1、 Standard Practice Electrical Isolation of Cathodically Protected 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 or she has ad
2、opted 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 manufacture, sell,
3、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 use of better
4、 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 standard by othe
5、r parties and accepts responsibility for only those official NACE International interpretations issued by NACE International in accordance with its governing procedures and policies which preclude the issuance of interpretations by individual volunteers. Users of this NACE International standard are
6、 responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. This NACE International standard may not necessarily address all potential health and safety problems or environmental
7、 hazards associated with the use of materials, equipment, and/or operations detailed or referred to within this standard. Users of this NACE International standard are also responsible for establishing appropriate health, safety, and environmental protection practices, in consultation with appropria
8、te regulatory authorities if necessary, to achieve compliance with any existing applicable regulatory requirements prior to the use of this standard. CAUTIONARY NOTICE: NACE International standards are subject to periodic review, and may be revised or withdrawn at any time in accordance with NACE te
9、chnical committee procedures. NACE International requires that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of initial publication and subsequently from the date of each reaffirmation or revision. The user is cautioned to obtain the latest edi
10、tion. Purchasers of NACE International standards may receive current information on all standards and other NACE International publications by contacting the NACE International First Service Department, 1440 South Creek Dr., Houston, Texas 77084-4906 (telephone +1 281/228-6200). Reaffirmed 2007-03-1
11、0 Reaffirmed 2002-04-11 Revised 1997-June-27 Approved 1986 NACE International 1440 South Creek Drive Houston, Texas 77084-4906 +1 281/228-6200 ISBN 1-57590-041-6 2007, NACE International NACE SP0286-2007 (formerly RP0286) Item no. 21032 SP0286-2007 NACE International i _ Foreword This standard pract
12、ice is to be used in conjunction with the latest revisions of NACE SP01691and SP0177.2Each of these standards refers to electrical isolation or isolation joints, but details are not provided. This standard, which was prepared to supplement those standards, provides engineers, designers, and technica
13、l personnel dealing with pipelines the necessary information to isolate cathodically protected pipelines electrically. This standard was originally prepared in 1986 and revised in 1997 by former Task Group T-10A-15 on Electrical Isolation of Cathodically Protected Pipelines, a component of Unit Comm
14、ittee T-10A on Cathodic Protection. The standard was reaffirmed in 2002 and 2007 by Specific Technology Group (STG) 35 on Pipelines, Tanks, and Well Casings. It is issued by NACE International under the auspices of STG 35. In NACE Standards, the terms shall, must, should, and may are used in accorda
15、nce with the definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall and must are used to state mandatory requirements. The term should is used to state something good and is recommended but is not mandatory. The term may is used to state something conside
16、red optional. _ SP0286-2007 ii NACE International _ NACE International Standard Practice Electrical Isolation of Cathodically Protected Pipelines Contents 1. General . 1 2. Definitions . 1 3. Need for Isolation1 4. Methods of Isolation 2 5. Isolation from Other Metallic Structures 7 6. Selection of
17、Isolation Device or Method . 9 7. Equipment Specifications 9 8. Equipment Installation. 12 9. Field Testing and Maintenance. 15 References 17 FIGURES Figure 1a: Full-Length Bolt Sleeves 2 Figure 1b: Half-Length Bolt Sleeves 2 Figure 2: Typical Isolating Monolithic Device 3 Figure 3: Typical Isolatin
18、g Monolithic Joint 3 Figure 4: Typical Isolating Yoke-Type Device . 4 Figure 5: Typical Isolating Union . 5 Figure 6: Typical Isolating Spools 5 Figure 7: Typical Isolating Couplings. 6 Figure 8: Typical Isolating Tapping Sleeve 7 Figure 9: Typical Casing/Sleeve Installation 7 Figure 10: Typical Use
19、 of Isolating Devices at Each End of a Bridge for a Cathodically Protected Pipeline. 8 Figure 11: Isolating Joint Test Station . 12 Figure 12: Isolating Device Leakage Test . 16 _ SP0286-2007 NACE International 1 _ Section 1: General 1.1 This standard explains the importance of pipeline electrical i
20、solation in achieving and maintaining adequate, reliable, and economical corrosion control. The standard outlines the types of devices used for isolation; precautions to be observed; and selection of devices based on pipeline characteristics, site, and contents. The standard describes isolating flan
21、ges, gaskets, sleeves, washers, joints, unions, couplings, and spools, and discusses materials for pipeline casing isolation. Installation, field testing, and maintenance of isolating devices are also included. 1.2 This standard describes the application of isolating devices intended only for cathod
22、ic protection (CP) purposes when voltages across the isolating device are 1 to 2 volts direct current (DC) and the alternating current (AC) exposure does not exceed 15 volts root mean square (rms).31.3 This standard does not discuss situations in which isolating devices are incorporated purely for s
23、afety reasons; in those situations, reference should be made to relevant electrical safety codes. Isolating devices shall not be used in enclosed areas where combustible atmospheres are likely to be present. 1.4 Isolation of cathodically protected pipelines is recommended to minimize current require
24、ments, facilitate testing and troubleshooting, and improve current distribution. _ Section 2: Definitions Refer to the NACE International Glossary of Corrosion-Related Terms4for definitions. _ Section 3: Need for Isolation 3.1 CP current intended for a given pipeline can flow to other underground fa
25、cilities or equipment electrically connected to the pipeline. If protection of the other underground facilities is not intended, significant CP current can be lost unless preventive measures are taken. Generally called a current drain, this current loss can be reduced through electrical isolation of
26、 the pipeline. 3.2 CP even of well coated pipelines may not be economical or practical unless electrical isolation is achieved. 3.3 Pipeline casings should be electrically isolated from the carrier pipe. 3.4 If a pipeline passes through the wall of a valve pit or a building, metallic contact can occ
27、ur between the pipe and the steel reinforcement in the concrete, causing a significant loss of protective current. 3.5 Electrical isolation can minimize or eliminate galvanic corrosion caused by dissimilar metals in contact with each other or caused by similar metals in contact with each other when
28、one metal is bare or has a dielectric coating system while the other has a permeable (e.g., concrete or mortar) coating system. 3.6 If a pipeline is designed to be electrically continuous but is supported by another metallic structure in contact with soil or groundwater, the pipeline should be isola
29、ted from that structure. The isolating supports must prevent damage to the pipeline coating and must accommodate relative movement, vibration, and temperature differential. 3.7 Isolation of power and instrumentation grounding systems may be required when electrically operated valves and similar comp
30、onents form part of a pipeline system. All applicable safety codes and standards must be followed. 3.8 If a pipeline is to be protected by more than one type of CP system, isolation of one or more sections may be desirable. 3.9 Isolation of pipelines can be beneficial in controlling or limiting the
31、effect of stray currents such as telluric currents, currents associated with an electric traction system, or currents from nearby structures under CP. SP0286-2007 2 NACE International _ Section 4: Methods of Isolation 4.1 Electrically isolating devices may be specially manufactured or prefabricated.
32、 It may be possible for existing fittings to be retrofitted with isolating materials to serve as isolating devices. Selection of the type of isolating device depends on the mechanical forces due to its position in the system, the operating temperature range, pressure constraints, and other considera
33、tions. Provisions should be made for the connection of test wires for testing these isolating devices. 4.2 Flanges 4.2.1 A bolted pair of pipeline flanges may be converted into an electrically isolating device by inserting an isolating gasket between the flanges and isolating sleeves over the shanks
34、 of the bolts, and placing isolating washers under the external steel washers to isolate the bolts (see Figures 1a and 1b). Isolating gaskets may have diameters equal to or greater than the outside diameter of the flanges, or they may fit within the bolt circle of the flange faces or into the groove
35、 of ring-type joint flanges. Isolating sleeves (around bolts) and washers (over bolts and under nuts and bolt heads) may also be combined as one-piece units. In some underground applications, the nuts and bolts may be isolated from one flange only so that CP will also protect all bolts and nuts. In
36、some applications, isolating flanges are required to be pressure tested after assembly. When isolating flanges are being considered for use below ground, special consideration should be given to the installation (see Paragraph 7.2.5). If circumstances indicate that this type of installation would no
37、t be effective, an alternative device should be used. FIGURE 1a: Full-Length Bolt Sleeves This figure shows the use of full-length bolt sleeves. FIGURE 1b: Half-Length Bolt Sleeves This figure shows the use of half-length bolt sleeves. SP0286-2007 NACE International 3 4.3 Prefabricated Isolating Joi
38、nts 4.3.1 Pressure and electrical test certificates should be provided with any specially manufactured isolating joints. Unless the isolating device is pressure tested as part of the pipeline system, a pressure test certificate may be required in order to comply with applicable codes. These codes in
39、clude Parts 192 and 195 of U.S. Department of Transportation(1)Regulations,5 ANSI(2) B31.3,6 ANSI B31.4,7and ANSI B31.8.84.3.2 Isolating monolithic joints for pressure services over 1,000 kPa(3)(150 psi) (see Figure 2) consist of a pair of hubs on short pipe lengths; one hub is extended at its perip
40、hery by a barrel that overlaps the other hub. The two sections are aligned with the isolating materials and held in position with a large compressive force that is locked by welding, wedging, or swaging and is pressure sealed. These units do not include any threaded components and cannot be disassem
41、bled on site. 4.3.3 Isolating monolithic joints for pressure services below 1,000 kPa (150 psi) are generally one of two types. One type consists of short lengths of pipe. The end of one length is enlarged and its internal surface serrated. An isolating sleeve bonded to the external serrated surface
42、 of the other pipe fits into the enlarged pipe, which is swaged to hold the assembly in position. The second type (see Figure 3) is similar to the higher-pressure joint described in Paragraph 3.3.2. FIGURE 2: Typical Isolating Monolithic Device High PressureOver 1,000 kPa (150 psi) FIGURE 3: Typical
43、 Isolating Monolithic Joint Pressure ServiceBelow 1,000 kPa (150 psi) (Other methods of construction are available.) _ (1)U.S. Department of Transportation (DOT), 400 7th St. SW, Washington, DC 20590. (2)American National Standards Institute (ANSI), 11 West 42nd St., New York, NY 10036. (3)1 kPa = 0
44、.01 bar. PROTECTIVE COATING PROTECTIVE COATING SP0286-2007 4 NACE International 4.3.4 Isolating yoke-type joints (see Figure 4) include two hub assemblies. The back of one hub is conical. The two hubs are sealed using O-rings and isolating rings or spacers. The hubs are held together under pressure
45、by an encircling yoke clamped by bolts through lugs that are normally tack welded. FIGURE 4: Typical Isolating Yoke-Type Device 4.3.5 Prefabricated isolating flanges are factory assembled isolating devices that are welded to a short pipe length with welded or screwed end preparations. 4.4 Unions (se
46、e Figure 5) An isolating union consists of two flanged bodies screwed onto the end of each connecting pipe. One flanged end is externally threaded, and the joint is held in position by a nut that is electrically isolated from the other end. The pressure seal may be achieved by using a molded seal or
47、 a gasket between mating faces. 4.5 Spools (see Figure 6) An isolating spool for pipelines carrying fluids may be made either by inserting a long piece of nonmetallic pipe into a piping system or by inserting a long piece of metallic pipe into the pipeline in combination with one or two of the devic
48、es described in Paragraphs 3.2 through 3.6. One of the isolating devices described in those paragraphs may also be used with an extended pipe length that has a high-electrical-resistance lining bonded to the isolating flange or joint and to the inside of the extended pipe length. When using this des
