Piping Fundamentals

The piping system includes pipe, fittings, valves, and speciality components. All piping systems are
engineered to transport fluid or gas safely and reliably from one piece of equipment to another. Piping can be divided as • Small bore lines • Large bore lines As a general practice, those pipelines with nominal diameters 2” (50mm) are characterised as a small bore and preceding that as a large bore. Pipe sizes are on the basis of Diameter and Thickness. In some places, pipe size is designated by two non-dimensional numbers: Nominal Pipe Size (NPS) and schedule (SCH). Some major relationships:

• Nominal pipe size (NPS) is to describe a pipe by name only. Nominal pipe size (NPS) is generally related to the inside diameter (ID) for sizes 1/8” to 12”. For pipe sizes of 14” and beyond, the NPS is equal to the outside diameter (OD) in inches. Outside diameter (OD) and inside diameter (ID), as their names imply, refer to the pipe by their actual outside and inside measurements. The Outside diameter (OD) is the same for a given size irrespective of pipe thickness.

• The schedule belongs to the pipe wall thickness. As the number increases, the wall thickness
increases and the inside diameter (ID) is reduced.

• Nominal Bore (NB) with schedule (wall thickness) is used in British standards classification.
The main purpose of piping design is to configure and lay equipment, piping and other accessories
meeting relevant standards and statutory regulations. The piping design and engineering involve the following six (6) steps:

Selection of pipe materials according to the characteristics of the fluid and operating conditions including maximum pressures and temperatures.

• Finding economical pipe diameter and wall thickness.

• Selection of joints, fittings and components such as flanges, branch connections, extruded tees, nozzle branches etc.

• Developing piping layout and isometrics.

• Performing stress analysis as per the potential upset conditions and an allowance for those upset
conditions in the design of piping systems.

• Estimating material take-off (MTO) leading to material requisition.

The Pipe Material Specification (PMS) is the major document for piping engineers. This document
describes the physical characteristics and specific material attributes of pipe, fittings and manual valves necessary for the needs of both design and procurement. These documents are contractual to the project and those contractors that work under them. A piping specification must contain those components and information that would typically be used from job to job. The following items below provide the primary component report and notes required for a typical piping system. − Pressure/Temperature limit of the Limiting factor for Pressure/Temperature − Pipe material − Fitting type, rating and material − The flange type, rating and material − Gasket type, rating and material − Bolt & nut type and material Manual valves grouped by type − Notes − Branch chart matrix with corrosion adjustment 1.14. DESIGN FACTORS The design factors that affect piping engineering include:

• Fluid Service Categories (Type)

• Flow rate

• Corrosion rate

• Operating Pressure and Temperature All this information is available in the Process Flow Diagrams (PFD’s), Piping and Instrumentation Drawings (P&ID’s) and Piping Material Specification (PMS).