Noise and vibration problems detected during construction phase. Several noise issues and excessive vibrations of structure supporting drawworks. These issues would impede delivery, delay the first operation contract, and subsequently prompt daily penalties.
Initial inspections and measurements revealed problems and outlined the risk of potential problems.
Further calculations and laboratory measurements revealed insufficient silencer, inappropriate location of noise sensitive areas and poor selection of outfitting materials in working and accommodation areas. The structure supporting the drawworks was too soft.
Installation of silencers, mounting of steel plates to increase sound insulation in living quarters. The structure supporting the draw-works was stiffened by installation of additional steel beams
The West Elara rig was ordered to be built by a shipyard in Singapore. As the original owner was facing bankruptcy, the yard decided to continue construction, although they had no previous experience building to the strict Norwegian NORSOK S-002 Working Environment standard. Seadrill bought the rig when the design was 98% finished and the construction 85% complete. During the due diligence, several issues relating to the working environment were then discovered.
Although some of the initial and required noise and vibration studies had in fact been performed, these data were not adequately consulted during the engineering, procurement and construction phase. This negligence had led to several issues that would preclude the acceptance of the rig by the Norwegian authorities. As part of Seadrill's troubleshooting team, we carried out an investigation to identify potential noise problems and outline suitable and practicable solutions.
Initial inspections and measurement campaign.
The work was kicked-off by an initial visit to the rig involving visual inspections and measurements. Although construction was still on-going and only very limited equipment was operational, it was possible to identify non-compliance with legislative requirements and pinpoint the problems that were likely to surface during commissioning.
The outcome of the visit was a long list of follow-up items, including recommendations to probable problems.
Poor sound insulation in living quarters
Through measurements, we identified insufficient sound insulation in the living quarters. The noise reduction between cabins, etc. was very low, however, it was not evident whether this was the result of a meagre attention to detail during construction or the effect of poor outfitting materials. Laboratory tests revealed that the partition wall panels delivered by the Korean vendor did not meet the specifications as promised in the data sheets. Had there been a proper follow-up, this would have been detected during procurement and delivery and a mock-up test of cabins, which is recommended as good practice.
The proposed solution had to respect the fact that much of the accommodation was already outfitted with furniture. The cost of replacing all partition panels would have been excessive and delayed the delivery of the rig, thus breaking the first operating contract with daily penalties. Our recommendation was to improve the sound insulation of the already installed panels by mounting steel plates on all relevant walls. To verify the suggested solution, a laboratory test was performed.
Excessive noise levels
In many areas of the rig, excessive noise levels were detected as noise requirements were not properly defined and included in the design. Examples of findings and recommendations were:
- More than 30 silencers should be installed in air intakes and outlets to reduce noise on open deck
- Construction was needed of buffer zones between noisy working areas and areas with strict noise requirements
- Installation of 50 m of noise screening wall was required to separate noisy equipment from walkways on Tank Top
- Dishwashing machine in galley had to be replaced
- Improvement was needed of equipment foundations and resilient mounting to reduce vibration and structure-borne noise.
Drawworks noise and vibration
In the driller's cabin, high vibration levels were caused by the drawworks; levels that exceeded the NORSOK S-002 limits for human exposure to whole-body vibration. Furthermore, vibration levels close to the drawworks caused concern for structural damage due to vibration induced fatigue.
The drawworks and support structure were investigated by measuring vibration levels and performing operational deflection shape measurements during different running conditions and speeds of the drawworks. The measurements showed the movement of the structure during operation and revealed insufficient stiffness of the support structure. Based on this, the location of additional stiffness was suggested and combined with balancing of the drawworks drum, vibrations were reduced to acceptable levels.
Noise from the drawworks also caused excessive noise levels on drillfloor, and installation of a screening wall was recommended.
The rig left the yard in Singapore and was transported to a final stay at the Westcon Yard in Ølen Norway. The final noise and vibration measurements were performed at this stage. The rig was accepted by the authorities and was ready to start the contract.
In future projects, Seadrill has decided to:
- Employ noise and vibration experts from early stages in the project
- Require training of yard personnel to increase knowledge about noise and vibration, and relevant requirements
- Follow-up of noise requirements during factory acceptance tests of equipment
- Create documents defining "Noise, acoustics and vibration philosophy" and "Noise and vibration procedure"
- Verify that recommendations and findings in design phase are disseminated to procurement and construction phases.