Subsea pipeline Repair and Maintenance

SUBSEA Pipelines, repair and
maintenance
jsk/subsea/pipeline/Aug 20 1

J S Kalsisjskalsi3110@yahoo.com
SUBSEA Pipelines, repair and maintenanceSUBSEA Pipelines, repair and maintenanceSUBSESUBSEA Pipelines, repair and maintenance
A Pipelines, repair and maintenance

Disclaimer
The information contained in this
presentation is of general nature.
It is for education & information
purpose only.
Views in the presentation are
those of presenter.

Subsea Hydrocarbon
Ecosphere
4
jsk/subsea/pipeline/Aug 20

Subsea
systems
Offshore production arrangement typically consists of subsea
systems namely:
a. Subsea well heads.
b. Pipelines [For transportation and injection]
c. PLEMs [Pipeline end module]
• Pipelines are the most effective method of transportation.
• Subsea facilities are exposed to external (by the seawater) &
internal (by the flowing fluids) corrosions.
• Quite often superior corrosion resistant alloys are used to provide
the necessary resistance to loss of parent metal because of
corrosion.
• Unexpected glitches owing to complexity of offshore facilities can
lead to unpredicted corrosion control.
5

Offshore
pipeline (OISD-139)
OFFSHORE PIPELINES - are those
pipelines which carry crude petroleum or
its products or natural gas from producing
sources, such as, well head platforms or
from Single buoy mooring system to main
platforms in the offshore and are
transporting crude petroleum or its product
or natural gas from main platform or
Single buoy mooring system to the place
where facilities are available to receive
them on land.
(OISD-Oil Industry safety Directorate)
6

Pipe
manufacturing
process

Protective
Coatings for
pipelines
• Coatings are applied externally to pipelines [about
12m long] as well as internally (application based) and
these are critical part of protection.
Mostly 3LPP, 3LPE or FBE are used as external
coatings
• Since, the ends [about 175mm] of the pipe must be
left bare for welding, there is a risk always of damage
/ disbondment occurring to the edge during offshore
fabrication / installation.
• Necessary safeguards need to be adopted to avoid
coating damage during fabrication / welding stage,
otherwise, it could lead to substantial deterioration
from day one.
9

Pipeline Laying Technique
• “S-lay” technique is normally usually used
for laying of offshore pipelines from a lay-
barge.
• Coated Pipe length [12m] except for 175
mm on either end are welded [field joint]
together on the lay-barge to form a string.
• After the welding, the field joints are also
protected by coating.
• Pipe length is then fed to the “stinger” of
the barge to lay it at seabed.

Subsea pipeline – Environment
The pipelines are exposed to severe
meteorological conditions.

Shifting seabed

Threat of damages due to external
agencies, anchor drag, falling objects etc.
13

Free spanning & crossings
Waves and currents may expose the pipeline
during the design life and span corrections will have
to be made if the spans exceeds the allowable
limits.
Free span can be triggered by:
• Unevenness of Seabed.
• Change of seabed topology (e.g. scouring,
sand waves).
• Artificial supports of pipeline.

Corrosion External
(owing to seawater) &
Internal (owing to fluids)

Corrosion
Corrosion……..?????????
Fundamentally, all environments are
corrosives with variations in intensity.
In oil industry more corrosion occurs due
to salt [Nacl], sulphur, acids [Hcl,H2SO4]
and water than crude oil.
16

Corrosion of
pipeline
• Worldwide pipeline corrosion is a well-known issue
in the Oil and Gas industry.
• Pipeline corrosion occurs naturally, due to the
gradual & continuous environmental attack on pipe
materials.
• Some critical components, such as flanges etc.
have remained largely unchanged for the past 50
years.
• Industry sources estimate the global cost of
corrosion in the Oil and Gas industry to be in
excess of $1.3 billion.
• For offshore facilities, some operators estimate 60
to 70% of maintenance costs are directly related to
corrosion issues.
17

Corrosion of
pipeline (1)
• Corrosion of metals is generally the destructive attack to
parent metal through interaction with its environment.
• In natural environments (external i.e. seawater) the
reaction is mainly related to dissolved oxygen.
• In other environments ( by produced fluids) the reaction
is mainly related to dissolved acidic gases in the fluids
(CO2 & H2S).
• Some other factors that can promote corrosion are such
as two dissimilar metals resulting galvanic corrosion,
MIC (Microbiologically influenced corrosion) mainly due
to sulfate reducing bacteria (SRB).
18

Corrosion of
pipeline (2)
• Internally the dissolved CO2 & H2S together with
other organic acids can lead to severe corrosion of
unprotected carbon steel resulting:
a. Corrosion rates of > 20 mm/yr is possible
particularly in high temp./ high pr. systems.
b. Attack can be to pipeline – as uniform metal loss
or localized.
c. Preferential corrosion of welds – weld root attack
or knife attack at heat effected zone(HAZ).
• Seawater also causes corrosion to unprotected CS,
with corrosion rates ranging from 0.1 to 0.5 mm/yr.
19

Corrosion of
pipeline (3)
• In oil industry we also come across corrosion
called BIOCHEMICAL corrosion, it is virtually
degradation resulting from the activity of living
organisms such as bacteria [micro-organisms]
and mussels, algae etc. [macro-
organisms].These organisms can live and
reproduce in the environments having pH in the
range of 0 and 11, temperatures from -100C to +
800C and pressures of several hundred bars.
• The macro-organisms attach themselves to the
walls and further accumulation creates
conditions similar to crevice corrosion and is
generally seen in heat exchangers.
20

Corrosion of
pipeline (4)
• The micro-organisms mainly bacteria are of
about 1µ in size but capable of reproducing
very fast by cellular division and get
necessary energy of sustenance from
enzymes catalysed by metabolic reactions.
• The biological corrosion generally appears
in the form of closely packed tubercles and
generates crevice corrosion. It is seen that
the laminated tuberculiform accumulation is
often hollow and contains blackish fluid
mass. The presence of iron sulphide in it
can be detected by release of H2S on
adding a few drops of HCL acid.
21

Corrosion of
pipeline (5)
Following are the main types of bacteria seen in the
biological corrosion:
• SRB [Sulphate reducing bacteria-desulfovibrio,
desulfuricans]-These sulphate reducing bacteria
produce sulphite in anaerobic conditions and get
required hydrogen from the organic compounds in
the environment.
• SOB [Sulphate oxidising bacteria-thiobacillus, thio-
oxydans] – These are aerobic bacteria capable of
oxidizing the sulphur contained in sulphur
compound. They are found in oil reservoirs and
sewage systems where they cause fast attack of
the cement. Virtually there is combined effect of
SRB at the lower part [anaerobic fermentation] and
SOB at upper part [aerobic].
22

Corrosion of
pipeline (6)
Iron bacteria [gallionella-bacterial
filaments of ferrous oxide]-These bacteria
live in an aerobic environment and get
their synthesis energy from ferrous ions
and their oxidation form ferric ions. The
chemical reaction consumes ferrous &
hydroxyl ions and depolarise both
resulting in corrosion. This growth of
ferrous bacteria eliminates oxygen and
covers the steel surface with tubercles
there by favouring crevice corrosion.
23

Corrosion
Impact
“WHILE YOU ARE READING THIS, 760 KILOGRAMS OF IRON
HAVE BEEN CORRODED”
• Every year in India about 4% of GDP is lost owing to corrosion of
infrastructure, industrial equipment and other vital installations.
• About 20% of the steel produced goes into the replacement of
corrosion damaged steel.
• This leads to the depletion of associated natural resources such
as metal, water and energy required to produce the steel and
steel structures.
• Corrosion represents about 25% of maintenance cost.
• In a study conducted by NACE, it is estimated that pipeline
corrosion costs anywhere between $5.4 billion and $8.6 billion in
the U.S. alone.
24

Corrosion
Impact
• The other impact of corrosion can be either direct in
the form of cost of replacement of corroded
structures / machinery including the protection
costs or indirect costs in the form of shutdowns,
loss of product, loss of efficiency and
contaminations etc..
• The uncertainties in the corrosion rates often lead
to the overdesigning and it also demands improved
safety measures for the systems.
There would be too many advantages of planning
for corrosion control and its mitigation and
mainly it can be extended life of assets and
reduction in maintenance time and cost.
25

Options
to control
corrosion
The different options available for corrosion control of pipelines viz:
– Material Selection
– Chemical Treatment
– Protective Coating
– Cathodic Protection/Impressed current protection
– Process Modification / Change Environment
– Increasing the flow rate
– Use of bactericides / inhibitors.
– If possible, to replace the steel pipes with other
suitable material.
26

Material
Selection
There are good range of materials that can be considered bearing in
mind both internal and external threats and compatibility issues:
– Carbon / low alloy steel – Standard Stainless Steels (including
13Cr, SS316L)
– Corrosion Resistant Alloys
– High grade stainless steels (including duplex 22Cr, super duplex
25Cr & hyper duplex 27Cr)
– Nickel alloys (904L, 6Mo, Alloy 625, Alloy 825)
– Titanium
– Copper alloys (9010 CuNi, Monel)
– Non-metallic materials (GRE, GRP, HDPE)
27

Chemical
Treatment
• Chemical treatment is a standard method used to provide
internal corrosion control for carbon / low alloy steel
pipelines in hydrocarbon production by:
– Corrosion inhibitors
– Oxygen scavengers
– Biocides
Corrosion inhibitors / oxygen scavengers are normally
injected continuously with a typical injection rate of 20 to
100 ppm.
Performance needs to be critically monitored to maintain
adequate concentration. Because when inhibition is lost
corrosion can re-start quickly.
28

Difficulties
with chemical
treatment
subsea
• For subsea facilities providing chemical
treatment (corrosion inhibitors) can be
complex.
• Hence often the majority of chemical is
injected into the lower pressure lines,
leading to under protection in the higher-
pressure lines.
• Ideally individual feed lines / pumps /
valves required to ensure correct dosing.
29

Cathodic
Protection
• DC current is impressed onto the structure to suppress
the electrochemical process of corrosion reaction
• Two different types of cathodic protections:
– Sacrificial (galvanic) anodes
– Impressed Current Systems
• The cathodic protection :
– Is an active system
– The protection only occurs when sufficient
current is being provided.
– High strength steels and some corrosion
resistant alloys can suffer damage if over
polarized i.e if too much current is provided.
30

Sacrificial
Anode
Systems
• Sacrificial anodes made of
electrochemically active metal alloys
such as Zn, Al or Mg are connected to
submerged steel structures. Such active
alloy undergoes galvanic corrosion and
preferentially corrodes i.e release
electrons.
• The DC current generated by anodes
promotes the cathodic reaction on the
steel surface there by protecting the
metal and sacrificing itself.
• That is why is called Sacrificial Anode.
31

ICCP - Impressed
Current Cathodic
Protection Systems
• When dc current from a source (anode) is
impressed to the steel structure, it
(transformer-rectifier) forces electrons to
flow onto the steel.
– This process promotes the cathodic
reaction and suppresses the anodic
reaction.
– When the only reaction on the steel
surface is the cathodic reaction the
steel is protected
• Hence the term Impressed Current Cathodic
Protection
32

CP
monitoring
• New generation of cathodic protection
monitoring systems are now available.
• Permanent reference electrodes and
meters can be installed.
33

Subsea
pipeline -
efficiency
• The efficiency of pipeline depends on
factors such as :
❖If the pipeline is operated
continuously.
❖The required outputs are
obtained with least capital
investment and lowest
operating cost.
34

Maintenance
of Subsea
pipeline
Utility pigs and inline inspection tools
[ intelligent / smart pigs ] play a major role
in maintenance of basic fundamentals of
pipeline i.e continuous operation &
efficiency.
When to pig?
35

When to pig?
PIGGING is required during each phase
in the pipeline life.
• During construction.
• During operation.
• For Inspection.
• For general maintenance repair.
• During renovation / rehabilitation.
• Decommissioning.
36

Pigging……..
“In short pigs help to ensure that
pipeline is constructed properly
and stays that way”.
• It is generally agreed that a pipeline
should be pigged, but the reasons for
doing so are not always appreciated.
• There may be improper pigging & / or
use of wrong pigs.
• This can have adverse effect on the
pipeline’s operating & maintenance
costs as well as health.
37

Pigging……..
“In short pigs help to ensure
that pipeline is constructed
properly and stays that way”.
1. It also helps to ensure maximum
efficiency by removing debris / foreign
matter / deposits and monitoring the
operating & / or physical conditions of
the pipeline.
2. Removes any substance which might
damage the pipeline, prevent the
formation of corrosion cells and
provide timely information & data of
any developing problem.
38

ILI- In-Line Inspection
• In-line inspection is used to confirm existing condition of
pipeline
• New tools have increased range, flexibility and sensitivity
• However, most ILI tools are only reliable to ± 10% wall
thickness, hence for a 15 mm wall thickness pipe can only
detect metal loss > 1.5 mm
• But most gas export pipelines, have zero corrosion
allowance and operate at close to design pressure.
• Hence, significant corrosion, greater than that allowed for
in design has to occur before ILI can detect it!
39

Different types of pipeline
failures

Failures

Requirement
for pipeline
repair
• To prevent pollution and adverse
environmental effects
• To restore the pipeline capabilities.
“3 Rs”
REPAIR
REFURBISH
REPLACE
43

Subsea LEAK
Identification
• Pressure drop is noticed in the system.
• Leak Identification is undertaken with the
help of ROVs.
• A multi support diving spread (MSV) is
required to locate, identify the leak and
repair.
44

Pollution control
Containment &
Recovery
45

Repair
Methodology
• Water depth
• Pipeline diameter, coating, burial depth.
• Under water visibility.
46

Sequence of
the pipeline
repair
• Locate the leak
• Depressurization of the pipeline to hydrostatic
Pressure.
• Removal of concrete and protective coat.
• Surface preparation [sa 2.5].
• Metrology of the leak size health assessment
of pipeline.
• CP and UT survey in the effected area
• The repair can be undertaken i.e either by
repair clamps or sectional replacement .
47

Split sleeve and other types of clamp

Other methods of
SUBSEA Pipeline Repairs
- Sectional replacement

Pipeline Repair Procedure
1. Cut out damaged section or breakout to nearest flange

Option A: Weld flange to pipe subsea (Hyperbaric)
Pipeline
DSV
Sea Level
Strengths
Customer perception:
- Pipeline as new
- Traditional method
Weaknesses
Cost: Huge
Hyperbaric chamber
Trained divers,Vessels

Option B: Lift pipe and weld flange on barge
BARGE
Pipeline
BARGE
Pipeline
Sea Level
Sea Level
Strengths:
Simplistic
Weaknesses:
Not suitable for older pipe
Not a quality repair
Can cause extra stresses in pipeline

Option C: Install connector to pipe subsea
Cut pipe ends and remove coating
Pipeline
DSV
Sea Level
Coupling : Slide connector over pipe end

Installation
Requirements
• Pipe Condition
• Pipe Coating: Remove to approx 1.5 x
connector length
• Surface Finish: SA 2.5 finish; remove weld
bead
• Square Ends: Cut pipe using pipeline
cutters.
• End Gap adjustment : About 1D
• Ovality: designed for maximum ovality in
API-5L or to RP-F104
• Pipe misalignment: Misalignment flange
adapter
54

Bolt spool piece to flanges subsea
Sea Level
DSV
Sea Level
Courtesy Hydratight

Option C: Install connector

Weldless
connector &
MAF
• Connector comprises of gripping mechanism
to grip the pipe circumferentially &
structurally attaches the connector to pipeline
and sealing mechanism for sealing with the
outer surface of pipe for joint integrity. It has
telescopic adjustments to accommodate errors
in subsea measurements and provide the
necessary movement to seat of MAF.
• Misalignment flange is to accommodate the
angular adjustments.
57

Installation
Length of Compensation / End adjustment gap:
A-Contingency for errors
B-Expensive to replace a precut spool piece
58

MAF & CONNECTORS
Courtesy internet

Ensuring
Safety
Prior to commencing sectional replacement, following
safe measures are ensured:
• Venting of line
• Flushing the line with water to thwart hydrocarbon
flow during repair & to avoid contamination of
Diver’s
• Bathymetric survey upto two field joints on both
sides
• Action Plan for combating any further oil spill
during repairs.
• Thickness profile of connector installation
segment.
60

Thanks
Ref:
Personal Experience & Internet
61

Subsea pipeline Repair and Maintenance

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