Construction of LP and HP Heater should be performed as procedure and design. The selection of LP heater materials and method of construction remains with the design although the use of shells with a minimum number of joints, welded tube plate to channel joint, and welded feedwater pipe attachments are preferred. The corrosion resistance of the proposed tube material selection should make due allowance for the oxygen content that may prevail in the LP feedwater, particularly at low load and during start up.
The LP and HP heater should be of the conventional U tube and shell type for which the selection of tube and tube plate material, and their method of attachment should be described. The proposed selection of materials for the tubes, tube plate or header should be in accordance with Code and Standards, provided together with full details of the method of tube attachment.
This selection should be based on service experience with waterside velocities not exceeding previous good service experience. All tubes should be produced from single lengths of tubes and be hydraulically tested to the requirements of ASME standard or equivalent standard.
The bled steam inlets of both the LP and HP heaters should incorporate provisions to prevent erosion, impingement and vibration damage of the tubes by either steam or water. All bled steam and drain inlets should incorporate arrangements to prevent direct impingement of fluid against the tube nest.
The method of attaining access into the channel or headers should be described, to permit inspection and plugging of all tube ends. With divided channel designs, details of the construction and attachment of the dividing wall or chamber to the channel should be provided.
For both the LP and HP surface type heaters, only designs with proven service reliability whilst of similar size and rating should be proposed and reference listings should be made available during the contract.