Anomaly
An in-service survey
measurement, which is outside the threshold considered acceptable from the
design or most recent fitness-for-purpose assessment.
Assessment Initiators
Changes in platform
condition or operating experience, such as storms, which require an existing
platform to undergo an assessment to demonstrate fitness-for-purpose.
Collapse
The ultimate load bearing
capacity of the platform, at which the jacket structure or deck columns are no
longer able to support vertical loads.
Condition Assessment
The process of gathering the
information on the platform's present condition needed in order to perform a
fitness-for-purpose assessment.
Consequence
The adverse effects of an
extreme event, such as metocean, seismic, ice or accidental, on personnel, the
environment, or property.
Damage Tolerance
The quantity of
deterioration or damage that a structure can withstand without failing.
Design Level Analysis
A fitness-for-purpose
analysis of a platform using linear-elastic methods with an appropriate safety
margin, similar to the analysis methods used for new platform designs.
Design Life
The planned time period from
initial installation or reuse until permanent decommissioning, which may
include extensions justified through the SIM process.
Deterioration
The reduction in the ability
of a component to provide its intended purpose.
Exposure Category
The classification used to
categorize the platform consequence of failure based on the consideration of
life safety, environmental pollution, and business disruption.
Inspection
The visit to the platform
for purposes of collecting data required in evaluating its structural integrity
for continued operation.
Survey
A specific visual or
non-destructive examination of one or more platform components.
Fitness for Purpose
A demonstration that an
existing structure has adequate strength to resist the imposed assessment loads
Mechanical Damage
A defect type that includes
dents, bows, gouges, holes and separated or severed members.
Mitigations
Platform strengthening,
modification or repairs and/or operational procedures that reduce loads, increase
capacities, or reduce the exposure category.
DATA
Up-to-date platform
information is required for the SIM process.
Information on the original
design, fabrication and installation, structural analyses, in-service
inspections, engineering evaluations, structural assessments, modifications,
strengthening, repairs, and operational incidents, all constitute parts of the
SIM knowledge base.
SIM data falls into two
broad categories: platform characteristic data, and platform condition data.
Characteristic Data
The platform’s
characteristic data is the baseline data that represents the structure at
installation.
The characteristic data
includes :
- General Platform Data
- Design Data
- Fabrication data
- Installation data
Condition Data
The platform condition data
represents the changes to the characteristic data that may occur during the
life of the platform.
The condition data includes
the following :
- in-service inspection data;
- damage evaluation data;
- corrosion protection data;
- strengthening/modification/repair
(SMR) data;
- platform modifications;
- condition monitoring data;
- operational incident data
EVALUATION
SIM evaluation is the method of applying engineering to assess the
impact that new data has on the fitness-for-purpose and the SIM strategy for
the platform.
Evaluation is routinely
performed throughout the life of a platform. As additional data is collected,
an evaluation should be performed by a competent structural engineer.
The evaluation should
consider all relevant SIM data for the platform and similar platforms, where
appropriate.
Recommendations for the
performing data evaluation are provided in the following sections :
- Factors to consider
- The risk of platform failure
- The platform exposure
category
- The likelihood of platform
failure
- The requirement for platform
assessment
In many instances much of
this data will not be available; however missing data may impact the
evaluation, strategy and program for the on-going SIM of the platform. Where
characteristic data are not available, or are inaccurate, surveys of the
structure and facilities should be considered to collect the necessary
information.
A fitness-for-purpose
assessment of the structure shall be performed if the engineering evaluation of
relevant SIM data determines that an assessment initiator, has been triggered.
Damage Evaluation Process
The objective of the damage
evaluation process is to determine whether damage is potentially significant to
the structural integrity of the platform using the fitness-for-purpose
assessment.
Determining the effects of
damage on the strength of individual components, and used the results to
examine the need for risk reduction.
It is important to recognize
that not all damage is structurally significant. Light corrosion or minor
bowing of a member are examples of damage that may not be structurally
significant to the affected components.
A robust platform may be
fit-for-purpose throughout its remaining life, even if one or more of its
structural components (members and/or joints) have structural damage.
Degradation Mechanisms that
may reduce the structural capacity of the platform :
- Dropped objects, result in
mechanical impact damage to structural components and can cause gouging,
denting, bowing, holing of members, and also cause cracks at the end
connections of the member and/or member severance and/or joint deformation or
tearing. Examples: tubular components (e.g. drill strings and piles), drill
collars, scaffold poles, and from activities at link bridges, cranes, drilling
derricks, etc.
- Vessel Collision, result in
damage to structural components in the upper part of the jacket around the
splash zone: gouging, denting, and bowing of members. Can be prevented by
protective structures such as boat fenders, protection frames, etc.
Corrosion :
- Uniform corrosion of the
underwater structural components may result from a failure of the corrosion
protection system or through premature depletion of the system due to excessive
debris in contact with the structure. In the splash zone and above-water
locations of the structure, similar corrosion damage can result from failure of
the protective coating systems.
- Localized corrosion may
develop at areas on the structure not adequately protected by the CP system,
for example, dense conductor arrays or appurtenance connections, in particular
inside conductor guides and bolted clamps. Localized corrosion may also develop
due to galvanic (bimetallic) corrosion, for example, caissons housing stainless
steel pump/strainer components.
Strategy
A significant commitment to
ongoing in-service inspection with the goal of reducing the possibility of
major repairs (clamps, member replacements) in the future. This approach relies
on early detection of damage and defects with prompt implementation of
relatively inexpensive repairs and preventive measures. Early detection of
defects typically requires greater use of nondestructive testing (NDT)
techniques.
Minimization of in-service
inspection scope where adequate measures have been taken to reduce the risk of
damage, defects, or deterioration that would require major repair efforts in
the future. This approach assumes that in-service inspection without the use of
NDT techniques will be able to detect damage, defects, or deterioration before
structural integrity is threatened. This approach may be appropriate for robust
structures that are tolerant to damage and overload.
Inspection Strategy :
- Above-water inspections,
- Post-installation baseline below-water
inspections,
- Routine below-water risk-based, or
exposure-based inspections
- For non-routine special inspections.
