Why is it necessary to maintain the minimum distance of header to NOWL?

Maintaining the minimum distance of the header to the normal operating water level (NOWL) is crucial primarily to ensure the delivery of dry steam to the main. The header's position influences the gravitational pull on the water in the system, particularly in steam systems where the water and steam are separated. If the header is too close to the NOWL, there may be a risk of water carryover, where liquid water gets entrained with the steam. This can lead to wet steam, which is not only less efficient but may cause operational issues such as water hammer, increased corrosion, and pressure fluctuations within the system.

Ensuring that the header is at an adequate height above the NOWL mitigates these risks by allowing for a proper steam-slugging distance, optimizing steam quality, and enhancing system efficiency. This principle is critical in steamfitting design as it directly affects the performance and reliability of the entire steam distribution system. Therefore, maintaining this distance ensures that the steam reaching the main remains as dry as possible, allowing for better thermal transfer and system operation.