Petroleum Development Oman L.L.C.
Document Title: Gas Freeing Purging and Leak testing
Process Equipment and Pipework
Document ID
Document Type
Security
Discipline
Owner
Issue Date
Revision
PR-1073
Procedure
Unrestricted
Engineering and Operations
UOM - Functional Maintenance & Integrity Manager
April 2010
4.1
This document is the property of Petroleum Development Oman, LLC. Neither the whole nor any part of
this document may be disclosed to others or reproduced, stored in a retrieval system, or transmitted in
any form by any means (electronic, mechanical, reprographic recording or otherwise) without prior written
consent of the owner.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
This page was intentionally left blank
Page 2
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
i
Revision 4.1
Effective: Mar-11
Document Authorisation
Authorised For Issue – April 2010
Page 3
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
ii Revision History
The following is a brief summary of the 4 most recent revisions to this document. Details of all
revisions prior to these are held on file by the issuing department.
Revision
No.
Date
Author
Scope / Remarks
Apr-11
Robin Norman UOP6
Added Section 1.7 ALARP
4.1
Mar-11
Robin Norman UOP6
See Interim Amendment March 2011
(Rev 4.1)
4.0
Apr-10
Robin Norman UOP6
See Addendum 2 for details
3.2
Feb-10
Robin Norman UOP6
3.1
Jan-09
Robin Norman UOP6
1.0
Sept 01
UOP/1
Minor Revision – See Addendum 1 for
details
Revised Section 3 ‘Leak Testing’ to
provide clarity and remove any
confusion
Reviewed and revalidated
Sept 98
UOP/1
OP-32 rewritten to new format.
iii Related Business Processes
Code
EP 72
Business Process (EPBM 4.0)
Maintain and Assure Facilities Integrity
iv Related Corporate Management Frame Work (CMF)
Documents
The related CMF Documents can be retrieved from the CMF Business Control Portal.
CP-114
Maintenance CoP
CP-115
Operate Surface Product Flow Assets - CoP
See Appendix 4
Page 4
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
TABLE OF CONTENTS
1
Introduction ............................................................................................................................ 7
1.1
Background ...................................................................................................................... 7
1.2
Purpose ............................................................................................................................ 7
1.3
Scope ............................................................................................................................... 7
1.4
Distribution / Target Audience .......................................................................................... 7
1.5
Changes to the Document................................................................................................ 8
1.6
Step-out Approval ............................................................................................................. 8
1.7
ALARP .............................................................................................................................. 8
2
Roles and Responsibilities ..................................................................................................... 9
3
Gas-Freeing, Purging Process Equipment .......................................................................... 10
3.1
General ........................................................................................................................... 10
3.2
Draining of Vessels and Pipework to Open Pits ............................................................. 10
3.2.1
Considerations When Draining Vessels and Pipework ........................................... 10
3.2.2
Criteria for Using an Open Pit .................................................................................. 11
3.2.3
Control Required for using Open Pits ...................................................................... 11
3.3
4
Gas-Freeing and Purging ............................................................................................... 12
3.3.1
Preparation and Precautions .................................................................................... 12
3.3.2
Gas Freeing ............................................................................................................. 14
3.3.3
Atmospheric Pressure Method ............................................................................... 14
3.3.4
Cyclic Pressure Purge Method .............................................................................. 14
3.3.5
Water Displacement Method ................................................................................... 15
3.3.6
Series Purging ......................................................................................................... 15
3.3.7
Displacing To Air ...................................................................................................... 15
3.4
Purging Following Inspection or Maintenance ................................................................ 15
3.5
Sampling ........................................................................................................................ 16
Leak Testing......................................................................................................................... 17
4.1
Objective ........................................................................................................................ 17
4.2
Definitions for Leak Testing ............................................................................................ 17
4.3
Reinstatement Policy ...................................................................................................... 18
4.3.1
Method Options in Order of Consideration .............................................................. 18
4.4
Planning Reinstatement Leak Test ................................................................................ 19
4.5
Nitrogen Leak Testing of Systems ................................................................................. 21
4.5.1
Bubble Forming Solution.......................................................................................... 22
4.5.2
Acceptance Criteria for N2 Leak Testing (Bubble Test) ........................................... 22
4.6
Performing the In-Service Reinstatement Test .............................................................. 22
4.7
Vacuum Testing ............................................................................................................. 23
4.8
Reinstatement Testing of Relief Valves Connected to the Flare or Relief Headers ....... 23
Page 5
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
5
Revision 4.1
Effective: Mar-11
Hazards ................................................................................................................................ 24
5.1
Draining and Flushing to Open Pits ................................................................................ 24
5.2
Gas-Freeing and Purging ............................................................................................... 24
5.3
Leak Testing ................................................................................................................... 24
Appendix 1 – Working With Nitrogen Gas ................................................................................... 26
Appendix 2 – Method Statement ................................................................................................. 29
Appendix 3 - Abbreviations .......................................................................................................... 30
Appendix 4 – Reference Material ................................................................................................ 31
Appendix 5 - User Feedback Page .............................................................................................. 32
Addendum 1 – Changes at Revision 3.2 ..................................................................................... 33
Addendum 2 – Changes at Revision 4.0 ..................................................................................... 34
Interim Amendment March 2011 (Revision 4.1) .......................................................................... 35
TABLES AND FIGURES
Table 1 - Recommended Criteria Hydrocarbon / Nitrogen Purge .......................................... 16
Table 2 - Inert Gas End Points for Purging Equipment Out of Service ................................. 16
Figure 1 – Reinstatement Leak Testing Decision Chart .......................................................... 19
Table - Sample Checksheet for Testing of Pipework System .............................................. 29
Page 6
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
1
Introduction
1.1
Background
Revision 4.1
Effective: Mar-11
Process equipment in hydrocarbon services shall be subjected to periodic inspections
and maintenance which may result in the pressure containment being broken. Such
breaks in the pressure containment can result in explosive mixtures of air and
hydrocarbon vapour being present. Therefore whenever pressure containment is broken
measure must be taken to ensure that:

An explosive atmosphere is not present during such times that work is being
undertaken

An explosive atmosphere is not present in the equipment prior to its return to
hydrocarbon service

Pressure containment is tested and confirmed before the equipment is returned
to hydrocarbon service
IMPORTANT: This procedure will be used for gas freeing, purging and leak testing
process system and equipment that has been commissioned and is being operated as
a production unit.
1.2
Purpose
The purpose of this procedure is to detail the steps necessary to ensure that
hydrocarbon process equipment is correctly gas-freed before the pressure containment
is broken; purged of any explosive mixtures before being returned to hydrocarbon
process service; and leak tested to ensure pressure containment is confirmed.
This procedure may be used in conjunction with PR-1077 - Preparation of Static
Equipment for Internal Maintenance and Inspection.
1.3
Scope
This scope of this procedure1 covers gas-freeing, purging and leak testing of
hydrocarbon process equipment and pipework.
Specific plant / equipment level “Work Instructions / Method Statements” shall be
developed prior to the work being undertaken. These shall form part of the Scope of
Work.
1.4
Distribution / Target Audience
This procedure is intended for the use of Operations and Maintenance personnel and
Contractor staff working with Operations and Maintenance involved in intrusive work on
process equipment and pipework.
1
The procedure shall not detail removal of instrumentation lines where the volume of
hydrocarbon vapour / gas / liquid is small and will therefore not present an explosion hazard.
However safe working practice shall still be observed when undertaking this work.
Page 7
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
1.5
Revision 4.1
Effective: Mar-11
Changes to the Document
Responsibility for the upkeep of the Document shall be with the Functional Production
Team Leader UOP, the Owner. Changes to this document shall only be authorised and
approved by the Owner.
Users of the Document who identify inaccuracy or ambiguity can notify the Custodian or
his/her delegate and request changes be initiated. The Requests shall be forwarded to
the Custodian using the “User Feedback Page” provided in this Document.
The Document Owner and the Document Custodian should ensure review and reverification of this procedure every 3 years.
1.6
Step-out Approval
This procedure is mandatory and shall be complied with at all times. Should compliance
with the procedure be considered inappropriate or the intended activity cannot be
effectively completed or safely performed, then step out authorisation and approval must
be obtained in accordance with PR-1001e – Operations Procedure Temporary Variance,
prior to any changes or activities associated with the procedure being carried out.
1.7
ALARP
ALARP is the acronym for ‘As Low As Reasonably Practicable’ which simplified means,
‘reducing the risk to a level at which the cost and effort (time and trouble) of further risk
reduction are grossly disproportionate to the risk reduction achieved’. Full Compliance
to PDO Standards and Procedures is a key element in achieving ALARP.
For more details refer to ALARP Definition
Page 8
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
2
Revision 4.1
Effective: Mar-11
Roles and Responsibilities
Delivery Team Leader
Production Coordinator
Production Supervisor
Production Operators
Specialist leak
Testing Contractor
Page 9

Awareness of the Procedure

Ensuring compliance to the Procedure

Procedure compliance checks

Approving monitoring Levels

Approving use of flammable liquid / gas for in-service
reinstatement leak testing

Equipment selection

Review and approve method statements. (Technical
Authority level-2 required)

Witnessing leak testing

Process equipment & pipework isolation.

Logging isolation details.

Nitrogen purging operations.

Gas testing.

Leak testing.

Process equipment & pipework reinstatement

Preparing and undertaking all works required for
specialist leak testing
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
3
Gas-Freeing, Purging Process Equipment
3.1
General
Revision 4.1
Effective: Mar-11

Gas-freeing – This is the process whereby a safe atmosphere is established
within the process equipment / pipework prior to opening. Gas-freeing will
normally be undertaken in conjunction with the draining and flushing processes.

Purging – This is the process whereby the atmosphere within the process
equipment / pipework is purged of air by an inert gas i.e. nitrogen prior to final
leak testing and reinstatement.
The following procedures shall be referenced in conjunction with this Section and
Section 3.
PR-1076 - Isolation of Process Equipment
PR-1077 - Preparation of Tanks and Vessels for Internal Work Procedure
PR-1086 - Locked Valve Control
PR-1148 - Confined Space Entry
PR-1154 - Gas Testing
PR-1172 - Permit to Work
3.2
Draining of Vessels and Pipework to Open Pits
Before vessels and pipework can be gas freed they require to be drained and flushed /
cleaned of hydrocarbons. The preferred method for draining and flushing of vessels and
pipework is via a closed drain system to a sealed drain tank. On a large number of
facilities in PDO this means of safely draining hydrocarbons liquids was not provided in
the design. Because of this draining and flushing in some instances is carried out to
‘open pits’.
3.2.1
Considerations When Draining Vessels and Pipework
The following will be considered when draining vessels and pipework;
NOTE: The list is not limited to, there could be more

Volume of liquid;

Size of pipework and flanged sections etc.;

Type of medium i.e. hydrocarbon; hydrocarbon / water; oily water; H2S content
etc.;

Pressure;

Location;

Concurrent activities;

Type of work to be undertaken;

Hazard and Associated Risks of the operation identified (Risk Assessment
required)
NOTE: When draining and flushing to an ‘Open Pit’ a ‘Risk Assessment’ reviewed and
signed by the appropriate authority shall be required.
Page 10
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
3.2.2
Revision 4.1
Effective: Mar-11
Criteria for Using an Open Pit
It shall be a mandatory requirement to ensure that the following criteria are met before
draining or flushing operations can be carried out to an Open Pit.

The liquids to be drained shall not contain NORM, H2S, or Mercury

The Residual Risks associated with the draining / flushing operations are LOW
(after putting controls in place as part of the Risk Assessment)

All hazards identified can be managed safely

The systems, equipment, vessels or pipe work is depressurised to atmospheric

A detailed Job Safety Plan has been developed and approved

A TRIC Discussion is held and a TRIC Card completed before the operation is
commenced

Hydrocarbon monitoring instruments are within calibration and certification

The operation is continuously supervised by the appropriate Area Authority
Failure to meet the above criteria shall require a Variance to be raised in
accordance with PR-1001e – Operations Procedure Temporary Variance.
3.2.3
Control Required for using Open Pits
Draining / flushing to ‘Open Pits’ in the most part will have common risks attached to it
and therefore the following require to be adhered to
Open Pits

Open pits shall be no larger than 3m x 3m x 1m (deep).

Liquid levels in the open pit shall be maintained as low as possible.

Open pits shall be lined with ‘thick gauge PVC’ covered with firefighting foam to
reduce evaporation of hydrocarbon to atmosphere.
Hazardous Areas

A hazardous Zone 1 will be established 1m above the pit and 3m around the pit.
The pit itself shall be Zone 0

All electrical equipment that does not meet the specification for operation within
these Zone ratings shall be isolated
Vacuum Tankers

Vacuum tankers shall meet PDO Specification SP-1207 – Specification for
Vacuum Tankers.
Vehicle Access and Control

Vehicles shall be not be allowed to within 5m of the pit.

Continuous gas testing will be required if vehicles such as mobile cranes and
vacuum tankers are required to be run in the vicinity of the pit.

Local gas testing shall be required before other vehicles are allowed to enter or
are restarted in the vicinity of the pit.
General

Page 11
When breaking flanges sufficient bolts will be retained to enable the flanges to
be ‘closed’ in the event of uncontrolled draining.
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
3.3
Revision 4.1
Effective: Mar-11
Gas-Freeing and Purging
As general guide process equipment containing 96% nitrogen by volume shall be
considered (hydrocarbon) gas free.
The key steps in the process of gas-freeing and purging with Nitrogen are:

Isolate from all other equipment.

Reduce pressure.

Remove hazardous liquids.

Remove hazardous vapours by depressurisation.

Flush with water if appropriate.

Purge with nitrogen.

Purge with air, if necessary.
Nitrogen for purging purposes shall be supplied in ‘quads’ or for large operations tankers
or portable high volume tanks. The nitrogen tanks and associated equipment are
normally supplied by a contractor, who will also supply competent personnel to
operate the equipment. However, this does not remove the responsibility of the PDO
Operations staff for the overall supervision and the safe completion of the work under the
PDO PTW System.
3.3.1
Preparation and Precautions
The following shall be taken into account in the preparation of gas-freeing and purge
procedures:

Hired equipment shall be inspected to confirm compliance with PDO
standards, particularly for diesel engines and electrical equipment.

Personnel, whether PDO staff or Contractors, shall be competent in the
use of the equipment being used for the purge.

Personnel must be in attendance whenever purging is taking place to monitor
system pressure and purging equipment.

Notwithstanding the classification of the hired equipment, it should be
located outside and in a non-hazardous area where possible.

All low temperature equipment must be cordoned off and appropriate
warning signs fitted. Entry shall be restricted to authorised personnel only.

Any low temperature equipment must be kept clear of decking or other
structural members and be provided with drip trays at joints. For details refer
to Appendix 1

Where equipment is located such that any spillages of nitrogen liquid may cause
structural damage, charged fire hoses must be available to deal with any spillage.

All nitrogen hoses shall have current pressure test certification, be visually
checked for condition.

Great care shall be taken with the choice of location to which temporary vent
lines are directed, due to the hazardous nature of the vented gas. Vent lines
should be vented external of closed modules / areas. Temporary vent
lines must also be secured against movement, especially where the gas
released may be under pressure.
NOTE: Consideration should be given to installing permanent supply and vent lines for
activities that are carried out regularly.
Page 12
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11

Prior to starting the purging operation, with the exception of the flare system
which may be required to complete the purge activity, the equipment being
purged shall be isolated from all other equipment.

If venting is into a common flare system, Operations staff should be aware of
the possibilities of gas being vented, or leaking across PCV's from another
system and thus recontamination the purged vessel.

When discharging nitrogen to the flare system, considerations shall be given to
the possibility of extinguishing a lit flare.

If nitrogen is being supplied by cylinders, a two-gauge regulator control, which
indicates cylinder and flowing pressure, shall be used, fitted directly onto the
manifold.
CAUTION: At no time, irrespective of the relative volumes of the operation
and the cylinder(s), shall nitrogen be used without a regulator.

If the nitrogen is being supplied by `quads', the cylinders shall not be removed
from the frame and the lifting slings shall not be altered in any way.

To avoid reverse flow of product into the nitrogen supply, the line up shall be
equipped with check valves.
CAUTION: Where temporary hoses are used for purging and re-pressurisation
these should be secured in position at 3m intervals to prevent ‘whipping’.
Where temporary hoses are fitted with ‘crow’s foot’ type connections these
must be fitted with ‘R’ clips and whip checks.
Page 13

Temporary hose connections and tie-in points shall be blanked off when not in
use and for all tie-in points an isolation valve shall be fitted. Where the
connection is envisaged as being required to operate against a pressure
in the vessel, the connection to the vessel shall comprise a hose
connection coupling, a bleed valve, a check valve and a block valve.

All temporary connections and vent points shall be controlled under the PTW
system. Labels should be fitted to identify all nitrogen purge points and regular
checks carried out to identify the valve status. This status should be recorded on
an Isolation Certificate (IC).

During periods when large numbers of temporary connections are in use (i.e.
during shutdown or startup) regular checks shall be carried out, referring to a
checklist, on all nitrogen utility points in service, in order to identify their status.

PVC or leather gloves must always be worn when handling anything that
contains, or has been in contact with, cryogenic liquids. These gloves should be
loose fitting so that they may be easily removed if liquid is splashed onto or into
them.

Where spraying or splashing may occur, a face visor must be worn to protect
the face and eyes.

Before the arrival of any temporary nitrogen equipment on site, the dangers of
nitrogen in both liquid and gaseous form should be discussed at a safety
meeting. Refer to Appendix 1.

It is very difficult to totally gas free a hydrocarbon vessel by nitrogen
purging, even if flushing with water is part of the procedure. It is therefore
most important that any hotwork in the vicinity of the vessel to be opened up is
stopped prior to the removal of any manway doors, access hatches etc.

The possible leakage of nitrogen in confined spaces/modules, whether
permanent or temporary (habitats), MUST be considered in the planning
of purging operations.
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
3.3.2
Revision 4.1
Effective: Mar-11
Gas Freeing
Before starting the purging operation, the nature and the properties of the substances to
be purged must be taken into account.
a.
Where practicable, liquid hydrocarbons must be cleared prior to purging.
Relatively small quantities of hydrocarbon liquid will produce significant
volumes of gas if vaporised.
b.
Where recontamination by solids or sludge is likely, the purge procedure,
where possible, should be preceded by a water flushing operation if purging
efficiency is not to be impaired.
c.
The relative densities of the gases to be purged must be considered.
Where possible, propane or heavier gases should be displaced by
downflow purging, and ethane or lighter gases should be displaced by
upflow purging.
NOTE: Certain equipment, particularly filter beds, may require to be purged in one
direction only. Generally this will be in a direction toward the support structure, but at all
times the manufacturer's instructions should be followed.
Several methods of nitrogen purge are available which are described briefly below.
Under normal conditions, a combination of these methods is generally used.
3.3.3
Atmospheric Pressure Method
The principle of this method is the displacement of system contents by a flowing
nitrogen purge.
This technique is most effective when applied to pipework. The volume of nitrogen should
be a minimum of 120% of the pipework volume.
Great care should be given to the routing of the vent gas. It should remain at, or near to,
atmospheric pressure to allow flow to take place.
In cases where the system is more complicated, some mixing of the nitrogen and the
purged gas occurs and a reduction of the concentration of any component of the purged
gas takes place, to a greater or lesser extent, by dilution rather than by displacement.
The effectiveness of the purge operation is governed at all times by the sampling
procedure.
3.3.4
Cyclic Pressure Purge Method
In this method, the equipment to be purged is pressurised with nitrogen and a period is
then allowed for complete mixing. The pressure is then released and the cycle repeated
until satisfactory samples are obtained.
This technique is most effective when applied to vessels and plant where baffles and
convolutions render flow purging inefficient or where a pressure is required to displace
residual liquids.
This method is restricted to equipment, which can withstand the necessary pressure,
although a relatively low pressure is required for suitable mixing of the gases.
The volume of nitrogen required may be estimated by a simple pressure / volume
relationship:
Page 14

If a hydrocarbon system at zero pressure is pressurised to 1bar (g) with
nitrogen, the hydrocarbon element will be 50%.

Four times one bar cycles require four volumes of nitrogen and results in 6.25%
hydrocarbons, whereas a single purge to nine bars will require nine volumes of
nitrogen and results in 10% hydrocarbons.
Printed 07/03/11
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Care must be taken that low-pressure instrumentation is not damaged by the purge.
In a typical case, the required purge will be obtained by use of successive purges, the
number required being based upon experience of the operation but governed at all
times by the sampling procedure.
3.3.5
Water Displacement Method
In this method the equipment is flushed with water initially, and any vessels filled to allow
oil to be floated off at a high point. The contents are then driven out and replaced by
nitrogen.
This technique is most effective when applied to oil process trains where the flushing
water is driven from vessel to vessel through the normal oil flow path.
The nitrogen pressure only requires being sufficient to overcome the head of liquids.
There is very little mixing so the concentration of nitrogen is not diluted. The volume of
nitrogen required need be only 100% of the process equipment volumes.
When considering utilising this method, checks must be made to ensure that the
additional weight incurred due to the process being filled with water will not exceed
structural design limits.
NOTE: This method may not be suitable in situations where water could enter into gas
compression equipment.
3.3.6
Series Purging
Where vessels or plant can be pressure purged in series, significant economies in time
and nitrogen can be made by passing each cycle purge forward to the next vessel
before releasing to the vent or flare. Can be used in conjunction with 2.3.5.
3.3.7
Displacing To Air
Following purging, it is normal to displace the nitrogen in the vessel or system with air to
ensure that it is safe to work on. Care must be taken, as with the nitrogen, that the
purge method used is appropriate to the conditions and to the system.
WARNING: AT NO TIME SHALL AIR BE PURGED INTO A LIVE FLARE OR
VENT SYSTEM.
3.4
Purging Following Inspection or Maintenance
When a vessel or pipework system has been opened up, it shall be purged with nitrogen to
remove the oxygen prior to re-introducing hydrocarbons.
As with the purging for removal of hydrocarbons, the purging for removal of oxygen can
use any, or a combination, of the methods described in: Purging for Gas Freeing
The main difference is that the sampling is for a different gas and to ensure that the vent
lines are not discharging an explosive mixture.
WARNING: THE INTRODUCTION OF HYDROCARBONS INTO A SYSTEM THAT
HAS NOT BEEN INERTED SHALL BE RISK ASSESSED. CALCULATIONS SHALL
BE CARRIED TO ENSURE THAT IT IS NOT POSSIBLE FOR THE OXYGEN
CONTENT TO REMAIN ABOVE 2% AFTER HYDROCARBONS HAVE BEEN REINTRODUCED. WHERE IT IS NOT POSSIBLE TO GUARANTEE THIS THE
SYSTEM WILL BE N2 PURGED.
Page 15
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Revision 4.1
Effective: Mar-11
Petroleum Development Oman LLC
3.5
Sampling
When purging hydrocarbons using nitrogen, it should be noted that the detector used
must be capable of measuring a hydrocarbon gas in an inert atmosphere. The MSA
Tankscope and Neotronics Digiflamm are examples of detectors that can be used.
For both flowing and cyclic purges the checks should be made at not only the
recognised vents but also at any dead legs in the system.
When purging the nitrogen out of the system with air, it is equally important that
representative checks are carried out. If the vessel or system is going to be entered,
conditions for the entry are as defined in PR-1148 Confined Space Entry.
The recommended criteria to give safe conditions when purging a mixture of
hydrocarbon gases with nitrogen are shown in Table 1.
Table 1 - Recommended Criteria Hydrocarbon / Nitrogen Purge
Mode
O2 Level
Hydrocarbon Level
N2 Level
HC to Inert
-
<_ 4 %
>t 96%
Air to Inert
<_ 4%
-
>t 96%
For specific criteria when purging individual hydrocarbon components with nitrogen,
refer to Table2.
Table 2 - Inert Gas End Points for Purging Equipment Out of Service
Purge
Medium
Combustible
Page 16
Nitrogen
Nitrogen
Nitrogen
Nitrogen
Percentage Inert
Gas required to
render mixtures
non-flammable
when air is added in
any amount
Purging end points
with 20% Safety
Factor
Percent of
Combustible below
which no mixture is
flammable when air
is added in any
amount
Purging end points
with 20% Safety
Factor
Hydrogen
95
96
5
4
Carbon
Monoxide
Methane
81
85
19
15
86
89
14
11
Ethane
93
95
7
5
Propane
94
95
6
5
Butane
95
96
5
4
Iso-butane
95
96
5
4
Pentane
97
98
3
2
Hexane
97
98
3
2
Gasoline
96
97
4
3
Ethylene
94
95
6
5
Propylene
96
97
4
3
Benzene
96
97
4
3
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
4
Leak Testing
4.1
Objective
Revision 4.1
Effective: Mar-11
The objective of this section is to guarantee the integrity of process equipment and /
or pipework that has been reassembled after inspection, maintenance, repairs,
modifications or replacement, prior to it being returned to operation. This is required in
order to eliminate the loss of containment of process fluids, thereby protecting the safety of
all personnel either involved with, or in the vicinity of, the plant and maintaining the
integrity of the Installation.
4.2
Definitions for Leak Testing
Vacuum Test
A test to prove that the equipment does not suffer from
ingress of fluid from external sources. Normally required for
any equipment that is designed to operate under vacuum
conditions.
Reinstatement Test
A pressure test, carried out at 95% of the Relief Valve setting,
prior to returning an item of plant into service after the
pressure containment envelope has been breached, to check
integrity of the system and confirm absence of leaks. For
hydrocarbon systems, this test is normally performed with the
use of nitrogen.
Gross Leak Check
A pressure test carried out at a positive pressure,
approximately 2 - 10 bar(g), for gross leak identification.
Sensitive Leak Test
A Nitrogen Leak Test carried out with a Nitrogen/Helium
mixture, using Helium Sensing instruments to monitor for
leakage from potential leak paths (flanges, seals etc.)
In-Service Reinstatement
Test
A pressure test carried out using the service fluid under its
maximum operating conditions and a leak search carried out.
Method Statement
A specific document or procedure produced to cover a unique
situation.
Operating Pressure (OP)
The OP is the gauge pressure which prevails inside
equipment and piping during any intended operation. The OP
is determined by the process engineer
Maximum
Operating
Pressure (MOP)
The MOP shall be determined by the process engineer in
consultation with the process control engineer.
The MOP is typically 105 % of the OP in order to provide
sufficient flexibility for the control of the intended operations.
The MOP shall be not less than 1.0 bar above the OP, except
in pressurised LPG storage facilities, where the MOP is equal
to the vapour pressure at the derived maximum operating
temperature and assessed LPG composition.
If this margin is not sufficient for control, starting up, shutting
down or other specific operations, a higher MOP shall be
specified. The reason for this increased MOP shall be stated
in the pertaining documents.
Page 17
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Design pressure (DP)
Revision 4.1
Effective: Mar-11
The DP (sometimes referred to as the upper design pressure,
UDP) is the gauge pressure at the top of the equipment in its
operating position that is taken to determine the minimum
thickness of equipment parts at the DT.
The DP is initially selected by the process engineer and finally
determined in close consultation with the mechanical design
engineer.
Since the DP is related to the top of the equipment, for other
parts or elements of the equipment the designer shall
establish the associated design pressures taking into account
the maximum pressure drop caused by flow through the
equipment, plus the fluid static head.
NOTE: The definitions for pressure were taken from DEP 01.00.01.30-GEN Definitions of
Temperature, Pressure and Toxicity Levels - December 2008 (DEP Circular 14/09 has
been incorporated)
4.3
Reinstatement Policy
This section address the decision making process to determine the testing that is required,
prior to reintroducing the process fluid into a system after intrusive inspection,
maintenance and / or engineering work.
The Standard is to carry out testing using Inert Medium or Sensitive Leak2 testing using
Nitrogen/Helium mix if assessed as necessary.
In-service Leak Testing may be utilised only if achieving the Standard is ‘Not
Practicable’ and has been Risk Assessed as acceptable. Minimum In-service
Reinstatement pressure is Maximum Operating Pressure as defined in 4.2 above and
shall be used for ‘Low Risk’ scenarios where 5 or less flanges have been disturbed.
IMPORTANT NOTE: It is a deviation from this Procedure, if In-service Leak testing is
proposed or carried out to Operating Pressure as defined in 4.2 above.
4.3.1
Method Options in Order of Consideration
1.
Sensitive Leak Test using N 2 /He to 95% RV pressure.
2.
Nitrogen Testing to 95% RV pressure - Acceptance criteria is 15 minutes
holding pressure.
The PDO Standard is Sensitive Leak Testing for Sour Service and Nitrogen for
Sweet Service. Option 3 below shall only be considered if Options 1 & 2 are ‘Not
Practicable’, the affected flanges are 5 or less and a Risk Assessment has been
conducted. Refer to Section 4.4 for more detail.
3.
Gross Leak Check (10% of MOP or 10bar maximum), followed by In-service
Leak Test to MOP.
2
On facilities where High H2S levels are encountered i.e. Harweel, Sensitive Leak testing shall
be enforced.
Page 18
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Revision 4.1
Effective: Mar-11
Petroleum Development Oman LLC
4.4
Planning Reinstatement Leak Test
In order to determine the testing required prior to restart of a process system reference shall
be made to Figure 1 – Reinstatement Leak Testing Decision Chart.
1
Have
all components had an
accepted Strength Test?
Reinstatement Leak
Testing Required
YES
WHICH REINSTATEMENT LEAK TEST?
1.
N2/He is the STANDARD for reinstatement leak testing Sour / Toxic systems
2.
Nitrogen is the STANDARD for reinstatement leak testing Sweet systems
3.
In-Service testing can be carried out only in particular situations where it can
be clearly demonstrated that 1 or 2 above are not reasonably practicable
and provided that a Risk Assessment has been carried out and controls are
in place to mitigate risks.
NO
3
Carryout hydrostatic /
pneumatic strength test
using a safe medium
2
4
Is Process Medium
Sweet?
YES
NO
5
8
Leak test with N2 to
95% of RV setpoint
Leak test with N2 / He
to 95% of RV setpoint
(5 or less
adjacent flanges)
13
YES
Can all leak paths be
monitored
simultaneously?
NO
YES
Discuss with
UOP Team
6
9
Is testing with N2 ‘Not
Practicable’ and the potential for
uncontrolled leak been Risk
Assessed as LOW ?
Contact Specialist N2
Contract Company
7
NO
10
Review quotations and
Method Statements /
Agree Terms &
Conditions
12
Prepare Method
Statement
Leak test with N2 to 95%
of RV setpoint
11
Is the reinstatement test
pressure achievable without
specialist pumping equipment?
YES
12
Prepare Method
Statement
PLAN
Gross Leak test with an
inert medium
EXECUTE
NO
Carryout leak test using
prescribed Medium
15
Reintroduce process
medium
16
14
Leak Testing
Completed
Figure 1 – Reinstatement Leak Testing Decision Chart
Page 19
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
1.
Revision 4.1
Effective: Mar-11
Prior to the reinstatement of items of plant, all connections that have been
disturbed (flanges, clamps etc) shall have been reinstated in accordance with
SP-2020 – Flange Connection Bolt Torquing.
Any replaced or modified item of equipment, which forms part of the pressure
envelope, must have previously undergone a successful strength pressure test
prior to installation. Also, any repairs to equipment shall have been carried
out in accordance with the design specification and in its original location.
2.
If the above cannot be satisfied, a hydrostatic or pneumatic strength test must
be carried out using a safe medium. The boundaries of this test shall ensure that
all previously untested items of equipment have been incorporated.
3.
The PDO Standards for reinstatement leak testing are;

For Sour Service - N2 / He at a pressure equal to 95% of the RV
setpoint for the system or equipment being tested

For Sweet Service – N2 at a pressure equal to 95% of the RV setpoint
for the system or equipment being tested
Where it can be clearly demonstrated that achieving the Standards above are
not ‘reasonably practicable’ inservice leak testing using the service medium
will be considered. A Risk Assessment requires to be completed and control
put in place to mitigate any risks that could be encountered by stepping out of
the Standard.
4.
Is the Process Medium Sour or Sweet Service?
5.
Sour service shall require that all reinstatement leak testing on process systems
containing or exposed to H2S or Toxics be carried out using a nitrogen with a
helium trace to a pressure equal to 95% of the RV setpoint for the system or
equipment.
6.
This method of testing also referred to as ‘sensitive’. Reinstatement leak testing
of this kind requires specialist equipment and shall normally be carried out by a
contract company.
7.
Operations shall obtain quotations for the work from an approved contractor,
based on the scope of work. The quotation should also have a method
statement detailing how the work shall be undertaken and all safety
considerations. Operations shall agree Terms and Conditions and authorise the
work.
8.
Sweet service shall require that all reinstatement leak testing on process
systems containing hydrocarbons be carried out using nitrogen to a pressure
equal to 95% of the RV setpoint for the system or equipment.
9.
If it is demonstrated that testing using N2 is not ‘practicable’ and that the
potential for an ‘uncontrolled leak’ after a Risk Assessment is Low the leak
testing shall be considered as detailed in 13.
10.
If it cannot be demonstrated then reinstatement testing shall continue using N2
to a pressure equal to 95% of the RV setpoint for the system or equipment.
11.
The volume and pressure of N2 required to undertake the testing will be
dependant on the system or equipment. Large volums of N2 can be supplied as
liquid and then ‘vaporised’. This method is ideal for gas freeing and purging and
can also achieve reinstatement testing requirements at the lower pressures. For
small volume, higher pressure testing ‘N2 quads’ can be used. Where large
volume and high pressure is required this will require putting the work out to a
specialist contractor equipped with equipment to pump-up the system. For this
work refer to the 6 and 7 above.
Page 20
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
12.
If the N2 reinstatement testing is to be carried under the control of Operations a
method statement will be required from the persons undertaking the work. As
for 7 above the method statement should cover how the testing will be carried
out, the boundaries and all safety precautions to be taken.
13.
Before authorisation can be obtained to conduct ‘inservice leak’ testing, the
number of ‘leak paths’ will be identified. Inservice leak testing shall only be
considered as an option if there are five or less adjacent disturbed flanges
which can be monitored simultaneously. If this criterion cannot be met then
UOP requires to be consulted.
As for N2 reinstatement testing undertaken by Operations a method statement
shall be required.
4.5
14.
Gross leak test the system / equipment with N2 or a suitable inert medium
before introducing the inservice medium. The gross leak test requires to be
undertaken at a pressure of 10% of MOP up to a maximum of 10bar, whichever
is achieved first.
15.
The reinstatement or inservice leak test can be carried out using the prescribed
test medium, to the required pressure and as detailed in the approved Method
Statement.
16.
Introduce process medium in accordance with the agreed start-up procedures
and bring the process to steady state.
Nitrogen Leak Testing of Systems
The purpose of the N2 reinstatement leak test is the same as that of the commissioning
N2 / He sensitive leak test, i.e. to render the production equipment and pipework safe for
the introduction of hydrocarbon gases and liquids, but is used for smaller scale testing.
It will not always be possible, or practicable, to use a contractor and / or the N 2 / He
sensitive leak test equipment for the replacement / reinstatement of piping and valves
and, in such circumstances, this sensitive leak bubble test should be used instead,
utilising Operations / Maintenance personnel and on site N2 supplies.
The N2 reinstatement leak test3.is the direct pressure technique of bubble leak testing to
locate leaks in a pressurised component, by the application of a solution that will form
bubbles as leakage gas passes through it.
For this leak test, 100% nitrogen gas supplied from cylinders or a compressor shall be
used for purging, testing and blanketing. When purging, the oxygen content should be
reduced to the order of 1%, so that it is well below the lower limit that will form an
explosive mixture. Oxygen levels may be measured using an Intrinsically Safe Oxygen
Analyser. The test shall be performed at a pressure equal to 95% of stage RV setting or
the maximum dead head pressure of any pump in the system not protected by a relief
valve. Prior to examination, the test pressure shall be held for a minimum period of 15
minutes.
On completion of the N2 reinstatement leak test, the N2 shall be depressurised to
approximately 2 psi (g) for inert blanketing the system.
3
N2 leak testing shall be performed by trained and experienced technicians.
Page 21
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
4.5.1
Revision 4.1
Effective: Mar-11
Bubble Forming Solution
The bubble forming solution shall produce a film that does not break from the area being
tested and the bubbles formed shall not break rapidly due to air drying or low surface
tension. Household soaps or detergents are not permitted as substitutes for bubble
testing solutions. If surface conditions give cause for concern in respect of the
establishment of a coherent soap film on the area of investigation, the technique /
procedure should be demonstrated in another area.
The bubble forming solution shall be compatible with the temperature of the test
condition. As a general rule, the temperature of the surface of the parts to be examined
should not be below 7°C or above 50°C, throughout the examination. Local heating or
cooling is permitted, provided that temperatures remain within the range 7°C to 50°C
during examination. Where it is impracticable to comply with the foregoing temperature
limitations, other surface temperatures may be allowed provided that the procedure is
demonstrated satisfactorily.
The bubble forming solution shall be applied to the surface to be tested by flowing,
spraying or brushing the solution over the examination areas. The number of bubbles,
produced in the solution by application, should be minimised to reduce the problem of
masking bubbles caused by leakage.
4.5.2
Acceptance Criteria for N2 Leak Testing (Bubble Test)
The presence of continuous bubble growth on the surface of the material indicates
leakage through an orifice passage(s) in the region under examination. The area under
test is acceptable when no continuous bubble formation is observed.
When leakage is observed, the position of the leak(s) shall be marked and recorded.
The system will then be depressurised for remedial action. After repairs have been
made, the repaired areas shall be retested in accordance with this procedure.
4.6
Performing the In-Service Reinstatement Test
In-service testing incorporates the testing for leaks, with the re-commissioning activity of
reintroducing the process medium. This method of reinstatement may be adopted only
when ALL the criteria, as determined by the Figure 1, are satisfied.
In all instances where there is a proposal to utilise a flammable fluid to perform an inservice reinstatement leak test, that proposal must be endorsed by the Production
Coordinator at the planning stage.
The In-service Reinstatement test must be carried out to the ‘Maximum Operating’
pressure. The process medium must be introduced slowly. The pressure shall be
increased in stages of not more than 20% of the maximum pressure obtainable or 10
bars (g), whichever is the greater, up to 80% of the maximum pressure obtainable and
thereafter in 10% or 10 bar (g) stages.
At each stage of pressurisation, all disturbed joints / flanges shall be monitored for
leaks, both visually and using appropriate gas meters. Production Supervisor must
satisfy himself / herself that there are no signs or detection of process fluid at any of the
relevant areas, for the test to be accepted.
Page 22
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
4.7
Revision 4.1
Effective: Mar-11
Vacuum Testing
Some systems are designed for vacuum service and must be tested for this service. It is
most important to determine that any equipment so tested is designed for vacuum
conditions4, and isolated properly before testing. The vacuum should be of the order of
0.1 bar absolute and this should be held for a period of time after the eductor has been
shut off.
If the equipment is in hydrocarbon service, it should be remembered that any
appreciable leak inwards, of air, may create the possibility of an air / hydrocarbon
explosive mixture.
In addition to the vacuum test, items for vacuum service will be tested to a positive
pressure of 1.0 bar (g) with either nitrogen or air.
4.8
Reinstatement Testing of Relief Valves Connected to the Flare or
Relief Headers
The removal for replacement, repair and recalibration of system “relief valves” requires
that the flanges on the process and flare / relief sides of the valves be subject to a
reinstatement leak test. On the process side this can be achieved by subjecting the
flange to 95% of the relief valve set point using N2 or an acceptable inert medium. The
flare / relief flange is normally subjected to atmospheric pressure which is not
‘practicable’ on an open ended systems such as the flare and relief headers. In this
instance it is acceptable to carry out the following;
1.
Ensure that SP-2020 – Flange Connections Bolt Torquing and Tensioning is
adhered to, ‘flange make-up certificates’ are issued and the flange break
register updated;
2.
Flange shall be ‘masked’ and a ‘single’ hole made for testing;
3.
Normal operating conditions (temperature & pressure) must be achieved;
4.
The flange shall be ‘sniffed’ from the single hole and measured for the presence
of hydrocarbons using the appropriate type of gas detector;
Provided that the above is complied with a waiver (step-out) is not required.
4
Items for vacuum service should be tested with a vacuum. The reason for this is that applying
a pressure test to vacuum equipment does not necessarily detect places where there can be
leakage in the opposite direction, e.g. a gasket fault.
Page 23
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
5
Hazards
5.1
Draining and Flushing to Open Pits
5.2
5.3
Revision 4.1
Effective: Mar-11

Release of hydrocarbons to the atmosphere due to evaporation

Exposure of personnel to hydrocarbon vapours

Fire or explosion from uncontrolled ignition sources and flammable vapours in
and around the open pit

Environmental contamination due to uncontrolled draining and flushing
Gas-Freeing and Purging

Entry of air into contaminated plant containing hydrocarbons can result in
subsequent fire or explosion where a source of ignition is present (e.g. static
electricity, pyrophoric materials).

Entry of hydrocarbons into a system that contains air (oxygen) creating a
flammable/explosive mixture.

If pure nitrogen is inhaled, only a few breaths will fully exchange the air in the
lungs to nitrogen and unconsciousness will rapidly ensue.

Cryogenic liquids have rapid cooling properties and consequently, flesh coming
into contact with un-insulated pipework or vessels containing these liquids may
stick fast due to the moisture in the skin.

Cryogenic liquids have low boiling points and quickly produce clouds of vapour
or gas at ambient temperatures, prolonged exposure to which can damage the
lungs.

Short exposure of the eyes to liquids or vapours quickly results in damage whilst
exposure of other skin tissues produces similar effects to a burn and prolonged
exposure may result in frostbite.
Leak Testing
Page 24

Failure of the equipment during the test, causing immediate release of
hazardous materials or dangerous amounts of energy.

Fire or explosion arising from the use of flammable fluids for in-service leak
testing.

Damage to the equipment during test, causing a weakness which might result in
a subsequent failure.

Failure or damage to the equipment during test might arise from:
o
Use of an excessive test pressure, due to either faulty calculation or
faulty pressure control equipment.
o
Testing at too low a temperature.
o
Local over pressurisation, due to water freezing.
o
Overloading, due to the weight of the test medium.
o
Drawing an unacceptable vacuum when removing the test Medium.
o
Corrosion, due to use of unsuitable hydraulic test medium.
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
o

Page 25
Revision 4.1
Effective: Mar-11
Internal explosion created by presence of explosive mixture and heat
source, as a result of compressions.
When carrying out pressure tests, consideration shall be given to adjacent
systems operating under pressure. For example, if the system undergoing test
were to fail, the adjacent pressurised system could suffer damage, thereby
increasing hazards.
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Revision 4.1
Effective: Mar-11
Petroleum Development Oman LLC
Appendix 1 – Working With Nitrogen Gas
Objective
This Appendix will identify the precautions and procedures that should be observed
when working with nitrogen, and when inerting systems using nitrogen gas for purging.
WARNING: NITROGEN IS AN ASPHYXIANT AND WILL NOT SUSTAIN LIFE.
General
Nitrogen is the main component of breathable air and, as such, is often wrongly
considered not to be a personal hazard. It is provided for use either in a gaseous form in
`quads' or from a nitrogen- producing skid, or in a liquid state in cryogenic bulk tanks
where it is stored at a temperature below its boiling point of -196°C.
If undiluted nitrogen is breathed, not only is the blood passing through the lungs not
replenished with oxygen, but also much of the residual oxygen in the blood passes out
into the lungs. The effect is therefore much worse than holding one's breath or rebreathing air. In practice it will take only a few breaths to fully exchange the air in the
lungs for nitrogen, and unconsciousness will rapidly ensue. There is no warning
because the normal stimulus to respiration is the build up of carbon dioxide, not lack of
oxygen. Carbon dioxide will not build up while breathing continues if the gas being
breathed is nitrogen.
Fatalities and serious injuries have occurred when performing activities on
equipment that has recently contained nitrogen. This has happened when, in order to
make progress with the work, sheeting, tarpaulins, boarding etc have been used to
screen or protect the work site, and a confined area has been created around the
equipment. Great care must be taken to ensure that a confined space is not created,
whether deliberately or inadvertently, which might allow the uncontrolled build up of
nitrogen and the consequent exclusion of oxygen. Where it is deemed necessary to
operate within a confined space that has recently contained nitrogen, an oxygen meter
shall be used to continuously monitor the atmosphere.
Liquid nitrogen, released into the atmosphere in an uncontrolled manner, will quickly
change form to a gas, thus producing an asphyxiation hazard from the nitrogen-enriched
atmosphere.
Precautions
Prior to using nitrogen in either a gaseous or cryogenic form, an assessment of the risks
to both personnel and equipment, from leaks or spills, shall be carried out. Particular
attention should be paid to:

Provision of drain paths for spills and leaks.

Routes for temporary hoses.

Provision of First Aid equipment and competent persons to use it.

Written procedures for the operation, including emergency procedures for
dealing with spills and leaks.
All work involving the use of nitrogen shall be controlled by the Permit to Work (PTW)
System. Barriers and warning notices shall be erected around the work area. All
openings, man ways, pipe ends etc must be clearly marked, and oxygen monitoring and
rescue equipment provided. All personnel involved in the operation shall be instructed in
the hazards associated with nitrogen operations and the types and functions of
monitoring equipment being used.
Page 26
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Where habitats or partial enclosures are required, these shall be treated as Confined
Spaces, and the controls and precautions associated with Confined Space entry shall be
applied.
Cryogenic Liquids - Occurrence
Cryogenic liquids are defined as those that are manufactured, stored or handled at, or
below -85 ° C. Liquid nitrogen is the cryogenic liquid in common use within the oil
industry.
Handling materials at low temperatures requires specialised procedures and safety
precautions, due to the hazards from spills or accidental damage to cryogenic tanks and
associated pipework.
Cryogenic Liquids - Personal Protection
PVC or leather gloves must always be worn when handling anything that contains, or
has been in contact with, cryogenic liquids. Such gloves should be loose fitting so that
they may be easily removed if liquid is splashed onto or into them.
Where spraying or splashing may occur, a face visor shall be worn.
Coveralls should be worn outside gloves and boots to ensure that liquid contamination
will run off and not become trapped.
Cryogenic Liquids - Mechanical Hazards
The physical properties of materials at low temperatures are markedly different from
those at ambient temperatures. This change, not a gradual one, takes place over a
short temperature range, resulting in an increased brittleness of the material at lower
temperatures. In this state, normal stresses or shock can result in brittle fracture, which
can be both sudden and extensive.
In the event of spillage of liquid nitrogen over a steel deck, the resultant drop in
temperature could cause the steel to crack. In such circumstances, the deck should be
flooded with copious amounts of water, which should assist the spilled liquid to `boil off'.
Wooden boards or rubber mats should be positioned under cryogenic tanks and hoses
to prevent them contacting the deck.
Drip trays are to be positioned under all cryogenic hose connections to catch any minor
spills.
Cryogenic Liquids - General Hazards
Warming, to ambient temperature, of vessels initially containing a cryogenic liquid may
result in high pressures.
When introducing cryogenic liquids to a system at ambient temperatures, care must be
taken with respect to the rate of flow of the liquid since sudden cooling may result in fast
contraction of pipework, which will stress joints thus causing damage.
Before cool down of plant, it is essential that all parts that may contain free moisture are
carefully dried as water freezing in the pipework may expand to a sufficient degree to
cause rupture.
Vapour fog clouds can form during draining of systems containing cryogenic liquid. This
vapour fog is composed of atmospheric water vapour condensed by the cooling effect of
the liquid being vaporised.
The fog should also be assumed to contain a possible hazardous concentration of the
vaporised liquid. This can, depending on the quantity of product being vaporised, create
asphyxiation and a visibility hazard.
Page 27
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Cryogenic Liquids - Fire Hazard
At equal pressure the boiling point of some cryogenic liquids, especially liquid nitrogen,
is lower than that of liquid air. Air will condense on the external surfaces of pipework
containing liquid nitrogen at an equilibrium pressure less than 1.5 bar(a) if the vessels
are either unlagged or lagged with a porous cellular type insulant that has not been
properly vapour sealed.
The liquid air produced can result in oxygen enrichment of the atmosphere local to the
equipment and, if the insulant is combustible there is a serious risk of fire. Special care
must therefore be taken before any maintenance or repair work is started, particularly
where the use of naked flames or other potential sources of ignition is intended.
Page 28
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Revision 4.1
Effective: Mar-11
Petroleum Development Oman LLC
Appendix 2 – Method Statement
A Method Statement must be prepared, and approved by the Production Supervisor, for
all Reinstatement Pressure Testing Operations, and such operations must be
controlled by the Permit to Work System.
The Method statement shall be fit for purpose and be attached to the Work Permit or as
a separate statement or document.
The Method Statement shall consider and include where necessary:

Details of the boundaries of the test including pressures, maximum and
minimum temperatures, test medium, method of filling, venting and, if
applicable, the method of draining the test medium from the system;

Drawings showing the relative positions of blanks, drains and vents, indicating
where valves have been removed, defeated or mechanically locked;

Checklists of all system components. Refer to example Table - Sample
Checksheet for Testing of Pipework System
The Method Statement shall detail the checks to be carried out which should include,
but not be limited to:

Checklist for the equipment refitted.

Flange make-up checksheet, to include a tagging system for

All flanges disturbed.

Valve position for test.

Additional blanks/spades for test.

Steps and precautions during the test.

The test pressure.

Steps to be followed after the test.

Valve position.

Steps and precautions to be taken.

Marked-up drawings, showing plant to be tested and boundary of safety
barriers.

Detail of all safety precautions.

Risk Assessment, including an appropriate Task Risk Assessment from the
PTW Activity Risk Assessment Tool.
Table - Sample Checksheet for Testing of Pipework System
Flange No. Joint
No.
(tick)
Bolts to
Correct
Torque (tick)
Test Leak
Rate
Re-Test
Leak Rate (if
required)
NOTE: Flanges to be identified by suitable code number on attached P&ID.
Page 29
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Appendix 3 - Abbreviations
The following abbreviations are used in this Procedure.
Page 30
ALARP
As Low As Reasonably Possible
He
Helium
IC
Isolation Certificate
N2
Nitrogen
PCV
Pressure Control Valve
PTW
Permit to Work
RV
Relief Valve
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Appendix 4 – Reference Material
PDO Procedures
PR-1001e – Operations Procedure Temporary Variance
PR-1076 - Isolation of Process Equipment
PR-1077 - Preparation of Static Equipment for Internal Maintenance and Inspection.
PR-1078 Hydrogen Sulphide Management
PR-1081 The Buddy System
PR-1086 - Locked Valve Control
PR-1148 - Confined Space Entry
PR-1154 - Gas Testing
PR-1172 - Permit to Work
PR-1515 – Onsite Mercury Management Procedure
PR-1721 Shutdown Management
PDO Standards
SP-1005 HSE Specification - Emissions to Atmosphere
SP-1006 HSE Specification - Aqueous Effluents
SP-1170 Naturally Occurring Radioactive Materials (N.O.R.M.)
SP-1207 – Specification for Vacuum Tankers
SP-2020 – Flange Connections Bolt Torquing and Tensioning
SP-2087 – Specification for Onsite Mercury Management
Page 31
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Revision 4.1
Effective: Mar-11
Petroleum Development Oman LLC
Appendix 5 - User Feedback Page
PR-1073 – Gas-Freeing, Purging and Leak Testing Process Equipment
and Pipework User Feedback Page
Any user who identifies an inaccuracy, error or ambiguity is requested to notify
the custodian so that appropriate action can be taken. The user is requested
to return this page fully completed, indicating precisely the amendment(s)
recommended.
Name:
Ref ID
Page Ref:
To:
Date:
Brief Description of Change Required and Reasons
UOP7
Custodian of Document
Page 32
Date:
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Addendum 1 – Changes at Revision 3.2
Page
Description of Change
17
Section 3.3 added footnote “ On facilities where Very High H2S are encountered i.e.
Harweel, Sensitive Leak testing shall be enforced”
18
Section 3.3.1 – Changed Preferences to Considerations and added Note “NOTE: InService Leak Testing on it’s own should only considered when all other options are
not Technically feasible”
19
Figure 1 – Changed wording Step 18
22
Section 3.4 Step 16 para 2 “If this is not possible, due to either the size of system
under test or the availability of N2 at site then an approved 3rd party company will be
contracted.”
22
Section 3.4 Step 18 changed wording “N2 leak testing activities will be carried out by
a 3rd party contractor controlled by Operations personnel under the PTW system.”
Added “NOTE: Sensitive Leak Testing shall be used where High H2S is present in
the production streams. Details of Sensitive Leak Testing can be referenced from
SP-2051 Specification for Flushing, Pressure Testing, Pickling and Sensitive Leak
Testing of Mechanical Equipment and Piping.”
Page 33
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Addendum 2 – Changes at Revision 4.0
Page
Description of Change
8
Removed Section 1.5 – Structure of the Document not needed
8/9
Moved Roles and Responsibilities to Section 2 – All following sections moved up
one number i.e. 2 to 3 etc.
8/9
Moved Abbreviations to Appendix 3
24
Added Section 5.1 – Draining of Vessels and Pipework
10
Section 3.2 – Draining of Vessels and Pipework to Open Pits added
18/19
Section 4.2 – Definitions added
Operating, Maximum Operating and Design Pressure Definitions.
19
Section 4.3 changed following statements
“Minimum In-service Reinstatement pressure is Maximum Operating Pressure as
defined in 4.2 above”
“It is a deviation from this Procedure, if In-service Leak testing is proposed or
carried out to Operating Pressure as defined in 4.2 above.“
19
Section 4.3.1 changed
3. “Gross Leak Check (circa 2 - 10 bar), followed by In-service Leak Test to
Maximum Operating Pressure.
Removed 4
24
Section 4.6 para 3 changed to read “The In-service Reinstatement test must be
carried out to the ‘Maximum Operating’ pressure. The process medium must be
introduced slowly. The pressure shall be increased in stages of not more than 20%
of the maximum pressure obtainable or 10 bars (g), whichever is the greater, up to
80% of the maximum pressure obtainable and thereafter in 10% or 10 bar (g)
stages.”
26
Added Section 5.1 – Draining and Flushing to Open Pits
Added Appendix 3 and 4
Page 34
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.
Petroleum Development Oman LLC
Revision 4.1
Effective: Mar-11
Interim Amendment March 2011 (Revision 4.1)
Page 7 Section 1.1 – Added “IMPORTANT: This procedure will be used for gas freeing, purging
and leak testing process system and equipment that has been commissioned and is being
operated as a production unit.
Page 14 Section 3.3.2 – Changed sub-heading to “Gas Freeing”. This is to avoid confusion
with purging operations after the work is completed.
Page 18 Section 4.3 – Changed 3rd & 4th paras to read “In-service Leak Testing may be utilised
only if achieving the Standard is ‘Not Practicable’ and has been Risk Assessed as acceptable.
Minimum In-service Reinstatement pressure is Maximum Operating Pressure as defined in 4.2
above and shall be used for ‘Low Risk’ scenarios where 5 or less flanges have been disturbed”.
Page 18 Section 4.3.1 – Added para “The PDO Standard is Sensitive Leak Testing for Sour
Service and Nitrogen for Sweet Service. Option 3 below shall only be considered if Options 1
& 2 are ‘Not Practicable’, the affected flanges are 5 or less and a Risk Assessment has been
conducted. Refer to Section 4.4 for more detail”. Removed “NOTE: In-Service Leak Testing on
its own should only considered when all other options are not Technically feasible.”
Page 19 Section 4.4 – Section amended to reflect changes made in Sections 4.3 and 4.3.1.
Page 24 Section 4.8 –“Reinstatement Testing of Multistage Compressors” removed.
Page 24 Section 4.8 – “Reinstatement Testing of Relief Valves Connected to the Flare or Relief
Headers” added
Purpose for changes / additions – Strengthening the requirement for achieving the
Reinstatement Test Standards and assisting Operations where meeting the Standards are not
achievable i.e. Flare and Relief Systems.
Page 35
PR-1073 - Gas-Freeing, Purging and Leak Testing Process
Equipment and Pipework
Printed 07/03/11
The controlled version of this CMF Document resides online in Livelink®. Printed copies are UNCONTROLLED.