Description of Tests

Two different tests were used to determine the creep properties and the dynamic stiffness of nylon ropes. These tests were performed by DNV AS Energy Systems in Bergen, Norway, on one set of ropes from each of three vendors.

Creep Test

The first test is designed to determine the creep properties of the rope. The test is summarized in four steps:

• Load to a (low) reference load, measure the gauge length and start the data acquisition. 
• Tension the rope to 20 % of MBS (Minimum Breaking Strength) and maintain this constant load for 30 minutes. Relax to the reference load and measure any remaining elongation.
• Repeat the second step for 30 %, 40 % and 50 % of MBS.
• Increase the tension to 50 % of MBS and hold the constant tension for 18 hours. Record the rope elongation.

Syrope Test

The Syrope test is designed to find the dynamic stiffness of a rope. The test combines quasi static tension loads with irregular dynamic tension loads. The test is summarized in the bullet points below:

• The variation of tension level is defined by pairs of ramps and constant tension, both with duration 30 minutes. The constant tensions will vary from 10 % of MBS to 40 % of MBS
• An irregular tension variation, including both wave-frequency and low-frequency contributions, is superimposed on the ramp/constant tension sequence. The standard deviation is based on the expected, calculated response in the mooring system.