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Removal and Reinstatement of Pipe Stack

In the last year we have completed a unique world-first project which involved the destruct and reinstatement of a submerged cargo pump pipe stack while an FPSO was on-station and operational.  

Our team was first approached about the project by an oil operator early 2019. The client, third party inspection resources and our team of specialists, initially undertook an inspection in its off-spec tank No.4 (OST 4C). It was then we identified several cracked support brackets along the length of the pipe stack.  

Upon further inspection, it was discovered a foreign object had been trapped in the submerged cargo pump impeller. This had caused the pipe stack to vibrate, resulting in the bracket failures.  Subsequent checks and tests of the pipe stack’s integrity further confirmed damage to the pipe stack structure. 

The Solution

After extensive discussions with the client, we identified a feasible solution. We agreed to destruct the existing pipe stack and reinstate a new one, on-station and in operation. 

This was challenging for several reasons; most pipe stacks are installed while an FPSO is in dry dock. They are also normally installed in long lengths of flanged pipework sections of eight metres or greater (a pipe stack can be upwards of 20 metres in total from top to bottom). 

We devised, and trialled, several different methodologies for cutting the existing pipe stack into smaller lengths. Once the preferred method was established, we planned the project meticulously and refined the process of cleaning and destructing the existing pipe stack. Our team chose to use cold work cutting methods to allow for removal in shorter sections.  We then engineered the appropriate methods and sequences to install the new pipe stack sections from within the tank. 

Our engineers and naval architects designed and manufactured bespoke equipment to enhance the execution of the required work. The equipment included bespoke pipe stack trolleys to improve handling of the new pipe stack sections along the main deck. We then lowered it into the tank.  This equipment ensured the new pipe stack could be carefully manoeuvred around the congested deck without risk of damage.   

Height Restrictions

Another challenge for us was the height restrictions above the original pipe stack deck. This meant a traditional installation of the new pipe stack through the main deck trunk opening was not possible. 

We designed and manufactured a bespoke support trunk which was installed to the uppermost stringer of the tank.  This equipment allowed the installation to follow the intent of traditional methods, but was delivered predominately from within the tank, rather than externally.  

Once installed, the new pump head was connected, and the new pipe stack was recommissioned in accordance with the manufacturer’s procedures.  Due to the meticulous planning, engineering and care taken during installation, the new pipe stack passed all integrity checks during commissioning.  

The project took six of our specialists two months to complete, with several months of process driven planning and preparation before offshore project commencement.  

Going Over and Above

While onboard our team were also called upon to help with another project which involved the FPSO export hose. The team were more than happy to help, with no additional cost to the client. This just goes further to show that our team consistently deliver professional, high-quality services with dedication and a desire to do a good job.