS A RESULT OF HYDROGEN CHARGING HYDROGEN STRESS CRACKING (HSC)(A,B) SULFIDE STRESS CRACKING (SCC)(A) HYDROGEN BLISTERING(A,C) STRESS-ORIENTED HYDROGEN-INDUCED CRACKING (SOHIC)(C) ALKALINE STRESS CORROSION CRACKING (ASCC)(A) ENVIRONMENTS SUCH AS: -Caustic -Alkanolamine solutions containing CO2 and/or H2S -Alkaline sour waters containing carbonates