ENVITE intend to be among worlds foremost commissioning services company having developed and introduced many of the specialist techniques which are now regularly used during the commissioning of process plant and pipelines.
4.1 BOLT TENSIONING AND TORQUING
With the varying problems that occur during hook-up and commissioning or shutdown operations, it has become apparent that an integrated service is required. ENVITE’s response has been to form a team capable of finding and repairing leaks. Offering this extra dimension can help save time and money since one contractor can control a complete leak testing project with fewer personnel onboard overall, but effectively doing more work.
Once leaks are identified ENVITE’s integrated service team will carry out leak repairs with the system depressurised. All flange bolts over 1” would be hydraulically bolt tensioned and all bolts below 1” would be hydraulically torqued or hand torqued. ENVITE will not carry out flogging under pressure.
The bolt load on the leaking flange is initially taken to the minimum acceptable level in accordance with specifications. The tension is then progressively increased in increments until the leak is sealed or until the maximum recommended bolt load is reached. If at this bolt load the leak has not sealed then this will be reported to the client to approve further bolt tensioning or allow inspection, gasket renewal or reworking.
The equipment will be supplied containerised with a tool coverage based on 50% of the number of studbolts on the flanges to be tensioned.
Procedures will be supplied including tensioning or torquing data sheets on specific classifications of joints and bolt material calculations. A flange record would be kept and issued for each joint repaired by this method.
Calibration certificates for equipment will be available and a completion package will be compiled upon successful assembly or repair of each joint.
ENVITE is the company that took the initiative of working with an alliance partner on leak testing
operations. We are the only company who has a track record and can demonstrate genuine cost and time
savings by the use of the integrated approach to topsides work. Our personnel are already cross-trained so again no time is lost.
ENVITE can offer any client improved productivity by offering an integrated package covering
hydrotesting, leak testing and bolt torquing/tensioning. The proportion of personnel dedicated to either
tensioning or testing can be adjusted to suit instantaneous priorities. This flexibility provides increased
efficiency and overall time and cost savings over the traditional method of two separate contractors for
testing and repairs.
This approach was encouraged for notable contracts in 1995 with significant direct service savings to the client, but moreover with a logistical benefit with reduced beds and flights which made the project viable.
ENVITE have used Hedley Purvis to date as the specialist contractor for bolt tensioning, and flange records are kept for all joints tensioned and non conformance/concession report would be issued for each joint.
ENVITE’s GENIUS leak testing computer can be adapted to include all the information listed on the manually produced flange records created by the bolt tensioning technicians. This would allow the flange number, leak number and flange record details to be referenced under one unique number. This would allow the operator the flexibility to call up a host of reports and historical data for information or post job analysis. The information/reports could contain a wide range of information, for example:-
– Flange description
– Size and class
– Gasket type, size and make
– No. of bolts, bolt diameter and length
– Condition of flange faces
– Grade of lubricant used/condition of bolts
– Type of joint (RF, RTJ)
– Tools used and serial numbers
– Maximum tension/torque permissible
– Recommended tension/torque
– Date of make up
– Name of operator and inspector/company representative
If this data was processed, analysis could be carried out to highlight which flange, flange type, gasket type etc. were causing problems during commissioning leak testing. This could lead to proactive management of maintenance techniques which would ensure subsequent operations are carried out more efficiently, therefore minimising operational costs and reducing shutdown time.
This proposed technique of total leak and bolt tensioning management will realise significant cost benefits over the total life of any facility.
4.2 VALVES SERVICING AND INTEGRITY TESTING
Envite Nigeria Limited, provide full valve repair services and maintenance programs for the world’s industries. Our services save time and money by repairing large valves inline, onsite or in our valve repair facilities. Our leak repair services covers the following areas:
– Flange Leak Repair
– Leaking, Cracked, Or Broken Flanges.
– Hub – Weld Leaks.
– Out-of-round, Mismatched, Tapered Gap Leaks.
– Case Joint Leaks ( On Rotating Equipment ).
– Valve Bonnet Leaks ( Oval, Round Or Square ).
– Leaks From Rough Pitted
– Lap Joint Leaks.
– Flat Face Flange Leaks.
– Leaking Flanges Of Different Diameter ( With Common Center ).
– Line, Valve – End Flange Leaks.
– Leaks From Flanges With Smooth OD’s
Envite Provides Non Destructive, On Site, On Stream Leak Repair Services For Process, Steam, Water, Or Air Leaks. These Repair Services Are Made At Temperatures Ranging From Cryogenic To 1700 Deg. F, And Pressures From Vacuum To 6000 Psig.
Piping and Fitting Leak Repair
- Ell Leaks
- Screwed, Welded, Socket Welded or Seamless Leaks – 45 & 90 Deg. Ell leaks. Long or Short radius ell leaks.
- Tee Leaks
- Screwed, Welded or Socket welded leaks.
- Seamless leaks.
- Pipe ( Straight line ) leaks.
- Weld, Pinhole, Crack, or Corrosion Leaks.
- Underground, underwater, or overhead line leaks.
- Long or Short – Radius ell leaks.
- Union/Coupling leaks.
- All bellows-type joint leaks.
Effective on any temperature or pressure, applicable on any joint designated for longitudinal movement.
Any Chicksan joint, dock, loading arm leak.Ball joint leaks.Telescoping, other manufactured joint leaks.
Valve Seat Leak Repair, Ball valve drill & tap seat, Gate valve drill and tap seat, Plug valve drill & tap seat
Since the hydro test is at 1.5 times the design pressure, consideration has to be given to the state of the valve. With the valve closed, the high test pressure may cause damage to the seat of the soft seat valves. Alternatively, if the valve is tested in the open position, then unnecessary stresses may be applied to the stem seals.
The leak testing of a valve will generally involve five tests carried out at the normal working pressure of the valve, as follows:-
(1) Stem Seals
The valve is pressurised with the ball rotated through 45 degrees and the stem seal searched for the presence of helium with the mass spectrometer for leaks. When the stem has two seals then the mass spectrometer can be applied to the “tell-tale” connection.
(2) Main Seat
The valve is pressurised with the seat closed and the downstream side of the seat tested for helium leakage. Once the downstream cavity has seen the test gas, (eg if the valve is cycled), it is usually necessary to purge the space with compressed air. In the case of hard seat valves or where the leakage is expected to be high, it is often beneficial to fit a flowmeter to measure the flow. Flowmeters with ranges 38 to 840 cc per minute, 80 to 1,800 cc per minute and 0 to 150 cc per minute are available.
In the case of soft seat valves because of elastic conformation of the seat during operation a certain recovery time must be allowed after cycling otherwise leakage may be obtained. It is generally considered that a low pressure test is more searching for a soft seat valve, but if deformation of the seat occurs it is possible that the leak rate will increase with increasing test pressure. Once a leak is established then the rate will increase as the square of the pressure difference.
(3) Body Flange
Generally in the construction of a valve there will be a flange either to the stem seal assembly or to allow removal of the ball and main seal assemblies. These flanges should be taped so as to form a collecting space between the gasket and the outer edge of the flange. With the valve opened at 45 degrees and pressurised, the tape is pierced with the probe from the mass spectrometer and checked for leakage.
(4) Shell (Body) Leakage
The testing gas, even at 100% helium concentration will not pass through non-porous valve bodies. However, in some castings faults or lines of weakness are encountered giving rise to porosity. The valve bodies should therefore be probed for these leaks. It may be possible to bag a valve in order to look at total leakage, this can only be done if the source of leaks from all other areas is less than the allowable leak rate from the body.
(5) Connecting Flanges
Although not an essential part of the valve design, it is an ideal opportunity to check that the correct gaskets have been selected and that the flange surfaces have been properly machined. The leak test is carried out by taping the flanges and then piercing them with the probe from the mass spectrometer to check for leakage.
(6) Test Conditions
The tests mentioned in sections 1 to 5 inclusive can be repeated under the following conditions:-
(a) Ambient temperature
(b) Elevated temperature, dependent on application (tests have been carried out at 300 degrees
(c) Low temperature, some valves require cryogenic tests at the temperature of liquid nitrogen (-
196 degrees centigrade) and therefore 100% helium is used as the test medium
(d) The stem and main seal will be influenced by cycling the valve. The valves should therefore
be cycled at a controlled rate during all stages of the testing programme.
To assist in fixing a specification for leak testing, further details may be obtained from ASME section 5 on non-destructive examination.
4.3 PIPELINE CLEANING (ROUTINE PIGGING)
ROUTINE PIGGING, simply refers to a systematic programm carefully followed for the periodic clean of the production pipeline using pigs. This program when followed as outlined, enhance the follow of product and eliminate restriction which could result increase in pipeline pressure.
ENVITE Nigeria Limited is made strong personnel who have managed, supervise and operated this method of pipeline cleaning for over 15 years working with multinationals and indigenous companies alike. Considering the wealth of experience of ENVITE team, we have the network of pipelines both on land and swamp at our finger tip.
ENVITE experience shows that some pipelines have not been pigged for a very long time, or strong put, have not been pigged from the day of pipe laying completion. Hence to embark on such routine cleaning operation requires skill and techniques. ENL team member have managed and supervised challenging project of this nature successfully in the past.
This was done by the introduction of specialised chemicals that keeps the debris or sand in a loose form to ensure that compact sand does not occur hence leading to heavy load of debris in front of the pig resulting to high back pressure and pig stucking.
ENVITE Team have managed and supervised several of routine pigging operation using both product and auxillary pumping support for cases where the product flow rate can’t propel the pig at the desired pig velocity. Hence pipeline cleaning by use of pigging operation has been our regular routine. You can count on ENVITE anytime.
4 .4 PIPELINE HYDROTESTING
On completion of the cleaning, gauging and filling operations, the pipeline shall then be filled to eradicate all air bubbles, and be tested to the Acergy/Company specified test pressures (Design pressure x 1.4) and held for 24 hours. This operation shall be performed using a high pressure pump spread located on the Support Vessel. Water shall be sourced from the sea water and pre filtered through100 mesh size filters and chemically dosed.
Pipeline section shall be topped up with water and all air vented from the high elevation point. Pressurization shall commence at the rate of 1 bar/min from atmospheric pressure until 35 barg is reached where upon pressurization shall cease. The pressurizing pumps shall be shut down and a 15-minute hold implemented. During this period, an air entrapment calculation shall be carried out. A pressure volume graph shall be produced using figures obtained during pressurization.
Should the air content exceed the maximum allowable of 0.2%, the pipeline section shall be depressurized and all air vented. Re-pressurization shall recommence until acceptable air content is achieved.
On attaining a successful air entrapment, pressurization shall continue as before to 80% of test pressure at the same rate (1 barg/minute, and held for not less than 1 hour. Thereafter, at 0.5 bar/min up to 95% of test pressure and held for 30 minutes and then finally to the test pressure. The following data shall be recorded at half-hour intervals during pressurization
- Line pressure from dead weight or pressure gauge or Digital Pressure indicator
- Ambient temperature
- Volume of water injected
Stabilization and Hold Period
On completion of pressurization, the line shall be allowed to stabilize. During this period, re-pressurization may be carried out should the pressure drop below test pressure and the volume of water logged.
All instrumentation shall be certified fit for purpose prior to testing.
On completion of a satisfactory stabilization period of 3 hours or as may be requested by Acergy, the pressure shall be held for a 24 hour period. At this point, NO
further pressurization is to take place during this 24-hours period, unless attributed to temperature or environment effects etc.
The following data shall be recorded at every 15 minutes for the stabilization and the hold periods.
- Dead weight/ Digital Pressure indicator / Gauge Pressures
- Ambient Temperatures & Subsea Temperatures
Pressure drops not attributed to ambient temperature variations shall be agreed with the Acergy Representative on site may attract re-pressurization.
On test acceptance after completing a satisfactory hold period, as agreed with the Acergy Rep on site, depressurization shall commence at not more than 1 bar/min. The pressure recorder chart shall not be removed until the pressure is at ambient.
4.5 PIPELINE DEWATERING AND DRYING
Dewatering operation is an activity in the precommissioning of a new pipeline, depending on the use. If the pipeline is used for gas, then it must be dewatered. This operation follows a simple sequence of running bidirectional pigs on a given pipeline after hydrotesting operation. Couple of bidirectional pigs are run to carry out bulk dewatering, after which a pig train is run to carry out the final dewater operation. Once the final dewater is accomplished, the pipeline will be ready for the drying operation.
The typical dewatering sequence of operation is as shown below.
1st Bidirectional Pig
2nd Bidirectional Pig
3rd Bidirectional Pig
1ST High sealing Bidirectional Pig
2ND High Sealing Bidirectional Pig
3RD High Sealing Bidirectional Pig
The drying operation starts once the final dewatering is accomplished. The drying process involves the used super dry compressed air run couple of foam pigs through the pipeline, ranging from medium density foam pigs to soft foam pigs. These foam pigs will be run continuously until a dew point of -20oC, then the pipeline will be considered dry and ready for commissioning through the use of nitrogen. The typical drying sequence of operation is as shown below
DRYING PIG RUN SEQUENCE
1ST Medium Density Foam Pig
2ND Medium Density Foam Pig
3RD Medium Density Foam Pig
4TH Medium Density Foam Pig
1ST Soft Foam Pig
2ND Soft Foam Pig
3RD Soft Foam Pig
4TH Soft Foam Pig
4.6 PIPELINE NITROGEN/HELIUM LEAK TESTING
ENVITE NIGERIA Limited is an indigenous company that is foremost in providing Commissioning Services, having developed and introduced many of the specialist techniques, which are now regularly used during the commissioning of process plant and pipelines.
ENL has in the past been involved in leak testing operations using the soap bubble test method, but has recently purchase a nitrogen/helium mixing pump and a portable mass spectrometer. We have also trained our personnel accordingly to meet up with the demand for Nitrogen/Helium Leak Testing operation in the nation.
Nitrogen/Helium Leak Detection was first introduced in the late 1970’s and has been improved and refined continuously. Nitrogen/Helium Leak Detection is achieved by pressurizing the system or component to be tested to their design pressure with a test medium comprising of 99% Nitrogen and 1% Helium.
To obtain 1% Helium in Nitrogen gas mixture, the liquid Nitrogen is pumped from the Nitrogen storage tanks at the rate of 1000 scf/min. And then mixed with the Helium which is pumped by the Helium boost pump at the rate of 10 scf/min supplied from a quad of Helium cylinders.
To carry out the leak testing, all flanges are taped so that any gas leaking past the gaskets or seals is collected in the space between the outer edge of the gasket and the tape. Leak detection is performed by puncturing the tape with the remote probe. This in turn is connected to the portable Helium mass spectrometer. Hence, any Helium gas that has collected beneath the tape is sampled, detected and quantified.
Finally, a fully documented report is prepared covering all aspects of the leak testing process, highlighting the extent of the system undergoing the test and listing all leaking joints provides an invaluable record for future shutdown / maintenance planning.
Nitrogen/Helium leak testing offers the advantages of reducing the oxygen content of a process plant; systems are tested close to their operating pressure; all leaks are detected and repair before usage; and an inert nitrogen blanket can be left in the system prior to kick off. The system is tested at or close to its working pressure with a gas
closely simulating “live” conditions. This also allows instruments to be calibrated or checked and operators to gain familiarity with the system.
The purpose of Nitrogen/Helium Leak Testing is to render production equipment and piping systems safe for the introduction of hydrocarbon gases and liquids and to create an auditable leak testing report to demonstrate the integrity of all such systems.
Outlined below are the different stages involved in Nitrogen/Helium leak testing
All potentially leaking joints are taped with coloured adhesive tape to avoid leaking test gas from being blown away from the leaking joint and to aid system identification. A remote probe is then used to sample the gas beneath the tape.
The sample probe is attached to a helium mass spectrometer, which is used to quantify the concentration of helium beneath the tape and establish the leak rate from that joint.
The nitrogen and helium mix is used as it closely simulates the hydrocarbon gas that will be present in the system once it is commissioned.
Nitrogen gas is pumped into the system or plant as it may be, using a nitrogen converter unit. The system is pressurized at a rate agreed upon by both ENL and the client, often at low rate of 100scf/min for the initial period. The system is often pressurized up to 1barg and a walk is taken round the system to check for audible leaks or major pressure drop, should any leaks be observed, the system will be depressurized and repair work done. Upon no circumstance will repair work be allowed with system under pressure.
The system is then gradually taken to 25%, 50%, 75% and finally the predetermined test pressure.
Stabilization and Test Period
Upon reaching the test pressure, a predetermined and agreed stabilization time is observed to allow the system pressure to stabilize. Usually a pressure drop is observed due to the nitrogen gas cooling off; the system is then topped up once again to the test pressure. The stabilization period is often about 15 – 30mins, upon satisfactory stabilization the testing period will commence.
On acceptance of the leak test, the system will be gradually depressurized or left with a nitrogen blanket. The leak test acceptance criterion is less than 100scf/year.
4.7 NITROGEN PURGING
Purging means the replacement of an atmosphere of undesired composition in an enclosure by another atmosphere of required composition. ENVITE NIGERIA Limited has used Nitrogen extensively for replacing an active and explosive atmosphere because it is odorless tasteless, non-toxic and practically inert. The objective is to reduce the hydrocarbon level to below its Lower Explosive Level (LEL) so that on contact with air, the hydrocarbon concentration is insufficient to create an explosive mixture with atmospheric oxygen.
Nitrogen purging is used for both start up and shutdown operations in order to replace the existing system atmosphere with safe and inert nitrogen blanket. During start up operations, purging is performed to reduce the oxygen content to typically below 2% by volume and thus prevent any explosive mixtures being formed when hydrocarbons are introduced. During shutdown operations, the hydrocarbon content is purged out of the system to leave an inert atmosphere, which is below the lower explosive limit of that hydrocarbon.
Our subsequent experience on similar projects, we reckoned that both the designated vessels and their corresponding piping should be purged. Secondly, due to no information as per the piping isometrics etc, we intend to perform both displacement and dilution purging in order to reduce the hydrocarbon level to acceptable Lowest Explosive Limit
In this method, Nitrogen is pumped continuously into a vessel or system at one point, whilst the air or gas leaves from another point. The purged gas is normally vented to atmosphere so that the system remains at atmospheric pressure during the entire purging operation. The purging operation continues until the hydrocarbon content of the piping is less than 4% by volume, and this will be determined by the use of a gas meter which will be provided by ENL and or ACERGY.
The Nitrogen performs its function by displacement and / or dilution of the purged gas. In the typical case, both of these processes occur simultaneously. In a long narrow vessel such as a pipe, Nitrogen is passed in at one end and the purged gas leaves the other. The purge may take place almost entirely by displacement, with little mixing of Nitrogen and purged gas at the relatively small interface. In such cases, the amount of Nitrogen required to remove virtually all of the purged gas is almost the same as the volume of the pipe.
When performing a displacement purge, the pump rate should be moderate. If the pump rate is too slow it will allow time for diffusion and tends to result in a purge mainly by dilution. Similarly, a high flow rate and short purging time gives a turbulent jet of Nitrogen at the injection point which also tends towards mixing and purging by dilution. An intermediate flow rate reduces the chance of this happening, increases the amount of purge by displacement and uses the nitrogen more efficiently. As each purging application has a different set of circumstances, it is not possible to calculate optimum flow rates. Gas analysis and previous experience with similar systems can only determine this.
In the typical case, the required purge can be obtained by one or several successive cycles of pressurising and venting. The number of cycles depends on the pressure which the system can withstand, the initial gas concentration, the final gas concentration required and any gassing off which occurs during the purging operation.
The Nitrogen performs its function by displacement and / or dilution of the purged gas. In the typical case, both of these processes occur simultaneously. In a long narrow vessel such as a pipe, Nitrogen is passed in at one end and the purged gas leaves the other. The purge may take place almost entirely by displacement, with little mixing of Nitrogen and purged gas at the relatively small interface. In such cases, the amount of Nitrogen required to remove virtually all of the purged gas is the same as the volume of the pipe.
In more general cases, such as purging of separators, total displacement purging is almost impossible due to the restrictions of flow within separators caused by obstructions such as baffles. In this case purging is carried out almost exclusively by dilution.
Purging to a given concentration by dilution as opposed to displacement obviously uses more Nitrogen. When calculating the amount of Nitrogen required, it is best to assume that complete mixing will occur, as this will give a conservative estimate of Nitrogen requirements.
Injection and Venting Points
When selecting injection or venting points, the type of purge, the system to be purged and the composition of the undesired atmosphere must be taken into account.
When performing a displacement purge, injection and vent points should be at opposite ends of a system, away from any obstructions that may increase mixing.
When performing a dilution purge, the location of injection point is not critical. When venting, numerous points should be used to ensure “dead legs” etc are purged through.
When system vents are not in operation extreme care should be taken when venting. Gas should never be vented into enclosed modules. If gas denser than air is vented, extreme care should be taken to ensure that dense gasses do not collect in low areas to form explosive mixtures. In all cases when venting, it must be ensured that no gas is trapped due to non-return valves.
It is important to remember when taking gas samples from a system, that various sample points are used. Opposite ends of a system, as well as possible “dead leg” areas should be sampled.
Ensure that all meters used have up to date calibration certificates and are functioning properly before using. The two main gas meters used by ENL are the oxygen meter for measuring oxygen content and a hydrocarbon in Nitrogen meter, which is calibrated to measure LEL.