1、 Item No. 24253 NACE International Publication 61114 This Technical Committee Report has been prepared by NACE International Task Group (TG) 380,* “Underdeposit Corrosion Testing and Mitigation.” Underdeposit Corrosion (UDC) Testing and Mitigation Methods in the Oil and Gas Industry February 2014, N
2、ACE International This NACE International 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 manufacturing, marketing, purchasing, or using products, pro
3、cesses, or procedures not included in this report. Nothing contained in this NACE International 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 by Letters Patent, or as indemnifyin
4、g 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 relating to the subject. Unpredictable ci
5、rcumstances 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, environmental, and regulatory documents and fo
6、r 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 detailed or referred to within this report.
7、 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 requirements prior to the use of th
8、is 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 NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old. Purchasers of NACE repor
9、ts may receive current information on all NACE publications by contacting the NACE FirstService Department, 15835 Park Ten Place, Houston, Texas 77084-5145 (telephone +1 281-228-6200). Foreword This technical committee report presents an overview of the various methods used in the oil and gas indust
10、ry to test and mitigate underdeposit corrosion (UDC) occurring in corrosive pipeline environments when solids are present and carbon steel is used. The testing techniques are different in nature and in design and therefore assess and evaluate UDC in different ways. It is not the intent of this repor
11、t to favor one method over another. The objective is to provide industry users with some tools and means from which to choose when confronted with such an issue. The choice of methods relates mainly to the type of application at hand and how well the methods apply to such situations. The user is cau
12、tioned that the testing discussed in this report may not be representative or applicable to all pipeline conditions. UDC testing under majority hydrocarbon conditions or in the presence of wax, asphaltenes, and biofilms is still in its infancy and was excluded from this report. This NACE technical c
13、ommittee report was prepared by Task Group (TG) 380, “Underdeposit CorrosionTesting and Mitigation,” which is administered by Specific Technology Group (STG) 61, “InhibitionCorrosion and Scaling,” and is sponsored by STG 31, “Oil and Gas ProductionCorrosion and Scale Inhibition,” and STG 60, “Corros
14、ion Mechanisms.” This report is issued by NACE International under the auspices of STG 61. * Chair Mohsen Achour, ConocoPhillips, Bartlesville, OK. NACE International 2 NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In
15、 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 and guidance for consideration when applying this technology in the future. However
16、, these statements are not intended to be requirements or recommendations for general application of this technology, and must not be construed as such. Table of Contents Introduction . 3 Examples of UDC Testing Methods 3 Bubble Test Method 3 Artificial Pit Test Method . 5 Sand Deposit Test Method .
17、 7 Iron Sulfide Test Method in Inhibited Systems . 12 UDC Autoclave Method. 15 Coupled Multi-Electrode Array Test Method . 17 UDC Mitigating Methods . 24 Mitigation by Design 25 Mechanical and Physical Methods 25 Chemical Treatment 26 Challenges and Gaps 26 References 27 FIGURES Figure 1: Photo of b
18、ubble test apparatus 3 Figure 2: Bubble test used for UDC 4 Figure 3: Typical results from bubble test with solids and inhibitors 1 through 8 . 5 Figure 4: Schematic of artificial pit test . 6 Figure 5: Pit probe detail showing location of iron sulfide deposit that builds up during the test . 6 Figu
19、re 6: Glass cell with accessories used for the inhibitor tests with sand deposits 8 Figure 7: Sketch of the test specimens mounted in the specimen holder 9 Figure 8: UDC experiment schematic (PTFE = polytetrafluorethylene) 13 Figure 9: UDC experiment photo ER probe coated with FeS 14 Figure 10: Corr
20、osion plot ER probe coated with in situ precipitated FeS deposit 14 Figure 11: Corrosion plot ER probe suspended in brine phase . 15 Figure 12: Stirred autoclave for inhibitor testing . 15 Figure 13: Specimen arrangement in autoclave . 16 Figure 14: Flat specimen in a PEEK cup. . 16 Figure 15: Schem
21、atic diagram of test setup . 22 Figure 16: Photograph of setup for ambient-pressure tests . 23 Figure 17: Photograph of setup for high-pressure tests . 23 Figure 18: Example of evolution of average galvanic corrosion rate with time 24 Figure 19: Example of evolution of individual galvanic corrosion
22、rates with time 24 TABLES Table 1: Specimens Description and Surface Areas 9 NACE International 3 Introduction Failures caused by UDC occurrence have been reported in the oil and gas industry in various applications. The solid deposits to be addressed in this report are limited to sand, scale, and c
23、orrosion products inside pipelines. Wax, asphaltenes, and biofilms certainly affect UDC; however, they are beyond the scope of this report. Accelerated corrosion under iron sulfide and iron carbonate films is thought to cause pitting initiation and propagation in CO2 and H2S containing environments.
24、 Pipeline mechanical cleaning becomes a key issue and is usually achieved using aggressive pigging programs on a regular basis. Moreover, corrosion inhibitors have the potential to prevent this type of corrosion, or at least minimize the pigging frequency. It is general practice to establish laborat
25、ory testing protocols that are able to assess UDC and evaluate the performance of a given inhibitor in protecting the pipe wall in the presence of solids on the surface. Examples of UDC Testing Methods Bubble Test Method The standard bubble test is probably the simplest laboratory testing method use
26、d to assess UDC at ambient pressure. It simulates stagnant conditions and is capable of accommodating any type of solids, as the solids are simply dropped to the bottom of the test cell. The main objective of this test is to assess how the presence of solids affects the efficiency of the corrosion i
27、nhibitor to provide protection as a result of either inhibitor adsorption/loss to solids or competition between solids and the inhibitor to cover the steel surface. Test Apparatus Figure 1 shows a photo of a typical bubble test apparatus. The test vessel hosts fluids and electrodes (reference, worki
28、ng, and counter) as well as the gas bubbling tube and the temperature controller. It sits on a magnetic stir mantle and is normally wrapped with heat tape to operate at a given temperature range. As shown, and because of glassware arrangement, the bubble test is typically operated at ambient pressur
29、e and temperatures below boiling point. Figure 1: Photo of bubble test apparatus Test Procedure This test is normally designed in various ways, depending on the purpose of the investigation, the solids present in the system, and the corrosion measurement technique. The following is an example of a t
30、est procedure that is typically used to assess the effect of sand presence on inhibitor performance. 1. Two test vessels (vessel 1 and vessel 2) are used, one for testing without solids and one with solids. 2. Linear polarization resistance (LPR) electrodes are prepared by polishing the carbon steel
31、 working electrode, and then rinsing with non-aqueous solvents and drying. The reference electrodes are usually rinsed with xylene, then acetone. One set of electrodes is used for each chemical to be tested. Weight of the working electrodes is normally recorded if weight-loss measurements are to be
32、made. The electrodes are not inserted into vessel at this time. 3. Solids are weighed and placed in vessel 1. NACE International 4 4. Volumes of brine and oil are then added. 5. The stirrer bar is placed in vessel 1 and the stirrer is activated. The immersion heater is then activated and the tempera
33、ture set at the desired value. 6. The CO2 sparge is usually started at this point. The electrodes are inserted and connected to the multiplexer. The electrochemical acquisition software is started. Usually, the vessel is allowed to sparge, and the electrochemical acquisition software is programmed f
34、or LPR measurements for 1 h (uninhibited case). 7. The LPR program is paused after 1 h. 8. Normally, the desired amount of chemical is injected into the water phase in the vessel or on top of the oil phase, if oil/condensate is used. 9. The test is allowed to run for 48 h. 10. If weight-loss measure
35、ments are to be made, then the working electrode is cleaned and weighed. The average general corrosion rate is commonly calculated from the weight-loss measurements. Data Collection and Analysis Figure 2 is a picture of the test vessel used, including solids. The working electrode does not commonly
36、touch the solids (e.g., the sand in this case). Typical performance curves obtained from the test are shown in Figure 3. In this case, a total of eight inhibitors were tested for performance when 10 grams of solids were present. The horizontal section of the curves represents the pre-corrosion step
37、(for 3 h) before adding the inhibitor. This is an indication of a high blank corrosive environment (corrosion rate of about 250 mpy .635 mm/y). Once the inhibitor is injected, corrosion rate drops and reaches a low level at steady state. As shown in Figure 3, different inhibitors perform differently
38、 in the presence of sand. Inhibitor 1 is the worst performer, and inhibitor 8 showed the best performance. The lack of performance is likely because of the loss of inhibitor to the solids. Figure 2: Bubble test used for UDC. NACE International 5 LPR Bub ble T ests: 5pp m CI w ith 10 gram Solids0 .11
39、 .01 0 .01 0 0 .01 0 0 0 .00 2 4 6 8 10 12 14 16 18 20 22Time (hrs )Corrosion Rate (mpy)Bla nk12345678Inj e c ted I nhibito rFigure 3: Typical results from bubble test with solids and inhibitors 1 through 8. Artificial Pit Test Method1 A conservative approach to inhibitor development is to address t
40、he ability of the inhibitor to stifle localized corrosion that is already propagating at a known rate. This is often achieved using an artificial pit or pencil electrode subjected to pre-corrosion and coupled through an ammeter to a large piece of steel immersed in the environment. The main objectiv
41、e of this technique is to simulate accelerated corrosion in local areas where semi-protective corrosion products (e.g., iron sulfides and/or iron carbonate) have not formed or have broken down, and where the pit is covered with a non-protective oxide cap. Commercial inhibitors are usually evaluated
42、using this technique. This technique is based on using a zero-resistance ammeter (ZRA) to measure the current between an artificial pit electrode connected to a counter electrode of the same material, but of a much larger area. A typical schematic diagram is shown in Figure 4. A typical area ratio b
43、etween the external electrode and the artificial pit is 1,000 to 1. The potential of the coupled electrodes is usually dominated by the large bar electrode, whereas the coupled galvanic current is typically controlled by the artificial pit. The coupling currents flowing before and after inhibitor ad
44、dition are normally used as an indication of the ability of the inhibitor to retard corrosion in the artificial pit. Usually, this current can be related to the rate of pit propagation. The potential of the couple (and thus the bar electrode) before and after inhibitor addition normally gives useful
45、 complementary information. This technique is typically supported by the use of polarization resistance measurements with the electrodes periodically de-coupled to enable measurement. This enables an uncoupled corrosion rate for both the pit and the bar to be established. An indication of the total
46、corrosion rate in the pit is normally obtained by adding the corrosion rate implied by the couple current to the uncoupled pit corrosion rate. Polarization curves at the end of an experiment are often used to examine corrosion rates and inhibitor function. LPR Bubble Tests: 5 ppm Cl with 10 g solids
47、 Time (h) 1 mpy = 0.0254 mm/y NACE International 6 P l a t i n u m c o u n t e rR e f e r e n c e L u g g i nP o l y p r o p y l e n e f l a n g eT h e r m o c o u p l e p o c k e tS o l u t i o nG a s i nG a s o u t t o s c r u b b e rF l u i d L e v e lA r t i f i c i a l p i tL a r g e c a t h o
48、d eZ R AFigure 4: Schematic of artificial pit test. Sample Preparation Both the artificial pit electrodes and the 12 mm rod counter electrodes are prepared from the same steel. The wire electrodes are recessed by anodic polarization of the polished electrode in an acid solution (see Figure 5). After
49、 removal from the acid solution, the “pit” is cleaned by injecting 1 mL of concentrated nitric acid followed by rinsing and drying with warm air. The actual pit depth is measured directly with a plunger-type pit depth gauge and a final adjustment to achieve the normal depth (typically 1 mm) is made by polishing the face of the mounted sample. r e c e s s e d e le c t r o d eI r o n s u lf id e c a pm o u n t in g r e s inFigure 5: Pit probe detail showing location of iron sulfide deposit that builds up during the test. Test Procedure The following test procedure is generall
