Assessment Services
Axiom Consulting Engineers, LLC has experience in
the assessment of fixed offshore platforms. Whether you need
assistance in the screening and classification of your platforms or need an
assessment analysis performed, we can work with you.
We have performed
assessments on
platforms installed in the 1950's as well as ones installed in recent years.
We have assisted firms in the screening of their platforms and platform
data gathering. Need a Level I inspection or field visit to
confirm or evaluate damage reported? Our engineers have hands-on
experience to accomplish this for you. |
Assessment Analyses
Q:
What kind of assessment analyses are there?
A: There are four
different analysis that
can be performed.
 Simplified Assessments
Requires minimal or, in most cases, no computer modeling. A
simplified assessment can also be performed during the platform
screening phase. This type of assessment requires a few hand calculations,
or use of some developed system or program, to justify minor damage,
minimal load change, or both.
Design Level Analysis
Computer analysis of the platform using standard allowable stresses and safety
factors. Use of an offshore structural analysis program such as
SACS is required.
Linear Ultimate Strength Analysis
(or Linear Global)
Computer analysis of the platform similar to the Design Level
Analysis except that removal of safety factors from all equations and taking
stresses to mean yield strength is allowed.
Non-Linear Ultimate Strength Analysis
(Pushover or Non-Linear Global)
Most commonly known as a 'pushover'. This analysis is a
non-linear computer analysis allowing structural members to exceed their yield strength and have plastic deformation.
Another
feature is the use of joint flexibility at tubular connections greatly
increasing their capacity.
Assessment analyses can be performed in the order listed above. If
the structure passes the first method, then no additional analysis is
required. However, if it fails the first one, then you continue to
the next one and so on. One key point is that if you know the
structure has substantial damage to primary members or has had many
additions that caused large load increase on the structure, then you can
jump straight into, say, a push-over analysis without the need to
perform the previous three methods.
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Why Assess?
Q:
Why do I need to perform a platform
assessment?
A: Many are asking this very question.
Is it because the MMS requires an assessment
on all platforms per NTL No. 2003-G16?
Yes and No! Yes, it has been
mandated; however, as soon as the NTL
expires this year (2006), platform assessments
will still be required if one or more of
the five initiators are ever triggered!
Initiators?
Q: What is an initiator?
A:
Section 17 of API RP 2A has five initiators that can trigger the need to perform
an assessment. The initiators are:
Change in personnel
status?
Change in facilities?
Deck height adequate?
Load increase by over 10%?
Damage causes more than 10%
reduction in structural capacity?
Be aware that
the combined increase in loading and reduction in capacity due to
damage must not exceed 10%!
Advantages?
Q:
There can't be any advantages or benefits to this assessment thing, right?
A: YES there are! Here are some to consider.
(1) During an assessment, you can account for modifications performed
in the past that did not increase wave loading (or global base shear) on the
platform. Note that platforms where modifications involve adding items in
the wave zone can NOT be check using the Section 17 criteria. You can also
use this assessment process to catalog all of the changes that many have
occurred to the platform.
(2) Ever see those Level I, II, and III inspection reports sitting on office shelves?
Well, in order to screen your platforms properly, you
should review them to determine if there is
reported damage. At the very least, you should review records from the
last few years. What, You call this a benefit? Yes, since you will now know the
condition of your platforms, the damages can be catalogued in a database
and properly addressed in the analysis.
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