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A Review of Monolithic Insulating Joints

By Jose L. Villalobos, P.E.
and Brian J. Chapman, P.E.

As corrosion engineers, the design of a cathodic protection (CP) system is simple and straight forward. However over the years, experience has shown that the effectiveness of the CP system is dependent on the quality of materials and the experience of the installer. For example, during construction, time constraints, weather impacts, or inexperience of the contractor can cause a CP system to be incorrectly installed. One example of this is the installation of insulating joint flange kits to electrically isolate a pipe from another pipe.

Over the years, corrosion engineers have learned that insulating joints can fail especially on pipes greater than 48 inches in diameter. Test stations consisting of two test leads on either side of the flange (Insulating Joint Test Station) have traditionally been installed to monitor the electrical isolation of the pipes. Other precautions can include the design of a concrete vault to house the insulating flange and other equipment such as blow-off valves, SCADA equipment, etc., to allow for closer monitoring.

Monolithic insulating joints were developed as an alternative to the traditional insulating flange kits. The more confidence the cathodic protection industry gains in monolithic insulating joints the more they will be used. Today they are widely used in the European and Middle Eastern oil and gas industry for small diameter pipelines. Figure 1 shows an example of a monolithic insulating joint.

Courtesy of Advanced Products Systems

Figure 1. Cross-sectional view of monolithic insulating joint

Benefits of the pre-fabricated monolithic insulating joints are that they:

1. Are less likely to fail due to improper installation which will drain a cathodic protection system current and render it ineffective.
2. Are pre-assembled.
3. Do not require maintenance after they are buried.
4. Do not require labor to assemble several pieces together.
5. Do not require inspection pits/vaults.
6. Undergo several hydrostatic, temperature, electrical isolation, and weld integrity tests before being shipped out to the job site.

The disadvantages of monolithic insulating joints are:

1. Long lead times due to manufacturing sites in Europe .
2. Possible damage during shipment may occur.
3. Initial cost may be two times higher than an insulating flange kit.
4. There may not be many contractors that are familiar with monolithic insulating joints or the lead time required for manufacturing and delivery.

The advantages of insulating flange kits are:

1. Initial cost is at least two times less expensive than monolithic insulating joints.
2. Most commonly used pipe isolation equipment by contractors.

The disadvantages of insulating flange kits are that they:

1. Require skilled labor to assemble several pieces together.
2. May become shorted when buried in soil due to settling, over-tightening, or thermal expansion.
3. Cost significantly more than the initial cost of a monolithic insulating joint if they leak or are damaged.
4. Are more likely to require a shut down of the pipeline during maintenance or replacement if it fails.

Monolithic IJ’s are seldomly used in the United States because of the lead time needed to have them shipped from Europe and the initial costs are higher than insulating flange kits.  However when life cycle costs are factored in, it appears that monolithic insulating joints are an attractive alternative to the traditional insulating flange kits used for pipes greater than 48-inches in diameter.  In addition, if an insulating flange kit becomes shorted, it may result in internal/external corrosion or may overload a cathodic protection system.

V&A’s Role in Cathodic Protection Services

V&A has specified monolithic insulating joints for large diameter (96-inch) pipelines but also has extensive experience with insulating flange kits. V&A recommends that test stations be installed on both types of insulating joints to monitor electrical isolation. Readers should contact V&A at the number below if any further information or guidance is needed with respect to these services.

V&A Consulting Engineers
1999 Harrison Street, Suite 975, Oakland, CA 94612
Tel. (510) 903-6600, Fax (510) 903-6601
www.vaengr.com
Copyright 2005