THE UNIFIED DESIGN OF AN ANCHOR CHAINS

Objective

A failure of an anchor chain mooring a floating production system could cause the loss of the vessel, with loss of life, environmental pollution, and an interruption in the supply of hydrocarbons. A similar mooring failure affecting a heavy lift vessel working in close proximity to a fixed offshore structure could cause serious damage to the platform with similar consequences to life, pollution and to interruption in the supply. The principal objectives of this project on anchor chains are to :
- Collate all existing test data on the static and fatigue strength of anchor chains.
- Perform fatigue tests on range of anchor links in order to produced a
systematic assessment of their fatigue strength.
- Review all existing regulations, recommendations and guidance on anchor
chains.
- Review current in-service chain inspection techniques.
- Develop new and rational design guidelines which are capable of use by
practising engineers.
A significant data base of fatigue results has been produced covering anchor chain in straight tension.
A limited number of tests were performed to investigate the fatigue effects of chain at fairleads.
Fatigue results for Kenter shackles were also obtained.
Design guidelines have been formulated which can be used to predict the fatigue life of anchor chain. The final report includes guidance on the detection of fatigue by inspection.
Details of this workscope to meet the above objectives are given below :
a) REVIEW OF EXISTING DATA
The detailed work includes :
- Identification of previous research work, worldwide.
- Gathering of test data from previous research projects.
- Gathering of test data from anchor chain manufacturers.
- Screening, or validification, of the existing test data.
- Analysis of the shortfalls of the existing test database.
- Preparation of a programme of laboratory tests on anchor chain.
- Production of an interim report on all this work on existing test data.
b) LABORATORY WORK
The laboratory programme considered the effects caused by the following variables :
- Chain size : to determine scale effects.
- Grade of steel : to determine variations in fatigue performance.
- Stud welded or left free : to determine variations in fatigue performance.
- Stress range : to determine variations in fatigue performance.
- Tension-bending : to determine bending effects on tension fatigue strength.
A total of thirty-six fatigue tests were performed at Delft University and the detailed work included :
- Design of the test equipment.
- Placing of strain gauges on the test pieces.
- Static tests on each test piece to determine the stress concentrations.
- Fatigue tests to destruction on each test piece.
- Production of a technical report giving the full testing details and the test results.
- Formulate guidelines for fatigue design for use by practising engineers.
c) REVIEW OF INSPECTION METHODS
- Review current inspection, maintenance and repair methods for anchor chains.
- Appraise their effectriveness and suggest improvements.
d) REVIEW OD DESIGN CODES
- Review all existing costs and guidance notes, with particular reference to fatigue and inspection for damage.
- Prepare new guidance for design and inspection.

Programme(s)

ENG-HYDROCARB 2C - Programme (EEC) of support for technological development in the hydrocarbons sector, 1986-1989

Topic(s)

1.3 - ENVIRONMENTAL INFLUENCE

Call for proposal

Data not available

Funding Scheme

DEM - Demonstration contracts

Coordinator

Billington Osborne Moss Engineering Ltd (BOMEL)

EU contribution

No data

Address

LEDGER HOUSE FOREST GREEN ROAD FIFIELD
SL6 2NR MAIDENHEAD
United Kingdom

Total cost