FMECA of Subsea Control Module

Chess Subsea Engineering (UK) Limited is registered in England (registration number 9616564) and having its registered office at London, Erith, Kenth, DZDA18, United Kingdom.

Tel: +447903310642, +447419706555, +2348139340494. Email: [email protected]

FMECA of Subsea Control Module

The Field Subsea Control System Architecture

Subsea Control System (SCS) is made up of the electrical

power unit (EPU), hydraulic power unit (HPU) and the master

control station (MCS). An uninterrupted power supply (UPS)

provides and maintains power for the complete SCS units in

redundant configurations (see Fig. 1.0).

Each UPS unit is equipped with inverter, rectifier

and a standard sized battery bank. The SCS

provides a comprehensive power, control and

monitoring starting from the surface interface to

all the subsea installed equipment. Acquired

data is displayed on the topside HMI, allowing

for proper monitoring of the entire system. The

MCS, located topside had a dual redundant

operating system operating. The system is

equipped with dual redundant programmable

logic controllers to allow for the monitoring and

control of the Electrical Power Unit (EPU)

functions including the Emergency System

Distribution (ESD).

The HPU provides the hydraulic supply to the

field routed through a topside umbilical

termination unit (TUTU) to a dynamic umbilical.

The control fluid from the HPU is maintained at a

cleanliness level of SAE AS 4059C Class 6B-F

or better. The HPU supply is regulated and

monitored from the operator's workstation in the

control room.

Dynamic umbilical delivers power, control and

chemical injection functions from the topside

umbilical termination assembly (TUTU) and

electrical junction boxes to a 6-port subsea

distribution unit (SDU) on the seabed.

The umbilical contains 2-off Low Pressure lines

plus a spare, 2-off High Pressures lines plus a

spare, methanol injection and other chemical

injection lines for flow assurance purposes. The

topside tie-in is such that the dynamic umbilical

runs down to an umbilical termination assembly

(UTA) located at the seabed while hydraulic fluids

and electrical flying leads tie-in the UTA to the

SDU.

On the other end also, a hydraulic flying leads

(HFL) in combination with a pair of EFLs in

redundancy connects the SDU to each of the out-

going infield static umbilicals to the trees. Finally,

the HFL at the end of the infield umbilical UTA is

connected to the tree Multi Quick Connector

(MQC) while the EFLs are directly connected to

the SCM.

Fig 1.0



The SCM receives low pressure (LP), high pressure

(HP), multiplexed electrical power and signal via the

umbilical connected to the master control station

(MCS) at the surface. When energized a hydraulic

signal is transmitted to the appropriate hydraulic

valve in the subsea Xmas tree, manifold, downhole

instrumentation or any other subsea equipment. An

electric signal decoded by the SEM operates

solenoid directional control valves (DCVs) and

direct the fluid to the appropriate subsea system or

safety valves. Signals from the subsea sensors are

also encoded through the SEM, analyzed and sent

back to surface facility (see Fig 2). The SCM is

connected to the subsea Xmas tree functions and

monitoring equipment via the Subsea Control

Module Mounting Base (SCMMB).


SCM Mode of Operation

Component of SCM

• Electrical Equipment

Subsystem

• Hydraulic Equipment

Subsystem

• Mechanical Parts

• SCM Housing

Fig. 2.0

Bottom - Down method consists of Event Tree Analysis (ETA); FMECA and

Hazard and Operability Study (HAZOP). Bottom Up reliability technique using FMECA was used to determine the reliability of SCM system.

Subsea Control Module (SCM) is made up of

several components (see Appendix A). The main

components can be divided into sub systems

namely;

Reliability Engineering

Reliability is associated with

unexpected failures of

products or services and

understanding why these

failures occur is critical. The

two methods of accessing

system reliability are :

• Top - Down method

• Bottom -Up method

Top - Down method consists

of Fault Tree Analysis (FTA);

Reliability Block Diagram

(RBD) and Markov Analysis.




Failure Mode Effect Critical Analysis

FMEA is defined as a structured qualitative analysis

of a system, sub-system, components or function

that highlights potential failure modes, their causes

and the effects of a failure on system operations.

FMEA major objective is to identify potential failure

modes, evaluate and determine what could

eliminate or minimise the chance of failure. The

building block of FMECA analysis is shown in figure

3 below.

Fig. 3.0: Building block of FMECA analysis

In conducting an FMEA, the first step is to define the

scope of the exercise.

The system design is broken down into sub-

assemblies and components such that key failure

modes and effects are not overlooked. Design

FMEA examines system components and

subsystems failure modes and mechanism.

Manufacturing and assembling is analysed at the

process level. Service FMEA focuses on service

functions of the system.

FMECA extends the FMEA to include criticality

analysis by quantifying failure effects in terms of

probability of occurrence and the severity of any

effects.

There are two key ways of performing

failure modes critical analysis, namely;

• Calculating Criticality Number

(CN)

• Developing a risk priority number (RPN)

In this reliability case study RPN was

used.

The chance of failure mode occurrence is ranked O, the

chance of being undetected D and the severity S. A

numerical scale of 1 to 10 is used for ranking.

Mathematically;

RPN = O * S * D

Appendix A shows SCM components and sub-Systems

with their respective FM ID numbers. Appendix B shows

SCM Components Failures Modes, Causes, Effects,

Risk Factors and RPN Values Evaluation.

Criteria for SCM FMECA RPN Calculation

Severity S ranking = 1 – 10

Chances of being undetected D ranking = 1 – 10

Chance of failure mode occurrence is ranked O = 1 – 10



Appendix A: SCM components and sub-Systems with their respective FM ID numbers

FM ID 1

2

3

4

5

6

7

8

9

Subsystem

Or Component

SCM

Podlock

Dieelectric chamber

over pressure

relief valve

Seawater

check valve

SCM

Housing

SCM

Dielectric fluid

chamber

Electrical

Connectors/Cabling

(internal)

Electrical

Connectors

(External)

Return line check/dump

valves

HP circuit hydraulic

filters

FM ID

10

11

12

13

14

15

16

17

18

Subsystem

Or Component

LP circuit hydraulic

filters

Return line flowmeter

HP supply flowmeter

LP supply flowmeter

HP circuit pressure

transducers + Return

Line

LP Circuit Pressure

Transducers +

Return line

Baseplate mounted hydraulic couplings

HP

Directional Control Valves (DCV)

Choke

DCV valve

FM ID

19

20

21

22

23

24

25

26

27

Subsystem

Or Component

LP

Directional

Control Valves (DCV)

Hydraulic circuitry

Subsea

Electronic Module (SEM)

HP

Accumulation

System

LP

Accumulator System

HP Manifold

System

LP

Manifold System

HP Shuttle

Valve

LP Shuttle

Valve

FM ID

28

29

Subsystem

Or Component

HP

Selector Valve

LP

Selector Valve



FMECA of Subsea Control Module Data Analysis

A high RPN value corresponds to SCM components with high

critical failure mode. A further analysis was performed on top

seven (7) SCM components with high RPN values based on their

combined failure mode (see Table 1).

Results from data analysis of the SCM FMECA shows that most

failures result from SCM hydraulic component followed by the

Subsea Electronic Module (SEM) (see Fig 4). Hydraulic

components such as HP Directional Control Valves (DCV), Choke

DCV Valve, Hydraulic Circuitry, HP Shuttle Valve, LP Shuttle

Valve and LP Directional Control Valves (DCV) all have

occurrence (O) level ranges between moderate (5) to very high

(9) with severity (S) levels ranging from moderate (5) to serious

(9). All though the level of detectability (D) is high, more reliability

has to be factored into this component as most failure results to

non productive time (NPT).

Subsea Electronic Module (SEM) is another major critical SCM

component with high vulnerability to failure. SEM failure results often to

loss of control and communication to the topside, loss of power to all

DCV valve solenoids, loss in SCM system redundancy and complete

loss of production. Although its level of detectability (D) fall within the

range of very high to most certain; most of its identified components

failure severity level is extreme if it ever occurs.

Table 1.0: Top seven (7) SCM components with high RPN values

Conclusion

Reliability of SCM systems and sub component is critical for the safe and optimum

performance of subsea production system. Most failures resulting from SCM are related to

internal valve failures, failure of the valve solenoid coils, hydraulic leakage from supply or

block lines i.e. HP Directional Control Valves (DCV), Choke DCV Valve, Hydraulic Circuitry,

HP Shuttle Valve, LP Shuttle Valve and LP Directional Control Valves (DCV). Reliability should

be incorporated in the design of this SCM sub components. The SEM is not an exception.

Although its level of detectability (D) fall within the range of very high to most certain, reliability

has to be factored in from design as the industry moves into deep and ultra deep waters.



Fig 4: Pie chart of the top seven (7) SCM components with high RPN values



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk Profile Number (RPN)

1

SCM Podlock

SCM not correctly locked to SCMMB

• Number of turns is

insufficient

• Inability to function all

LP and HP control functions

3

8

4

96

Inability to unlock the SCM from the mounting base

• Debris (sand,

calcium carbonate) • Worn couplings

during SCM installation

• Corrosion and wear of the base couplings

• Dead Hydraulic lockdown

• Live hydraulic lockdown

• Inability to retrieve the

SCM to the surface for repairs

• Inability to disconnect the SCM from its SCMMB

• Severe loss in production.

• For VXT, Tree assembly retrieval to the surface

• For HXT, Tree and Well Completions retrieval

2

6

4

48

144

Appendix B: SCM Components Failures Modes, Causes, Effects, Risk Factors and RPN Values Evaluation



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk

Profile Number (RPN)

2

Dieelectric chamber over pressure relief valve

Failure of valve to function on demand

• Dynamic Instability • Components of

valve might be worn out.

• Embrittlement of valve components

• Hydraulic components

failure • Electronic components

failure • Total loss of electronic

and hydraulic functions • Total Loss in well

production

3

7

4

84

84

FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


3

Seawater check valve

Leakage of seawater check Valve

• Dynamic Instability • Installation damage • Embrittlement of

valve components • Wear

• Seawater migration into

the SCM • Dielectric fluid

contamination • Failure of electrical

components • Total loss of electronic

and hydraulic functions • Total Loss in well

production

5

7

3

105

105



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


4

SCM Housing

Loss of communication due to Water ingress Sensor

• Internal fault in the

Water Sensor.

• Internal housekeeping

water ingress monitoring loss.

• All DCVs remain in their current positions.

• Partial Loss of subsea monitoring

• Total Loss in well production

2

8

2

32

Loss of SCM pressure compensation.

• Dielectric fluid

leakage from SCM via vent.

• Dielectric fluid leaks

from SCM whilst installed subsea

• Possible water ingress into the SCM.

• Damage to electronic components due to water ingress.

• Total loss in well production.

2

7

2

28

Inability to disconnect SCM assembly from tree.

• Failure due to

hydraulic coupler

• Unable to disconnect

the SCM from the tree. • Effect is Nil under

normal condition. • High Cost Tree retrieval

and replacement • Loss in well production

+ Pull completion.

2

4

7

56



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Unable to connect SCM assembly to tree.

• Faulty Hydraulic

couplers

• Unable to connect the

SCM to the tree. • Non Productive Time

from retrieval and possible replacement of the SCM assembly

• Loss in well production

3

4

6

72

• Damaged SCM

Baseplate




• Loss in well production.

3

4

5

60

• Debris (sand,

calcium carbonate)




• Loss in well production.

3

4

6

72

• Seal carrier

misaligned or damaged



from retrieval and possible replacement of the SCM assembly Loss in well production

3

4

6

72



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Loss off internal temperature sensor

• Temperature sensor

failure

• Partial loss in subsea

monitoring. • No loss in subsea

systems operation

6

4

2

48

Loss off internal pressure sensor

• Pressure sensor

failure

• Partial loss in subsea

monitoring. • No loss in subsea

systems operation

6

4

2

48

488

FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk Profile

Number (RPN)

5

SCM Dielectric fluid chamber

Dielectric protection loss to the electrical system

• SCM housing

system leakage • Wrong installation

procedure.

• Ingress of seawater into

the SCM • Contamination of the

dielectric fluid. • Electrical component of

the SCM failure. • Total Loss in well

production

2

6

8

96

96



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


6

Electrical Connectors/Cabling (internal)

Power loss from the SEM to the valve units

• Short circuit / open

circuit.

• Loss of power to the

associated valve solenoid

• DCV valve remains in its last latched position

• Control and communication loss to the topside

• Power loss to all the associated subsea/well Instrument


4

6

2

48

• Faulty Electrical

cable or connector

• Loss of power to the

associated valve solenoid

• DCV valve remains in its last latched position

• Control and communication loss to the topside

• Power loss to all the associated subsea/well Instrument


48

96



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


7

Electrical Connectors (External)

Loss of power from the SCM electrical connectors

• Internal fault in

the electrical connectors

• Loss of power to one SEM channel in

the SCM • Loss of DHPT signal from the SEM

channel • Control and communication loss to

the topside • Loss of power to all associated valve

solenoid • DCV valve remains in its last latched

position • Power loss to all the associated

subsea/well Instrument

• Total loss in well production

6

4

2

48

• Leakage in the

connector system

• Loss of power to one SEM channel in

the SCM • Loss of DHPT signal from the SEM

channel • Loss in SCM system redundancy. • Control and communication loss to

the topside • Loss of power to the associated valve

solenoid • DCV valve remains in its last latched

position • Total loss in well production

6 6 2 72

120



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


8

Return line check/dump valves

Reduction in LP hydraulic dump capability.

• Blocked dump

return lines.

• Unable to completely "dump" LP hydraulic

supply pressure to compensation circuit. • All DCVs remain hydraulically latched with

tree valves remaining in last position. • Production flow is not shut in. • No Loss in Production

4

3

2

24

LP Dump Valve fails to operate on demand.

• Internal fault in

the dump valve system

• Unable to completely "dump" LP hydraulic

supply pressure to compensation circuit. • All DCVs remain hydraulically latched with

tree valves remaining in last position. • Production flow is not shut in. • No Loss in Production

4 4 2 32

56

FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk Profile

Number (RPN)

9

HP circuit hydraulic filters

Clogging Blockage

• Unfiltered

contaminated Hydraulics

• Unfiltered contaminated

hydraulics - Blockage and Wearing of SCM components

• Stop or slow slowly moving of actuators.

• Malfunction of subsea components

• Complete Loss in well production

4

4

4

64



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Loss of HP hydraulic fltration

• Filter element missing • Rupture of filter element • Wear filter element

components • Holed or filter by-pass

spuriously operates. • Inadequate filter elements. • Design error in the filter

porosity

• Dormant failure in normal

operation • Clogging or binding of

mobile parts of the DCV valves

• Unfiltered contaminated hydraulics - Blockage and Wearing of SCM components




4

4

4

64

128

FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


10

LP circuit hydraulic filters

Loss of LP hydraulic fltration

• Inadequate filter

elements. • Design error in the

filter porosity

• Clogging or binding of

mobile parts of the DCV valves and other components,



4

5

4

80



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


• Filter element missing • Rupture of filter element • Wear filter element

components • Holed or filter by-pass

spuriously operates.

• Dormant failure in normal

operation • Clogging or binding of

mobile parts of the DCV valves

• Unfiltered contaminated hydraulics - Blockage and Wearing of SCM components




4

5

4

80

• Clogging Blockage due to

fluid contamination

• Clogging or binding of

mobile parts of the DCV valves and other components,

• Wearing of SCM components



4

5

4

80

240



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


11

Return line flowmeter

Loss of electronic monitoring of the Return line flow.

Internal fault in the Return line flowmeter

• Loss of flow monitoring in

the Return Line • No direct impact on a

normally operating tree. • Partial Loss in subsea

monitoring

4

4

2

32

32

12

HP supply flowmeter

Loss of electronic monitoring of the HP Supply flow.

Internal fault in the HP flowmeter

• Loss of flow monitoring of

the HP supply. • No direct impact on a


monitoring

4

4

2

32

32

13

LP supply flowmeter

Loss of electronic monitoring of the LP Supply flow.

Internal fault in the LP flowmeter

• Loss of flow monitoring of

the LP supply. • No direct impact on a


monitoring

4

4

2

32

32



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


14

HP circuit pressure transducers + Return Line

Loss of electronic monitoring of a single hydro quad function.

• Loss of DCV Output

Pressure Transducer.

• All associated DCV's

remain latched in their last position

• Loss of monitoring and positional status of a single DCV.

• No direct impact on a normally operating tree.

• Partial Loss in subsea monitoring

4

3

2

24

Loss of electronic monitoring of the HP Supply Pressure.

• Loss of HP Pressure

Transducer.






4

2

2

32

56



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


15

LP Circuit Pressure Transducers + Return line

Loss of electronic monitoring of a single hydro quad function.

• Loss of DCV Output

Pressure Transducer.






4

2

2

16

Loss of electronic monitoring of the LP line Pressure.

• LP Pressure

Transducer is Faulty






6

4

2

48

64

16

Baseplate mounted hydraulic couplings

Inability to connect the SCM to the Xmas tree

• Couplings worn out

during SCM • Installation

Corrosion and wear of the base couplings

• Inability to makeup the

SCM to the Xmas tree • Complete Loss of

Production

2

4

2

32

32



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


17

HP Directional Control Valves (DCVs)

SCSSV DCV fails to open on demand from the closed position.

• Failure of the valve

solenoid coils

• SCSSV fails to open. • Unable to start

production from the well.

• Complete Loss in Production

5

6

4

120

• DCV internal fault of

the latching mechanism

• SCSSV fails to open. • Unable to start

production from the well.

• Complete Loss in Production

5

6

4

120

SSCSV shuts spuriously from the open position.


the latching mechanism.

• SCSSV spuriously

closes. • Unscheduled loss of

production. • Complete Loss in

Production

5

6

4

120

SCSSV fails to shut on demand from the open position.


solenoid system

• Loss of SCSSV

protection • Reduced well barrier for

the SPS • Partial Loss in Well

Control

6

6

3

108


the latching mechanism to latch.

• Loss of SCSSV

protection • Reduced well barrier for

the SPS • Partial Loss in Well

Control

6

6

2

72



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


540

18

Choke DCV valve

Choke DCV fails to open on demand.


solenoid coils

• Unable to set required

choke valve position • Reduction in flow of oil

from the well. • Partial Loss of

Production

4

4

2

32

• DCV internal valve

failure.

• Unable to set required

choke valve position • Reduction in flow of oil

from the well. • Partial Loss of

Production

6

4

2

48

Choke DCV fails to shut on demand.

• Solenoid valve

sticks in energized position.

• Production Choke

Valve Close actuator (PCVC) fails to extend to required position.

• Reduction in flow of oil from the well.

• Partial Loss of Production

4

4

2

32

• DCV internal valve

failure.





6

4

2

48



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk



solenoid coils





4

4

2

32

192

19

LP Directional Control Valves (DCV)

LP tree valves DCV fails to open on demand


solenoid coils

• Selected Xmas tree

valve fails to open on demand

• DCV remains in the last latched and shut position.

• Well remains in the shut-in position

• Complete Loss of Production

6

6

3

108


DCV latching mechanism

• Selected Xmas tree

valve fails to open on demand

• DCV remains in the last latched and shut position.

• Well remains in the shut-in position


6

6

3

108



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


LP Tree valves DCV shuts spuriously from the open position.


DCV latching mechanism

• Associated tree valve

spuriously closes • Unscheduled Loss of

production • Complete Loss of

Production

4

6

3

72

LP Tree DCV fails to close on demand


solenoid coils

• Unable to shutoff

production • Partial Loss in well

control

7

5

3

105

393

20

Hydraulic circuitry

Loss of single LP hydraulic supply

• Solenoid valve

spuriously operates

• Loss of single LP

channel in the tree SCM.

• Pressure drop in the shuttle valves

• Total loss of Tree controls


4

6

3

72

• Leakage from LP

hydraulic Lines / connectors

• Loss of single LP

channel in the SCM. • Leakage of hydraulic

fluid into the sea. • Loss of Production

6

6

3

108



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


• Single LP hydraulic

line blocked

• Loss of LP pressure in

the affected channel. • Loss of Xmas Tree

controls • Loss of Production

5

6

2

60

Loss of single HP hydraulic supply

• Loss in HP hydraulic

line/connector in a single channel.

• Loss of single HP

channel to all the Xmas tree.

• Severe leakage of hydraulic fluid into the sea.

• Eventual drop of all the HP DCVs

• Loss of Production

6

6

2

72

• Leakage from HP

hydraulic lines

• Gradual loss of single

HP channel to all the Xmas tree/Well.

• Leakage of hydraulic fluid into the sea.


6

5

3

90

• Single HP hydraulic

line blocked

• Loss of HP pressure in

the affected channel. • Loss in SCSSV and

FCV Controls • Loss of Production

4

6

2

48



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Loss of both LP hydraulic supplies

• Line/connector

Leakage in the LP supply Lines

• Loss of hydraulic

suplies to the LP DCVs • Loss of Xmas Tree

controls • Complete Loss of

Production

5

8

2

80

• Blocked LP

hydraulic lines


suplies to the LP DCVs • Loss of Xmas Tree

controls • Complete Loss of

Production

5

8

2

80

Loss of both HP hydraulic supplies

• Leakage in the HP

supply lines


suplies to the HP DCVs • Loss of SCSSV and

IWCV controls • Complete Loss of

Production

5

8

2

80

• Blocked HP

hydraulic lines


suplies to the HP DCVs • Loss of SCSSV and

IWCV controls • Complete Loss of

Production

5

8

2

80

770



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


21

Subsea Electronic Module (SEM)

Complete Loss of Power supply from the SEM

• Internal fault

with the SEM power supply units

• Water ingress into the SCM unit

• Loss of DHPT signal from

the SEM channel • Loss of control and

communication to the topside

• Loss of power to all DCV valve solenoids

• Loss in SCM system redundancy


6

8

2

96

Loss of Controller board functionality

• Failure of

controller board

• Loss of single LP channel in

the tree SCM. • Loss of Tree Controls • Loss of control and



6

8

2

96

Loss of Signal from one SEM

• I/O card failure

in SEM, Corrupt software

• Loss of single LP channel in

the tree SCM. • Loss of Tree Controls • Complete Loss of

Production

5

8

2

96

Complete Loss of signal from both SEM

• I/O card failure

in SEM, Corrupt software

• Loss of DCV Valve controls • Loss of all associated

subsea instrumentation. • Loss of Xmas Tree controls • Complete Loss of

Production

5

8

2

96



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Loss of I/O Interface Board

• I/O Board

Internal fault.

• Loss of the channel I/O

Board. • Inability to monitor one set

of external instrumentation. • All DCVs will remain latched

to their current positions.


8

8

2

128

Loss of DHPT Board

• DHPT Board

Internal fault.

• Loss of Communication to

the Tree DHPT instruments from the Channel.

• All DCVs remain in their last positions.

• The redundant DHPT board provides the service

• Complete loss of monitoring

6

8

2

96

Loss of Modem Functionality - Interface to topside

• Modem Failure.

• Loss of one communication

channel to the topside • Loss of control and


• The control function of the SCM is unaffected.


6

8

2

96

• Modem

Freezes - produces steady output

• Partial Loss of monitoring • Loss of control and



6

8

2

96



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Critical Loss of Electronic Control

• Combinational

loss of power supply, modem and control board

• Inability to monitor subsea

instrumentation or command Inability to open or close any valve from the topside

• All hydraulically actuated valves remain in last positions

• Inability to shut in the tree in a controlled manner through the integrated system

• Complete loss of subsea monitoring


6

8

2

96

896

FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


22

HP Accumulation System

Reduction in HP Accumulation.

• Single HP

accumulator loss of precharge.

• Reduction in HP

accumulation • Excessive drop in

supply during valve operation

• All DCVs delatch/All tree valves close


4

7

3

84



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


• Reduction in

HP accumulation

• Reduction in HP

accumulation • Excessive drop in supply

during valve operation • All DCVs delatch/All tree

valves close • Loss of Production

4

7

3

84

Loss of HP Accumulation.

• Loss all HP

accumulator pre-charge.

• Loss/reduction in HP

accumulation • All DCVs delatch • Complete Loss of

Production

4

7

3

84

Loss / reduction of HP supply pressure.

• HP supply line

plugged with particulate.

• Loss/reduction in HP


during valve operation • All HP DCVs delatch • Complete Loss of

Production

4

7

3

84

336



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


23

LP Accumulator System

Loss/reduction in LP Accumulation.

• Loss all LP

accumulator pre-charge.

• Loss of common LP supply

pressure • All DCVs eventually unlatch • Complete Loss of

Production

6

7

3

126

• Severe leak

from the LP Common Header Pressure Transmitter.

• Reduction in LP



valves close • Complete Loss of

Production

5

7

3

105

• Single LP

bladder failure.

• Reduction in LP



valves close • Complete Loss of

Production

5

7

3

105

336



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


24

HP Manifold System

Severe Leak in the HP Manifold (E.G. Seals etc)

• Faulty seals

and other system malfunction.

• Loss of common HP supply

pressure • All HP DCVs eventually

unlatch and Well shutting. • Loss of Production

3

5

3

45

45

25

LP Manifold System

Severe Leak in the LP Manifold

• Faulty seals

and other system malfunction


pressure • All LP DCVs eventually

unlatch and Well shutting. • Complete Loss of

Production

3

5

4

60

60

26

HP Shuttle Valve

Shuttle Valve fails to change over to the next HP supply line.

• HP Shuttle

valve internal fault.

• Inability to select/change

over to an HP supply on demand.

• No direct effect if both lines remain serviceable

• All DCVs unlatch and Well shutting if 2nd line is not available


6

7

2

84



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


Severe Leak in the Common HP Hydraulic Header.

• Severe leak

from the HP Shuttle valve.


pressure • All DCVs eventually unlatch • Loss of Production

6

7

2

84

• Severe leak

from the HP manifold (seals etc).



6

7

2

84

• Severe leak

from the HP Common Header Pressure Transmitter.



6

7

2

84

• Severe leak

from the HP Common Header Pressure Transmitter.



6

7

2

84

• Severe leak

from the HP Common Header Flow Meter.



6

7

2

84

504



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


27

LP Shuttle Valve

Shuttle Valve fails to change over to the next LP supply line.

• Shuttle valve

internal fault.

• Inability to select/change

over to an LP supply on demand.

• No direct effect if 2nd line is serviceable

4

7

3

84

Severe Leak in the Common LP Hydraulic Header.

• Severe leak

from the LP Shuttle valve.



4

7

3

84

• Severe leak

from a LP Accumulator.



5

7

3

105

• Severe leak

from the LP Common Header Pressure Transmitter.



5

7

3

105

• Severe leak

from the LP Common Header Flow Meter.



5

7

3

105

483



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


28

HP Selector Valve

HP selector valve spuriously closes..

• HP selector

valve internal fault of the latching mechanism.

• Selector Valve spuriously

isolates and vent down an incoming supply

• Loss of a single HP hydraulic supply to the SCM.

• No Effect on normal operation

• Loss of HP hydraulic supply redundancy

4

6

2

48

HP selector valve fails to open.

• Failure of the

valve solenoid system.

• Loss of a single HP

hydraulic supply to the SCM.


• Loss of hydraulic supply redundancy

6

4

2

48

• HP selector

valve internal fault of the latching mechanism

• Loss of a single HP


• No direct Effect on normal operation


4

4

2

48

144



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


29

LP Selector Valve

LP selector valve spuriously closes.

• LP selector


• Selector Valve spuriously

isolates and vent down an incoming supply

• Loss of a single LP hydraulic supply to the SCM.



4

6

2

48

LP selector valve fails to open.

• Failure of the

valve solenoid system.

• Loss of a single LP




6

6

2

72

• LP selector

valve internal fault of the latching mechanism

• Loss of a single LP


• No direct Effect on normal operation


4

6

2

48



FM ID

Component

Failure Mode

Failure Cause

Failure Effects

O

S

D

Risk


LP selector valve fails to close.

• Complete

failure of the selector valve solenoid system

• Unable to select LP channel

as required • No direct Effect on normal

operation • Loss of hydraulic supply

redundancy

4

6

2

48

LP selector valve fails to open.

• LP selector


• Unable to select LP channel

as required • No direct Effect on normal

operation • Loss of hydraulic supply

redundancy

4

6

2

48

264

Documents

FMECA of Subsea Control Module