1、 Standard Practice Wet Gas Internal Corrosion Direct Assessment Methodology for Pipelines 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
2、 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 manuf
3、acture, 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
4、 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 st
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11、d 2010-10-22 NACE International 1440 South Creek Dr. Houston, Texas 77084-4906 +1 281-228-6200 ISBN 1-57590-241-9 2010, NACE International NACE SP0110-2010 Item No. 21146 SP0110-2010 NACE International i _ Foreword This standard practice formalizes a methodology to assess internal corrosion for onsh
12、ore and offshore pipelines and other piping systems that normally carry natural gas with condensed water, or with water and liquid hydrocarbons, termed wet gas internal corrosion direct assessment (WG-ICDA). This standard is intended for use by gas pipeline operators and others who manage gas pipeli
13、ne integrity (both onshore and offshore) in which pipelines are normally under wet loading conditions and are beyond the application of NACE SP02061and NACE SP0208.2The WG-ICDA methodology has been developed to meet the needs of gas pipeline operators to assess the integrity of pipelines with respec
14、t to internal corrosion. WG-ICDA is a structured process that combines preassessment, indirect inspection, detailed examination, and postassessment to evaluate the effect of predictable pipeline integrity threats such as internal corrosion. Specifically, the goal of WG-ICDA is to identify locations
15、with the greatest likelihood of internal corrosion, and its influencing factors such as water content, flow regime, liquid holdup, flow velocities, temperature changes, and pressure changes. These locations shall be exposed and examined in accordance with criteria established in Section 4. The resul
16、ts of these detailed examinations are used as a basis for assessing the condition and integrity of the remainder of the pipeline segment (with less likelihood of corrosion). WG-ICDA does not depend on the ability of a pipeline to undergo in-line inspection (ILI) by smart pigs or pressure testing, ma
17、king it most valuable to those pipeline segments unable to accept pigs or that cannot be hydrostatically tested. This standard is intended to be a stand-alone assessment methodology for internal corrosion in lieu of ILI analyses; however, the WG-ICDA methodology may also serve or assist those cases
18、in which ILI may have been performed or is contemplated to demonstrate the reliability of the WG-ICDA process. It may also be used for optimizing the selection/justification or prioritization of pipelines that are subjected to ILI. In wet gas systems, WG-ICDA subregions of a WG-ICDA region may accum
19、ulate water and liquid hydrocarbons. The accumulation of water and liquid hydrocarbons can be determined by a flow model that uses a phase envelope for dew point (water and hydrocarbon) prediction under flowing conditions and shows local temperature, pressure, and gas composition for a pipeline. Dep
20、ending on the flow conditions (e.g., velocity, gas quality, temperature, pressure, wall surface conditions), the liquid in some WG-ICDA regions and the subsequent WG-ICDA subregions of a pipeline segment can flow or accumulate until the WG-ICDA subregion is full and then carries over to the next dow
21、nstream WG-ICDA subregion. For specific operating conditions, the liquid can accumulate and remain stagnant within the WG-ICDA subregion (liquid holdup). As liquid continuously travels between accumulation points, the effects of flow regimes shall be considered. These flow dynamic characteristics in
22、fluence internal corrosion, and thus are a threat to the pipeline integrity. SP0110-2010 ii NACE International The goal of WG-ICDA is to identify confirmatory or most probable locations (MPLs) along a WG-ICDA region for determination of the position of assessment sites. These assessment sites are wh
23、ere internal corrosion damage has been identified by means of integrating available historical information in combination with the use of flow models to determine liquid holdup and flow regimes and internal corrosion prediction models (ICPMs) that a pipeline operator deems appropriate for its specif
24、ic application to predict or calculate internal corrosion rates. The essential focus is the discrimination of conditions along the length of a WG-ICDA region so that possible local WG-ICDA subregion integrity threats with respect to internal corrosion are identified for prioritized damage assessment
25、, repair, and mitigation. WG-ICDA emphasizes damage distribution over absolute corrosion rate, and the ICPMs can fit into the overall process by serving as a tool, whenever possible, to predict wall losses within one flow pattern (e.g., stratified, slug, annular, or annular/mist) within a specific W
26、G-ICDA region and/or WG-ICDA subregion. This standard was prepared by Task Group (TG) 305, “Internal Corrosion Direct Assessment for Wet Gas Pipelines.” TG 305 is administered by Specific Technology Group (STG) 35, “Pipelines, Tanks, and Well Casings.” This standard is issued by NACE International u
27、nder the auspices of STG 35. 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
28、state something good and is recommended, but is not considered mandatory. The term may is used to state something considered optional. _ SP0110-2010 NACE International iii _ NACE International Standard Practice Wet Gas Internal Corrosion Direct Assessment Methodology for Pipelines Contents 1. Genera
29、l 1 2. Definitions 7 3. Step 1Preassessment 10 4. Step 2Indirect Inspection . 15 5. Step 3Detailed Examination 23 6. Step 4Postassessment 25 7. Records . 26 References 28 Appendix A: Factors Influencing Corrosion Severity (Nonmandatory) . 33 Appendix B: Internal Corrosion Prediction Models (Nonmanda
30、tory) 38 Appendix C: Examples of WG-ICDA Region and Subregion Identification, and Assessment Site Selection (Nonmandatory) . 40 FIGURES Figure 1Preassessment Step 4 Figure 2Indirect Inspection Step 5 Figure 3Detailed Examination Step . 6 Figure 4Postassessment Step 7 Figure C1WG-ICDA region identifi
31、cation for an idealized example 41 Figure C2Example of a flow pattern map 43 Figure C3WG-ICDA Subregion identification example . 44 Figure C4Graphical representation of the example pipeline segment showing elevation profile, liquid holdup, and WG-ICDA regions identified . 45 Figure C5Graphical repre
32、sentation of WG-ICDA subregions identified within WG-ICDA Region 1 47 TABLES Table 1Typical Data for Use of WG-ICDA Methodology . 12 Table 2Summary Table . 19 Table 3Minimum Number of Final Assessment Sites . 21 Table 4Final Assessment Site Selection . 22 Table C1Summary Table for WG-ICDA Region 1 a
33、nd Its Subregions . 49 Table C2Final Assessment Site Selection 55 _ SP0110-2010 NACE International 1 _ Section 1: General 1.1 Introduction 1.1.1 This standard covers the NACE internal corrosion direct assessment (ICDA) process for wet natural gas pipeline systems (i.e., WG-ICDA). It is intended to s
34、erve as a guide for applying the WG-ICDA process to onshore and offshore natural gas pipeline systems that: (a) contain wet gas (gas-liquid ratio GLR 5,000); (b) are not covered by dry gas internal corrosion direct assessment (DG-ICDA); and (c) meet the feasibility requirements described in Paragrap
35、h 3.3 of this standard. 1.1.2 The two primary purposes of the WG-ICDA methodology are (1) to enhance the assessment of internal corrosion in natural gas pipelines, and (2) to improve pipeline integrity. 1.1.3 The WG-ICDA methodology assesses where along a pipeline segment the internal corrosion seve
36、rity is potentially highest. The methodology includes existing methods of detailed examination available to a pipeline operator to determine occurrence, as well as the extent and severity, of internal corrosion. 1.1.4 WG-ICDA also uses flow modeling results (e.g., dew point, flow velocities, liquid
37、holdup, and flow patterns) and provides a framework to use those models. 1.1.5 WG-ICDA was developed for onshore and offshore natural gas pipelines that have produced or condensed water as a normal impurity. WG-ICDA is applicable to wet gas gathering and gas producing pipelines.3,4 The basis of WG-I
38、CDA is for wet gas pipelines and consists of a detailed examination of selected assessment sites with the highest expected corrosion severity where there may be a reduction of the pipe wall thickness to an extent that would pose a threat to the pipeline if mitigation or other measures are not taken
39、before the next assessment. This allows inferences to be made about the remainder of the pipeline segment. 1.1.6 One benefit of the WG-ICDA approach is that, for gas pipelines, an assessment can be performed on a pipeline segment for which alternative methods (e.g., ILI, hydrostatic testing) may be
40、impractical. 1.1.7 WG-ICDA has limitations, and not all pipelines can be successfully assessed with WG-ICDA. These limitations are identified in the preassessment step. 1.1.8 Drips, compressing stations, vessels, and other equipment unrelated to pipelines are not included in this standard. 1.1.9 The
41、 provisions of this standard shall be applied by or under the direction of competent persons who, by reason of knowledge of the physical sciences and the principles of engineering and mathematics, acquired by education or related practical experience, are qualified to engage in the practice of corro
42、sion control and risk assessment for pipeline systems. Such persons may be (1) registered professional engineers, (2) recognized as corrosion specialists by organizations such as NACE International, or (3) professionals (i.e., engineers or technologists) with professional experience, including detec
43、tion/mitigation of internal corrosion and evaluation of internal corrosion on pipelines. 1.1.10 For accurate and correct application of this standard, the standard shall be used in its entirety. Using or referring to only specific paragraphs or sections may lead to misinterpretation or misapplicatio
44、n. SP0110-2010 2 NACE International 1.1.11 In the process of applying WG-ICDA, other pipeline integrity threats such as external corrosion, mechanical damage, and stress corrosion cracking (SCC) may also be detected. When such threats are detected, additional detailed examination or inspections must
45、 be performed to ensure that pipeline integrity is not compromised, regardless of mechanism. 1.1.12 This standard does not address specific remedial actions to be taken when corrosion is found. However, guidance is provided in ASME(1) B31.85and other relevant, jurisdictionally applicable documents.
46、The pipeline operator should use appropriate methods to address threats other than internal corrosion, such as those described in ASME B31.8, ASME B31.8S,6API(2)1160,7API 579,8CSA(3) Z662,9BS(4)7910,10ASME B31G,11 RSTRENG,12NACE standards, international standards, and other documents. 1.2 Four-Step
47、Process 1.2.1 WG-ICDA requires the integration of data from the pipelines physical characteristics, current and historical operating conditions, multiple field examinations, and inspections to determine the remaining thickness of the pipeline wall. 1.2.2 WG-ICDA includes the following four steps, as
48、 shown in Figures 1 through 4. Details of each step are described in Sections 3, 4, 5, and 6. 1.2.2.1 Step 1Preassessment. The preassessment step includes the collection and organization of all existing, relevant, essential, historic, and current operating data about the pipeline relevant to assessment of internal corrosion. This includes determining whether WG-ICDA is feasible and defining the pipeline segment to be assessed. This step includes identification of WG-ICDA regions within the pipeline segment based on
