Qty: Or The importance of pipeline electrical isolation in achieving and maintaining adequate, reliable, and economical corrosion control. Types of devices used for isolation; precautions to be observed; and selection of devices…Historical Document 1. 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 flanges, 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.

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Its acceptance does not in any respect preclude anyone, whether he or she has adopted 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, 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 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 other 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 responsible for reviewing appropriate health, safety, environmental, and regulatory documents and for determining their applicability in relation to this standard prior to its use. Users of this NACE International standard 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 standard.

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 edition.

Each 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 technical personnel dealing with pipelines the necessary information to isolate cathodically protected pipelines electrically. 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 considered optional. Need for Isolation Methods of Isolation Isolation from Other Metallic Structures Selection of Isolation Device or Method Equipment Specifications Equipment Installation Field Testing and Maintenance 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 flanges, 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. Isolating devices shall not be used in enclosed areas where combustible atmospheres are likely to be present.

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 the pipeline. The isolating supports must prevent damage to the pipeline coating and must accommodate relative movement, vibration, and temperature differential. All applicable safety codes and standards must be followed.

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 considerations.

Provisions should be made for the connection of test wires for testing these isolating devices. 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 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 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. If circumstances indicate that this type of installation would not be effective, an alternative device should be used.

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 include Parts and of U. 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 disassembled on site. 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 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 higherpressure joint described in Paragraph 3.

SW, Washington, DC 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 by an encircling yoke clamped by bolts through lugs that are normally tack welded. 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 a gasket between mating faces.

One of. When using this design, the extended length should also be the protected length. Isolation may be provided by an isolating gasket under one of the follower rings and an isolating sleeve for one pipe end. The sleeve is equipped with an isolating gasket, an isolating sleeve, and an isolating pipe spacer. One end of the fitting is equipped with isolating material. The casings are normally electrically isolated from the pipeline.

Isolation is provided by isolating spacers located circumferentially around the pipe. After these isolators are placed at intervals along the carrier pipe, the pipe is inserted into the casing see Figure 9. NOTE: Other methods, such as coating pipes with concrete, are also used for isolation.

The effectiveness of methods other than isolating spacers should be evaluated on a caseby-case basis. Isolating spacers should be designed and spaced to withstand the loads caused by the movement of the carrier pipe under operational conditions.

Plastics, neoprene, fiberglass reinforced plastic, or glazed ceramics may be used for these pads. The material chosen should be the most suitable for the pipeline service and environmental conditions.

The jumper wire must be sized to conduct the required CP current. When this is not possible, consideration should be given to installation of isolating materials between the structures. If the riser support is designed to allow movement of the riser pipe, then roller guides, flexible collars, or other suitable parts made of isolating materials can be used to ensure effective electrical isolation.

Electrical isolation can be obtained by using one of the following methods. Any measure taken should not conflict with applicable electrical codes. Care should be taken to ensure that the dimensions selected will allow the use of the standard size bolt. They should be a minimum of 3. Thinner gaskets may be appropriate to reduce blowout potential. Preference should be given to materials with low y and m factors. The y factor is a measure of the compressive load required to establish an initial seal, while the m factor is an indication of the additional load required to hold the fluid pressure needed to keep the seal in operation.

The smaller these factors are, the less pressure is required to establish and maintain the seal. For pipelines carrying water or watercontaining fluids, gaskets may consist of a laminate core material faced with a suitable sealing material e. For cryogenics, the core should be a suitable epoxy with either polytetrafluoroethylene PTFE or fluorinated ethylene propylene FEP seals, depending on the product and temperature. For high-pressure, high-temperature steam, gasket manufacturers should be consulted.

For pipelines carrying hydrocarbons and other fluids, the gasket selected should be suitable for the particular application product, pressure, temperature, etc. Gaskets should have the highest compressive strength suitable for the service conditions. They should be suitable for the service conditions of the particular application. Special consideration should be given to ensuring that the materials selected for the isolating sleeves and washers are not damaged during tightening at the time of installation.

Elastomer seals shall have permanent residual elasticity to ensure leak tightness. The primary function of the casing isolator is to isolate electrically and support the carrier pipe in the casing and protect the pipeline coating.

The carrier pipe should be fully supported within each end of the casing and externally to the casing at either end see Figure 9. For most applications, the following tests are conducted: 7. The information given to identify the device could be as follows: 7. The thickness, spacing, and components of the casing isolator should be designed to prevent contact between the carrier pipe and the casing. The procedures are designed to ensure that: 8. This should be considered when equipment locations are selected.

The equipment chosen must be suitable for the mechanical forces to be encountered at the selected site. Isolating devices should not be installed in gas systems at locations where the accumulation of internal moisture is likely.

When feasible, the flanges and isolating devices should be assembled and tested before and after installation. Particular care should be taken in supporting the yoke joint and adjacent pipe to ensure that minimum strain is applied during welding and backfilling. In the case of linings, additional care should be taken to ensure that the direction of the joint is correct.

The side of the joint that has the longer length of internal lining must be attached to the protected side of the pipeline. Linings must be fused or bonded to the internal surface of the pipe.


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RP0286-HD1997-SG Electrical Isolation of Cathodically Protected Pipelines-HD1997


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