There are many reasons why in-situ machining of wellhead components is required. They normally fall into one of three categories: it could be part of a preventative maintenance programme, when corrective action is needed, or if recovering the wellhead as part of a decommissioning project.
Valves and actuators used in a wellhead Christmas tree can fail through seizure and breakage, often caused by a lack of suitable lubrication and long periods of non-operation. Additionally, corrosion and erosion problems arise over a period of time, with hydrocarbons causing issues inside the valves and external components being either sand blasted by the wind, or exposed to corrosive salt-water.
So what portable machining equipment is available to help the on-site team commissioned to solve these problems?
Below, we’ve listed 9 essential machines we think every wellhead engineer should know about.
Split Frame Cutter
Mirage split frame clamshell cutters are available to cut diameters from as little as 2” up to 48”. As the name suggests, the machine assembly comprises of 2 main sections, which enable the machine to be assembled around the work piece. The Mirage split frame cutter range are used regularly for cutting, bevelling and counter boring pipe sections with accuracy, but can also be used to cut through heavy wall valve casings with a thickness as large as 90mm.
Flange Facing Machine
For flange connections where leakage occurs, it likely that the flange surfaces will need to be re-machined. A flange facing machine can be used on site to product a phonographic/spiral groove surface finish meeting the required ASME specifications. Machine options include external or internal mount versions to suit different situations, and kits to machine RTJ and BX ring grooves.
The heavy duty band saws in the Mirage range are frequently used for either surface or subsea applications, to sever conductors, caissons and multiple grouted strings of various sizes. If a rough cut of this type is sufficient, (for example in a decommissioning project) the band saw would be a suitable product capable of cutting through an inactive wellhead Christmas tree.
Diamond Wire Saw
The diamond wire saw is another option to consider, especially for subsea decommissioning projects. These machines can be operated by an ROV and if needed, can be used with buoyancy modules.
Single and Double Drill Units
These can be used to drill, pin and lift large components needing removal. The casing pin double drill unit (DDU) allows simultaneous drilling from 2 sides for the creation of lifting holes. The single drill unit (SDU) is an innovative tool which uses a cutter which remains in the job, to act as a lifting pin.
Bolt Slitting Saw
If bolts in a wellhead assembly cannot be loosened, the bolt slitting sawprovides an efficient solution. It works by clamping around the flange diameter and inserts a rotating blade into the gap between the two flanges. After each bolt is cut, the unit is simply rotated around the diameter and clamped into position for the next one.
Valve Hot Tapping Machine
The VHT965-4000is a variation on the standard hot tapping machine and is adapted for the purposes of drilling through items such as seized slab gate valves.
VHT 200 - 500 Hot Tapping Machine for relief pressure
These are a range of hot tapping machines rated to 10,000 psi for drilling relief pressure in wellheads. The modular design enables the machine to drill from ½” to 2” holes to relieve trapped pressure. The Compact design enables the machine to fit into confined spaces and is pressure balanced for ease of use.
External Threading Machine
This is a specialist external threading machine that was developed to enable wellhead refurbishment to take place.
One customer needed to work on 9-5/8” casing, which required cutting and extending by re-threading in situ. The machine made it possible to create a tapered buttress thread with an Api profile.
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