Nitrogen Purging

Contractor: SACL

Client: MPN NITROGEN PURGING PROCEDURE Document No.

SWP-OCIP- -080

Contract No. A2041122OFFSHORE CONSTRUCTION &

INSTALLATION PROGRAM (OCIP)04/12/08

RISER REPAIR PROJECTREPAIR OF UTUE- KP -UBIT PP 16’’ GAS

RISER FROM UTUE KP –UBIT PP ( UTUE KP END)

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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

MikeGreen

Rev. Date Name Sign Name Sign Name Sign Name SignPrepared By Reviewed By Approved Accepted (MPN)

16” UTUE KP-UBIT PP Gas Pipeline Dewatering & Nitrogen Purging Procedure

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TABLE OF CONTENTS

1.0 Introduction

1.1 Generalities1.2 Work objective1.3 Determination of nitrogen requirement1.4 Nitrogen unit’s conversion.1.5 Work scope

2.0 Work Procedure2.1 Base Preparation2.2 ON-site Preparation2.3 Procedure for purging pipeline with nitrogen

3.0 Personnel manning levels3.1 Work hours/Work duration.

4.0 Safety4.1 Preamble4.2 Riser repair project safety system4.3 Risk Assessment4.4 Emergency action4.5 Management of change procedure.

5.0 Equipment List

6.0 Attachments(typical JSA)


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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 OBJECTIVEThe 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.


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1.2.1 MAJOR STEPS TO BE TAKEN DURING THE PURGING OPERATION.

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:


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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.

Provision of skilled persons to carry out the nitrogen purging services

safely.16” UTUE KP-UBIT PP Gas Pipeline Dewatering & Nitrogen Purging Procedure

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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.

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. 16” UTUE KP-UBIT PP Gas Pipeline Dewatering & Nitrogen Purging Procedure

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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.

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.


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(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.

(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.


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(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.

(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.


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(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 LEVELFor 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 DurationPersonnel shall be organized in two shifts of one supervisor and two technicians per

shift. Each shift works 12 hours per day. .


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4.0 SAFETY4.1 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.

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


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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.

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.


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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.

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.


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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

Gross Weight 11.6 ton

Quantity Three


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5.2 VAPORISERType : 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

Type Reciprocating

Working pressure 400bar

Flow rate 500Nm3/H


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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


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Nitrogen Purging

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