• MUX 101 series: What’s a subsea BOP pod?

    The subsea pods control the valves on the BOP stack, and are designed for redundancy.

    The Lower Marine Riser Package (LMRP), which sits on top of the lower Blow Out Preventer (BOP) stack contains redundant pods (see Figure 1). These redundant pods are referred to as blue pod and yellow pod.

    Figure 1: LMRP with subsea pod.

    One pod is selected from the surface as the active pod. Each pod has its own separate umbilical cable connection to the surface. The umbilical cable provides power from the surface to the subsea pod electronics as well as communication links between the surface control system and the subsea pod. Each umbilical cable is attached to the outside of the riser string, running the entire depth between the surface drilling vessel and the subsea stack.

    Components of the pod

    Figure 2: GE/Hydril subsea pod.

    The GE / Hydril pod is made up with an upper electronics section and a lower hydraulics section (see Figure 2). The lower hydraulics section (Figure 2 yellow arrow) contains the subsea valve control manifold and pod flow meter.

    The upper electronics section (Figure 2 red arrow) contains the one atmosphere dome, which protects the subsea electronics modules (SEMs) from the harsh subsea elements. The upper electronics section also contains the transformers, which convert the power supplied from the surface into a power scheme suitable for the subsea electronics.

    The solenoids and pressure transducers are also mounted on the upper electronics section of the subsea pod.

    The SEMs (not SEMS)

    The GE / Hydril subsea pod contains redundant SEMs within the one atmosphere dome (see Figure 3). The redundant SEMs are referred to as SEM A (Figure 3 upper section) and SEM B (Figure 3 lower section). Each SEM is comprised of an off the shelf single board computer, off the shelf analog & digital I/O cards and custom made interface boards.

    Figure 3: One Atmosphere Dome removed showing SEM A (upper) and SEM B (lower).

    Only one SEM within each pod is selected from the surface as the master SEM. The master SEM is responsible for activating and de-activating solenoids based on function commands received from the surface.

    The master SEM also is responsible for sending all the monitored sensor readings such as pressure and temperature up to the surface for viewing by drilling operators. The non-master SEM is referred to as the standby SEM and communication is constantly maintained with this SEM to ensure good communications are present in case it is needed to become the master SEM. Each SEM has its own separate communication link to the surface.

    Therefore with two pods and four SEMs, the system can suffer failures on three SEMs and still maintain control of the subsea stack via the remaining fourth SEM. The multiple level of redundancy is needed as these SEMs could be up to 12,500 feet below the surface of the water. That means several days of pulling the stack back to the surface, correcting the failure and sending the stack back down.

    In the next discussion we will begin looking at the surface MUX BOP control system.


     Eric Milne is a principal engineer for the Systems and Controls division of WEST Engineering Services, a member of the Lloyd’s Register Group.  He has more than 20 years experience with systems and controls in various industries, most recently with BOP MUX at Hydril/Tenaris/GE. Have a question or suggestion for future topic for Eric? Leave us a comment below.

    Posted in Blogs, HSE and Process Management
    1 Comment
    Tags: , , , , , ,

One Response to “MUX 101 series: What’s a subsea BOP pod?”

  1. Amandeep Singh Kalra says:

    Dear Eric,

    I read your article above and it was quite informative. I am a first year MBA student currently working on a consulting project underwritten by client. The focus of this project is understand the current trends of SEMs.

    Will it be possible to connect with you over email and discuss with you some topics that I am currently researching on ?

    Regards,
    Aman
    520 450 3461

Leave a Reply