Triangle Oilfield Services

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Services > Flow line Construction Services

Since the year 2000 and with the state of the art equipment, Triangle Oilfield Services has constructed, pressure tested and completed in excess of 2600 kms in threaded flowlines. Although not often utilized, threaded and coupled connections provide

an alternative with significant benefits in terms of hardware costs, installation cost and improvement in schedule flexibility.

Pipeline and flowline engineers have a preference for welding and a distrust of mechanical connections. Conversely, drilling engineers are confident with threaded connections but have a concern with welding, which are often perceived as brittle and full of defects. These preferences often stem from experience in that engineers tend to stick to what they know and what worked well last time.

The primary concern with the use of threaded connections for dynamic applications is the introduction of leak paths, reducing the reliability of the system. However, there is strong evidence from suppliers and industry databases to show that threaded connections have the same or better leak reliability compared with welded connections.

The SINTEF, Reliability of Well Completions database noted that 182 leak failures were recorded from approximately 2390 Km of tubing and 4315 years of service experience (10.3E + 06 Km-years). This equates to a loss of containment of 8.07E-06 [3].The equivalent loss of containment from welded pipelines is observed to be 1.00E-04,

from 48 leaks occurring during 127.850 Km-years, as defined by UKOOA/HSE [3].

This shows that threaded connector reliability (tubing) is equivalent to, or better than, the welded pipeline. It is appreciated that both applications are primarily static and that under dynamic loading higher leak rates could be expected for both methods of construction.

Under dynamic applications weld performance is complex and dependent on local material properties and the size, shape and location of defects.

Threaded connections which do not require welding are more predicable with fatigue performance, dependent on the properties of the base material. However both connections methods require strict quality control procedures.

Threaded and coupled connections are made up with high levels of torque, and no completion of the make up, the immediate breakout torque is commonly seen to be 10-20% higher than the make up torque. This improves with time as thread lubrications are squeezed out of the mating faces and after a number of days the breakout torque can be 40-50% greater than the make up torque, indicating that there is no possibility of back off occurring, during service since in service there is no way for high torques to be generated.

Benefits of Threaded and Coupled Connections

Threaded and coupled connections tubing or casing connections as they are often referred to, are a cost effective method of joining pipes together. There are a

large number of threaded connector designs available on the market, many of which are proprietary.

Faster make -up speed compared to welding
Threaded connections can be made up in 2-5 minutes compared to 30-50 minutes for a typical weld and inspection procedure for a fatigue sensitive application. An average of one (1) Km per day is achieved with threaded connections, if not more in smaller size pipe.
Use of special application make up equipment
The special application make up equipment are specifically designed to efficiently handle and install threaded connections. Experienced crews are readily available and procedures and tooling are established.
Application of high strength steels
As discussed previously, non-welded construction allows the use of high strength steel.
Improved fatigue performance
Qualification testing of threaded couplings shows that the fatigue performance is comparable or even better than what can be achieved with a good quality single sided weld.
Cost
The cost of pipe machined with threaded and coupled connections is greater than that of plain ended pipe. However, it is noted that the steel cost is a small proportion of the total system cost and also that with threaded connections the cost saving is achieved through installation.

When the individual benefits described above are considered collectively in a systems approach, the impact on flow line cost and performance can provide significant improvement. Essentially, it is the fact that threaded and coupled connectors enables the installation of flow lines 5 times faster than the equivalent welded construction installation.