There are circumstances when working on pipelines while they remain in use is unavoidable. Needless to say it is always a hazardous operation, but especially so when the pipe is conveying highly inflammable petrochemicals.
Corrosion and accidental damage are always likely at some point – however rugged the original installation may have been. But frequently maintaining supplies is critical too. In other cases, there may simply be no way of diverting or suspending the flow – in fact, a common reason for a hot-tap is to install an isolation valve.
The success and safety of hot taps is usually critical for the safety of the crew and the wider environment. Consequently, equipment manufacturers are motivated to work with their industrial customers to constantly improve the tapping machines and the procedures for using them, (see this recent success story https://www.petroleumafrica.com/subsea-7s-new-hot-tap-technology-a-success/).
Before using tapping machines
Safety first is always the rule. Procedures must be scrupulously adhered to and the crews thoroughly trained. In parts of the world where multinationals operate alongside underprivileged communities, illegal tapping devastates the environment making the inequality worse.
After training, comes contingency planning, followed by suitability testing of the proposed hot-tap location. This must be in good condition and metal thickness established using an ultrasonic thickness gauge. The quality and condition of the hot tap machine must also be guaranteed: UK tapping machines are known to be some of the best.
Performing a hot tap
The three main components of a hot tap are the pipe fitting, the isolation valve and the hot tap machine itself. The fitting and valve are attached first, usually by welding into place, and pressurisation checked.
The design of the fitting is very important and so is the quality of their construction. The quality of welds should be non-destructively tested.
The hot tap is then performed in one continuous operation. The section of pipe, called the “coupon”, is captured if possible by retaining guide-wires on the cutter. The cutter can then be retracted back into the adaptor and the valve closed. Once the pressure has been safely released the cutter can be removed and the new flow established.
Despite the apparent dangers, accidents during professional hot tap operations are almost unheard of. In parts of the world where illegal tapping poses serious problems the solution needs to be social and economic, not technological.