Nitrogen purging

Contractor:
SACL
Client:
MPN NITROGEN PURGING PROCEDURE
Document No.
SWP-OCIP- -080
Contract No. A2041122
OFFSHORE CONSTRUCTION &
INSTALLATION PROGRAM (OCIP)
04/12/08
RISER REPAIR PROJECT
REPAIR OF UTUE- KP -UBIT PP 16’’ GAS
RISER FROM UTUE KP –UBIT PP
( UTUE KP END)
Page 1 of 17
16” UTUE KA-UBIT PP GAS PIPELINE NITROGEN
PURGING PROCEDURE.
Document Status – FOR REVIEW AND ACCEPTANCE
A 04 th
.12.08
DAF
Osiki
Ajibulu
Charles
Mike
Green
Rev. Date
Name Sign Name Sign Name Sign Name Sign
Prepared By Reviewed By Approved Accepted (MPN)
16” UTUE KP-UBIT PP Gas Pipeline Dewatering & Nitrogen Purging Procedure

Contractor:
SACL
Client:
Document No.
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04/12/08
( UTUE KP END)
Page 2 of 17
TABLE OF CONTENTS
1.0 Introduction
1.1 Generalities
1.2 Work objective
1.3 Determination of nitrogen requirement
1.4 Nitrogen unit’s conversion.
1.5 Work scope
2.0 Work Procedure
2.1 Base Preparation
2.2 ON-site Preparation
2.3 Procedure for purging pipeline with nitrogen
3.0 Personnel manning levels
3.1 Work hours/Work duration.
4.0 Safety
4.1 Preamble
4.2 Riser repair project safety system
4.3 Risk Assessment
4.4 Emergency action
4.5 Management of change procedure.
5.0 Equipment List
6.0 Attachments(typical JSA)

Contractor:
SACL
Client:
Document No.
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1.0 INTRODUCTION.
1.1GENERALITIES
Nitrogen purging is a generally accepted method of getting rid of unwanted gases
from pipelines and vessels. Three methods can be distinguished from each other
namely; Displacement method, Dilution method and Pressurization method In the
oil and gas sector, nitrogen purging is used mainly in the:
(a) Reduction of combustible gas and oxygen content of pressure vessels to an
acceptable level before hot work can be carried out on it in order to prevent
explosive mixtures and fire.
(b) After maintenance and reassembly of gas pipelines and vessels, it is used to
remove oxygen to an acceptable level of 2% so that flammability and explosion
do not occur when the flammable gas is lined in the pipeline or vessel.
(c) It is also used to dry gas pipeline after hydraulic pressure testing and the
attendant dewatering pigging.
In this particular case, we recommend a combination of pressurization and
dilution methods.
1.2 OBJECTIVE
The objective of the nitrogen purging of this UTUE -UBIT pipeline is to remove the
hazardous gas the nominated gas pipeline to an acceptable level of 2% LEL in
order to ensure safety during cutting, repair and reassembly. After reassembly, it
may also be to remove oxygen from the pipeline to about 2% so that during the
natural gas line in, there will be no fire and explosion.
1.2.1 MAJOR STEPS TO BE TAKEN DURING THE PURGING OPERATION.

Contractor:
SACL
Client:
Document No.
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04/12/08
( UTUE KP END)
Page 4 of 17
• Isolation of the section of the line by closing main end valves
• Controlled depressurization of the line to zero bar gauge to the flare or
to the atmosphere but away from people
• Spade off the line
• Remove ESDV at Utue KP end of line
• Attach a blind valve that is reduced to a one inch nipple
• Use the nipple as nitrogen tie in point on the line
• Install nitrogen tie in manifold and hoses.
• Pressurize the line to 4 bar (g) pressure.
• Vent the gas mixture through the drain line at Ubit PP end and away
using a suitable length of hose
• Repeat for three cycle purges and measure LEL at a vent valve on Ubit
end of line.
• When LEL value of exiting gas is below 5 %, commence action to repair
line.
• If after three cycle purges the LEL value does not fall down
progressively, it shows presence of slug. Attach a temporary pig
launcher at UTUE END and temporary pig receiver at UBIT END.
• Pig the line.
• Carry out repair of the riser.
• After repair of the riser flush with nitrogen to 2 % oxygen content after
reassembly and leak check the line.
1.3 DETERMINATION OF NITROGEN REQUIREMENT.
Total nitrogen requirement necessary for the purging of the pipeline using this
combined method can be calculated from the equation:

Contractor:
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Client:
Document No.
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04/12/08
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Page 5 of 17
V= 1.2*Vo (P-Pa) *N.
Where V= volume of nitrogen in normal cubic metres.
Vo=free volume of pipeline in cubic metres.
P = Absolute pressure of pipeline after pressurization.
Pa = Absolute pressure of pipeline after depressurization.
N = number of times the pipeline is purged.
The units of pressure are stated in bar (g).
The number of times (N) necessary for obtaining the required concentration of
gas can be obtained from the equation:
N= Log C- Log Co
Log Pa- Log P
Where Co is the initial concentration of gas in the pipeline to be removed while
C is the final concentration of gas after purging.
1.4 NITROGEN UNITS CONVERSION TABLE.
1 litre of liquid nitrogen is equivalent to 0.68Nm3
1 US gallon of liquid nitrogen 2.57Nm3 (gaseous)
1 bar (g) pressure 14.5 psi (g)
Nm3 of gaseous nitrogen 1 cubic metre @ NTP.
1.5 WORK SCOPE
• Mobilization of the equipments safely to Onne jetty
• Supply of high purity liquid nitrogen gas (99.9%) in cryogenic
containers (10,000USG).
• Supply of nitrogen purging equipments.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 6 of 17
• Provision of skilled persons to carry out the nitrogen purging services
safely.
• Setting up of the equipments at work site.
• Purging the pipeline to about 2% LEL value (as measured from the
sample point with a gas analyzer) safe enough for hot work.
• Prepare nitrogen purging report.
• Demobilization from work site.
2.0 WORK PROCEDURE.
2.1 Preparation at base before mobilization
• Preparation of work procedure.
• Preparation of check list of equipments and tools.
• Obtain approval of work procedure and equipment list from MPN.
• Test running of equipments to ensure reliability at work site.
• Confirm and or renew certification status of equipments, instruments,
lifting slings, pad eyes, hoses and valves.
• Ensure pre- mobilization inspection of equipments by client.
• Pre- work briefing of personnel on work procedure and safety at work
site.
• Preparation of equipments for mobilization.
• Mobilization of equipments to Onne jetty. Ensure safe off-
loading/loading.
2.2 On site Preparation
• Participate in site induction by client.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
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• Carry out site safety briefing of personnel and prepare job hazard
analysis.
• Obtain work permit from MPN representatives to carry out work.
• Permit must have job safety analysis attached.
• All personnel must wear complete PPE at all time during the work and
while on board.
• Rig up equipments safely onto the platform.
• No personnel should stay under an overhead load
• Check the condition of equipments, hoses, valves and instruments and
ensure non damage of them due to transportation.
• Position and connect equipments in line with equipment layout plan.
• Check equipments for proper functionality.
• Cross check level(s) of nitrogen tank(s) with MPN representative.
• Discuss permit requirements with work crew.
• Inspect work site facilities with client representatives.
• Carry out anomaly hunting of equipment layout and facility.
• Report any anomaly to MPN if found on facility.
• Identify and mark the pipeline shut off valves; sample test point; vent
valves; nitrogen injection points (in liaison with MPN representatives).
• Demarcate or delineate work area with safety tape to restrict entry of
unauthorized personnel within the area.
• Post safety signs such as `NITROGEN PURGING IN PROGRESS,
KEEP OFF “, etc
• Check good functionality of communication radio with the crew at the
opposite end of the pipeline.
• Obtain authorization to commence work from MPN operations.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 8 of 17
• During crew shift change, carry out tool -box briefings; complete the
shift change form in the presence of the out going supervisor.
NOTE: These procedural steps are mandatory and should be
respected strictly.
2.3 PROCEDURE FOR PURGING UTUE – UBIT 16” PIPELINE WITH NITROGEN.
(1) Obtain work permit to carry out nitrogen purging.
(2) Work permit must have JSA attached.
(3) MPN Operations to depressurize the pipeline and facility through the UBIT end to
the flare or through a vent valve on the pig receiver and channelled away from
people with a hose. The depressurization should be done preferably in a controlled
manner and in the evening when there is no threat of lightening.
(4) People should be kept away from the venting area.
(5) All activities capable of generating sparks should be discontinued.
(6) In liaison with MPN representatives and with facility pressure down to zero bar
gauge, remove the ESDV valve after the pig receiver.
(7) Install a flange that is reduced to one inch threaded nipple.
(8) Connect nitrogen tie in fitting for the purging of the facility.
(9) Align the valves on the facility accordingly preparatory to purging.
(10) Install two calibrated pressure gauges at both ends of the line
(11) Connect up nitrogen hose(s) from vaporizer dryer to the tie in point using
suitable pipe threaded fittings.
(12) A non return valve and a ball isolation valve should be connected at the
nitrogen tie in point.
(13) Anchor the hose with whip checks at intervals to prevent probable hose
whipping during hose failure.
(14) Connection to the facility tie in point shall be from the vaporizer dryer.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 9 of 17
(15) In liaison with MPN operations representatives, ensure that valves have
been aligned accordingly for purging of the facility as per isolation check-
list.
(16) One personnel must be positioned at both ends of the line and must be
equipped with communication radio.
(17) By closing the nitrogen tie-in inlet valve, carry out pressure test of the
injection hose(s) and tie-in fittings at a pressure of 4 bar (g) for 10 to 30
minutes.
(18) When the result of the test is satisfactory, depressurize the hose system
and open up all the marked injection inlet valves to the facility.
(19) On receipt of approval from MPN inject gaseous nitrogen into the facility
gradually at 300Nm3 flow rate, Increase the flow rate up to 500Nm3/h at
operators discretion until the purge pressure of 4bar (g) is reached.
(20) Operator stops nitrogen injection, shuts off the injection valves,
depressurizes the hose slowly and leaves the system safe.
(21) Allow about 60 minutes time interval to enable good dilution and
homogenization of nitrogen and the combustible gas content to take place.
(22) Vent the nitrogen combustible gas mixture gradually to 0.5 bars from the
drain valve on the pig receiver at Ubit end. A hose should be connected to
the drain line to enable venting the mixture far away.
(23) With the pipeline depressurized to 0.5 bars, all drain and vent valves closed,
carry out analysis at the venting point using gas analyzer (gas detector).
(24) If the result is not satisfactory (not below 5 % LEL). Repeat steps above
two or more times until the result of the purge is successful as obtained from
the sample points with the use of a properly calibrated gas analyzer.
(25) With MPN representative satisfied with the result, disconnect the nitrogen
injection hoses and tie-in injection fittings from the facility and ensure safe
situation of the site.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 10 of 17
(26) Record in the purging data sheet the results obtained for example;
 Number of purge cycle
 Start/Stop time per cycle.
 Quantity of nitrogen used.
 LEL % obtained.
(See attachment-purging data sheet).
NOTE. The above procedural steps are to be complied with in sequence and
witnessed by MPN. If after two or three cycle purges and the LEL value of the venting
mixture does not show a reasonable progressive drop, then it shows that there is slug
presence in the line. The line should then be pigged using medium density foam pig.
3.0 PERSONNEL MANNING LEVEL
For the purging of this pipeline we recommend a work team of the following personnel:
3.0.1 Field Engineer-----------One (with a minimum qualification of a bachelor’s degree
in engineering and sciences and five years hands- on work experience).
3.0.2 Supervisors: Two in number (one per 12 hour shift).
Minimum qualification of HND in engineering or OND with at
least ten years hands on experience in a process plant in the
oil and gas plant.
3.0.3 Technicians-----------Two personnel (each with minimum qualification of city and
guilds certificate in engineering and over ten years work
experience.
3.0.4 Operators: Same as the technicians.
3.2 Work hours/ Work Duration
Personnel shall be organized in two shifts of one supervisor and two technicians per
shift. Each shift works 12 hours per day. .

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 11 of 17
4.0 SAFETY
4.1 PREAMBLE.
In line with WWC objective of zero accident, we have already put in place a safety system
that ensures personnel and equipment safety at all times during the riser repair project.
The system ensures that:
• Equipments conform to standards used in the oil and gas industry.
• Equipment layout is safe.
• Operators are adequately trained, understand the operating procedure
of equipments and facilities in the oil and gas fields and must comply
with the good practice of obeying instructions.
• All risks associated with this project have been studied and shall not be
ignored
4.2 RISER REPAIR PROJECT SAFETY SYSTEM
4.2.1 All WWC personnel involved in this project shall have the required
personal protective equipments PPE of safety helmet, safety boot,
long sleeve coveralls, hand gloves, eye protective glasses, ear
protectors and life jackets at all time when at work.
4.2.2 All equipments shall be duly certified for safe operation.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 12 of 17
4.2.3 Before mobilization, the crew leaders will be briefed of the work
scope and safety obligation.
4.2.4 On arrival at work site, MPN induction programs shall be availed to
the crew.
4.2.5 Before commencement of work, the work permit shall be obtained
from the MPN operations (with JSA attached). The permit shall be
studied to ensure that it is duly authorized. At the expiration of the
permit, it shall be renewed. In the event of change or deviation from
the procedure, MPN Construction manager shall be duly consulted
for authorization of the procedure change.
4.2.6 Before commencement of work, a safety meeting shall be held with
the MPN representative and quality inspectors to ensure harmony,
thorough understanding of the work procedure by all, the minutes
shall be duly entered into the pre- job safety meeting report form.
4.2.7 The safety implication and safety hazards shall be discussed so that
every one is conscious of it and what to do in emergency situation.
4.2.8 An anomaly hunting exercise shall be undertaken by the work crew
and any anomaly on the facility shall be brought to the attention of
the MPN representatives.
4.2.9 During shift change, the work progress report shall be discussed with
the in coming crew. The leader of the in coming crew signs and
accepts the hand over note
4.2.10 A brief safety meeting (tool box meeting) shall held before the
commencement of a new task in the procedure, such meeting usually
involves the work crew and their supervisor, the details are also
documented in the daily work report.
4.2.11 The no smoking, no swimming and no alcohol drinking prohibition
shall be respected and enforced.

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 13 of 17
4.3 RISK ASSESSMENT
In order to achieve the zero accident goals on the Riser repair project, MPN
JSA No 03-13-07 must be fully complied while MPN JSA form will be used
when carrying out a job safety analysis.
In conjunction with MPN procedure No 03-13-07 and its requirements the
crew will carry out the following:
• Analysis of risks to personnel, equipment and the corporate image of
the organizations.
• Articulation of the probable causes and preventive actions/methods
• In the event of accident, the emergency action to take.
Analysis of the risks involves the listing and description of the tasks to be
performed, the equipments to be used, the personnel requirements and the
nature of the environment where the task is to be performed. It also involves
detailing out the probable risks that could result from the execution of the
task on a risk analysis paper.
The preventive action plan examines the equipment safety, work
procedures, personnel training and communications, personnel motivation;
shut- off/isolation method, etc. These preventive actions have already been
embodied in the work procedure recommended for the project, equipment
certification and safety meetings discussion items.
4.4 EMERGENCY ACTION.
The crew shall assures that the nitrogen purging operation for the Riser
Repair Project will be an accident free one like others carried out in the past.

Contractor:
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Client:
Document No.
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04/12/08
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Page 14 of 17
However, safety regulations demand that emergency action plan be put in
place in the event of an accident.
Some typical ones are listed in the attachment copy (refer to approved
medical evacuation procedure).
4.5 MANAGEMENT OF CHANGE PROCEDURE.
In the event of change to the work scope or anomaly hunt finding of critical
nature, the report must be communicated to the crew (Operations Manager t
who will advise on the suitable change to the work procedure. Such
suggested modification to the work procedure must be discussed with MPN
representatives on site and agreed upon before implementation.
Under no circumstances can the work crew in the field modify any work
procedure or equipment especially when it has critical safety implications
without a revised procedure being endorsed by MPN representative.
Instructions from MPN representative in the field will comply with the already
approved work procedure but any changes can only be made after
consideration and endorsement by MPN.
5.0 EQUIPMENT LIST
5.1. CRYOGENIC TANK (s) WITH BUMP FRAMES
Capacity 2,000 US gallons
Operating Pressure 3 bar

Contractor:
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Client:
Document No.
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04/12/08
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Gross Weight 11.6 ton
Quantity Three
5.2 VAPORISER
Type : Ambient
Flow rate : 500 NM3
/H
Working Pressure: 320 bar
Length 4.4m
Breadth : 1.88m
Height : 2.2m
Approx. weight : 1.5 ton
5.3 NITROGEN PUMP

Contractor:
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Client:
Document No.
SWP-OCIP- -080
04/12/08
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Type Reciprocating
Working pressure 400bar
Flow rate 500Nm3/H
Quantity Two
5.4 ACCESSORIES
1. ONE oxygen Analyser
2. ONE Gas Detector
3. Two Communication radio
4. Five sets of 1” *15bar SWP flexible hoses.
5. Fittings, Flanges, tools
6. Two sets of pressure gauges
7. One tool box

Contractor:
SACL
Client:
Document No.
SWP-OCIP- -080
04/12/08
( UTUE KP END)
Page 17 of 17

Nitrogen purging

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Nitrogen purging