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Maintenance Integrity: Managing Flange Inspections on Aging Offshore

Production Facilities

Article · January 2011

DOI: 10.1115/OMAE2011-49050

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 Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering
OMAE2011
June 19-24, 2011, Rotterdam, The Netherlands

OMAE2011- 49050
MAINTENANCE INTEGRITY: MANAGING FLANGE INSPECTIONS ON AGING
OFFSHORE PRODUCTION FACILITIES
*R.M. Chandima Ratnayake1,2 S.M.S.M.K. Samarakoon1
1 1
University of Stavanger, N-4036 Stavanger, Norway University of Stavanger, N-4036 Stavanger, Norway
2
Akersolutions, P.O. Box 589, N-4003 Stavanger,
Norway.

Tore Markeset1
1
University of Stavanger, N-4036 Stavanger, Norway

ABSTRACT .
The flange inspection associated with piping on 1 INTRODUCTION
offshore production facilities is a time-consuming As per the present state of affairs in relation to
activity as the flanges should physically be opened the high performing hydrocarbon production and/or
in order to perform close visual inspections. In process industry, nothing is more important than
order to sustain maintenance integrity, a number of safety. For instance, high pressures, high
inspections are allocated for a subsystem based on temperatures, explosive atmospheres, continuous
factors such as: condition of the medium flowing in processing at high speeds and volumes and hostile
the line, risk perception of the pipeline system, and locations contribute to unforgiving high-risk
the date of installation. Inspection teams environments. Failures under these circumstances
recommend inspections based on the data, can be costly, and even minor errors can turn
experience, and exposure to offshore production catastrophically critical in milliseconds. To
facilities, as well as the intuition and intentions of safeguard society, the return on investment, and the
those individuals involved with inspection planning natural environment against the consequences of
and with carrying out implementation during the failures occurring to production and/or process
preventive maintenance shutdowns. However, facilities, an assessment of the condition of the
there is a tendency for the operating company existing infrastructure (major process units, piping
representatives to raise queries with the contractor on production/process facility, etc.) is vital. A
company representatives about the number of condition assessment quantifies the degradation of
flanges to be opened during the preventive material and provides the basis for the decision-
maintenance shutdown as flange inspection making process regarding a Preventive Maintenance
consumes a considerable portion of time and (PM) and/or replacement. Also production systems
resources. Hence, it is vital to interpret sensibly the and subsystems have non-self-announcing modes.
importance of recommending close visual These non-self-announcing modes can only be
inspections for flanges if the maintenance integrity detected through inspections [1].
is to be sustained. This study focuses on analyzing
the historical data limited to flanges on flowlines In order to keep a system at a desired level of
over the last fifteen years. The final results provide operation, PM strategies and actions are utilized.
a snapshot of the present status of the flanges of the With limited maintenance resources (i.e. time,
production facility. budget, human, etc.), it is essential that the available

_____________________________
*Associate Professor and Author of Correspondence Copyright © 2011 by ASME
funds be distributed in such a way that they are Salma [11] states that “rarely reported and
most effective in reducing potential risks. Hence, accounted for in inspection-related statistical
the management of the maintenance integrity (in analysis”. Tukey [12] observes that statistics are
this context ‘maintenance integrity’ is assured when enlightening and highly relevant to the field of
there is an opportunity of maintaining the mathematical modeling in maintenance.
production facility with lesser financial burden to Consequently, it is important that mathematical
the operator, reduced societal health & safety risks modeling in maintenance is validated in tackling
and environmental degradation, through optimized real problems.
risk management and zero failures) of a large
number of aging process components is a subject of In the late 1980s, risk-based approaches in the area
prime importance to hydrocarbon production and/or of maintenance started gaining ground, initially in
process industries all over the world. However, the petrochemical and offshore industry in the USA
“most companies devote insufficient effort for and later, spreading over other areas of application
modeling their systems and optimizing their (e.g. power plants) and other countries, notably in
maintenance strategies, to benefit fully from the Europe and Japan [13]. In practice, terms like RBI
advantages that they offer” [2]. (risk-based inspection), RBIM (risk-based
inspection and maintenance), RCM (reliability
On the same grounds, the optimization of an centered maintenance), RBLM (risk-based life
inspection policy and PM action is the subject of management), or simply RBM (risk-based
much research [3, 4]. For example, [5] presented a management), are used in industrial applications. In
basic inspection model in 1963. In the middle of the the early 1990s, the principles of risk-based
1990s, Christer and Wang [6] put forward a inspection (RBI) were formulated for fatigue
different approach introducing the possibility of deterioration. However, RBI principles have been
updating an inspection schedule at each inspection limited to a few industrial projects (e.g. the
based on the new information obtained at current inspection of static process equipment and
and past inspection times (also see [1]). structures on offshore production plants) where the
Furthermore, there are tremendous efforts in risk is used as a criterion to prioritize inspection
mathematical modeling. For example, Turco and tasks for the components in a production and/or
Parolini [7] develop a condition-based monitoring process plant based on RBI strategy. This provides
model for generating the inspection times allowing many advantages, which incorporate: 1) an increase
the minimum maintenance and operating costs per in plant availability; 2) a decrease in the number of
unit time. Also, Chelbi and Ait-Kadi [8] address the failure occurrences; 3) a reduction in the level of
problem of generating optimal inspection policies risk due to failure; and 4) a reduction in the direct
for randomly failing systems where imminent inspection cost of the production and/or process
failure is not obvious and can only be detected facility [14]. The complexity of the approach
through inspections. However, Scarf [9] comments combined with the required numerical efforts, has
about the fundamental challenge that the hindered its implementation in an efficient software
mathematical modeling of maintenance rather than tool or an operator company’s plant strategy. Thus
with management processes relating to maintenance its integration into the general maintenance integrity
where “too much of attention is paid to the management procedures of the contractors and/or
invention of models, it seems, with little thought as operators of production facilities is not widespread.
to their applicability”. Ascher and Feingold [10], On the contrary, once the equipment subsystems are
further advocate the importance of paying attention categorized into a hierarchy based on RBI, the most
to data collection and to consideration of the popular approach is to use successive inspection
usefulness of models for solving real problems results to estimate the progress of corrosion and
through model fitting and validation. Moreover, recommend (or plan) future inspections on similar

2 Copyright © 2011 by ASME

locations in the production facility. This approach The production field under study is in its late life.
usually assumes linear growth between inspections At this phase, the system configuration is changed
[11]. However, the approach faces considerable to low-pressure production together with the change
challenges due to the inspection uncertainties in from oil and gas to gas production. During the gas
interpreting the inspection results (e.g. radiography production, the reduced operating pressure results in
films), errors due to the calibration of non- an increase in flow rates in the flowlines leading to
destructive testing (NDT) approach (e.g. ultrasonic accelerated erosion. The increased flow rate
testing) as a result of inherent manufacturing increases the noise level limiting the time an
tolerances [15], etc. In addition, corrosion average human can work at the flowlines’ premises.
monitoring and process data; i.e. the substances in a
production flow (such as amount of Oil, Gas, sand, A considerable number of the carbon steel
H2S, CO2, H2O, etc.) also provide a valuable components on flowlines are replaced by
feedback to optimize an inspection plan. components made up of duplex stainless steel.
However, there are still some carbon steel
Oil, gas, and other product transmission piping components. In the actual environment, carbon steel
components are connected by flanges and welded can suffer from corrosion and erosion, while duplex
joints of varying sizes, designs and materials. stainless steel will merely suffer from sand erosion.
“Piping components are among the most critical Hence, flowlines are continually monitored for
components of offshore installations” [16]. General possible sand production. Although currently the
acceptance is that risk cannot be eliminated but sand production is very little, but have to be
must be managed [17]. In this paper, we consider monitored regularly for different production wells.
flowlines on an offshore production facility located Additional inspections are recommended based on
on the Norwegian Continental Shelf (NCS), which the sand production which can be observed on a
are subject to a random deterioration and monitored daily basis on the operator company’s database.
through perfect inspections. The production facility The carbon steel flowline components are followed
was built in the early 1980s and the inspection up with more frequent inspection schedules based
history data is recorded in the operator company’s on the risk hierarchy. The flowlines made up of
Piping Inspection Data Base (PIDB) from the duplex are followed up with inspections to reveal
middle of the 1990s. Hence, the flowlines have been degradation in terms of erosion. The plans for
inspected for about fifteen years to date and the random checks on selected erosion vulnerable
PIDB comprised of historical inspection data for points are followed up with Non Destructive Testing
about fifteen years. The study is focused on (NDT) methods such as radiography, ultrasonic
performing statistical analysis on these available testing, etc. The transition points (material
data in order to assure future maintenance integrity specification shifts) between carbon steel and
of the production facility through justifying the duplex are inspected within three years after the
validity of recommending close visual inspections date of modification (or installation).
for flowline flanges.
The flowlines that have been turned to gas
2. FLOWLINES AND RISK OF FAILURE production are considered to have a high risk with
Flowlines are comprised of high pressure tubing regard to personnel health & safety, loss of
between a Christmas tree and production manifolds production, damage to adjacent assets, etc. The
(also see [18]). The main product transportation is probability of failure is higher for carbon steel
two-phase (liquid and gas) unprocessed components of the flowlines. The probability of
hydrocarbon directly from a reservoir. On some failure of the components which are made of duplex
occasions it can be three-phase: liquid, gas and material is dependent on the flow rate (i.e. erosion).
sand. The consequence of flowline failure is generally

3 Copyright © 2011 by ASME

considered to be very high in terms of personnel flange and the Graylock flange. In the RTJ flanges
health & safety, loss of production, damage to the ring groove has two sealing surfaces. Both sides
adjacent assets, etc. of the ring groove are exposed to damage. A large
amount of damage on both the inside and outside of
Possible flowline degradation mechanisms are CO2 the ring slot is not acceptable. The following
corrosion, Microbiologically Influenced Corrosion descriptions apply to damage to the inside and
(MIC), H2S corrosion, erosion, and atmospheric outside of the ring groove.
corrosion. The degradation mechanisms have been
recognized based on the past experience of the Damage from the end-face down to the “ring
production field under study. In general, flowline seal/contact surface” can normally be accepted (see
inspection has been concentrated on areas where it Figures 1(a), (b)).
may experience a change in flow rate (e.g. flow rate
changes occur just after T-junction, at the injection
quills, etc.), areas where there can be flow
turbulence, and areas where there is a danger of
static medium (e.g. at dead legs, blind flanges, etc.).
Corrosion is also observed on both high-pressure
and low-pressure sections of the chokes (choke-
valves), and there are serious corrosion findings on
drainage dead legs. There has been a particular
focus on the increased flow rates, MIC, dead ends,
water production, and increased sand production. (a)

3. FLOWLINE FLANGE INSPECTION: ACCEPTANCE

OR REJECTION CRITERIA FOR RING TYPE
JOINT AND GRAY LOCK TYPE FLANGES
Usually corrosion on flange surfaces is identified
through close visual inspections (i.e. after opening
the flanges). When evaluating the damage due to
the corrosion, the following factors are generally
taken into account: (b)
Figure 1: RTJ flange – acceptable edge damage
 The medium in the line (e.g. corrosive liquid
may result in increase of degradation, and However, the possibility of further developments,
require more frequent inspection), frequency of inspection and the media’s
 Pipeline system risk with respect to safety and corrosiveness are taken into consideration when
production regularity, making a decision about accepting or rejecting a
 Type of degradation (i.e. mechanical fatigue flange. The local damage outside a ring sealing
or corrosion). surface is also accepted. For instance, the sealing
ring is usually softer than the flange material and as
Past experience reveals that the corrosion damage a result of that it will adapt flange deviation due to
has greater development potential than other damage (see Figure 2).
degradation mechanisms.

Basically there are two major types of flanges

available on a flowline: the Ring Type Joint (RTJ)

4 Copyright © 2011 by ASME

 Local damage in the sealing/contact faces for the
ring that exceeds 25%, or crosswise on the sealing
surface is not acceptable (see Figure 4).

Figure 2: RTJ flange – acceptable edge damage

Local damage in the sealing ring contact face is not

normally accepted. However, a local damage is Figure 4: RRTJ flange - Not acceptable damage
accepted if it is below 25% of the ring’s sealing
surface (see Figure 3a). Small spots of surface Moreover, when it comes to the Graylock type
damage on the sealing surface which do not connect flanges, only one sealing surface is available (see
with each other are accepted if they do not cover Figure 5(a)). Hence, the acceptance criteria are
more than 2.5% of the flange sealing face (see more restrictive than for RTJ flanges. The local
Figure 3b). Nevertheless, the acceptance criteria can damage is usually accepted up to 6 mm deep,
be changed from one Operator Company to another. maximum 60% of the circumference (see Figures
5(a), (b)).

(a) Maximum 25 %
(a)

(b) Maximum 2.5% (b)

Figure 3: RTJ flange – acceptable local damages at the Figure 5: Graylock flange - Acceptable damage
sealing ring contact surface
Local damage in the sealing sealing/contact surface
of the ring is normally accepted if it does not cover
more than 20% of flat width. Usually the sealing

5 Copyright © 2011 by ASME

ring has a lesser hardness than the flange material the visual inspection of flanges) are carried out
which can squeeze into the damage area. Hence, during PM-shutdown(s) and other non-destructive
according to the location of the damage (see Figure evaluations like radiography, ultrasonic, eddy
5(a)), it is accepted or not accepted (see Figure 6). current, etc., are carried out during production
(called in-line inspection). In general, at the
Local damage in the sealing/contact surface of the beginning of the life cycle of a production well, the
ring that exceeds 20% of the surface width is not medium of the flow does not have much effect on
acceptable. The location of the local damage is also carbon steel piping due to the lesser amount of
taken into consideration when rejecting a flange water, CO2, H2S, etc. during production. However,
(see Figure 6). in the late life of the production field, the former
substances increase. They accelerate the technical
condition deterioration of carbon steel piping,
necessitating regular inspection and PM.

Currently, phased array NDT method is a proven

method, which is good enough to inspect the
technical condition of flanges (i.e. without opening)
Figure 6: RTJ flange - Not acceptable damage without necessitating close visual inspections.
However, the information gathered through phased
array technique may not be sufficient to conclude
4 INDUSTRIAL CHALLENGE
the technical condition of the flange and seal ring
In general, the number of inspections are due to the inherent manufacturing tolerances.
allocated for a subsystem (e.g. flowline, seawater, Furthermore, the flanges should be opened and
gas, etc.) on an offshore production facility based inspected based on the last inspection date and/or
on factors such as: condition of the medium flowing the installation date of the flange. As per the
in the line (e.g. water, sand, oil and gas), risk company regulations, during visual inspections the
perception of the pipeline system, and the date of available ring is always replaced with a brand new
installation (the flanges from the date of the one, whether the technical condition of it is
production facility installation or from sufficient or not. As a result of that, there are no
repair/modification later due to corrosion). data available about the technical degradation
Inspection teams recommend inspections based on behavior of the rings in the pipe inspection
the data, experience, and exposure to offshore databases. However, according to NORSOK
production facilities, as well as the intuition and standard L-005, seal rings may be reused if they
intentions of those individuals involved with have sufficient standoff and are free from defects.
inspection planning and implementation. The Figure 7 illustrates Ring Type Joint compact flange
recommended close visual inspections (it requires (RTJ) (adopted from [19]).
an inspection location to be opened physically; e.g.

6 Copyright © 2011 by ASME

 Figure 7: The ring, flange and load distribution for RTJ flange

The Ring Type Joint flanges (RTJ) and all the other to interpret the importance for recommending close
types of flanges (e.g. Graylock, raised faced, etc.) visual inspections of flanges, if the maintenance
have their own inherent tolerance limits based on integrity is to be assured.
the manufacturing process. These tolerance limits
allow minor changes within the tolerance region 5. CRITERIA FOR THE FLANGE INSPECTION DATA
from one flange to the other. As a result of that, the COLLECTION
reliability of the phased array NDT results may not The case study production and process facility is built up
be sufficient to conclude the technical condition of a during the late 1970s. Hence, the majority of piping
flange in different situations. Hence, it is vital to components are made up of carbon steel. Therefore, the
open the flanges and perform close visual criteria for flange inspection are described for carbon steel
inspections. On the contrary, there is a tendency for flanges which are highly vulnerable for corrosion attacks.
raising queries by the responsible operating 1. In this study the diameter (φ) range: (6” < φ < 10”)
company representatives from the contractor is selected. Usually, the majority of flowlines are
company representatives (i.e. mainly engineering within 8” of the diameter and one might feel this
service providing companies), especially about the analysis is sufficient to carry out only on 8” pipe
number of flanges that have been recommended to flanges. However, due to the different types of
be opened during the PM-shutdown. Thus, it is vital valve connections, reducers and risers, the flanges

7 Copyright © 2011 by ASME

 can range from 6” to 10”. Hence, the overall accepted. Alternatively, when the T-joints are
searching criterion is made based on the (6” < φ < visually inspected, the blind flanges are also taken
10”) range. for granted.

2. The flange inspection time durations range from two When it comes to situations like Flange 2 (see
to ten years. [For instance, at dead legs (see Figure Figure 8), the flow is constantly moving without
8: Flange F5), Microbiologically Influenced generating turbulence. As there is no standstill
Corrosion (MIC) is evident in some of the medium at these types of locations, based on past
production facilities on the NCS.] For example, experience, it can be concluded that flanges of this
when a T-joint is comprised of a blind flange (see kind are less vulnerable to degradation. Hence, as a
Figure 8: Flange F4 and F5), relatively less time and rule of thumb, they are opened for visual inspection
effort are required for carrying out visual inspections in at least five to ten years’ time. Therefore, in this
during a PM-shutdown. Due to the non-uniform study, the searching criterion for the flanges that
thickness variations in the T-joint, other NDT have not been inspected is made at 10 years’ time.
methods like ultrasonic or radiography would not This visualizes the worst scenario of the production
provide reliable information about the degradation facility.
level. Hence, whenever possible, carrying out close .
visual inspections for the T-joints is generally

F4
F3 T1
S2
F2 S3
S1
F1 T2 F6
S4
F5

Note: Fi = ith flange; Si =ith spool; Ti=ith T-joint

Figure 8: A segment of PM isometric drawing: Different flange locations

3. When it comes to the real grounds on a recommending an inspection for a flange.

production facility during a shutdown period, However, based on the focused flange,
the following difficulties/constraints against the inspection planner must decide which
opening a recommended number of flanges can spool has to be taken out. For instance, if
be come across. the flange to be inspected is F2, then
either S1 or S2 should be disassembled.
i. When a flange requires opening, merely Inspection planners select the most
loosening the nuts and bolts on the suitable flange for inspection based on
particular flange is not sufficient as the historical data such as: recent finding
whole spool has to be taken out so both reports, last inspection date, installation
sides of the spool get the opportunity to date, surrounding space, etc.
be inspected. The inspection planners
take this fact into consideration when

8 Copyright © 2011 by ASME

 ii. The surrounding space is usually during a certain PM-shutdown period. As
congested, because of the layout of a result, this can lead to cancellation of
pipelines (especially when it comes to the planned inspections. Therefore, a
manifold area on some production searching criterion is made to avoid
facilities located on the NCS built in the planned inspections not being carried out.
late 1970s or early 1980s). This leads to This is done based on the comments
additional work related to the available on PIDB.
disassembling of the surrounding piping
or other components of the flange under Table 1 illustrates the number of flanges which have
consideration. not been inspected in ten years in relation to the
current year.
iii. The first and second factors can limit the
number of flanges which can be inspected
Table 1: Number of flanges not inspected in 10 years
N umbe r of N ot inspe cte d a fte r 10 ye a rs
S ubsyste m
Fla nge s 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
1 94 19 19 19 19 19 19 19 0 0 0 0
2 82 76 76 76 76 76 76 8 0 0 0 0
3 98 60 57 57 54 54 54 52 44 21 19 12
4 98 65 57 56 48 34 32 29 26 10 7 3
5 81 58 55 54 47 44 40 40 25 19 13 5
6 83 74 74 66 56 52 51 46 28 21 20 13
7 109 83 72 65 64 58 56 50 20 17 11 5
8 157 91 86 86 86 78 75 76 75 21 21 14
9 92 63 55 45 43 44 42 34 25 20 18 11
10 77 48 47 41 37 25 26 23 21 13 12 10
11 103 75 69 57 50 41 36 33 19 19 22 8
12 113 53 45 43 38 31 28 26 23 21 20 20
13 133 70 70 70 70 25 17 7 6 6 6 0
14 99 49 47 42 42 39 36 38 42 17 11 10
15 125 73 73 72 72 66 64 48 3 3 3 3
16 58 6 5 5 5 5 5 4 4 4 4 4
17 89 70 68 59 52 43 42 38 26 26 19 16
18 73 61 58 49 41 25 20 18 15 13 12 2
19 65 41 34 26 24 23 23 17 9 9 7 6
20 68 54 54 9 9 9 7 7 6 6 4 4
21 59 2 2 0 0 0 0 0 0 0 0 0
22 100 62 59 48 50 46 44 31 27 20 19 12
23 68 51 51 49 49 42 41 25 18 17 17 13
24 81 54 50 46 46 42 42 41 38 23 23 16
25 273 87 87 87 86 86 18 18 12 11 7 5
26 72 58 57 51 48 43 37 29 29 20 10 4
27 160 83 83 74 70 37 34 32 19 17 4 0
28 80 0 0 0 0 0 0 0 0 0 0 0
29 114 86 84 72 63 59 50 36 8 7 6 1
30 103 61 55 50 40 45 46 45 34 24 19 17
31 94 70 62 56 50 41 36 35 25 15 15 18
32 129 117 116 114 113 112 112 104 30 13 13 13
33 84 53 47 39 39 30 30 26 19 18 18 12
34 149 55 55 54 53 41 39 37 33 27 20 18
35 184 80 71 59 53 38 35 27 26 21 17 9
36 196 83 83 81 81 82 82 82 82 17 17 17

However, the inspection personnel are supposed to

strike a balance between maintenance, operations
6 DATA ANALYSIS
(e.g. if you spend more time on maintenance the
flowline is not in production), and HSE The main focus in this study is to organize data
consequences (e.g. if the flowline is not inspected and then construct appropriate graphs to represent
then there is no evidence for carrying out them in a concise, easy-to-understand form. The
maintenance, which can lead to failures resulting in purpose of graphs in this analysis is to convey the
damage to adjacent assets and significant data to the viewer in pictorial form where graphs
implications for operators in terms of lost are useful in getting the audience’s attention in a
production and cost of replacement, repair, publication or a presentation. Many people are
cleaning, etc.). visual learners and need to ‘see’ data; “a picture is

9 Copyright © 2011 by ASME

 𝑥
worth a 1000 words” when one is aware of its scope Where 𝑓𝑖 = 𝑦𝑖
𝑖
and able to use it flexibly [20]. For instance,
fi Relative frequency of non-inspected
frequency distributions enable:
flanges in ith subsystem (flowlines
connected to ith production well)
 one to organize the data in a meaningful,
within ten years with respect to the
intelligible way.
current year.
 the reader to make comparisons among different
xi Number of flanges that have not been
data sets.
inspected within ten years in ith
 one to facilitate computational procedures for
subsystem.
measurements of average and spread.
yi Total number of flanges in the ith
 the reader to determine the nature (trend) or
subsystem (flowlines connected to ith
shape of the distribution.
production well).
 the presenter to draw charts and graphs for the
m Total number of subsystems.
presentation of data.
Fi Total relative frequency of non-
inspected flanges in the jth year over
The following formula has been used for carrying
m-subsystems.
out different frequency distribution calculations.
𝑚 Figure 9 illustrates the status of overall flowline
𝐹𝑗 = ∑ 𝑓𝑖 flanges that have not been inspected in each year
since 2000 to 2010.
𝑖

Figure 9: Variation of total relative frequency of non-inspection flanges (Fi) vs. Time (year)

However, in order to illustrate the technical status of independently performed for each subsystem and
the flowlines belonging to different production visualized are shown in Figure 10.
wells, the relative frequency calculations

10 Copyright © 2011 by ASME

 1
2
3
4
5
6
7
8
1 9
10
0,9
11
0,8 12
13
0,7 14
15
0,6 16
17
fi 0,5 18
19
0,4
20
0,3 21
22
0,2
3 2 1 23
6 5 4 24
0,1 8 7
9 25
11 10 26
0 14 13 12
2000
16 15 27
2002 19 18 17 28
20
2004 22 21 29
25 24 23 30
2006 26
Year 2008 29
28 27 Production well 31
30 32
31
2010 32 33
33
34
35 34
36
35
Figure 10: Variation of relative frequency of non-inspected flanges connected to the flowline of ith production well (fi): Time 36
(year) vs. Production well

According to Figure 10, in subsystem 1 the same Figure 9 reveals that about (0.08 x 3843) ~ 307
percentage of flanges appears to have been flanges have not being inspected during ten years
uninspected for ten years, then this becomes zero (i.e. during the period 2000-2010). This reveals that
after 2007. The reason is that initially the flanges according to the basic requirements, in 2010, about
were carbon steel and during 2006 the whole 307 flanges should be inspected. However, this
flowline was converted to Duplex. That is the case might not be possible as it is an agreed fact that
for subsystem 2 as well. However, when it comes to visual inspections lead to more time-consuming and
subsystem 3, until 2007 a reasonable portion of laborious activities with a high financial burden for
flanges appears not to have been inspected during the operator company. The analysis and illustrations
ten years, and in 2006 there was a sudden reduction help the operator company personnel to visualize
in non-inspected flowline flanges. The reason is that the status of the production facility. Also, the results
part of the flowline has been converted to Duplex. reflect the maintenance integrity and/or technical
However, for subsystems 4 and 5, the majority of integrity [17] of the production facility.
piping is carbon steel to date. Hence, it shows
uniformly reducing the amount of non-inspected
flowline flanges. Similar kinds of interpretations 7 DISCUSSION AND CONCLUSIONS
can be given for the other subsystems as well.
Failures due to loss of containments in petroleum
flowlines constitute a significant threat as such
Figures 9 and 10 reveal why the contractor
failures may result in human injuries, fatal
company should recommend a certain number of
accidents, environmental pollution, and damage to
visual inspections to be carried out during the
adjacent or total assets. The failures also have
preventive maintenance shutdown. For example,

11 Copyright © 2011 by ASME

significant implications for the operator companies have been rejected. This can help to save/optimize
of the oil and gas industry in relation to the loss of time and money at the inspection planning stage as
production and cost of replacement/repair. well as reveal what difficulty or difficulties are
Furthermore, the failures as well as longer PM- faced most frequently on a production facility when
shutdowns can lead to economic losses leading to the recommended inspections are carried out during
postponed return of investments and unfulfilled a certain PM-shutdown. Alternatively, this kind of
sales obligations. Based on the seriousness of the study also can help to improve the maintenance
consequences of failures (e.g. estimated with RBI integrity of an oil and gas production facility (plant)
approaches) in a subsystem, the inspection activities in future.
should be carried out regularly in order to ensure
the maintenance integrity and to meet regulatory 8 ACKNOWLEDGMENTS
requirements. The costs associated with inspection We thank Gustavo Adolfo Romero in Akersolutions offshore
activities constitute a significant portion of the total partner, Norway, for extending support to accomplish this
operation costs of offshore installations. However, it manuscript.
is vital to carry out essential inspections as the
piping components often quickly corrode under
9 REFERENCES
aggressive industrial environments and harsh
operating conditions, thereby causing significant
[1] Baohe, S., (2002), “An optimal inspection
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