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Hydrostatic Testing Procedure Including Pigging, Draining, Swabbing and Drying of Pipelines

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Hydrostatic Testing Procedure Including Pigging, Draining, Swabbing and Drying of Pipelines

The purpose of this hydrostatic testing procedure is to list out various steps involved in hydrostatic pressure testing, pigging, draining, swabbing and drying of pipelines for the in lines with the project specifications.

Scope of work covers the Water Supply, Quality and Treatment, Internal Cleaning, Pigging, Gauging, Flooding thereafter pressurizing, depressurizing on successful completion of testing and disposal of water of pipeline as per contract technical specifications.

Experienced specialists crew coordinated by a qualified and experienced lead person who shall be responsible for all testing and associated works shall carry out testing.

Sufficient experienced personnel shall be required as per the requirement to enable all aspect of testing to be fully supervised and completed as per the project plan and program.

Relevant References and Codes:

Test package documentations

Test package shall include but not limited to the followings:

a) Pipeline pressure testing cover sheet

b) Pre-hydro test checklist.

c) Punch list for Pipeline

d) Marked P&ID for the line to be tested.

e) Pipeline General arrangement drawing

f) Pipeline profile drawing

g) Weld map

h) Pipe Book

i) Calibration records for the used instruments.

j) Diagram of Hydro test Header, Launcher / Receiver

k) Pipeline cleaning inspection report

l) Gauging inspection report

m) Filling log

n) Pressurization Record

o) Pressure and Temperature Log

p) Pressure/volume calculation for entrapped air percentage.

q) Pressure Test Certificate

r) Pressure Test Specification

s) De pressurization Record.

t) Pipeline swabbing report

u) Pipeline drying report

v) Post hydrostatic test checklist

Hydrotesting Equipment List

Testing equipment’s shall depend upon the test to be carried out as per the Technical Specification of the Contract.

The following equipment’s are generally used:

List of necessary Instruments:

Calibration of test Instruments

All instruments used for Hydro testing shall be calibrated before hydrostatic testing to meet the accuracy of +/- 0.1% and sensitivity of 0.05% and shall have a valid calibration certificate during the period of hydro testing.

All instrumentation shall operate in the range of 40% to 70% of their maximum indicator level during operation.

The instruments to be calibrated and calibration certificate for the same shall be presented prior to test.

Pig material for pipelines

High/ Medium Density foam Pig shall be used before cleaning pig to ensure that the line is free from obstacles.

Cleaning pig (with brush and neoprene cup)

Batching pigs with 4 neoprene cups suitable for Filling /dewatering

Foam/ Sponge Pigs for drying & swabbing the Pipeline

Health and Safety Requirements during Hydrotesting

Safety officer must be present at site at all times.

Proper care should be taken to safeguard personnel and property during the hydro testing.

No work shall be permitted on sections of pipeline or the associated connections under test.

Prior to pressurization, proper measure should be taken to prevent damage to personnel and property or disrupt any other existing services.

Area where test equipment is placed shall be clearly demarked to prevent unauthorized entry.

Warning notice reading “WARNING: PIPELINE UNDER TEST” shall be placed at appropriate locations for the duration of the hydrostatic test.

All local and statutory requirements are taken care of.

Requirements stated Contract Health, Safety and Environmental (HSE) Plan shall to be used during execution of the hydrostatic pressure testing works at site.

Ensure that availability of barrication of pipeline, First Aid Kit, emergency phone no etc.

Communication facilities for the team involved in the test have been checked and backup arrangements are also available.

The personnel engaged in the testing works have been briefed on the emergency plans.

During pressurization process, both side operators shall be instructed by the test engineer regarding the limiting pressure which shall apply to the test section.

Water Source

Test medium will be brackish water dosed with client approved non-foam corrosion inhibitor to manufacturer’s recommendations.

The chemical dosing of brackish test water shall follow the requirement of specifications.

Calculated quantity of approved corrosion inhibitor shall be added to the water using dosing pump.

It is recommended to use the chemical that acts as a Corrosion Inhibitor, Bactericide & oxygen scavenger, which is designed as a single product for treatment of water resident in pipelines and prevents corrosion due to oxygen attack, anaerobic bacteria and salt water. Normally its dosage rate recommended by the manufacturer is 500ppm.

All test results, recommended inhibitor type and dosages shall be sent to the consultant representative for approval prior to start of filling operation.

Requirement of water for Pipeline filling shall be determined by using the formula.       

                                    V          =          Π/4 x D2 x L

            Where             V          =          Geometrical Volume of the test Section (M3) 

                                    D         =          Pipeline Internal Diameter (M)

                                    L          =          Pipe Line Length (M)

Quantity of Brackish water required for filling each pipeline section is mentioned in relevant sections.

Water will be arranged from nearest storage or by water tankers. After hydro-test release, the water will be transferred from one section to the other by temporary connections.

The corrosion inhibitor must be applicable for multi-use.

Internal Cleaning of Pipe Lines

Confirmation prior to pigging

A pre-test check shall be performed before pigging is commenced.

The check list shall include the followings:

Cleaning Process:

All pipelines shall be internally cleaned to ensure the removal of construction debris and loose scale.

Cleaning shall be done in one section, from Launcher to Receiver.

The 1st run of cleaning process shall be done by Medium Density Criss Cross Foam Pig equipped with Pig Locator.

Second run of the cleaning process shall be done by High seal Bi directional cup pig with wire brush equipped with pig locator.

A compressor will be used to drive the cleaning pig. The pig speed shall be between 0.3 meter/second and 1.0 meter/second, this speed can be controlled by throttling release valve at receiving header.

Two technicians with proper communication will be available at each end of the pipeline in order to control pig movement and arrival.

The operators shall immediately report to the test engineer about any apparent variation which may result in failure or danger such as any abnormal rising of the pressure behind the pig.

Passing of the pig to any particular area such as Hot Bends/Barred Tees may be detected by the non intrusive pig signaler that can be positioned in the required place to detect the time at which the pig has passed that location.

Upon pig arrival and detected by the non intrusive pig signaler, compressor will be stopped and pressure will be released to atmosphere prior to removal of the pig.

Cleaning of the test line shall be witnessed by consultant/client representative and contractor QC Inspector.

Minimum 2 runs will be carried out in pipeline and additional runs shall be made if required to ensure satisfactory cleanness as accepted by client representative.

After each run of pigging, the pig shall be inspected by consultant representatives.

The cleaning operation shall be continued until the volume of the received materials by the last pig is less than 5 liters.

The following data shall be recorded by using pipeline pigging inspection form by the test Engineer:

After cleaning operation, the pipeline shall be protected by closing the openings at both ends.

Cleaning of non pig able line shall be carried out by using compressed air before starting the water filling.

Gauging Operation

Following internal cleaning, gauging run shall be made on the entire complete pipeline to demonstrate that the pipe line is free of buckles, wrinkles, dents etc.

Gauging plate shall be made from aluminum plate and shall be 95% of the minimum internal bore of the line pipe.

Caliper Pigging with GPS mapping operation

 After completion of internal cleaning& Gauging, Caliper Pigging with GPS mapping shall be done by approved Subcontractor. Subcontractor for Calliper Pigging with GPS Mapping shall first get method statement approval and then perform the test.

Water Filling Operation

Filling of test line shall be carried out in two stages:

Stage 1: Brackish Water from source will be pumped into tank.

Stage 2: Water will be pumped from the tanks to test header using filling pump. Please refer for connection details in Test sequence diagram enclosed.

Filling water will be filtered through a strainer fitted with 50 micron filter.

Calibrated flow meter shall be installed downstream of the filling pump in order to calculate the volume of test water filled. Inhibitor, will be injected into water as per manufacturers recommended dosage rate as approved by client.

The filling operation shall be performed through the test headers on each pipeline.

Launcher shall be preloaded with 2 nos. of bi-directional pigs for filling operation.

Launcher shall be fitted with 3 nozzles for filling water.

Nozzle no. 1 will be used for pre filling water equivalent to 250m length of test section.

Nozzle no. 2 shall be used for launching first pig and inhibited water equivalent 250m section length shall be pumped into the line.

Nozzle no. 3 shall be used for launching second pig and required volume of water to fill the test line will be pumped into the line.

The filling pig speed shall be in range 0. 4 ~ 0.8m/sec.

Pumping will continue until pigs are received at the pig receiver.

Air expelled from test section shall be vented out through vent valves.

The valves shall be manually operated while filling to maintain a back pressure of 1.0 bar to avoid uncontrolled run of pigs and removal of all trapped air at the headers risers.

Records during water filling:

During filling operation the following will be recorded on the approved form for every 30 minutes.

Upon arrival of filling pig at the receiver end, filling operation will be considered as completed and the test section is ready for stabilization.

Thermal Temperature Stabilization

After completion of filling operation, thermal stabilization of test section will be carried out.

The temperature of the water inside the line can be considered the same as that of the pipeline outside wall.

Two numbers of temperature recorders with 48 hour graduated charts will be fixed on the test line.

One recorder will be fixed to pipe surface near launcher, other one to soil at 0.5 meter from pipe.

These temperature recorders will be provided with different color pens.

Thermocouple with read out shall be installed at a distance of 0.5 km from each end of the test section.

Thermocouple should be firmly attached to the bare pipe after removing corrosion protection coating and covered with insulating materials.

For soil temperature measurements, they should be buried at pipe centre line depth and 0.5m laterally from the pipe.

All thermocouple along the pipeline shall be installed before the start of the filling operation.

For above ground test section temperature measurements, the thermocouple should be firmly attached to bare metal and covered with insulating materials or installed into line-fill water.

Temperature reading for pipe and soil, at various locations, shall be measured every 8hrs. for a period of 24 hrs. and shall be recorded in the water filling record form.

During stabilization period, the following data shall be recorded:

Stabilization shall be considered satisfactory when the difference between the average soil and average pipe skin temperature is not more than 1ºC.

Pipeline Pressure Testing Procedure

A pre-test check shall be performed before pressurizing is commenced.

The check list shall include checks to confirm the followings:

Stabilization has been accepted by all parties.

All instruments and gauges to be used during pressurizing and test have been calibrated and valid test certificates have been checked.

All equipment and devices are in good condition and well functional.

A test cabin equipped with a dead weight tester and chart recorder is installed at a safe distance of not less than 20m from test line.

At launcher and receiver pressure recorders with 48 hour rotating charts will be installed for continuous recording or pressure during pressurizing.

4 numbers of temperature recorders are installed at launcher and receiver for recording soil and pipe temperature during pressurization.

A high pressure pump equipped with built in calibrated relief valve set at 5% above test pressure shall be used to pressurize the test line:

Calculations of Air Content 

To determine the residual air volume in the line the below diagram shall be drawn:

The theoretical slope shall be calculated from the following formula:

∆V/∆P = V [(D/t) x (1/E) x (1- ע2) + (1/β)]

Where:

∆V: Incremental of volume in (M3)

∆P: Incremental of Pressure in (Bar)

V: Filled Volume(M3)

D: Outside Diameter (M)

t: Wall Thickness(M)

E: Young` S Modulus Of Elasticity(Bar) (For Carbon steel E=2.07×106 bar)

ע: Poisson` S Ratio (0.3)

β: Bulk Modulus of Water  =  23.1×103 bar

Before pressurization starts, the above calculation shall be done and the theoretical P/V plot and 0.2% offset volume line shall be drawn.

The following diagram shall be used:

Pressurizing shall proceed at a maximum rate of 1 Bar / Minute.

During pressurization, the following readings shall be taken and recorded:

The line shall be pressurized to 50% of the final test pressure.

An actual P/V plot shall be drawn in order to determine the air content in the test section.

The percentage of air content shall be calculated from the PV-Graph as above by plotting on graph.

Percentage of Air = (Volume of Air /Volume of Line) x 100

Air content should not exceed 0.2% of test line volume comparing to theoretical quantity.

The slope of the linear part of the P/V plot shall be compared with the slope of the theoretical plot for 100% water content. The slope shall not differ by more than 10%.

If air content is greater than 0.2% of the line volume, the pressurizing can not go on. The test section shall be depressurized and additional pig passages shall be performed to remove the air pockets.

Upon the acceptance of the air content in the test section, the pressurization shall continue until 80% of the maximum test pressure is reached.

Pressure is then stabilized for a period of 2 hrs. During this hold period the line must be checked for any possible leaks.

The pressurization rate above 80% shall be at a uniform rate no more than 0.5 Bar/ Minute until maximum test pressure is reached. Pressure shall be recorded every 0.5 Bar.

When the pressure becomes 100% of test pressure, pressurizing pump will be stopped and all connections from test pump will be isolated from test section and 24 Hr. hold period will start. The start of the hydrotest shall coincide with the highest temperature of the day.

24 Hour Hold Period

Before commencement of 24 hour hold period charts for temperature and pressure recorders will be replaced with new charts.

During 24 hr. hold period following readings will be recorded at every half an hour:

The pressure test shall be deemed acceptable if any pressure change can be accounted for by corresponding temperature change using the following formula: 

ΔP/ Δ T :  Y-2α /(DX(1-v2)/Et+1/B)  Bar/ °C

ΔP: Pressure change (Bar)

Y: Volumetric expansion coefficient of water

Δ T: Temperature change (°C)

D: Pipeline outside Diameter (M)

E: Young’s Modulus of carbon steel (E=2.07×106 bar)

t: Nominal Pipe Thickness (mm)

v: Poisson’s Ratio (0.3)

B: Bulk modulus of water at temperature and pressure of the water 23.1X103 bar

α: Coefficient of linear expansion of steel (11.7X10–6)

The difference between the theoretical pressure and measured test pressure at the end of hold period shall not be greater than ±0.2 % of test pressure.

For acceptance criteria, static pressure changes shall be accounted by temperature changes. The test shall be accepted if change in pressure is within acceptable limit and no leaks are found during the test. A pressure change of ±0.2 % of the test pressure shall be accepted.

If greater pressure drops occurs, the holding period shall be extended another 24 hours or the cause of lack of water tightness shall be established. In either cause the Company will be informed.

A pressure vs. time graph shall be prepared for 24 Hour hold period to ascertain the actual pressure changes.

On acceptance, Pressure will be released gradually at the rate of 1 Bar/Minute.

Leaks or failures will not be accepted. All leaks or failures shall be rectified. The test section/Line shall be tested again. Before attending any repair, test line shall be depressurized to static pressure. After attending repairs the line shall be retested to ensure, there is no leaks or failures.

Dewatering Procedure

Hydro test water shall be disposed nearest to drainage of temporary disposal pit.

Prior to start the draining of test water permission must be taken from applicable authorities.

If there is no suitable location for draining of test water, then vacuum tankers with temporary facilities for collection shall be used for disposal of test water.

It shall be ensured that pipeline section tested has been depressurized 1 bar above static head condition and left filled with inhibited water.

All the temporary fittings and connections shall be cut off or disconnected, and the entire pipeline shall be fixed with all the requirements as per the final approved drawing.

Dewatering of each line shall be performed by the Bi-Directional/Cup Pig pushed by compressed air.

Minimum speed and backpressure of the pigs shall be maintained in order to obtain a continuous operation with no blockage of the pigs.

At the receiving end the discharge and flow shall be throttled down to avoid damage to the receiving facilities.

The velocity of the pig during dewatering run shall not exceed 1.5 km/hr [0.4 m/sec.]

Pig shall be tracked by pig signals installed at launchers and receiver.

During the arrival of the pigs at the receiving end of the pipeline the discharge flow shall be throttled down such that the pig speed is almost zero when entering into the receiver, to avoid damage to the receiving facilities.

Upon pig arrival at trap. The pig will be pulled out in presence of Contractor/Client representative and will be carefully examined.

After the acceptance of dewatering by consultant/client, pipeline shall be released for subsequent swapping and drying activities.

The water will be directly transferred by temporary spools to the 2nd section to be hydro-tested.

Swabbing the Pipelines

Swabbing operation shall be performed only after satisfactorily removing bulk of water from the pipeline.

Foam/Sponge  pig shall be launched through pig launcher and propelled with compressed air. During swabbing operation, the valve at receiver shall be throttled for keeping a back pressure of 0.5 bar. This will be pulled out at the receiving end in the presence of client representative.

Foam pig shall be weighed prior to and after completion of each run. Weights shall be recorded to determine the amount of water collected by foam pig.

Foam/Sponge pigs runs will be repeated, until satisfactory result is obtain and accepted by client.

Date and Times of pig launching and receiving as well as condition of pigs at receiver shall be recorded in the attached formats.

Air Drying the Pipelines

The air-drying operation shall be commenced within 24 hours of completion of the dewatering and swabbing operation.

The inlet air is to be dry and have a maximum dew point of -50°C at atmosphere pressure. The drying shall be verified by measuring the air dew point at inlet and outlet. The dew point shall be     – 20° C.

During drying the dew point shall be continuously recorded at both ends of pipeline sections to detect peaks in water dew point. In particular, the drying shall be considered complete when the required dew point of- 20° C at atmospheric pressure shall be recorded continuously.

After completion of drying operation, all temporary piping and fittings shall be removed. The pipe line section shall be closed off.

Purging

Purging shall be as per approved procedure to be submitted before commissioning.

Attachments

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