2.1.2 Tube Pitch and Layout. The selection of tube pitch is a compromise between a close pitch (small values of p /di) for increased shell-side heat transfer and surface compactness. and an open pitch (large values of pr/d) for decreased shell-side plugging and ease in shell-side cleaning. In most shell-and-tube exchangers. the ratio of the tube pitch to tube outside diameter varies froni 1.25 to 2.00. The minimum value is restricted to 1.25 because the tubesheet ligament may become too weak for proper rolling of the tubes and cause leaky joints. The recommended ligament width depends on the tube diameter and pitch: the values are provided by TEMA (1999).