In-line inspection of two North Sea crude-oil pipelines- operated by Texaco Nederland B.V. and owned by Texaco and Esso-was completed earlier this year by NKK Corp., Tokyo.
The contract, NKK's second in Europe, covered inspection of an 8-km, 40-in. line and a 2-km, 40-in. parallel line that connect Maasvlakte Olie terminal and Texaco Esso Maatschap Europoort terminal on the North Sea coast near Rotterdam.
CLEANING, INSPECTION
The primary objective, according to NKK, was to check the extent of porous corrosion on the pipelines' internal and external surfaces as well as any deformation. To reduce incidental work, the inspections used a bidirectional ultrasonic instrumented in-line device (an "intelligent pig").
During freezing temperatures in December 1993, cleaning, profile, and ultrasonic inspection pigs (in that order) were run first through the parallel line, then through the 8-km line.
All inspection work-from preparation to packing the inspection tools-was completed in 24 days. NKK has submitted an analysis showing the inspection findings.
TWO TECHNOLOGIES
Pipeline inspection technologies, according to NKK, can generally be divided into a magnetism-based magnetic-flux leakage (MFL) system and NKK's ultrasonic wavebased (UT) system.
The latter, designed to measure directly the time lag of the ultrasonic waves' reflective signals from the inside and outside walls of a pipeline, can ensure highly accurate measurements compared with MFL systems, says NKK.
Data processing of plane and sectional images of pipeline wall surfaces enable the reporting of the size and shape of any porous corrosion. The UT device can also detect porous corrosion around welds' heat-affected zones, a capability that NKK says is generally beyond that of MFL systems.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
