In Process Repair of Leaking Cooling Water Pipe work

Alcan Primary Metals - Europe

Chemco International were requested the Senior Mechanical Engineer at Alcan Primary Metal Europe to provide a repair system that would not require a process shut down to a leaking section of 60" (1500mm) diameter of their main cooling water pipe work. The pipe work carries seawater, which is used for cooling on the main condensers. The problem was a through perforation emanating from the internal to the external, close to both the V J coupling and the pipe flange adjacent to a butterfly valve. Photo 1 shows the extent of the leakage and the difficulties in accessing the leak whilst under load. It was explained to Chemco the importance of carrying out this repair whilst on load, isolation of this section of pipe work would result in the station having to shut down one of the generation units with considerable loss of revenue.

Alcan had attempted a temporary arrest of the flow by wedging techniques to the damaged area, whilst this gave support to the pipe work it did not reduce the rate of leakage. In conjunction with Alcan, Chemco carried out an inspection to assess the safety implications, feasibility and techniques to be employed in this critical situation. The decision was taken to manufacture a split clamping ring, designed to fit between the VJ coupling screwed adjustment rods and the flange bolts, the ring was fabricated from carbon steel, with gusset plates welded to the half split flanges to take up the pressure required to effect a seal. The ring was shipped to Chemco for surface preparation and subsequent application of a 10/12 mm thick flexible Epoxy Silicone sealing compound, developed by their R&D department, this was locally reinforced with grp multidirectional matting. The grp was introduced as a means of not only adding strength but also to give erosion resistance to the patched area both during the fitting operation when water jetting would take place and during service.

Following clean up of the site and final inspection by Chemco, Alcan staff. Risk assessment, COSHH assessments, and methods statements were submitted to and approved by Alcan prior to on-site fitting of the ring, this was loosely positioned prior to removal of the temporary wedging, it was then evident that the hole in the pipe was within 50mm of the back face of the flange and very close to the flange bolts. Compression of the flexible sealant was carried out with some difficulty this being due to a combination of water pressure increase as the area of damage was reduced by the clamp ring being secured and limited access, leakage was reduced to a few drops per minute. Jacks used to support the ring during installation were left in place during the application of Chemco RA500 solvent free epoxy laminating resin, developed for application in wet conditions this was used in conjunction with a layer of heavy duty laminate to ensure a full seal and add strength to both the pipe and clamping ring. Following overnight cure a second application of the reinforcement was carried out. See photo 2, which shows the successful sealing of the leak.

The contract was carried out in a safe and efficient manner, within budget and programme. The input from Alcan staff assisted in leading to the satisfactory conclusion of the project.

 Recommendations:

In the event of requiring a similar repair to be carried out discussions as to modification of the clamp ring design, prior identification by Alcan of the defect position would be of considerable benefit to both companies.

From our company’s experience within industries utilising the use of seawater it is our opinion that the correct selection of coating material is imperative to full corrosion protection. Chemco would strongly recommend that an independent inspection of the cooling water system be carried out prior to application of any further corrosion protection. We would consider that the mode of failure experienced can be fully eliminated by adopting a very rigid programme of inspection, correct material selection, surface preparation and application by a specialist coating contractor.

Chemco International would wish to meet with you to discuss any point raised, from the carrying out of the above contract to the solving of potentially what could be an on going problem, we are pleased to have been of service to Alcan and look forward to being of assistance in the future.

For further information contact the Engineer Responsible – Alan Hortin – alanhortin@chemcoint.com

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