offshore rig life extension
TRANSCRIPT
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IIW Document XIII-2430r1-12
Specimens sprayed with artificial salt water
Specimens
Specimens
The As-welded corroded specimens exhibited a slight improved fatigue strength compared to the As-welded non corroded specimens.
The surface layer with detrimental residual tensile stresses may be removed by the corrosion process
and/or
Possible stress concentrations such as weld toe notches and corrosion pits are ‘softened’ by corrosion
The reduction of the compressive layer (induced by the Ultrasonic Peening treatment) due to corrosion is detrimental to the fatigue life improvement.
Only a improvement factor of 1.6 was observed after 7.5 years of corrosion
Compare real situation to drawings and/or finite element models
A bracket, which had not been taken into account in the FE model had been installed at the fatigue hot-spot after a crack repair
The original planned extent of Ultrasonic Peening:
Is this extent of treatment sufficient?
Just because something is written in ink does not mean it is true
Just because something is written in ink does not mean it is true
Visual inspection of fatigue hot-spots is strongly recommended prior to planning of work. Difficulties with access can easily be assessed on site, but can be hard to predict from a drawing and/or from a picture.
ASSET INTEGRITY
Is a result of optimizing the combination of:
• understanding of plant or structure criticality
• degradation mechanisms
• appropriate design
• construction
• plant operation
• maintenance
ASSET INTEGRITY MANAGEMENT
Actions to ensure that a critical equipment or structure is:
– designed
– constructed
– and operated
so that it remains safe and fit-for-purpose throughout its entire intended life
ASSET INTEGRITY ASSURANCE
is a combination of many factors of
which Risk Based Inspection
is one important component
Is the optimized application of appropriate inspection methodology to equipment or structures based on the risk and consequence of their failure in such a manner as to provide reliable information on condition and deterioration rates
RISK BASED INSPECTION
• Helps understanding the current condition • Provides information about rate of degradation when baseline data as
– design philosophy – operating conditions – maintenance regimes – other such data
are also known and linked in to the condition assessments and prediction.
Benefits of Risk Based Inspection
RBI is an evolution from
• prescriptive regulations
• is a method for optimizing the inspection process
• supports good Asset Integrity Management
It relies on knowledge of other factors in order to design the RBI programme and,
• to interpret the results
• to predict future condition
Designing a RBI System for an FPSO
• define the key stakeholder objectives
• agree on key project issues such as
– data availability
– baselines
– database selection
– database inputs and outputs.
RBI system depends on • complete and accurate data • at the set up stage • throughout the asset life.
• This data includes:
– Line / Vessel Lists – Material of construction – Operating temperatures and pressures – Design temperatures and pressures (if operating values not available) – Insulation / lining / cladding details – System criticality information – Basic fluid composition – Heat and Material Balance – Process System Description – Materials selection basis – Fabrication drawings, Datasheets etc – Plus many others
RIS
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SCREENING
• Screening can be performed at any level such as a complete facility or process unit, down to multiple or individual pieces of equipment. It is recommended to do a good quality risk screening where data is readily available such as a complete process line list/vessel list.
• If data is less readily available a risk screening by system/structural component may be more appropriate.
Structural Integrity Life Extension for FPSO
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Possible number of people in a confined space - Alternative escape route - Escape route length - Company policy - Not a exact science….
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A temporary platform is spot-welded into a bulkhead. All personnel continuously secured with Rope Access methods No extensive testing/safety measure of the platform itself is necessary before work can start. Advantages: -Quick to set up -Improves working quality Drawbacks: -Hot-work
- Fatigue hot-spots found in four FPSO cargotanks - Bulkhead and bracket welds treated by UP rope access team - January 2011 to February 2012
Transverse cargo tank bracket; 6 hours required Ultrasonic Peening treated area; - 300mm on each side of bracket
Transverse cargo tank bracket
Bulkhead connection; 8 hours required
Scenario Fatigue hot-spot located in cargo oil tank Weld improvement method; Ultrasonic Peening
12m
-Quick to install
-Good access to fatigue hot-spot
-Equipment can rest on platform
Fatigue hot-spot
Drawings recieved from client; Planned extent of Ultrasonic Peening
