In August 2012 Nautec carried out Pumpability Tests of UHPC grout for the strengthening of Goodwyn-A Flare Tower. Woodside Energy Ltd were studying the available strengthening options for the flare tower legs of the Goodwyn-A platform and engaged Nautec to carry out finite element analysis (FEA) of the entire flare tower.
Analysis results showed that grouting was required to fill up 200mm above top cone of the flare tower leg and the required grout height for each leg was 85m. Due to some concerns about the execution of the flare tower strengthening work, Nautec was requested by the client to conduct a pumpability test.
The objectives of the test were to determine the pumpability of the UHPC grout after 5 hours at 30-35°C ambient temperatures; to determine whether the UHPC was mouldable and could conform to the transition cone after 5 hours pumping time under 30-35°C; and to estimate the required grouting pressure for the flare tower legs.
The grout pumpability test was performed for approximately 5 hours to fill each specimen by adjusting volume flow rate. It was conducted in Malaysia and witnessed by DNV Singapore.
Based on the test results, the UHPC grout remained pumpable for more than 5 hours at ambient temperatures of 30-34°C. The grout was able to conform to the shape of the transition cone without entrapping air voids.
Test results showed that the pressure inside each test specimen was hydrostatic pressure and the required grouting pressure for the flare tower legs was estimated by D’Arcy equation. In addition, the test allowed for the behaviour of the grout flow pattern inside the test specimen to be observed. The grout was dyed with 4 types of inert colour pigments before grouting and it was found that the initial grout was pushed upwards and the less flowable grout gave way to the more flowable grout.
The use of UHPC material for flare tower strengthening work is the most feasible and effective option due to its pumpability, perfect flow retention and high compressive strength.
By using UHPC grout, the risk of blockage inside the flare tower legs during long hour grouting can be eliminated.
The filling of the 85m height of flare tower leg was completed within the specified time frame.