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Are you using bulkhead unions/coupling joints for your pipe penetrations?

3 reasons why you should consider changing.

The industry is moving away from traditional bulkhead unions or coupling joints and starting to use other systems to protect metal pipes passing through fire rated or watertight divisions. Here is why.

1. Increased weight per penetration

Both non-approved, standard and traditional bulkhead connections and type approved or certified bulkhead unions, tested for use in marine and offshore structures are heavy.

Accepted traditional bulkhead unions are often a 900mm length of steel pipe attached via a coupling on each side to the thin walled metal pipe used for the pipe system. In addition to the weight of the pipe, each bulkhead union attracts additional weight: 

  • 900mm length of thick walled steel pipe
  • 2 x coupling joints (one for each side)

Approved bulkhead unions are shorter and thicker, but still heavy. When extrapolating the weight increases over thousands of installations, the weight impact becomes significant.


Learn more about installation time for bulkhead unions in this comparison video or read a comparison analysis on metal pipe seals.

2. Time-consuming installation process

Due to the two-sided nature of bulkhead unions, the installation time is double the already significant time required for one connection. It can also be hard to access both sides of any installation.

Multiple installation steps are required for each side of every penetration:

  • Weld the pre-prepared 900mm length of steel pipe (or an approved shorter bulkhead union), which includes the union connection joints.
    — Many shipyards manufacture connection joints (bulkhead unions) themselves out of scrap material believing it is cost-effective, but the man hours required are more significant than expected.
    — Holding in place and welding a 900mm length of large steel pipe normally requires a more costly two-man installation. 
  • Cut the pipe. Deburr and clean the rough edges.
  • Clean the outside of the cut pipe.
  • Place the union nut and the cutting ring onto the cut pipe.
  • Tighten the union nuts to form the seal.
  • Move to the other side of the structure – and repeat. 

When you include fabrication and repeated cutting, cleaning, welding and movement from one side of every division to the other, the total installation time increases to become a costly issue. 

3. Negative impact on integrity and increasing number of joints

The pipe material selection is fundamental to the long-term performance of the piping system. Cutting the pipe of choice and connecting it to a bulkhead union is compromising the integrity, quality and performance level at every penetration. 

When the material is transitioned to an inferior steel length of scrap material or a shorter length of carbon steel, all the positive reasons why it was selected become irrelevant. The transition pieces introduce stress points and become corrosion risk hot spots scattered throughout the piping system.  

Every connection or joint is a potential weak point in the system, introducing extra cavities and ridges inside the piping system where bacteria and corrosion can form and occur. Joints are risk points for drips and leaks, and the foreign bodies can create blockages and corrosion zones inside the pipe, which lead to increased maintenance issues and repair costs.