SHUTDOWN of two plants was avoided for Sabic’s Saudi Arabian Fertiliser Company (Safco), when pipe freezing expertise from specialist technical and engineering services company 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 replacement. Located on the main six inch control valve by-pass line, the faulty gate valve was passing, and causing considerable disturbance to the feed water flow to the boiler creating operational difficulties. The faulty valve needed to be replaced to maintain a steady flow and enable the six inch control valve to operate smoothly.
To depressurise and drain the main feed water header to allow the valve replacement to take place would have involved full shutdown of two plants, at considerable cost. Instead, Furmanite was called in to help, with a solution to allow the valve to be replaced without shutdown.
Pipe freezing was selected as the preferred method 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 -196 degree C in a purpose-designed pipe freezing jacket installed around the pipe. The line content thereby 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 120 degree C, 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 successfully 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 strictly controlled process to ensure smooth thawing of the plug without causing any disturbance to the line operation.
Furmanite Middle East general manager Graham McKay comments: “The project involved a number of challenges. Among them was the complex pipework configuration at the freezing point locations, as sound pipe with no bends or welds is required for pipe freezing. The tightly restricted space also meant ventilation had to be carefully considered. These and other aspects were thoroughly investigated and studied with Safco as part of the job safety analysis carried out before the job went ahead. The work was successfully carried out by highly qualified Furmanite technicians in line with Furmanite’s high quality and safety standards, with full engineering support.”
Following completion of the project, Safco carried out pipe inspections at the two freezing locations to confirm line integrity. All the pipe’s mechanical properties were found to be normal.
McKay adds: “Pipe freezing, like our hot tapping and line stopping service, is a highly efficient and cost-effective means of achieving a temporary isolation without interrupting production. It is one of a range of services we offer to help operators keep their assets operating and earning.”