Sample Problem – Equivalent Length Calculation for Piping Fittings

Tutorial for equivalent length calculation

This tutorial uses sample calculations to demonstrate how to calculate equivalent length for piping fittings, joints and valves.

Problem Statement -

Calculate the equivalent length and combined K-factor for following set of fittings,90⁰ elbows - 5 nos. 45⁰ elbows - 2 nos.Gate valves - 3 nos.Ball valve - 1 no.Check valve - 1 no. The line size is 6 inches while there is a 8"-6" reducer at the beginning of the line.

The 6" line with 'STD' schedule handles 100,000 kg/hr of water. Approximate length of this line is around 200m. This water stream is available at 5 barg pressure and 30⁰C.

Solution -

This sample problem is solved in following 3 basic steps.

Step 1.

First step of solving this sample problem requires determination the important physical properties of given fluid (water) at given temperature and pressure conditions.

Using EnggCyclopedia's Liquid Density Calculator, water density at 30⁰C =993.41 kg/m³

Using EnggCyclopedia's Liquid Viscosity Calculator, water viscosity at 30⁰C =0.81 cP

From EnggCyclopedia's standard pipe dimensions calculator, for 6" pipe with STD schedule, internal diameter is 154.1 mm.

Step 2.

Total K factor for the set of fittings can be calculated using EnggCyclopedia's K factor calculator. Refer to the screenshot below for demonstration of use of this calculator.

Step 3.

In the third step of solving this sample problem, inputs from steps 1 and 2 are fed to EnggCylopedia's equivalent length calculator to get equivalent length for the given set of fittings. Refer to the screenshot given below for guidance to use the calculator. Thus the set of fittings in given 6" line are equivalent to 60.36 m of that line. Along with the original 200 m of straight pipe, the total equivalent length of the given 6" line becomes 260.36 m. This length can be used to quickly calculate variation of pressure drop for minor variations in the flowrate, using EnggCyclopedia's pipe pressure drop calculator. For manor variations in the flowrate, the Darcy friction factor and hence the equivalent length has to be recalculated.