Industrial equipment

PN stands for nominal pressure, in bar: a body marked PN16 is designed for 16 bar at the standard's reference temperature.

Two cautions. Pressure rating falls as temperature rises: a PN16 will not hold 16 bar at 150 °C. And PN also fixes the geometry of the flanged connection — two flanges of different PN do not mate properly, even at identical diameter.

They are two incompatible families. BSP is British and its thread has a 55° flank angle; NPT is American, at 60°. Screwing one into the other seems to work for a few turns, then leaks or damages the threads.

Within BSP, distinguish parallel from taper: parallel requires a flat or O-ring seal on a face, whereas taper seals through the engagement of the threads themselves, with a sealant. The choice therefore follows what is already installed, never preference.

316, without hesitation. It contains molybdenum, absent from 304, which gives it far better resistance to pitting corrosion — the kind caused by chlorides, and therefore by sea air and spray.

On a coastal site such as Pointe-Noire, 304 pits within a few seasons where 316 holds. The L grades (304L, 316L) are low-carbon: they weld without risk of intergranular corrosion near the bead, and are preferable wherever there is welding.

Five parameters, each of them disqualifying. Actual working pressure, peaks included, never the average. Inside diameter, which sets fluid velocity and therefore pressure drop. Compatibility of the inner tube with the fluid carried. Temperature range, of the fluid and of the surroundings. And minimum bend radius.

The last is the one most often overlooked: a hose bent tighter than its specification keeps its reinforcement under permanent strain, and fails well below its proof pressure.

First add up the ratings of only the loads to be supplied, then look at their starting: an induction motor draws several times its rated current on start-up, and that transient peak sizes the set more reliably than the sum of steady-state ratings.

Next account for the duty — occasional standby or continuous running, which do not permit the same output from the same machine — and finally altitude and ambient temperature, which cost the engine power.