Cool solution avoids shutdown of fertiliser plant

Sabic's Saudi Arabian Fertilizer Company (SAFCO) recently avoided shutting down two plants when Furmanite enabled a valve replacement to take place while the plant remained live.

A faulty three-inch class 1500 gate-valve on the boiler feed water-main header at the fertiliser plant needed replacing.

The faulty gate valve, located on the main six-inch control-valve bypass line, was passing and causing considerable disturbance to the feed water flow to the boiler, creating difficulties.

The faulty valve needed to be replaced to maintain a steady flow and enable the six-inch control valve to operate smoothly.

Two plants would have needed to be shut down to depressurise and drain the main feed water header to allow the valve replacement to take place.

Furmanite selected pipe freezing to isolate the line and facilitate the valve replacement, due to the limited access around the pipework and to avoid intervention into the line.

Furmanite applied its cryogenic pipe freezing expertise to freeze the boiler feed water content in the six-inch line, at an operating pressure of 56 bar, using liquid-nitrogen boiling off to atmosphere at -196C in a purpose-designed pipe-freezing jacket installed around the pipe.

The line content forms a solid plug under pressurised line conditions, stopping flow temporarily and providing a safe and effective method of isolation.

In this case, because the line was branching directly from the main header running at 120C, a double freeze was used, with the first acting as a cooling barrier to reduce the effect of the thermal flow between the header and the isolated branch.

After achieving the plug formation, integrity tests were carried out to ensure that the plug was solid and firmly in position.

Once this was confirmed, permission was given to the maintenance team to break the valve flanges and replace the valve.

The line was then brought back to normal in a controlled process to ensure smooth thawing of the plug without disturbing the line operation.

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