Reel lay method installs offshore pipeline by sending the pipeline from a reel mounted on a special pipeline installation vessel. Instead of connecting each joint of pipe line at an offshore location like other methods (S-lay and J-lay method), the pipeline is pre-assembled in a spool which is mounted on the deck of the reel barge. This method can lay pipe up to 16” diameter and water depth capacity for 16” pipeline is about 800 m (2,600 ft). This method cannot lay such a big size pipe because the big pipeline is not flexible enough to be rolled into a reel.
The reels can be installed either horizontal or vertical. Horizontal reel barges can do only S-lay installation; however, vertical reel barges can perform both J-lay and S-lay pipeline installation.
The reel lay method is considered to be the fastest laying method because the majority of welding and inspections are performed onshore in order to minimize time for installation. Once all pipe on the reel is laid, the barge either head back to shore of another reel or lift a new reel from a supply boat. This is dependent of each vessel.
Some of the images of reel lay barges are shown below;
Figure 1 – Vertical reel-lay barge in S-lay configuration
J-Lay pipeline installation method is frequently used in deep water pipeline installation. The curvature of pipe line is similar to J shape (Figure 1) while the subsea pipeline is being installed. J-Lay method can handle a full range of pipeline size and it is particularly suitable for deep water pipeline installation up to 2,000 m (6,560 ft). Furthermore, the J-Lay method can withstand higher underwater current and sea state than the S-Lay method.
The J-lay method puts less stress on the pipe line because the pipeline is installed in an almost vertical position. Whereas the S-lay method puts on more stress due to two curvatures at the sag bend and over-bend region. The pipeline is sent into water at a small angle reference to a vertical line and continues at a steep angle until a sag bend is formed.
Figure 1- J-Lay pipeline vessel
This works very well in deep water environment where distance from a vessel to a touchdown point is quite far because sag bend is not too much. If the short distance from a vessel to a touchdown point. Continue reading
Collapse happens when differential between external and internal pressure exceeds a collapse rating pressure of material. This situation can happen due to several cases, such as pressure testing in annulus, trapped pressure in the annulus or well fully evacuated with gas, etc.
Figure 1 – Collapse Pressure Diagram
Collapse pressure equations come from experiments from test specimens and the full details can be found in API Bulleting 5C3, Formulas and Calculations for Casing, Tubing, Drillpipe, and Line Pipe Properties. From the experimental results, there are 4 collapse regimes based on Diameter of pipe/Wall thickness (D/t) and yield strength of material which are yield strength collapse, plastic collapse, transitional collapse and elastic collapse. Continue reading
Burst is a condition where internal pressure exceeds pressure loading. Burst can happen in several situations, such as well control, pressure test casing/tubing, pumping operation, etc.
Figure 1 – Burst Pressure Diagram
Minimum burst rating pressure (internal yield pressure) can be calculated by the following equation.
Oil field tubular is typically designed to work under its minimum yield strength so it means that the tubular will work with tensile load within the elastic limit. This article will discuss about tensile properties and how to determine tensile of oilfield tubular.