Flowline Design

Flowline piping on offshore platforms is a meticulous and intricate endeavor, primarily due to a combination of factors. These factors include the need to manage high-pressure systems, cope with limited space constraints, adhere to strict regulatory timelines, and meet client demands for the successful initiation of gas production. Achieving precision in flowline piping is essential, as there is little room for error in this critical aspect of offshore operations.

Here are the factors that Piping designers should consider:

Wellhead and X-mas Tree

A Christmas Tree is an assembly of valves, spools, and fittings used for an oil well, gas well, water injection well, water disposal well, gas injection well, condensate, and other types of wells. It is named for its resemblance to a decorated tree at Christmas. ¹

When formulating a flowline design, it’s crucial to account for the wellhead’s motion. The wellhead displacement may involve an upward expansion of as much as 100mm and a downward contraction of up to 50mm, with a typical horizontal shift of 25mm. It is of utmost importance to validate these displacements through stress calculations and incorporate them into the design.

This information can be acquired and confirmed through consultation with the client.

The most common flowline connection to the X-mas Tree is achieved using a 4.1/16″ 16K# (equivalent to 6″ pipe) API6A flange. Here are the other size,

Elbow, Bends, or Target Tee

The presence of sand in the product can create problems due to its abrasive nature, leading to the gradual erosion of the pipe wall thickness, especially at locations like elbows where the flow direction changes. It’s prudent to obtain this information from the client.

If sand is confirmed to be present, using a target tee is a recommended solution, as it effectively mitigates the issue by preventing the sand from gaining excessive velocity and causing damage to the pipeline. The sand builds up in the target tee and absorbs the impact.² Alternatively, bends can be considered, but they often require a significant amount of space.

Flanges and Hubs

Pipe fittings, valves, and flanges are produced by various industry standards, including API, ASTM, and ANSI/ASME. f its material composition, specification, and grade, along with a traceable link to the source foundry.³ This information can be also found in pipe specifications available by the client

Hub and clamp can be also a good choice as it is lighter and smaller than ASME B16.5 flanges, reduced downtime, fewer bolt to install, leak-free and economical solution⁴

Typical Wellhead Flowline Piping Design

The layout should be as flexible as possible but make all operational items such as valves and instruments reachable. Material handling of the valve should considered and put in the design by adding a lifting lug or the possibility of a beam clamp.

During the construction phase, all flowlines are installed in pre-shutdown except for the closing spool to minimize downtime. To get the right dimension of the closing spool, a scan is made and the closing spool is adjusted as per the scan.

Reference:

1. Christmas Tree or Wellhead? https://www.croftsystems.net/oil-gas-blog/the-difference-between-a-wellhead-christmas-tree/ ↩︎
2. Flowlines, Piping, and gathering systems; https://ocw.snu.ac.kr/ ↩︎
3. Petrowiki, Pipeline design consideration and standards; https://petrowiki.spe.org ↩︎
4. What is a Hub and Clamp Connector? https://www.aspireenergy.com/ ↩︎