Method for Hot Tap Connections Capable of Saving Millions

Since 1997, Advantica has been developing the Grouted Tee connection technique for onshore and subsea applications. This technique does not require any welding (i.e. hot works) and offers no disruption to production during installation, making it suitable for diverless intervention and saving millions of dollars by eliminating lost production. The hot-- tap process using this technique is simple and surface preparation is less critical, compared to the current methods (i,e. welding or bolt-on-mechanical).

The Grouted Tee accommodates much larger linepipe ovality. The technique involves two half shells. The branch is either welded or extruded onto the shell prior to installation. The shells also consist of a high-pressure saddle seal, which eliminates the need for longitudinal and circumferential seals, which are required for the current bolt-on mechanical fittings. The shells are then placed around the main pipeline and firmly locked together. The whole fitting is sized to allow a gap between the bore of the shells and the outside diameter of the parent pipe. This annular gap is then filled with a grout.

Extensive analysis and full-scale testing for onshore pipelines were successfully completed in December 2000. They addressed many technical and safety issues. The grouted tee has a 40-year design life specification.

The main benefits of the Grouted Tee connections are:

• No welding to main pipelines;
• Eliminate the need for skilled divers;
• No need for pressure reduction and hence normal production can be maintained during hot tapping;
• Simple field installation in comparison to the current welded or bolt on mechanical;
• It is independent to the main pipeline materials;
• Due to its simplicity, it is highly feasible to assist with deepwater pipeline intervention;

Diverless hot-tapping allows pipeline intervention beyond the reach of shallow water platforms and divers which has great potential to lower operational costs and removes many of the safety issues.

Design Analysis/Codes IGE/TD/1 Requirements:

The Grouted Tee connection was designed to conform to the requirements of IGE/TD/1 Edition 3: Institution of Gas Engineers. Recommendations on Transmission and Distribution Practice-Steel Pipelines for High Pressure Gas Transmission.

The requirements of IGE/TD/1 are:

• The tee must be suitable for pipelines with design factors up to 0.72 with 10%/o additional allowance for over pressure.
• The tee must be suitable for 15,000 pressure cycles resulting in 125 N/mm2 nominal hoop stress range in thepipeline.
• The tee must be capable of withstanding hydrostatic pressure tests up to 105% SMYS nominal hoop stress in the nineline.

In reality, these loadings may result from the effect of temperature changes in the pipeline, ground subsidence, valve closures in the branch or pipeline, and ending anywhere in the vicinity of the tee. These were accounted for as part of IGE/TD/1 requirements.

IGE/TD/12 requirements: The design conditions in IGE/TD/12 define the pressure, temperature and various forces applicable to the design of the tree. It provides guidance for stress analysis to enable the grouted tee to be designed for the most severe conditions of coincident pressure, temperture and loading that may occur during installation and normal operation of the frout-ed tee.

It also provides guidance on various loading conditions:

• Pressure effects: hoop and longitudinal expansion
• Amblent considerations such as ambient loss, fluid expansion.
• Thermal expansion and contraction effects
• Dynamic effects: shock effects, discharge reactions, vibration, etc.
• Weight effects: live loads, dead loads
• Cyclic loading
• Corrosion effects

The maximum permitted sustained stress adopted by the Grouted Tee in normal conditions is 80% SMYS. It is to this stress level that the test program was applied to the grouted tee. Adoption of the 105% SMYS pressure test IGE/TD/1 criterion ensured that additional requirements were met.

Design Description

The Grouted Tee technique [Fig. 11 involves placing two half shells around the pipe and bolting them together. The shells, with a specified wall thickness, have a similar material grade to the parent pipe. They are sized to allow a generous gap between the bore of the shells and the outside diameter of the parent pipe. This annular gap is filled with grout which, when set, transfers the local high stresses in the pipe to the outer shell.

Pressure containment is achieved via the "saddle" seal, which is positioned next to the opening of the main pipe. The sealing specification is unusual and demanding. The primary function accommodates large variations in the annular gap between pipe and shell. It also has to cope with a grit-blasted surface preparation which is equivalent to SIS 05-59-00 Sa 2.5 finish. It also needs to withstand elevated temperatures during the drilling operation. Moreover, the saddle seal has been designed to be independent of the quality of the grout and on its own should maintain the integrity of the pressure containment.

Design Lead Considerations

The loads the Grouted Tee is required to withstand are complex. Loading is caused during installation (i.e. cutting reaction forces), normal operation, ground/ seabed movements, equipment and pipe work mass and/or combinations of these. They can be divided into:

• Internal pressure
• Axial loads on the header and/or branch
• In plane bending moments on header and/or branch
• Out of plane bending moments on the header and/or branch
• Torsional loads on the header and/or branch

Loads On The Grout

The Grouted Tee connection is a structural component and the grout has to transfer loads between the pipe and the branch and vice versa. The properties of the grout, such as cohesive and adhesive shear strength, were selected to meet the specified structural strength and limitations of the Grouted Tee.

Operational Loads This includes internal pressure and external loads. The stresses in the branch jucction are complex. Internal pressure loading induces a hoop stress in the pipe, the header and the branch.

Stresses Around The grout Adjacent To The Primary Seal

The pipe around this area bulges outward at all locations around the hole. This induces tensile and bending stresses in these locations.

Cyclic Pressure Loads

Cyclic pressure loading gives rise to cyclic stresses in the pipe, the bonded area, the grout, the header and the branch. These stresses have a major effect on the fatigue life of the whole structure.

End Loads

Tensile axial stress is created by internal pressure acting on a bend or end cap or by external loading (i.e. seabed current). In plane and/or out of plane bending moments and/or torsional loads can also be induced.

ing moments and/or torsional loads can also be induced.

Thermal Loads

Temperature variation in the product flowing through the connection causes the structure to expand or contract. This induces appreciable loads at the connection. Stresses induced in the branch connection have also been considered.

Cutting Loads During Drilling

Other loading to be considered occurs during the drilling operation (both horizontal and vertical installation). This generates tensile loads acting along the axis of the branch of the tee and a torsional load about the header axis. This force acts to separate the bond between the pipe/branch and the grout, in the vicinity of the saddle seal.

The cutting operation generates vibrational and thermal loads. The thermal loads are unlikely to be significant because of the cooling effect of the fluid flow.

Seabed Currents

Wave loading is usually negligible because pipelines and connections are buried in water depths down to 200 feet and are designed to be stable on the seafloor beyond 200 feet water depth. Currents near the seafloor are used only for heat transfer calculations. Where high bottom currents or wave-induced water movements act on long pipe spans, the Morrison equation, together with appropriate drag and inertia criteria coefficients, can be used to quantify hydrodynamic loads.

Not Leads

Loads arising from anchors, fishing and trawl gear, mudslides,a nd sea floor scour are difficult to quantify. However, the branch connection can be designed and constructed to absorb movement of the lateral line due to external loads.

F.E. ANALYSIS

A full finite element analysis has been carried out on the Grouted Tee fittings under eight different cases of external applied mechanical loading to either the main pipe and/or the branch.

Results were obtained for the relative displacements of the main pipe and the branch at the positions of the seal around the hole and for stresses in the grout under arbitrary unit loading.

Ful-Sale Ton Program

Four 24-inch (610-mm) grouted tee connection prototypes were designed and manufactured to BS5500 and subjected to a comprehensive test program designed to the requirements of IGE/TD/1 and IGE/TD/12. The program was completed in 2000. The prototypes were chosen to accommodate testing on a main pipe of 610mm diameter x 12.7mm x API-5L-X52.

The prototypes were installed on either dome-ended or blank-flanged pipe sections for pressure and combined loading tests before and after drilling. The tests also included 150,000 fatigue cycles (exceeding by a factor of 10 the 15,000 cycles required by IGE/TD/1) with a hydrostatic internal pressure range of 20 to 75 bar (equivalent to a stress range of 125 N/mm2 in the main pipeline).

Following the above fatigue test, the same Grouted Tee connection was tested to failure; another part of the testing system failed at 163 bar (equivalent to 110% SMYS) but the seal and the grout did not fail. Further pressurization to 179 bar (equivalent to 120% SMYS) was applied until the pump could not overcome the leakage within the system.

To simulate the axial, bending and torsional loads arising from the pipe and ground movement, the prototypes were successfully subjected to a series of combined loading tests. (Figure 2) Combined loading included out-of-plane and in-plane bending to the main pipe to demonstrate all the requirements within IGE/TD/12 could be met.

Combined Loading Tests

The Grouted Tee prototypes were subjected to a combined loading of internal pressure and external loading such as bending and torsion to simulate pipe and ground movements. The main line pipe used for this combined loading study was API-51, X52 x 610mm Outside Diameter x 12.7mm Wall Thickness. The specified minimum yield strength, SMYS, of thispipeline is 358MPa. The Grouted Tee being subjected to an internal pressure of 7MPa.

The maximum principal stress should reach a minimum level of 80% SMYS but should not exceed the SMYS. This is based on IGE/TD/12.

Full-Scale Onshore RON Trw

In October 2000, a field trial was carried out at Advantica's purpose built test site in England. The purpose was to prove the concept and verification process prior to implementing the Grouted Tee technology in the National Transmission System which is owned and operated in the UK by Transco.

A 24-inch diameter Grouted Tee connection was manufactured, installed and hot-tapped [Fig. 31 on a 55 bar natural gas transmission line (610mm diameter x 11.9 mm wall thickness x API-SL-X42). Natural gas was flowing at a velocity of 5 rT/s.

The pipe was successfully intervened and gas flow was stopped with the stoppie equipment. (Figure 4)

Subsea Hot Tap

In the early years of underwater hot-tapping (1970-80), there were significantly more welded hot-tapsinstalled underwater than mechanical hot-taps (approximately 21). This was due to several factors:

• relatively high cost of the mechanical fittings
• lack of a proven track-record
• shallow depths involved with most applications.

Subsea Installation With The Grouted Tee

Advantica is leading development of a diverless subsea Grouted Tee connection to intervene an underpressure subsea pipeline. Diverless hot-tapping allows pipeline intervention beyond the reach of shallow water platforms and divers, potentially lowering costs. Subsea installations involve the following steps:

Pre-works Survey And Preparation

These procedures are generally performed from a diving support vessel (DSV), a jack-up type construction vessel or a construction barge. The choice of vessel depends on water depth, availability, cost and preference of the client.

The trunkline location is first established, based on the pipeline as-laid drawings. A section of the pipeline will be selected that is straight and level, close to but not necessarily on the intersection of the branch pipeline.

An ROV is used to carry out a survey of the pipeline to check the as-laid coordinates and condition of thepipeline, i.e. straight and free from damage, at the intended tee location. For pipelines on the seabed, a visual survey and inspection is carried out. For buried pipelines, a pipetracker or geopig can be used. In many instances, survey companies will have located and identified all pipelines in the area with marker buoys.

Pipeline Excavation

There is always a requirement to excavate around or under the trunkline. This can be time consuming in cases where extensive cover is encountered. Lifting of the operating pipeline should be avoided at all costs as this could lead to damage to coatings or in an extreme case, thermal snap buckling.

Diverless deburial will be carried out using a high-powered jetting ROV or specialist equipment such as the Aquaflow T8000.

Once the trunkline has been located, the initial excavation is directed at locating the field joint. This is required for two reasons:

1. First, it is desirable to install the hot-tap fitting at a location that does not cut through a girth weld.
2. Second, since most pipelines have a seam weld, locating the fieldjoint permits selection of a joint of pipe so the tapping does not cut through the longitudinal weld.

Once the field joint has been located and evaluated, the exact location for the hot-tap can be established and the remaining excavation can be completed.

Installation of The Base-Frame

After excavation, the base frame is lowered from the DSV and with the aid of the ROV is installed [Fig. 51 in the correct location around the pipeline.

The base frame contains the guideposts, which locate the tee frame, protective structure and various tools required during the operation. It is fitted with mudmats to prevent excessive vertical loads being transferred to the pipeline.

Depending on water depth of the installation, guidewires can be installed onto the guideposts from the installation vessel. If the location is too deep for guide wires, transponders are used at the top of two diagonally opposed posts.

Coating Removal IL Pine Peaakn

The concrete weight coating, reinforcing bars, and anti-corrosion coating must be removed over a length approximately 500 nrm longer than the overall length of the hot-tap fitting. Removal of the concrete is generally accomplished using a high-pressure (20,000-psi) water jet or concrete saw. The reinforcing bar (chicken wire) is removed using wire-cutting attachments on ROV manipulators.

Removal of the anti-corrosion coating is done using several different techniques, depending on the type of coating. For mastic or coal tar type coatings, a combination of a scraping blade and wire brush is generally effective. For thin film coatings, special grinding disks can be attached to the manipulators. It is not necessary to polish the outside surface of the pipe after removal of the anti-corrosion coating or to create any special surface finish on the pipe.

Pipe ovality is checked using a split-type hinged ring gauge, which simulates the maximum pipe diameter permissible, by API tolerance. The ring gauge is installed around the pipe after the cleaning operation. The gauge is a split-hinged device that is easily installed using a simple toy type clamp The gauge is passed over the entire cleaned area to ensure that it passed freely.

The curvature of the pipe is then checked, as this could adversely affect the installation of the hot-tap fitting. Generally a crown of 1.5mm is permissible in a length of 1.5 meters withour affecting installation of the fitting.

Grouted Tee Installation

While the initial underwater operations are being conducted, surface technicians prepare the hot-tap fitting and related equipment for deployment. This involves performing visual and functional checks of all surface operated equipment and rigging of the hot-tap assembly. The fitting is assembled with the isolation valve andhot-- tapping machine. The entire assembly is rigged for deployment in one operation to minimize the time required subsea.

The assembly is supported in the tee frame, which is then attached to the guidewires to help guide the assembly to the trunkline location. Guidewires prevent the assembly from rotating while being lowered to the seabed, assuring the direction of the tap.

The topside crane should be fitted with a heave compensation system that eliminates any heave motions that could affect the final installation of the hot-tap fitting around the pipe.

When the Grouted Tee installation frame reaches the seabed, it locates onto the base frame [Fig. 61 and the bottom section of the Grouted Tee hinges around the base of the trunkline, meeting with the top section. An ROV operated locking pin is then activated to secure the top and bottom sections of the Grouted Tee.

The saddle seal setting mechanism is then activated for the Grouted Tee, or a remotely operated mechanical clamp device that incorporates the tee securing system in the case of the mechanical tee.

For large diameter tie-ins, the combined weight of the Grouted Tee body and tapping equipment may be too heavy for the DSV crane and will require two trips for installation. The connections between the Grouted Tee and the valve, and the valve and tapping machine can be made using ROV-activated collet connectors.

Pressure Testing

The ROV stabs onto the hot-tap fitting. The volume bemeen the branch and the seal of the hot-tap fitting is then pressuretested using the ROV hydraulic supply.

This test also confirms the integrity of the valve connections and the hot-tapping machine. A satisfactory pressure test is essential before performing the actual tapping operation on the trunkline.

Grouting The Fitting

After the saddle seat pressure test, the Grouted Tee is permanently fixed to the trunkline by filling the annular space between the Grouted Tee body and the trunkline with grout. This is undertaken by the following actions:

• The grouting frame is lowered to the Grouted Tee location and located on the base frame and the ROV stabs the supply lines into the Grouted Tee body.
• The grouting system is then operated and this will mix and inject the grout into the annulus.
• When returns are observed at the outlet port, the injection is stopped and the inlet and outlet ports are closed.
• The grouting frame is recovered to the surface and the grout is allowed to cure (24 hours).

Tapping The Trunkline

The hydraulic lines (supply and return) for the tapping machine are connected using the ROV hydraulic supply. The ROV advances the tapping machine cutter by turning a crank a predetermined number of turns. This action first drills a pilot hole in the trunkline, and then cuts the hole in the trunkline. The tapping machines are designed to retain the coupon cut from the trunkline.

Once the tap is made, the cutter (and the coupon) is fully retracted by the ROV turning the crank in the opposite direction, the valve is closed, and the pressure inside the tapping machine is bled off.

De-rigging And Rectification Works

After completing the hot-tap, the tapping machine is disassembled from the valve and returned to the surface in the tee installation frame with the coupon cut from the pipe. The top flange on the valve will then be fitted with a blind flange or the branch tie-in spool can be fitted.

Generally, there will be several other operations performed to complete the hot-- tap fitting installation such as applying splash zone coating on the trunkline where the anti-corrosion coating has been removed and sandbagging any unsupported areas around the hot-tap fitting or valve.

If a protection frame is required, this will be installed onto the base frame guideposts.

Subsea Grouting Systems

Subsea grouting operations have been undertaken for many years for pile installation and for jacket andpipeline repairs. One such application that is almost identical to the Grouted Tee design is the grouted clamp repair connector, which is a common technique for repairing pipelines.

The problems foreseen for subsea grouting are:

• Difficult for large volumes
• Possible problems mixing subsea
• Water displacement of the annulus between the tee body and the trunkline
• Proving of density and strength of the grout after mixing and injection

Challenges Facing Grouted Tee Installation

For any subsea operation using either a welded, mechanical or Grouted Tee fitting, there are several hazards and challenges to be overcome. The challenges that have been identified for hot-tap operations are equipment failure or equipment lost subsea. This could be due to:

• Poor maintenance of equipment
• Human error
• Weather conditions

As water depth increases, probability of equipment fit re or loss will rise due to higher external pressure loadings on equipment and longer control umbilicals. Installation procedures for both types of tee and tie-in configurations are dependent on major equipment such as the vessel crane and ROV.

Crane failure will almost certainly lead to downtime and possibly personnel injury. Equipment can be recovered using auxiliary winches but it is unlikely that equipment will be run using these devices clue to lack of precise control.

The reliability of ROVs has improved considerably and most failures can be repaired by technicians on the vessels. Due to the cost of the equipment, it's unlikely a vessel will carry a backup ROV.

Potential Challenges For Grouted Tee Fittings

The installation of the Grouted Tee will, at the least, involve an additional roundtrip when compared with the bolt-on mechanical fittings, which increases the risks involved with the procedure. The Grouted Tee also requires additional equipment to be sent subsea to mix and inject the grout into the annulus. As the complexity of the operation and equipment increases, so does the risk of some kind of failure.

However, the design of the bolt-on mechanical fitting is more complex than that of the Grouted Tee, which would lead to an increase in the risk of something going wrong with the mechanical fitting itself.

Horizontal vs. Vertical Installation

The procedures and equipment for the installation of a horizontal branch are identical to the vertical tie-in, apart from additional equipment to pull-in the spoolpiece. This additional equipment increases the risk of the operation.

Consequences

The most likely consequences that have been identified from the above hazards are:

• Downtime
• Loss of containment/pollution
• Trunkline shut-in/production downtime
• Crew injury/fatality

As the operations contained within this report are carried out without divers, then the risks to personnel all relate to topside accidents. The most likely cause of crew injury will be due to deck handling of equipment, i.e. rigging and lifting installation frames, etc.

Equipment failure will always lead to operational downtime which has a financial loss associated with it. Dual redundancy for some items can reduce likelihood of downtime, although for major items this is not economic.

As the operation is undertaken on a live or hot pipeline, there will always be risk of pollution through loss of containment. With an oil pipeline there will be the additional cost of a cleanup operation. If the pipeline has to be shut-in, the financial loss due to lost revenue could be many times the original cost of the operation.

Conclusions

The onshore development of the Grouted Tee connection has been successhilly completed. An implementation process is currently being carried out for the National Transmission System which is owned and operated in the UK by Transco.

Offshore development feasibility studies have been completed, and a full-scale testing prograin is scheduled later this year, simulating diverless operation in subsea conditions. The subsea field trial will begin next year.

Sumber : "Method for Hot Tap Connections Capable of Saving Millions". 26 Januari 2014. http://search.proquest.com/docview/197502156?accountid=31562