1、 1 Item No. 24003 NACE International Publication 1C187 (2005 Edition) This Technical Committee Report has been prepared by NACE International Task Group T-1C-16* on Galvanic Probe Type Corrosion Monitors Use of Galvanic Probe Corrosion Monitors in Oil and Gas Drilling and Production Operations March
2、 2005, NACE 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 produ
3、cts, 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 by Letters Patent, or as indemnifying or p
4、rotecting 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 circumst
5、ances 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 for dete
6、rmining 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. Users
7、 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 this rep
8、ort. 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 NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old.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 reports may
9、 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 This NACE technical committee report was prepared to provide an overview of the galvanic probe a
10、s it may be used in corrosion detection and monitoring in the petroleum production industry. The report presents the background and theory of operation of galvanic probes, typical probe configurations, probe placement, and maintenance requirements. Typical applications for corrosion monitoring and i
11、nhibitor evaluation, including examples of data, are discussed. Galvanic probe corrosion monitors are simple, rugged instruments constructed of two dissimilar metals that are submerged in the electrolyte to be studied. The direct current generated by the dissimilar metals is a function of the corros
12、iveness of the electrolyte in which the probe is submerged.1-4This technical committee report was originally prepared in 1987 by NACE Task Group T-1C-16, a component of former Unit Committee T-1C on Corrosion Monitoring in Petroleum Production. Unit Committees T-1C and T-1D were combined, and the re
13、port was reviewed and reaffirmed by Unit Committee T-1D on Corrosion Monitoring and Control of Corrosion Environments in Petroleum Production Operations in 1995. It was reaffirmed in 2005 by Specific Technology Group (STG) 31 on Oil and Gas ProductionCorrosion and Scale Inhibition. This technical co
14、mmittee report is issued by NACE International under the auspices of STG 31. _ *Chair Tom McSpadden, Thomas Kelley Co. Inc., Tulsa, OK. NACE International 2 NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In many cases,
15、 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, these stat
16、ements are not intended to be recommendations for general application of this technology, and must not be construed as such. Introduction Historical Notes Current generation by two dissimilar metals submerged in an electrolyte has been recognized for at least 200 years. In 1780 Luigi Galvani (1737-1
17、798) found that if the feet of a frog supported by a brass wire driven into its spinal marrow were allowed to touch an iron plate, when the brass wire also touched the plate, the frogs legs contracted suddenly. Galvani found that the same effect could be produced with other pairs of metals besides b
18、rass and iron, but that electrical insulators gave no such effect. Galvani called the phenomena “animal electricity,” and the action was termed “galvanism.”5In 1800, Alessandro Volta (1745-1827) found that the flow of electricity was a result of contact between the two different metals, e.g., brass
19、and iron, when connected by a moist conductor such as a frogs body. Volta found that powerful electrical effects could be produced by a series of such metallic pairs. He made a pile of a large number of copper, zinc, and moist paper discs arranged in the following order: copper, zinc, paper, copper,
20、 zinc, paper, and so on. Volta found that if the bottom and top discs were touched, one with each hand, a distinct shock was felt that was not unlike that of a Leyden jar and that the sensation continued for as long as the pile was touched. Later it was found that if the paper discs were moistened w
21、ith dilute acids or salt solutions, the electrical effects were intensified. Voltas device became known as the “Voltaic pile.”6Theory of Operation The application of galvanic probes as corrosion monitors is a development based on the discoveries of Galvani and Volta. The steel-brass galvanic probes
22、duplicate examples of galvanic action often actually observed in the field, and almost any oilfield roustabout can cite examples of corrosion attack on steel pipe adjacent to brass valves. Changes in the electrolyte or on the probe surface result in changes in the potential and thus the current gene
23、rated by galvanic corrosion monitors. In many freely corroding systems, the current generated by a steel-brass probe is of sufficient magnitude that it is often measured easily by rather simple and inexpensive instruments. Also, carbon steel and brass rods are readily available and easy to machine.
24、Galvanic probes do not directly measure corrosion rates, but they are versatile indicating corrosion monitors. Galvanic probes are event meters, and changes in the system, e.g., temperature, velocity, pH, oxygen content, salinity, or inhibitor characteristics, result in a change in the current outpu
25、t of the probe. The action of probes with steel and brass elements has been satisfactory in many aqueous environments. Galvanic probes have been used in waters ranging from potable to saturated brine. Fortunately, in many aqueous systems there is only one principal variable, e.g., oxygen content or
26、changes in inhibition. However, any abrupt change in current output indicates a change in the system and often prompts an investigation into the cause of that change. Other than corrosion coupons, galvanic probes are among the least complicated of all corrosion monitors. The probes reflect changes i
27、n corrosion conditions very rapidly, usually within a few minutes. Oxygen entry is indicated immediately. Galvanic probes are usually the only oxygen detection instruments used continuously in dynamic systems. Polarization effects (e.g., buildup of inhibitor film or self-arresting corrosion products
28、), which are influenced by the environment and metals used for probes, are reflected less rapidly. Galvanic probe monitors are not the same as “nonchemical water treating devices.” Nonchemical water treating devices are marketed with the statement that they treat water by changing its physical prope
29、rties without altering its chemical composition.7,8These “water alteration devices” are described by their manufacturers as being effective in nonchemical water treatment to control scale, corrosion, and other effects. Such devices may be magnetic, electromagnetic, or dependent on catalytic action.
30、The galvanic probes described in this report reflect changes in an electrolyte but do not alter the electrolyte itself. They are indicating instruments and not water-treating devices. Figure 1 shows galvanic probes for installation in 33.4- and 60.3-mm nominal OD (1.00- and 2.00-in. National Pipe Th
31、read NPT9) female fittings. The threaded probes are generally used for pressures up to the rated working pressures shown in API(1)Spec 6A.10Probe elements are often installed in the appropriate class of blind flanges_ (1)American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005. NACE I
32、nternational 3 for higher-pressure applications. Probes that are installed and removed without depressurizing the system are available. Some of the retractable probes are rated at 17 MPa (2,500 psi) working pressure. The probes shown in Figure 1 are usually operated at temperatures up to 121C (250F)
33、. FIGURE 1: An Electronic Galvanic Probe Head for Use With Electronic Galvanic Current Monitor Single-element probes contained within threaded pipe plugs of 21.3- to 33.4-mm nominal OD (0.500- to 1.00-in. NPT) are also available. The single element can serve as either the anode or the cathode, depen
34、ding on the metal used for the element. The steel pipe or vessel is the other metal in the probe. Brass or high-potential aluminum is often used in the single-element probes. Steel often acts as the anodic element in a two-element probe, but galvanic probes are often constructed with almost any two
35、dissimilar metals. Selection of probe elements usually depends on the objective of the application. Some of the more commonly used metals include carbon steel coupled with brass, high-potential aluminum (aluminum mercury or aluminum indium alloy), admiralty metals, nickel, copper, and various stainl
36、ess steels (SSs). Nickel coupled with UNS(2)S41000 (type 410 SS) or UNS S31600 (type 316 SS) has been used in some geothermal drilling projects. Current generated by the probes is usually measured with panel or recording microammeters or potentiometers. Panel meters are generally used only at attend
37、ed locations. Small recording microammeters with 50-mm (2-in.) wide 30-day strip charts are frequently used. Both 110 V AC and 12 V DC chart drives are available. Recorders are used for providing a continuous performance record at unattended locations. When several probes are installed at a central
38、location, a multi-channel recording potentiometer is often used by installing a suitable value resistor across each pair of probe elements. Probe readings are also transmitted and logged through computerized data acquisition systems. The external circuit (meter) is generally connected to each elemen
39、t of a probe at all times. If the meter is disconnected even for a few minutes, the cathode depolarizes and it may take several hours for the probe to stabilize after the meter is reconnected. Recorders are sometimes located several hundred meters from the probes. Some of the small strip chart recor
40、ders have an internal resistance of 4,600 ohms; thus, a few ohms additional resistance in the lead wiring may not be detrimental. If electrical interference is observed, shielded wires are generally used. _ (2)Metals and Alloys in the Unified Numbering System (latest revision), a joint publication o
41、f ASTM International (ASTM) and the American Society of Automotive Engineers Inc. (SAE), 400 Commonwealth Drive, Warrendale, PA 15096. NACE International 4 The operating potential of galvanic probes is low (0 to 0.5 V); therefore, the spark hazard is low. In hazardous locations, however, probe termi
42、nals are generally enclosed in explosion-proof enclosures. Probe bodies that fit standard explosion-proof housings are available. Recorders are usually placed in areas that have been determined to be safe. Terminal connections of the probes are generally waterproofed to prevent corrosion of the term
43、inal connections because the corrosion products can block current flow. Rubber electrical tape, electrical putty, and various silicon compounds are generally used to protect the terminals. Placement of Probes The placement of galvanic probes, like the placement of any corrosion monitor, is usually g
44、iven much consideration. Galvanic probes generally function in any system that contains enough electrolyte (usually water) to bridge the area between the two elements of the probes. There is generally uniform surface area on the elements. In an electrolyte at a given flow rate, the probe current inc
45、reases as the area of the probe elements covered by the electrolyte increases. In most dynamic systems, the probe exposure is uniform. Probe current values fluctuate in systems experiencing nonuniform rates of flow. Current increases as the velocity increases. Varying rates of flow are generally enc
46、ountered in flow lines from gas-lifted wells that are on intermittent flow. In systems involving such changing flow rates a pattern of repeating current values is usually established. Any deviation from the established pattern usually indicates that another variable, e.g., inhibition treatment, has
47、been introduced. The following locations are usually considered for galvanic probes: (1) high-velocity fluid streams and impingement points, (2) dead fluid areas, (3) downstream from points where oxygen entry into aqueous systems is likely (such points include tanks, pumps, and water make-up lines i
48、n amine sweetening systems), and (4) locations where water is likely to collect in gas systems (i.e., suction scrubbers on compressors, separators, water drain lines from dehydrators, and low spots in wet gas lines). Galvanic probes are sometimes installed in water traps on gas lines that handle ver
49、y small volumes of water. When the performance of a corrosion inhibitor is being monitored, probes are often installed immediately downstream from the chemical injection point. Additional probes are sometimes placed further downstream to determine whether the inhibitor is being distributed to all points in the system. Maintenance Galvanic probes, like other corrosion-monitoring instruments, are not foolproof. Hydrates and foreign matter in lines can damage probe elements. Corrosion of terminal connections c
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