1、Designation: G 189 07Standard Guide forLaboratory Simulation of Corrosion Under Insulation1This standard is issued under the fixed designation G 189; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb
2、er in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the simulation of corrosion underinsulation (CUI), including both general and localized attack,on insulated specimens cu
3、t from pipe sections exposed to acorrosive environment usually at elevated temperature. Itdescribes a CUI exposure apparatus (hereinafter referred to asa CUI-Cell), preparation of specimens, simulation proceduresfor isothermal or cyclic temperature, or both, and wet/dryconditions, which are paramete
4、rs that need to be monitoredduring the simulation and the classification of simulation type.1.2 The application of this guide is broad and can incorpo-rate a range of materials, environments and conditions that arebeyond the scope of a single test method. The apparatus andprocedures contained herein
5、 are principally directed at estab-lishing acceptable procedures for CUI simulation for thepurposes of evaluating the corrosivity of CUI environments oncarbon and low alloy pipe steels, and may possibly beapplicable to other materials as well. However, the same orsimilar procedures can also be utili
6、zed for the evaluation of (1)CUI on other metals or alloys, (2) anti-corrosive treatments onmetal surfaces, and (3) the potential contribution of thermalinsulation and its constituents on CUI. The only requirementsare that they can be machined, formed or incorporated into theCUI-Cell pipe configurat
7、ion as described herein.1.3 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.4 This standard does not purport to address all of thesafet
8、y concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 106/A 106M Specification for Se
9、amless Carbon SteelPipe for High-Temperature ServiceC 552 Specification for Cellular Glass Thermal InsulationC 871 Test Methods for Chemical Analysis of ThermalInsulation Materials for Leachable Chloride, Fluoride,Silicate, and Sodium IonsD 1193 Specification for Reagent WaterG1 Practice for Prepari
10、ng, Cleaning, and Evaluating Cor-rosion Test SpecimensG3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTest
11、ingG31 Practice for Laboratory Immersion Corrosion Testingof MetalsG46 Guide for Examination and Evaluation of PittingCorrosionG59 Test Method for Conducting Potentiodynamic Polar-ization Resistance MeasurementsG 102 Practice for Calculation of Corrosion Rates andRelated Information from Electrochem
12、ical Measurements3. Terminology3.1 The terminology used herein, if not specifically definedotherwise, shall be construed to be in accordance with Termi-nology G15.3.2 Definitions of Terms Specific to This Standard:3.2.1 corrosion under insulation (CUI)the corrosion ofsteel or other materials under t
13、hermal insulation due to thepresence of water, oxygen and/or other corrodants.3.2.2 control conditionan exposure condition using apre-selected environment without the inclusion of inhibitors,protective treatments, or additives to the thermal insulation orexposure environment. It is selected to provi
14、de baseline data towhich data from other exposure conditions can be compared.3.2.3 protection ratioratio of the corrosion rate with thesurface treatment or particular insulative material, or both, withthat obtained for the control condition.1This guide is under the jurisdiction of ASTM Committee G01
15、 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved Feb. 15, 2007. Published March 2007.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
16、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Guide4.1 The CUI-Cell consists of three
17、to six ring specimensseparated by non-conductive spacers and held together by twoblind flanged pipe sections, one on each end. Thermal insula-tion is placed around one-half of the evaluation section of thecell and sealed providing an annular space to retain a corrosiveenvironment. The other half of
18、the insulation is put in place tohave proper heat transfer conditions as a typical insulated pipesection with internal heating. Provisions are given herein to usethe specimens as corrosion coupons or electrodes in twoseparate electrochemical cells. One half of the CUI-Cell can beused to perform a CU
19、I simulation under the control conditionwhile the other can be used to evaluate inhibitors, protectivecoatings or insulative materials.4.2 Corrosion measurements can be made using either massloss data (Procedure A) or electrochemical dynamic polariza-tion resistance methods (Procedure B), or both. T
20、his apparatuscan be used to conduct laboratory evaluations under isothermalor cyclic temperature and under wet or wet/dry conditionssimulating desired conditions in service. Comparison of themeasured corrosion rates from exposures conducted withvarious surface treatments on steel and/or with various
21、 insula-tive materials with corrosion rates obtained with bare steelunder the control condition provides the basis for assessment ofprotection efficiency. A value of protection efficiency of lessthan 1.0 indicates reduction in the severity of corrosion relativeto the control condition whereas a valu
22、e greater than 1.0indicates an increase in the severity of corrosion relative to thecontrol condition.5. Significance and Use5.1 The corrosion observed on steel and other materialsunder thermal insulation is of great concern for many industriesincluding chemical processing, petroleum refining and el
23、ectricpower generation. In most cases, insulation is utilized onpiping and vessels to maintain the temperatures of the operat-ing systems for process stabilization and energy conservation.However, these situations can also provide the prerequisites forthe occurrence of general or localized corrosion
24、, or both, and instainless steels, stress corrosion cracking. For example, com-bined with elevated temperatures, CUI can sometimes result inaqueous corrosion rates for steel that are greater than thosefound in conventional immersion tests conducted in either openor closed systems (see Fig. 1).3This
25、figure shows actual CUIdata determined in the field compared with the corrosion datafrom fully immersed corrosion coupons tests.5.2 This guide provides a technical basis for laboratorysimulation of many of the manifestations of CUI. This is anarea where there has been a need for better simulationtec
26、hniques, but until recently, has eluded many investigators.Much of the available experimental data is based on field andin plant measurements of remaining wall thickness. Laboratorystudies have generally been limited to simple immersion testsfor the corrosivity of leachants from thermal insulation o
27、ncorrosion coupons using techniques similar to those given in3Ashbaugh, W. G., “Corrosion of Metals Under Insulation,” Process IndustriesCorrosion, Ed. B. J. Moniz and W. I. Pollock, ASTM STP 880, West Conshohoken,PA, 1986.NOTEThe actual CUI corrosion rates can be in excess of the those obtain in co
28、nventional laboratory immersion exposures.FIG. 1 Comparison of Actual Plant CUI Corrosion Rates Measurements (Open Data Points Shown is for Plant CUI) with LaboratoryCorrosion Data Obtained in Open and Closed SystemsG189072Practice G31. The field and inplant tests give an indication ofcorrosion afte
29、r the fact and can not be easily utilized forexperimental purposes. The use of coupons in laboratoryimmersion tests can give a general indication of corrosiontendencies. However, in some cases, these procedures areuseful in ranking insulative materials in terms of their tenden-cies to leach corrosiv
30、e species. However, this immersiontechnique does not always present an accurate representation ofthe actual CUI tendencies experienced in the service due todifferences in exposure geometry, temperature, cyclic tempera-tures, or wet/dry conditions in the plant and field environments.5.3 One of the sp
31、ecial aspects of the apparatus and meth-odologies contained herein are their capabilities to accommo-date several aspects critical to successful simulation of the CUIexposure condition. These are: (1) an idealized annular geom-etry between piping and surrounding thermal insulation, (2)internal heati
32、ng to produce a hot-wall surface on which CUIcan be quantified, (3) introduction of ionic solutions into theannular cavity between the piping and thermal insulation, (4)control of the temperature to produce either isothermal orcyclic temperature conditions, and (5) control of the delivery ofthe cont
33、rol or solution to produce wet or wet-dry conditions.Other simpler methods can be used to run corrosion evalua-tions on specimens immersed in various solutions andleachants from thermal insulation. In some cases, these proce-dures may be acceptable for evaluation of the contribution ofvarious factor
34、s on corrosion. However, they do not provideaccommodation of the above mentioned factors that may beneeded for CUI simulation.5.4 With the CUI-Cell, the pipe material, insulation andenvironment can be selected for the desired simulation needed.Therefore, no single standard exposure condition can bed
35、efined. The guide is designed to assist in the laboratorysimulation of (1) the influence of different insulation materialson CUI that, in some cases, may contain materials or additives,or both, that can accelerate corrosion, (2) the effect of appliedor otherwise incorporated inhibitors or protective
36、 coatings onreducing the extent and severity of CUI. This guide providesinformation on CUI in a relatively short time (approximately72 h) as well as providing a means of assessing variation ofcorrosion rate with time and environmental conditions.6. Apparatus6.1 The CUI-Cell4can simulate the severity
37、 and modality ofcorrosion that has been described to occur under thermalinsulation.3,5Initially this cell was developed for the evaluationof various surface treatments to be applied on the externalsurface of pipe to remediate CUI problems. However, subse-quently, this same apparatus has been used su
38、ccessfully toevaluate the influence of various types of thermal insulation on4Abayarathna, D., Ashbaugh, W. G., Kane, R. D., McGowan, N., and Heimann,B., “Measurement of Corrosion Under Insulation and Effectiveness of ProtectiveCoatings,” Corrosion/97, Paper No. 266, NACE International, Houston, Tex
39、as,March 1997.5Ullrich, O. A., MTI Technical Report No. 7, “Investigation of an Approach forDetection of Corrosion Under Insulation,” MTI Project 12, Phase II, MaterialsTechnology Institute of the Chemical Process Industries, March 1982.NOTEThe electrical connections to the specimens and contact of
40、the thermocouple must be made outside of the wetted portion of the CUI-Cell (seeFigs. 3 and 4 for more details).FIG. 2 Schematic of CUI-CellG189073CUI. In the cell, corrosion is intended to occur on the outersurface of ring specimens machined from a selected material.Fig. 2 shows a schematic represe
41、ntation of the CUI-Cell. Thecomponents of the cell include the following:6.1.1 Blind Flange SectionsThe CUI-Cell consists of two,nominal two-inch diameter pipe sections that is, two-inchnominal diameter pipe material with a thickness of 0.187 in.(4.75 mm) as shown in Specification A 106/A 106M, Grad
42、e B,or alternative material to match that being evaluated by thissimulation; one for each end of the cell. Each end includes abolted flange pair consisting of a weldneck, threaded or lapjoint flange and a blind flange and attached pipe section. Pipeclamps or other suitable devices can be used to hol
43、d the flangedends and the ring specimens together. Any device is acceptablethat provide adequate sealing force between the various sec-tions of the CUI-Cell.6.1.2 Ring SpecimensThe CUI-Cell consists of six ringspecimens that are separated by nonporous, nonconductivespacers (see Section 7 for more de
44、tailed information). Theevaluation portion, which includes alternate ring specimens ofthe intended material and nonconductive rings, is held togetherby two blind flanged pipe sections on both ends. The two setsof three ring specimens and spacers should be separated by anextra thick, nonconductive ri
45、ng spacer (dam) at the center ofthe CUI-cell. This allows for separate corrosion measurementsto be made on each set of specimens. For electrochemicalmeasurements, each ring specimen should contain an attach-ment screw for connection of electrical leads to the potentiostat(Fig. 2). The connections sh
46、ould be made outside of the areaexposed to the corrosive environment. The nonconductivespacers should be made from a machinable, temperatureresistant, non-conductive material. Machinable polytetrafluo-roethylene (PTFE) resins with high melting points are suitablein most cases for use up to about 400
47、 to 450F (200 to 230C).6.1.3 Internal Heater and Temperature ControllerThetemperature on the outer surface of the ring specimens isachieved via an immersion heater (nominally 0.625 in. (1.6cm) in diameter) having 400 W located on the inside of thepipe section mounted through the center of one of the
48、 blindflanges using an NPT connection. The temperature of theevaluation section of the CUI-Cell should be monitored andcontrolled with a thermocouple contacting the outer surface ofthe innermost ring specimen at a location outside of the areaexposed to the corrosive environment but under the thermal
49、insulation as shown in Figs. 3 and 4. The inside of the pipesection is filled with a heat transfer oil stable at the maximumintended temperature. The oil inside the cell assembly isconnected to an oil reservoir of at least 100 ml capacity througha metal tube allowing for the expansion and contraction of theoil with temperature. The temperature controller employedshould be able to control temperature to 62F (1C). If cyclictemperature exposures are desired, the controller should havemultiple programmable temperature settings, heat-up rates andsoak times.NOTEOpposite half o
