AOD Isolation Risk Assessment Rev D2

Advanced Online De-Sander

RBG Ltd Document No: AQD/AOD 006

Title: Advanced Online De-Sander Isolation Risk Assessment

Revision Status

Revision Date

Section(s) Changed Prepared By

Checked By

Approved By

D2 11/10/05 Comments Incorporated CS DBD1 10/10/05 Initial Preparation for

CommentCS

AOD Controlled CopyUncontrolled if Printed

/tt/file_convert/5528bfec550346bc588b4929/document.doc


CONTENTS

Introduction

Summary Comment

Scenario Worksheets

Blank Worksheet

The Assessment Model



Introduction

The Advanced Online De-Sander (AOD) is intended to be connected to the client process vessel and perform ‘online’ de-sanding operations. The AOD effectively becomes a temporary extension of the client process system.

There is a need to provide assurance to the client that in an emergency there is an adequate isolation between the client process and the temporary AOD.This assessment will test the ‘as built’ isolations for adequacy.

While the AOD is in service there may arise circumstances where a part of the AOD needs to be worked on while the remainder of the AOD remains on line.This assessment will test the available isolations for adequacy.

The model used to assess the adequacy of the isolations is fully described in the Oil Industry Advisory Committee document “The Safe Isolation of Plant and Equipment” published in 1997.

A single page ‘worksheet’ is included to allow easy working of the model and recording of the results.

The assessment tool is reproduced at the end of this document for ease of understanding this assessment and as an aid to carrying out further assessments.

Scenarios Considered:1. Isolation from client vessel during rig up and rig down2. Isolation between the client separator and the AOD Skid in an emergency S/D3. Isolation between the client separator and the jetting unit in an emergency S/D4. Isolation between client separator and jetting unit can’t be accessed in an

emergency S/D (manual valve)5. Work on one hydrocyclone while the other two remain on line.6. Work on a centrifugal pump7. Changing a fine filter element



Summary Comment on Isolation Risk Assessments Considered:

Connection to Client SeparatorsGiven the separator pressures that the AOD skid is designed to De-Sand (up to 40 barg) the requirement for connecting to and disconnecting from such a separator is a single valve. However, it is RBG’s requirement for the client to have a double valve arrangement here as indicated on P&ID AQD/DSS/001 Rev 1 (6/10/05).

Isolation in Event of an Automatic / Emergency ShutdownThe AOD inlet S/D valve, BV3, is adequate for isolation purposes, though if time permitted it would be expected that manual valve GV or BV2 would also be closed.The concern here is that the hose from the separator to the AOD skid remains live, potentially crossing module boundaries.Ideally the separator mounted manual valves should also be closed.Alternatively, an automatic valve functioning in a similar manner to BV3 could be incorporated in the AOD set up for each of the separator connections.

A manual valve exists on the separator valve arrangement which is adequate for isolation purposes. However, access to the separator is required to close this valve. Additionally, before the valve can be closed the hydraulic ram must retract; withdrawing the ¾” jetting hose and nozzle before the valve can be operated.

If the ¾” hose/nozzle becomes stuck a shear device is installed in the line which will allow the isolation valve to be closed once the hydraulic ram retracts with the sheared hose.Careful consideration of the circumstances must be given prior to shearing the jetting line as this will then require a vessel entry to remove the sheared line / nozzle and make the vessel client isolation valves able to close.In any situation the decision to shear will be made in consultation with the OIM if there is no immediate risk or hazard. In an emergency situation the decision to ‘shear’ should be taken in line with the ‘pre operation meeting agreed actions’ agreed between the OIM and RBG supervisor if there is an immediate risk and evident hazard. The integrity of the separator is compromised while the sheared section of line remains in place.

Until the manual isolation valve is closed there remains a flowpath between the client separator and the jetting unit protected only by a non return valve (NRV).While this line and the NRV is designed for 250 barg and it is expected that the NRV will hold, it is not good practice to rely on a NRV for isolation.Ideally the separator mounted manual valve should also be closed.



Alternatively, an automatic valve functioning on the platform 24/110 v permissive to the Jetting unit could be installed in the 1” line.

Isolations of Skid Mounted EquipmentAssessments have been carried out on 2 scenarios of carrying out work on the AOD skid while the skid remains on line. While the works could be carried out after careful checking of the integrity of the butterfly valve isolations it must be concluded that the skid is not designed for work to be carried out while the skid remains on line. The skid should be S/D and adequately isolated if works are to be performed.

The only routine skid intervention while on line is for the changing of fine filter elements.Only single valve isolation is required and the skid is fitted with two valves. However, the valves are butterfly type which is not recommended for isolations other than non hazardous fluids.This is a border line case and can be considered if the integrity of the valves can be proven.Alternatively one of the two valves on each filter inlet and outlet could be changed for a different valve type (ball?) which is acceptable for an isolation service.



Isolation Risk Assessment Work Sheet:

Scenario Description (1):Isolation from client vessel during rig up / rig down, i.e. no flow situation.Situation is a separator module = B (client separator module)Substance is produced water = 6, could be hot, (could ultimately turn to hydrocarbons = 5).Line size is 3”Pressure is up to 40 bargHook up, say, 2 visits / year x 3 separators, rig up and rig down = 12 = monthly

Situation B Substance Best 6(Worst

5)

Effects score 2(3)

Line Size 4” System Pressure >20 Release score 3

Frequency M Duration <shift Time score 3

Effect x Release x Time =Hazard Factor

2(3) x 3 x 3 = 18(27)

Required Isolation Method:</= 30 Single Valve x (x)31 – 150 Double Valve151 – 450 Double Block & Bleed451 – 600 Single Valve, Spade & Bleed>600 Double Block, Bleed & Spade

Does design / as built meet the isolation standard? YSingle valve is the client valve. RBG would normally expect double valve isolation from the client vessel anyway.Assessment by: C Sherwood Date: 7/10/05




Scenario Description (2)( to be considered in conjunction with scenario 3 + 4):Isolation in event of a platform initiated S/D, i.e. flow path is isolated at AOD inlet.Situation is a separator module = C (location of AOD and most operators)Substance is produced water = 6, could be hot. (Could ultimately turn to hydrocarbons = 5).Line size is 3”Pressure is up to 40 barg.Frequency of platform initiating an AOD S/D during de-sanding operations is considered low, say, annual.

Situation C Substance 6(5) Effects score 1(2)


Frequency A Duration <shift Time score 2


1(2) x 3 x 2 = 6 (12)

Required Isolation Method:</= 30 Single Valve x31 – 150 Double Valve151 – 450 Double Block & Bleed451 – 600 Single Valve, Spade & Bleed>600 Double Block, Bleed & Spade

Does design / as built meet the isolation standard? YIsolation standard is adequate but line between client separator and AOD skid remains ‘live’ until the manual separator valves are closed; this could be a significant length crossing module boundaries.

Assessment by: C Sherwood Date: 7/10/05



Isolation Risk Assessment Work Sheet:Scenario Description (3) (to be considered in conjunction with scenario 2 + 4):Isolation in event of a platform initiated S/D, i.e. isolation between jetting unit and client separator.Situation is a separator module = B (isolation point rather than location of jetting unit)Substance is produced water = 6, could be hot. (Could turn to hydrocarbons = 5).Line size is 3”Pressure is up to 40 barg.Frequency of platform initiating an AOD S/D during de-sanding operations is considered low, say, annual.

Situation B Substance 6(5) Effects score 2(3)




2 (3) x 3 x 2 = 12 (18)


Does design / as built meet the isolation standard? YThis is not an automatic isolation function in an emergency situation.Hydraulic Ram retracts allowing manual isolation valve to be closed.Worst case, ¾” jetting hose is jammed, shear valve is operated, and hydraulic ram retracts allowing manual isolation valve to be closed.





Scenario Description (4) (to be considered in conjunction with scenarios 2 + 3):Jetting unit manual isolation can’t be accessed due to emergency situation.Situation is a separator module = B (isolation point rather than likely location of jetting unit)Substance is produced water = 6, could be hot.Line size is 3/4”Pressure is up to 40 barg.Frequency of platform initiating an AOD S/D during de-sanding operations is considered low, say, annual.

Situation B Substance 6 (5) Effects score 2 (3)

Line Size </=1” System Pressure >20 Release score 2



2 (3) x 2 x 2 = 8 (12)


Does design / as built meet the isolation standard? NIsolation between client separator and jetting unit is an NRV. This should not normally be considered an adequate isolation.





Scenario Description 5:Changing liners / blanks in H2 while H1 and H3 remain on line.Situation = C, AOD skid location.Substance = produced water (AOD will detect hydrocarbons and S/D)Line size =3”Pressure is up to 7 barg (AOD trips at 7.0 barg inlet)Frequency is low, say, annual.

Situation C Substance 6 Effects score 1

Line Size 4” System Pressure </=10 Release score 2



1 x 2 x 2 = 4


Does design / as built meet the isolation standard? NH2 inlet has a two valve isolation, outlet has a single valve isolation, however all valves are butterfly valves, not recommended for isolation purposes except for non hazardous substances.While the assessment does not prohibit the use of such isolation, consideration should be given to the need to perform such an operation while the AOD skid remains on line.Assessment by: C Sherwood Date: 10/10/05




Scenario Description 6:Work on a Centrifugal Pump while the AOD Skid remains on lineSituation = C, AOD skid location.Substance = produced water (AOD will detect hydrocarbons and S/D)Line size =3”Pressure is up to 7 barg (AOD trips at 7.0 barg inlet)Frequency is low, say, annual.





1 x 2 x 2 = 4


Does design / as built meet the isolation standard? NPump inlet isolation is a single valve; discharge isolation will be double valve. However all valves are butterfly, not recommended for isolation purposes other than non hazardous fluids.While the assessment does not prohibit the use of such isolation, consideration should be given to the need to perform such an operation while the AOD skid remains on line.




Isolation Risk Assessment Work Sheet:Scenario Description 7:Changing a fine filter elementSituation = C, AOD skid location.Substance = produced water (AOD will detect hydrocarbons and S/D)Line size =3”Pressure is up to 7 barg (AOD trips at 7.0 barg inlet)Frequency is, say, daily, taking less than 1 shift



Frequency D Duration <shift Time score 10


1 x 2 x 10 = 20


Does design / as built meet the isolation standard? NWhile the requirement is for a single valve, both the inlet and outlet have double valve isolations but all valves are butterfly valves, not recommended for isolations other than with non hazardous substances. The fluid, having passed through the AOD skid could now be considered to be non hazardous (fluid temperature?)While the use of such an isolation is not prohibited, if it is to be used, the integrity of the isolations must be carefully confirmed by use of the filter vent and drain valves and monitoring of the filter pressure gauges.





Scenario Description:

BLANK

Situation Substance Effects score

Line Size System Pressure Release score

Frequency Duration Time score


x x =

Required Isolation Method:</= 30 Single Valve31 – 150 Double Valve151 – 450 Double Block & Bleed451 – 600 Single Valve, Spade & Bleed>600 Double Block, Bleed & Spade

Does design / as built meet the isolation standard?

Assessment by: Date:



The Assessment Model:

Situation Substance Pressure Line Size Frequency Duration

Effects Matrix Release Matrix Time Matrix

EFFECTS FACTOR

RELEASE FACTOR

TIME FACTOR

CALCULATEHazard factor = Effects x Release x Time

SELECTION

ISOLATION METHOD

Situation, Substance, Pressure, Line Size, Frequency and Duration are defined and derived for each situation in the following tables:



Situation:Type Description Typical Examples

Onshore OffshoreA Congested or confined equipment or >20

people at risk.Offshore there is the potential for escalation resulting in the need for platform evacuation.

Crude distiller unit, catalytic cracker plant. Village or town within range of toxic effects.

Compression module heavily populated with pipework and objects of box type construction.

B Open process storage or product transfer plant or 11-20 people at risk. Offshore open or less congested modules where explosion hazard is minimal or escalation beyond the immediate area is unlikely. Large fire with the potential for local damage and multiple fatalities.

Treater Unit, LPG spheres, road car loading gantry.

Module containing large cylindrical vessels, such as separators, widely separated.

C Storage area or 6-10 people at risk. Offshore an area where gas is unlikely to accumulate to hazardous levels with minor fires contributing the highest risk.

Tank Farm, pumping manifold, unprotected control room or outside workers within range of toxic effects.

Wellhead modules or other non enclosed spaces open on two or more sides.

D Few items of equipment in an open area or 3 to 5 people at risk. Offshore utility systems with the potential to cause fatalities or structural damage.

Isolated pumphouse. Modules containing temperature or high pressure utility systems or corrosive substances.

E Remote single items or 1 or 2 people at risk. Offshore minor fires which are easily contained.

Remote pump or vessel.

Substance:Type Description

1 Toxic gasses e.g. HF, Cl2, SO2, H2S, HCN, HCl, CO. Note: Toxic liquids such as Cl2 and SO2 require special treatment since leaks may cause toxic effects over a wide area. In such cases the highest standard of isolation should be employed.

2 LPG, NGL or flammables above a temperature where more than 50% weight would flash on release. Material above auto ignition temperature.

3 Flammable liquids above their flashpoint.

4 Flammable gasses.

5 Flammable liquids below their flashpoint

6 Other hazardous fluids, e.g. steam, high temperature or low temperature (cryogenic) fluids, corrosives, acids, asphyxiants, etc.

7 Non hazardous substances. (Note that substances such as water and nitrogen may be hazardous in some situations)



Effects Matrix:Situation

Substance Type

A B C D E

1 10 10 9 8 72 9 8 5 4 33 8 6 4 3 24 5 4 3 2 15 4 3 2 1 16 3 2 1 1 17 1 1 1 1 1

Release Matrix:System Pressure

Line size > 100 barg > 50 barg > 20 barg > 10 barg </= 10 barg>/= 8” 10 8 6 5 4

6” 8 6 5 4 34” 6 4 3 3 22” 4 3 2 2 1

</= 1” 3 2 2 1 1

Time Matrix:Duration

Frequency < 1 Shift > 1 Shift > 7 daysDaily 10 10 -Weekly 7 10 -Monthly 3 7 10Annually 2 3 7Occasionally 1 2 3

‘Hazard’ Factor = ‘Effects’ x ‘Release’ x ‘Time’The result is a score between 1 (trivial consequence) and 1000 (disastrous consequence).



Selection of Isolation Method:Hazard Factor Isolation Method Reference No.

</= 30 Single valve Method 131 - 150 Double valve Method 2151 - 450 Double block and bleed Method 3451 - 600 Single valve, spade and

bleedMethod 4

> 600 Double block, bleed and spade

Method 5

Methods 1 – 5 refer to diagrams in the original document showing the required arrangements for valves, spades, bleeds and pressure monitoring points.

… “only use gate, plug, globe or ball type valves which provide a reliable, positive tight shut off seal for isolations of hazardous substances. Flow Control Valves and butterfly type valves are generally suitable only for non-hazardous substances, as they may not always provide a tight shut off. In general, non-return valves are not suitable for use in isolations unless the valve is designed to close against the pressure which is to be protected and can be positively locked closed in that position. If a suitable non-return valve is to be used in an isolation it should always be pressure tested to at least the maximum anticipated differential pressure.”


Documents

AOD Isolation Risk Assessment Rev D2