1、 Standard Practice Detection, Repair, and Mitigation of Cracking in Refinery Equipment in Wet H2S 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 preclu
2、de 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 o
3、r 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
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11、81-228-6200). Revised 2010-03-13 Revised 2004-02-12 Reaffirmed 2000-09-13 Approved 1996-03-30 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-013-0 2010, NACE International NACE SP0296-2010 (formerly RP0296-2004) Item No. 21078 SP0296-2010 NACE Intern
12、ational i _ Foreword NACE International Task Group T-8-16, “Cracking in Wet H2S Environments,” was formed in 1988 to conduct an organized study on the incidence and mechanisms of cracking in pressure vessels operating in refinery wet hydrogen sulfide (H2S) environments. Specific objectives were to (
13、a) define the nature and extent of the problem by means of an industry survey; (b) define mechanisms for the type of cracking found, to be accomplished primarily through a literature survey; (c) establish inspection guidelines for existing vessels; and (d) develop repair and mitigation guidelines fo
14、r cracked vessels. Four work groups were formed to address these tasks. In 1990, a fifth work group was formed with a fifth objective, (e) to investigate material specifications and fabrication practices for new pressure vessels. This standard practice summarizes objectives (a), (c), and (d) listed
15、above. A technical committee report (NACE Publication 8X294)1was issued to address objective (b). Finally, objective (e) was handled by another technical committee report (NACE Publication 8X194).2This standard is intended for use primarily by refinery corrosion and materials engineers and inspectio
16、n, operations, and maintenance personnel. Information and guidance presented in this standard reflect the work of many individuals representing numerous companies worldwide. The titles and source information of the codes, specifications, and standards referred to or discussed in this standard are pr
17、ovided in Appendix A (nonmandatory) rather than listed in footnotes throughout the standard. Confining this information to one appendix should help readers who have any interest in further research. This standard was originally prepared in 1996 by former Task Group (TG) T-8-16, “Cracking in Wet H2S
18、Environments.” It was reaffirmed in 2000 by Group Committee T-8, and revised in 2004 and 2010 by TG 268, “Wet H2S Cracking in Petroleum Refinery Pressure Vessels.” TG 268 revised this standard in 2010 to address a number of items raised by Specific Technology Group (STG) 34 members as well as to res
19、pond to revisions in other applicable NACE standards such as SP0472.3The original emphasis of this standard was on pressure vessels, and this emphasis remains. However, with this revision, some limited information on piping has been included at the request of TG 268 members and other members of STG
20、34. TG 268 is administered by STG 34, “Petroleum Refining and Gas Processing.” 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 Sty
21、le 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. _ SP0296-2010 ii NACE International _ N
22、ACE International Standard Practice Detection, Repair, and Mitigation of Cracking in Refinery Equipment in Wet H2S Environments Contents 1. General 1 2. Mechanisms of Cracking . 2 3. Inspection for Cracking . 4 4. Repair of Cracked or Blistered Equipment 11 5. Mitigation Considerations for Operation
23、 14 References 15 Bibliography 16 Appendix A: Cited Codes, Specifications, and Standards 17 Appendix B: Nature and Extent of ProblemResults from 1990 T-8-16a Survey . 19 Appendix C: Typical Cracks Found in Wet H2S Environments . 25 FIGURES Figure C1: SSC in HAZ of head-to-shell weld of FCCU absorber
24、 tower. The crack is on the ASTM A 516-70 shell side. The numbers in the photograph are Knoop hardness values. (nital etch) 25 Figure C2: Hydrogen blister in ASTM A 516-70 amine contactor/water wash tower. 26 Figure C3(a): Hydrogen blisters on ID surface of amine contactor/water wash tower. . 27 Fig
25、ure C3(b): Cross-section of plate shown in upper photo illustrating HIC (“stepwise” cracking). . 27 Figure C4: SOHIC in soft base metal extending from the tip of SSC in a hard HAZ of a repair weld in the shell of a primary absorber (deethanizer) column in an FCCU gas plant. The ASTM A 212-B steel sh
26、ell was given PWHT at original fabrication, but the repair weld was not. (nital etch) . 28 Figure C5: ASCC (carbonate cracking) of non-PWHT ASTM A 285-C steel shell of FCCU main fractionator overhead accumulator. Cracking was found near welds in the lower portion of vessel. . 29 TABLES Table B1: Ove
27、rall Summary 19 Table B2: Cracking Reported by Company 20 Table B3: Cracking by Process Unit . 20 Table B4: Cracking vs. Operating Temperature . 21 Table B5: Cracking vs. H2S Concentration . 21 Table B6: Cracking vs. Steel Specification 22 Table B7: Cracking vs. Steel Grade . 22 Table B8: Cracking v
28、s. PWHT 22 Table B9: Cracking vs. Blistering History 23 Table B10: Cracking vs. Weld Repairs 23 Table B11: Depth of Cracking . 23 Table B12: Crack Penetration . 24 Table B13: Disposition of Cracked Pressure Vessels . 24 _ SP0296-2010 NACE International 1 _ Section 1: General 1.1 This standard is int
29、ended to be a primary source of information on cracking in wet H2S petroleum refinery environments and provides guidelines on the detection, repair, and mitigation of cracking of existing carbon steel refinery equipment in wet H2S environments. 1.1.1 For the purposes of this standard, the term equip
30、ment refers to pressure vessels and piping made of carbon steel plate material. Refinery pressure vessels include items such as, but not limited to, columns or towers, heat exchangers, drums, reboilers, and separators. 1.1.2 Limited cracking has been noted in seamless piping; therefore, the informat
31、ion in this standard concentrates on longitudinally seam-welded pipe fabricated from plate. 1.1.3 Information on fabrication and inspection practices for new pressure vessels (never in service) is in NACE Publication 8X194. 1.2 For the purposes of this standard, the term wet H2S environments include
32、s, but is not limited to, refinery process environments known to cause wet H2S cracking resulting from hydrogen entry into the steel, as defined in NACE Standard MR0103.4Some environmental conditions known to cause wet H2S cracking are those containing an aqueous phase and: (a) 50 ppmw total sulfide
33、 content in the aqueous phase; or (b) 1 ppmw total sulfide content in the aqueous phase and pH 7.6; or (d) 0.3 kPa absolute (0.05 psia) partial pressure H2S in the gas phase associated with the aqueous phase of a process. However, the threshold total sulfide content in the aqueous phase required for
34、 cracking to occur has not been clearly established. Therefore, selective application of this standard may be appropriate when experience has indicated the presence of cracking or blistering in comparable service, regardless of total sulfide content. Alkaline environments such as alkanolamine soluti
35、ons that contain sulfides and carbonate-containing sour waters also are included in the term wet H2S environments and thus are within the scope of this standard. Two forms of alkaline stress corrosion cracking (ASCC) are commonly found in these alkaline wet H2S environments. Amine stress corrosion c
36、racking (commonly referred to as amine cracking) can occur in amine service under certain conditions, which are discussed in API(1)RP 945.5Alkaline carbonate stress corrosion cracking (commonly referred to as carbonate cracking) can occur in alkaline carbonate-containing sour waters under certain co
37、nditions. NACE Publication 341086describes where carbonate cracking has occurred in process equipment in petroleum refining service, the refining communitys current theory(ies) on the conditions and mitigation techniques that may have an impact on this type of cracking, and analytical and inspection
38、 techniques that have been used to address the issue. 1.3 Increased industry attention to the potential for cracking of carbon steel pressure vessels began in 1984 with the rupture of a monoethanolamine (MEA) absorber tower at a Lemont, Illinois refinery. The ensuing explosion and fire resulted in f
39、atalities and extensive damage to the facility.7In response to this incident, NACE Task Group T-8-14, “Stress Corrosion Cracking of Carbon Steel in Amine Solutions,” was formed in the fall of 1984. An industry survey to determine the nature and extent of the cracking problem was conducted by T-8-14.
40、 The results of the T-8-14 effort have been reported separately.8 (1)American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005-4070. SP0296-2010 2 NACE International 1.4 In 1988, some new results on vessel inspections and the cracking found were reported to the industry.9Among the sign
41、ificant findings was the observation that cracking problems were occurring in other wet H2S environments, not just in MEA. It was further reported that inspection techniques commonly used at the time (visual, liquid penetrant, and dry magnetic particle testing) were not sensitive enough to find thes
42、e cracks. In response to this new information, NACE Task Group T-8-16, “Cracking in Wet H2S Environments,” was formed in the spring of 1988. Work Group T-8-16a conducted a survey of cracking experiences in wet H2S environments to better identify the extent of the problem. Appendix B (nonmandatory) s
43、ummarizes the 1990 T-8-16a survey findings. _ Section 2: Mechanisms of Cracking 2.1 The objective of this section is to define the terms used to describe cracks that occur because of exposure to wet H2S environments and describe the mechanisms of cracking. Photographs of typical cracks found in wet
44、H2S environments are shown in Appendix C (nonmandatory). 2.2 Definitions 2.2.1 Sulfide Stress Cracking (SSC): Cracking of a metal under the combined action of tensile stress and corrosion in the presence of water and H2S. SSC is a form of hydrogen stress cracking resulting from absorption of atomic
45、hydrogen that is produced by the sulfide corrosion process on the metal surface. SSC usually occurs more readily in high-strength steels or in hard weld zones of steels. (See Figure C1.) 2.2.2 Hydrogen Blistering: The formation of subsurface planar cavities, called hydrogen blisters, in a metal resu
46、lting from excessive internal hydrogen pressure. Growth of near-surface blisters in low-strength metals usually results in surface bulges. Hydrogen blistering in steel involves the absorption and diffusion of atomic hydrogen produced on the metal surface by the sulfide corrosion process. The develop
47、ment of hydrogen blisters in steels is caused by the accumulation of hydrogen that recombines to form molecular hydrogen at internal sites in the metal. In its molecular state, hydrogen is too large to diffuse through the steel. Typical sites for the formation of hydrogen blisters are large nonmetal
48、lic inclusions, laminations, or other discontinuities in the steel. This differs from the voids, blisters, and cracking associated with high-temperature hydrogen attack. Hydrogen blistering is much more common in plate materials used for pressure vessels or longitudinally seam-welded pipe than in seamless pipe materials or forgings. (See Figure C2.) 2.2.3 Hydrogen-Induced Cracking (HIC): Stepwise internal cracks that connect adjacent hydrogen blisters on differ
