Leak-free start-up
23 Feb 2005
Ensuring the integrity of critical flanges and joints on a process plant is a prerequisite of safe and profitable operation — or, at least, it should be.
According to figures from the UK Offshore Operators Association (UKOOA), some 25% of critical joints leak on start-up.
Tony Nicholls, md of engineering service company Furmanite, also says that research has shown that 10% of hydrocarbon leaks offshore have been attributed to leaking flanged/bolted joints.
'Incorrect bolt loads, inappropriate gaskets, flange distortion and uncontrolled bolt tightening (often down to lack of training or competence) are the main reasons for joint leaks,' he says.
To address these problems, Furmanite is now introducing a new Pressurised Systems Integrity (PSI) Management service. A 'fully engineered service' that addresses all the factors known to cause joint leaks, PSI Management manages every stage — from engineering analysis of the joint, unbolting, inspection and machining as required, to gasket installation, assembly, and controlled bolting — all with full electronic documentation.
But what sets PSI apart from other joint management services is Furmanite's guarantee of a leak-free start-up — the recognised 'danger period' for leaking joints. The length of the guarantee (that the plant will not have to be shut down because of a critical joint failure) is governed by negotiations with the client, but effectively it covers the duration of all recognised plant start-up procedures.
To achieve this level of performance, the PSI process starts with a pre-engineering site programme, involving identification of critical flanges (including risk assessment) and engineering analysis of these joints, well in advance of the planned outage in the case of maintenance shutdowns.
'We like to be involved at the flange break-out stage,' says Nicholls, 'as we can learn a lot from that.' All the information gathered from these inspections — including analysis of the flange design, surface finish, bolt type, materials, bolt loadings and gaskets — results in documented recommendations that incorporate all the relevant data for each critical flange.
Only those joints requiring attention need then be worked on at shutdown, saving valuable time. 'This early stage is vital,' emphasises Nicholls, 'and helps to minimise time demands and work pressures and avoid delays during the outage.'
Once the work requirements for each critical joint have been identified, a flange-tagging system is implemented. Using a series of colour-coded tags attached to each joint, this provides an immediate indication of the status of each joint, as the tags are updated to reflect the relevant stages as the work is carried out.
But importantly, apart from this physical indication, this information is simultaneously recorded online into the PSI Management system.The bespoke software system offers real-time reporting that can be accessed and interrogated remotely by the client's engineers.
The html-based system carries all the relevant mechanical and work status data for every joint. Accessible at any time during and after shutdown without having to be on site, this aspect of the system provides the client with a complete overview of the outage work scope status and progress.
Work carried out under the PSI Management programme will typically include ensuring an appropriate surface finish, flatness and condition of the existing gasket face, and remachining to achieve this as required. It may also include installing a new gasket, followed by flange alignment and controlled bolt tightening to the determined load using hydraulic tensioning or torquing.
Specialist techniques available include hot bolting, removal and replacement of damaged fasteners and bolt stress measuring (mechanical and ultrasonic). Full engineering support, including CAD systems, is available to provide tightening, torquing and tensioning procedures and bolting patterns for any size and range of flange.
Furmanite technicians who carry out the work are fully certified, externally accredited to UKOOA standards and guidelines, and work within the remit of ISO 9000, ensuring that issues of 'adequate training and competent personnel' as highlighted by the HSE are fully addressed.
As the work proceeds, a full and detailed history of each critical joint is built up. This provides a comprehensive record that is easily accessed, incorporating all relevant information from mechanical data to work history for full traceability.
Moreover, following a shutdown the data can be accessed for future maintenance planning, helping to eliminate disruption while the plant is in operation and enabling the next scheduled shutdown to be handled that much more efficiently.
Typical of the scope of operation of the PSI Management service was a recent shutdown project for Western Mining Corporation at a fertiliser plant in Australia.
Over a 20-day period, Furmanite removed, overhauled and reinstalled 970 critical flanges, including work on steam traps, gate and globe valves, components in the syngas and turbine compressor and refrigeration skid, PSV valves and all critical joints — and all achieved with a zero leak start-up.
