18"x12" Subsea Mechanical Clamp, Valve and SureTap Hot Tap Machine
STATS were contracted by a global engineering and construction company to provide a subsea mechanical clamp and hot tapping services in the Bass Strait, offshore Australia. The 18” clamp incorporated a 12” offtake to provide a tie-in point to allow a new gas field to be brought online and fed into the existing 18” gas pipeline.
STATS designed and manufactured a mechanical clamp based on the pipeline parameters and to the client's exact specification. The 18” clamp was designed to class 900 with the 12” branch was designed to class 1500. Following manufacture, STATS conducted a full client witnessed Factory Acceptance Test (FAT) programme on both the mechanical clamp and hot tap machine at their headquarters in Kintore, Aberdeenshire.
The FAT was conducted using STATS live remote monitoring system, which offers a unique opportunity for clients to witness an FAT without the need to attend their facilities in person. The remote monitoring system is a collection of live feeds from cameras and other devices, all brought together in a centralised and secure web console. The FAT was carried out and captured using high-definition video, real-time voice communication and file sharing to allow two-way communications and interaction between client personnel and STATS on-site team throughout testing. This system was particularly beneficial to the client who was based in Australia, due to travel restrictions in place due to the COVID pandemic. Post pandemic, the remote monitoring system will provide significant savings in travel and accommodation costs and time out of the office. In addition, this approach allows clients to reduce their carbon footprint and therefore help to protect the environment.
Upon successful completion of all FAT operations and procedures, the equipment was mobilised to Victoria, Australia where diver familiarisation training was conducted prior to mobilisation. With the vessel and equipment at location in the Bass Strait, divers began preparation works at the tie-in point to dredge the pipeline and remove marine growth. A hot tap skid was then overboarded and positioned in the trench next to the pipeline. A hot tap assembly including STATS SureTap hot tap machine, valve and mechanical clamp, which was pre-assembled and rigged onto the frame, was overboarded and lowered onto guideposts on the hot tap skid. Once positioned next to the pipeline, the hot tap machine was angled by 3 degrees and rigged onto the pipeline. The clamp was then hydraulically activated, closing the two halves of the clamp around the pipeline and bolted together.
STATS mechanical clamp design incorporates dual seals and locks, the locks are mounted outside the pressure boundary which positions the locks away from the pipeline contents and provides optimal loading to the pipeline. Clamp seal compression flanges were then actuated to set the seals which are energised against the pipewall without setting the clamp locks. This allows a pressure test of the seal annulus cavity to be carried out, confirming that the seals are leak-tight and the pressure boundary sound. Once the seal test is confirmed the locks are then set, each lock segment is independently activated to ensure each lock fully engages onto the pipewall. A feature that is particularly beneficial on pipelines that are oval, ensuring full lock engagement. A final seal test ensured the clamp integrity prior to hot tapping into the pipeline.
A leak-test of the clamp against the closed valve was successfully conducted, this allowed the pressure to be equalised from the hot tap machine and the valve was opened. The hot tap cutter was manually fed by diver against the pipewall before the divers returned to the dive bell. The hot tapping operation was then conducted while the 18” pipeline remained at 72.5 barg, the cut pipe coupon was retracted with the hot tap cutter and the 12” valve was closed. With hot tapping completed the hot machine was unbolted from the valve and removed from the water with the deployment frame. A short pipe spool was lowered and positioned onto the subsea skid before being rigged and bolded onto the 12” valve providing the new tie-in point for the 6 kilometre flowline.
Gareth Campbell, Regional Manager for Asia Pacific at STATS Group, said: “The subsea tie-in was safely completed without incident and the successful project is testament to the teamwork and good communication between all parties.”