Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

Issue link:

Contents of this Issue


Page 30 of 80

28 JUNE 2019 W W W.MATERIALSPERFORMANCE.COM CATHODIC & ANODIC PROTECTION E Monolithic isolating joints of buried pipelines are fundamental to ensure the performance of a cathodic pro- tection (CP) system. This article dis- cusses testing, analysis, and root cause identification of a leak occurred on an isolating joint installed on an oil transfer pipeline only seven months into operation. The lab testing and CP data were reviewed and analyzed. The design of the monolithic isolating joint for conveyance of an electrolyti- cally conductive fluid was reviewed as per different engineering methodol- ogies and supported the conclusion that the fluid conductivity was not fully appreciated in the design of the isolating joint. E l e c tri c a l i s o l ati on i n pi p e li n e s or piping occurs when one of the following takes place: • A dissimilar metal joint is in the pres- ence of an electrically conductive fluid. • A transition occurs from an under- ground to an aboveground section of a cathodically protected pipelin e w hen the aboveground section is grounded at some point. • The amount of cathodic protection (CP) current required is limited to protect the structure and achieve the right level of polarization. A description of the different devices that can be used to achieve electrical isola- tion can be found elsewhere. 1 The selection of the specific isolating device depends on the mechanical forces exerted on the line, pressure constraints, and maintainability, among other considerations. Isolating Joint Failure Gervásio Pimenta and a bdulla l uqman, ADNOC Onshore, Abu Dhabi, UAE Monolithic isolation joints (MIJs) are one type of isolating device. Basically, an MIJ consists of a pair of short pipe lengths; one is extended at its periphery by a barrel that overlaps the other. The two sections are isolated from each other by nonmetal- lic materials that are restrained and main- tained in position by large compressive forces locked by welding, wedging, or swag- ing and are pressure sealed . There are advantages to these devices, such as they do not contain threaded components; they are factory assembled, reducing the risks associated with installation; and they are designed and produced according to pipe- line codes and specifications. MIJs are complex items as they congre- gate a series of materials with different properties, notably steel, elastomers, glass- reinforced epoxy (GRE), and coatings. The properties of all these materials must be considered when producing and assem- bling an MIJ, and matching their properties with the operation envelope is paramount to ensure a good performance. A recent paper reviewed the requirements that must be addressed to ensure the proper perfor- mance of an MIJ. 2 These included the limi- tations associated with isolating devices, which are essentially related to a high degree of quality assurance/quality control (QA/Q C) required during construction , assembly, and installation, given the differ- ent materials involved. L o ss of c ont ainm ent at MI Js were related to failure of the compression set of th e O-ring, cracked en ergized springs, excessive hard welds, low QA/QC perfor- mance during MIJ fabrication, and design flaws when the electrical isolation sheet is used simultaneously as an isolation com- ponent and as a critical sealing compo- nent. 3 Other possible causes were attrib-

Articles in this issue

Links on this page

Archives of this issue

view archives of Materials Performance - JUN 2019