1、Item No. 24250 NACE International Publication 10A292 (2013 Edition) This Technical Committee Report has been prepared by NACE International Task Group (TG) 014,* “Corrosion Control of Ductile and Cast Iron Pipe.” Corrosion and Corrosion Control for Buried Cast- and Ductile-Iron Pipe May 2013, NACE I
2、nternational 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 manufacturing, marketing, purchasing, or using products, p
3、rocesses, 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 protect
4、ing 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 circumstances
5、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 determinin
6、g 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 of th
7、is 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 report. C
8、AUTIONARY 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 NACE reports are subject to periodic review, and may be revised or withdrawn at any time without prior notice. NACE reports are automatically withdrawn if more than 10 years old.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 recei
9、ve 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 purpose of this technical committee report is to review data on corrosion and corrosion protection
10、 of ductile and gray cast-iron pipe from literature in the U.S. and abroad (gray-iron pressure pipe is no longer produced in North America). Throughout this report, gray cast iron is referred to as “cast iron.” The following subjects are covered in this technical committee report: Engineering practi
11、ces with respect to ductile- and cast-iron pipe; Reported protective measures and results obtained by their use; Influence of the different properties of the two types of iron pipe; and Case histories of installations spanning decades in a wide range of soils. This report provides the user, owner, e
12、ngineer, contractor, and other interested parties with technical and general information as to the state-of-the-art with regard to understanding techniques and methods used to mitigate corrosion of iron pipe and fittings. It includes discussions of both historical and recent practices in which corro
13、sion is a potential problem. This technical committee report is not a standard, and as such, it does not cover compliance with any particular specifications, although specifications and standards are cited as references. _ *Chair Ronald L. Bianchetti, Russell Corrosion Consultants, El Dorado Hills,
14、CA NACE International 2 There are a variety of opinions concerning the benefits of various corrosion control systems for cast- and ductile-iron pipe, which are discussed in pertinent sections of this report. Each method or technique presents the designer and the user with numerous factors that have
15、an impact on installation and operating costs. It is intended that the reader use the report in its entirety and use the information as well as the cited resources when he or she makes decisions about corrosion control for his or her particular situation, and that he or she finds this report a usefu
16、l source of information and an engineering tool in making decisions associated with corrosion protection. This report was originally prepared in 1992 by NACE Task Group T-10A-21, a component of Unit Committee T-10A, “Cathodic Protection.” It was revised in 2012 by Task Group (TG) 014, “Corrosion Con
17、trol of Ductile and Cast Iron Pipe.” TG 014 is administered by Specific Technology Group (STG) 35, “Pipelines, Tanks, and Well Casings,” and is sponsored by STGs 02, “Protective Coatings and LiningsAtmospheric,” 03, “Protective Coatings and LiningsImmersion/Buried,” 05, “Cathodic/Anodic Protection,”
18、 and 39, “Process IndustryMaterials Applications.” This report is published by NACE under the auspices of STG 35. NACE technical committee reports are intended to convey technical information or state-of-the-art knowledge regarding corrosion. In many cases, they discuss specific applications of corr
19、osion 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 statements are not intended to be recommendatio
20、ns for general application of this technology, and must not be construed as such. Historical Perspective on Iron Pipe The earliest recorded installation of cast-iron pipe occurred in 1455 at the Dillenburg Castle in Germany. In 1664, French King Louis XIV ordered the construction of a cast-iron pipe
21、line extending 24 km (15 mi) from a pumping station at Marly-on-Seine to Versailles to supply water for the fountains and town. Sections of this cast-iron pipeline are still functioning after more than 340 years of service (as of 2005).1 Cast-iron pipe was installed in the U.S. in Philadelphia, Penn
22、sylvania, as early as 1804.2 Currently, more than 600 utilities in the U.S. and Canada have cast-iron pipe that has provided service for 100 years or longer. Currently, at least 22 utilities in the U.S. and Canada have cast-iron mains that have served continuously for 150 years or more.3 Over the ye
23、ars, cast-iron pipe has been manufactured in sizes ranging from 50 to 2,100 mm (2 to 84 in) nominal diameter, and in various laying lengths from 0.9 to 6 m (3 to 20 ft). The first cast-iron pipes were statically cast in horizontal molds. The position of casting the molds changed from a horizontal po
24、sition to a sloping position, and finally to a vertical position around the year 1850. Centrifugal casting methods have been in the process of commercial development and refinement since 1925. The first ductile-iron pipe was cast experimentally in 1948 and entered the marketplace in 1955. Since 1965
25、, ductile-iron pipe has been manufactured in accordance with ANSI(1)/AWWA(2) C 151/A 21.514 by centrifugal casting methods. In the centrifugal casting process, a controlled amount of molten metal that has the proper characteristics is introduced into a rotating mold, fitted with a socket core in suc
26、h a way as to distribute the metal over the interior of the mold surface by centrifugal force. This force holds the metal in place until solidification occurs. Pipe removed from the mold is furnace annealed to produce the prescribed physical and mechanical properties and to eliminate any casting str
27、esses that are present. By 1979, ductile-iron pipe had succeeded cast-iron pipe as the predominant water and wastewater piping material. Ductile-iron pipes are manufactured in standard sizes ranging from 80 to 1,600 mm (3 to 64 in) nominal diameter with nominal lengths of 5.5 m (18 ft) and 6.0 m (20
28、 ft) and employ rubber-gasket jointing systems. Although several types of restrained joints are available for ductile-iron pipe, the push-on joint and the mechanical joint are the most prevalent. For water applications, ductile-iron pipe is typically furnished with cement-mortar lining to prevent in
29、ternal corrosion. The exterior of the pipe normally has a 1.0 mil (25 m) thick asphaltic coating that offers some protective value, but is not intended to provide long-term corrosion protection. (1) American National Standards Institute (ANSI), 25 West 43rd St., 4th Floor, New York, NY 10036. (2) Am
30、erican Water Works Association (AWWA), 6666 Quincy Ave., Denver, CO 80235. NACE International 3 Metallurgical Differences and Similarities Between Ductile and Cast Iron The mechanical properties of iron-based alloys are largely dependent on their microstructures. Ductile and cast iron have similar c
31、hemical analyses including carbon contents, but very different microstructures. During solidification of cast iron, the carbon precipitates in the form of an interconnected continuous phase of graphite flakes intermixed with the iron matrix. The weak graphite phase provides a continuous path for cra
32、ck propagation and is responsible for the brittle nature of this alloy. While detrimental to mechanical strength and ductility, the flakes provide excellent vibration damping and thermal conductivity, which are utilized in cast iron machine tool bases, dryer drums, engine blocks, and similar applica
33、tions. During solidification of ductile iron, graphite precipitates as discrete spheroids and does not form a continuous phase. The mechanical properties of ductile iron reflect those of the continuous iron matrix phase and have yield and tensile strength similar to mild steel. However, ductility an
34、d impact strength of mild steel are higher than those of ductile iron. The small amount of sulfur that is normally present in cast iron plays a major role in graphite morphology, as it precipitates from the molten iron during solidification. In the presence of sulfur, carbon precipitates from soluti
35、on in the form of graphite flakes. By the introduction of a small amount of magnesium into the molten iron, sulfur is effectively removed, and carbon precipitates as graphite spheroids. Figure 1 shows the differences in the microstructures of these two different forms of iron. If less than an approp
36、riate amount of magnesium (or magnesium and cerium) is introduced into the iron, the ASM(3) Metals Handbook5 indicates that graphite shapes intermediate between a true nodular form and a flake form are possible and yield inferior properties compared to those of a typical ductile-iron structure. The
37、ASM Specialty Handbook on Cast Irons6 states, “It is common to attempt to produce greater than 90% of the graphite in this form ( 90% nodularity), although structures between 80 and 100% nodularity are sometimes acceptable.” During the long history of iron pipe, numerous iron ore deposits all over t
38、he world were used to make pig iron that went into pipe making. Each iron ore deposit has its own unique chemistry. In the early 1900s, only five elements were routinely analyzed in iron: carbon, silicon, manganese, sulfur, and phosphorus. With the many sources of iron ore and only basic chemical an
39、alysis, it would only be speculation as to what other elements and concentration were present in pig iron before the 1940s. Whereas in the early days of ductile iron production, more pig iron was used, scrap iron usage now approaches 80%; trace quantities from the scrap possibly affect corrosion pro
40、perties for the better in some instances and for the worse in others.7 It has been reported that chemical composition sometimes varies among pipe from the different pipe companies and even between different pours from the same company.7 As stated in the ASM Metals Handbook,5 “most of the specificati
41、ons for standard grades of ductile iron are based on properties; that is, strength and/or hardness is specified for each grade of ductile iron, and composition is either loosely specified or made subordinate to mechanical properties.” Today, even though AWWA and ASTM(4) do not specify a particular c
42、hemistry for a particular grade of ductile iron, strict chemical limits are used to achieve the desired mechanical properties. Industry representatives report that spectrographic analyses routinely provide the concentrations of more than 15 elements from each ladle of iron used in pipe production. A
43、lso, care normally is taken to prevent elements that might have undesirable effects on the strength of the pipe or quality of the potable water being transported from being introduced into the iron. ANSI/AWWA C151/A21.514 includes the minimum mechanical properties for ductile-iron pipe. The standard
44、 does not mention chemical limits and processing parameters. ANSI/AWWA pipe standards rely on the improved mechanical properties, modern manufacturing processes, and sound engineering design principles with significant factors of safety to determine the appropriate wall thickness for different class
45、es of ductile-iron pipe. As a result, ductile-iron pipe has been produced in thinner sections over the years. For instance, while a 36 in (910 mm) cast-iron pipe designed to hold up to 150 psig (1 MPa), pressure would have been 1.58 in (40.1 mm) thick in 1908. A 36 in (914 mm) ductile iron pipe toda
46、y rated for 150 psig (1 MPag) is 0.38 in (9.7 mm) thick, with both types of pipe having varying thicknesses in spots as a result of manufacturing tolerances.7 Significant differences exist between both the metallurgy (cast and ductile iron) as well as pipe production techniques from the era of cast
47、iron to todays ductile iron. (3) ASM International, 9639 Kinsman Rd., Materials Park, OH 44073. (4) ASTM International, 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959. NACE International 4 Figure 1(a): Cast iron (polished sample). Figure 1(b): Ductile iron (polished sample). NACE Internationa
48、l 5 Internal Corrosion General This state-of-the-art report primarily covers external corrosion of cast- and ductile-iron pipe. For those concerned with internal corrosion, this section provides a brief overview of common corrosion problems and the solutions that are often applied. Potable Water Sys
49、tems The first cast-iron water mains were not lined, but they were installed, following cleaning, in the same condition in which they came from the molds. After many years, it became evident that certain types of water might affect the interior of the pipe. The use of bituminous coatings was proposed, and most of the cast iron sold for waterworks service after about 1860 was provided with a hot-dip bituminous lining and coating, usually made of molten tar pitch. In those systems in which water was relatively hard and slightly alkaline, bituminous
