NDTnet 1998 Aug, Vol.3 No.8

Abstract

Floating oilrigs and production vessels have been struggling with measurement systems for anchor line load which are unreliable, and where operators and governments demandcalibration.

In the marked, there is equipment and methods available, whereby one unloads the chain withhydraulic jacks, and measure the load with load cells. This is a rather time consuming and costly operation.

Det Norske Veritas has developed an alternative method based on the principle of vibrating wires, where one utilises the relationship between vibration frequency and load in a wire (or anchor line) that is fixed at both ends.

The following constants is involved in this relationship



• Distance between fixed ends (m)
  
• Mass per unit of length (kp/m)

A battery-operated notebook computer equipped with a PCMCIA data acquisition card measure the vibration signal from an accelerometer, and standard acquisition software with Fast Fourier Transform (FFT) calculate the frequency distribution of the signal. Standard spreadsheet software is then used to calculate the actual load on the anchor line.

DNV has already carried out measurements offshore with good results to verify the usefulness of the method, and we will perform controlled tests in our large scale testing machines to verify the accuracy.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

Publication Contact:
7th ECNDT, Park Alle 345, DK-2605 Broendby, Denmark, Fax: +45 46 26 70 11, Email: 101373.3414@compuserve.com