1、 Item No. 24179 NACE International Publication 8X194 (2006 Edition) This Technical Committee Report has been prepared by NACE International Task Group 301* on Refinery H2S Pressure Vessels: Revision of NACE Publication 8X194: Report Materials and Fabrication Practices for New Pressure Vessels Used i
2、n Wet H2S Refinery Service December 2006, NACE International This NACE International (NACE) technical committee report 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 from manufactur
3、ing, marketing, purchasing, or using products, processes, or procedures not included in this report. Nothing contained in this NACE report 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
4、by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent. This report should in no way be interpreted as a restriction on the use of better procedures or materials not discussed herein. Neither is this report intended to apply in all cases relat
5、ing to the subject. Unpredictable circumstances may negate the usefulness of this report in specific instances. NACE assumes no responsibility for the interpretation or use of this report by other parties. Users of this NACE report are responsible for reviewing appropriate health, safety, environmen
6、tal, and regulatory documents and for determining their applicability in relation to this report prior to its use. This NACE report may not necessarily address all potential health and safety problems or environmental hazards associated with the use of materials, equipment, and/or operations detaile
7、d or referred to within this report. Users of this NACE report 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
8、 requirements prior to the use of this report. CAUTIONARY NOTICE: The user is cautioned to obtain the latest edition of this report. NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10
9、 years old. Purchasers of NACE reports may receive current information on all NACE International publications by contacting the NACE FirstService Department, 1440 South Creek Drive, Houston, Texas 77084-4906 (telephone +1 281/228-6200). FOREWORD The objective of this technical committee report is to
10、 provide a state-of-the-art overview of the materials selection, fabrication, postweld heat treatment (PWHT), inspection, and testing practices that have recently been applied to new pressure vessels (referred to in this report as equipment) destined for use in wet hydrogen sulfide (H2S) refinery se
11、rvice. This report is intended as a technical resource for material manufacturers, fabricators, and users involved in the specification and fabrication of new equipment used in wet H2S refinery services. Many of the practices discussed in this report were identified in informal industry surveys of r
12、efiners, process licensors, and engineering contractors conducted in 1991 by NACE Work Group (WG) T-8-16g and in 2004 by NACE Task Group (TG) 301. This information has been supplemented by the experiences of the work group and task group members and their colleagues. In this report the term “user” r
13、efers to the end user of the equipment, i.e., refiners or engineering contractors acting on behalf of refiners during equipment design, purchase, and installation. This report makes extensive use of the terms “some users,” “many users,” and “most users.” These terms were adopted by the work group an
14、d task group to give a qualitative feel to the types of user responses received in the informal surveys and follow-up user comments received during the preparation of the report. There is no accurate quantitative correlation between these terms and the actual responses and comments received other th
15、an that the progression from “some” to “most” indicates, in the opinion of the task group, a trend from the minority to the majority of users. The titles and source information of the codes, specifications, and standards cited or discussed in _ *Chair Terrell T. Phillips, Fluor Corporation, Sugar La
16、nd, Texas. NACE International 3 this report or the appendixes are provided in Appendix A rather than listed in footnotes throughout the report. Confining this important source document information to one appendix should help readers who have any interest in further research. The intent of the practi
17、ces reviewed in this report has been to minimize the susceptibility to several forms of low-temperature (ambient to 150C 300F) hydrogen damage that have occurred when fabricated carbon steel (CS) equipment has been exposed to corrosive refinery environments containing wet H2S. These damage mechanism
18、s have been reported to include sulfide stress cracking (SSC), hydrogen blistering, hydrogen-induced cracking (HIC), and stress-oriented hydrogen-induced cracking (SOHIC).1Background information on refining industry practices that have been used to prevent SSC of hard welds is provided in NACE Stand
19、ard RP0472, which was developed in response to a number of SSC failures that occurred in hard weld deposits in CS equipment in the late 1960s. In addition, a form of alkaline stress corrosion cracking (ASCC) commonly referred to as “carbonate cracking” has been identified in some wet H2S environment
20、s, mainly overhead streams in fluid catalytic cracking units (FCCUs) and some process water-handling equipment.1,2,3ASCC damage mechanisms are not covered in this report, but are defined and discussed, along with SCC, hydrogen blistering, HIC, and SOHIC, in NACE Standard RP0296. Also, Appendix A of
21、American Petroleum Institute (API) RP 945 provides a concise overview of the cracking mechanisms, including figures showing typical crack morphologies. From the 1991 and 2004 informal surveys, it was determined that many users have selectively specified materials, fabrication, inspection, and testin
22、g practices for new equipment after considering and evaluating some of the following factors: Experience with similar equipment; Type of process unit involved; Type of equipment involved; Process environment, including but not limited to: Total sulfide concentration in the aqueous phase; Potential f
23、or hydrogen activity; pH value of aqueous phase; Cyanide concentration in aqueous phase; CO2(carbonate) concentration in aqueous phase; Ammonium bisulfide concentration in aqueous phase; Amount of aqueous phase; Temperature; Pressure; and Upset, start-up, and shut-down conditions, including steamout
24、. Corrosion control program to be used; Future inspection requirements; Life-cycle cost; and Safety and economic risk based on consequence and probability of failure. It is beyond the scope of this report, and available industry experience, to fully address all of these factors and their impact on t
25、he materials of construction and fabrication practices that have been used for new equipment; therefore, for the purpose of this report, TG 301 has developed a simplified scheme by creating three general categories of service. This approach is further described in the section of the report titled Ca
26、tegories of Service. Many of the practices reviewed and discussed in this report, particularly the use of special clean steel plate materials in severe refinery environments, have been shown to have mixed success by extensive plant experience; therefore, even with the use of these practices, damage
27、to CS equipment in severe wet H2S environments continues to be a concern for users. Some refineries have had some degree of success in mitigating the effects of wet H2S environments on CS equipment by the use of water washing, polysulfide injection, or corrosion inhibitors. Some experiences when usi
28、ng such methods are reviewed and discussed in Appendix B. One established method of preventing damage in wet H2S environments has been the use of corrosion-resistant alloy cladding or weld overlay. The experiences and benefits of these methods are reviewed and discussed in Appendix C. Appendix C als
29、o includes information on the use of other types of liners such as organic thin-film coatings, cement linings, and thermal spray coatings. These types of liners have been used for the protection of previously operated equipment but have generally not been used for new construction. Most users have u
30、sed a corrosion-resistant alloy cladding or weld overlay when a liner has been specified. Appendix D contains comparative equipment costs for different materials of construction used in wet H2S service. A significant percentage of the problems found during in-service inspection of CS equipment in we
31、t H2S environments has been found to be the direct or indirect result of pre-existing fabrication flaws. Many of the practices reviewed and discussed in this report have been specified by users to improve the overall quality of fabrication. By employing these practices, users have attempted to reduc
32、e the extent and frequency of in-service inspections, make inspection results easier to interpret, and reduce the overall costs associated with performing inspections and making repairs. This report was originally prepared by WG T-8-16g, a component of TG T-8-16 on Cracking in Wet H2S Environments.
33、It was revised in 2006 by TG 301 on Refinery Wet H2S Pressure Vessels: Revision of NACE 2 NACE International NACE International 3 Publication 8X194. TG 301 is sponsored administratively by Specific Technology Group (STG) 34 on Petroleum Refining and Gas Processing and sponsored by STG 32 on Oil and
34、Gas ProductionMetallurgy. This report is published by NACE under the auspices of STG 34. It is one of many committee activities that have been sponsored by STG 34 related to the general problem of cracking of CS equipment in wet H2S refinery services. NACE technical committee reports are intended to
35、 convey technical information or state-of-the-art knowledge regarding corrosion. In many cases, they discuss specific applications of corrosion mitigation technology, whether considered successful or not. Statements used to convey this information are factual and are provided to the reader as input
36、and guidance for consideration when applying this technology in the future. However, these statements are not intended to be recommendations for general application of this technology, and must not be construed as such. INTRODUCTION This report reviews and discusses materials selection, fabrication,
37、 PWHT, inspection, testing, and corrosion control practices that have been used for recently manufactured new equipment destined for use in wet H2S refinery environments. Some users choose to take a risk-based assessment approach to the application of the following service categories to new equipmen
38、t using individual plant operating experience when available. For the purpose of this report, it has been assumed that the equipment was designed and built to the ASME Boiler and Pressure Vessel Code (BPVC), Section VIII, Division 1 or Division 2. Piping and atmospheric storage tanks are excluded fr
39、om the scope of this report. RISK-BASED ASSESSMENT Risk-based principles have been used to help users make decisions concerning materials selection and fabrication practices for equipment. Evaluation of risk has used industry standard approaches such as those found in API RP 580 and API Publication
40、581 or similar procedures and methodologies unique to the user. In either case, the risk assessment process addresses the likelihood of cracking and the consequence of failure. Materials selection options evaluated have included whether to use steels with special chemistry controls such as carbon eq
41、uivalent (CE) and microalloy limits to specify HIC-resistant steel, or to use stainless steel (SS) cladding or solid SS (duplex SS or UNS(1) S30000 series 300 series SS) equipment. Fabrication decisions have included whether special welding procedures addressing preheat, heat input, and/or other fac
42、tors are used, whether and at what conditions to postweld heat treat equipment, and whether 100% weld inspection is performed to help determine whether fabrication flaws are present prior to placing equipment in service. Several factors have been considered in assessing the probability of low-temper
43、ature hydrogen damage of equipment exposed to wet H2S service. The severity ofthe environment (e.g., the expected level of H2S or NH4HS) and the presence of other crack-promoting agents (e.g., cyanides) are significant factors considered by most users. The strength of material specified has also bee
44、n considered. For example, some users assign a lower likelihood of cracking to a lower-strength material (e.g., 414 MPa 60,000 psi tensile strength) than to a higher-strength material (e.g., 482 MPa 70, 000 psi tensile strength). Another factor is the experience in the exposure environment of existi
45、ng equipment when replacing or revamping existing units. Finally, whether PWHT of the equipment has or will be used is a factor considered by most users. Operating environments change with time because of changes in feed stock, debottlenecking, temperature changes, etc. The concentration of H2S wher
46、e vapor streams first come into contact with water is also considered by most users. Stream conditions are typically analyzed and risk assessments reevaluated as these environments change during equipment operating lives. _ (1)Metals and Alloys in the Unified Numbering System, a joint publication of
47、 ASTM International (ASTM), 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, and SAE International (SAE), 400 Commonwealth Drive, Warrendale, PA 15096-0001. NACE International NACE International 4 CATEGORIES OF SERVICE Background Generally, when specifying materials and fabrication practices
48、 for new equipment, most users have classified refinery process environments in which the concentration of total sulfide is greater than 50 ppmw in the aqueous phase as wet H2S service. In addition, some users have reported applying some of the practices discussed in this report to process environme
49、nts with lower concentrations of total sulfide, specifically in cases in which experience has shown wet H2S cracking or blistering to have occurred in equipment exposed to a comparable process environment or operated under comparable upset, start-up, or shut-down conditions. Industry survey results have not established a concentration of H2S below which cracking or blistering problems have not occurred. In the absence of operating experience or more relevant information, Figures 1 and 2 of
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