Introduction
Fluid friction plays a crucial role in determining the efficiency and energy losses in any piping network. Whether in chemical plants, powder systems, or laboratory-scale experiments, understanding frictional pressure losses helps engineers design safer and more efficient systems. Process simulation software is crucial for engineers to visualise, calculate, and optimise fluid flow behaviour—including friction losses in pipes and fittings—without extensive manual computation. In this article, we explore how pipe fittings can be used to model friction and pressure drops in complex piping networks.
When a fluid flows through a pipe, part of it is lost because of friction between the fluid and the pipe's internal surface. This energy loss is called head loss.
- Pressure drop across the pipeline.
- Increased pumping power requirements.
- Reduced flow efficiency.
In real systems, friction losses occur in two main forms:
Major Losses—because of friction along the length of the pipe.
Minor Losses—because of valves, fittings, and expansion/contractions.
Understanding and quantifying both are essential for accurate process design.
Modelling Fluid Friction
DWSIM allows us to understand the model, both simple pipelines and complex ones, by interconnected networks using built-in unit operations like:
Each Pipe Segment unit in DWSIM can simulate pressure drop because of friction using correlations such as:
In real piping networking, frictional resistance also rises from
elbows,
Bends, and
tees, Valves (globe, gate, ball),
reducers and
expanders. These fittings are essential for changing the direction of flow and also reducing the size of the pipes with each fitting step.
Stainless steel pipes are excellent for resistance to corrosion, high strength and durability under both high temperature and pressure conditions. It depends on the piping length, Thickness that is driven by the Schedule Numbers (SCN). Good SCN means better compatibility and utilisation for high-pressure ranges.
Figure 1: Piping Network and Fluid Friction
Applications
1. Chemical Process Industries: In Chemical Process Industries, the piping network is essential for fluid transfer. The estimation of data or evaluation of flow rate, pressure drop, and fluid velocity at various cross sections is contingent upon the flow regimes in fluid dynamics, with fittings also exhibiting variability. This can improve operational conditions to reduce losses in piping systems.
2. Wastewater Treatment Plants: In WWT plants, pipes and fittings are essential for transporting raw sewage, process water, sludge, and treated effluent between different units. The choice of pipe type, materials, and fittings depends on pressure, chemical exposure, temperature, and different flow characteristics. Pipes are made up of ductile iron,
HDPE, or
PVC. Diameter size around (100-200 mm) for the main inflow. Fittings like elbows, reducers, and tees for directing flow.
Materials of Fittings used in Different Units:
- Primary Treatment - Butterfly valves, gate valves, bends, T-joints.
- Biological Stage - Diffuser pipe connections, check valves, reducers, and manifolds.
- Tertiary Treatment and Filtration - Tee and elbow joints, reducers, valves and union fittings for chemical dosing lines.
- Sludge Treatment - Flanged elbows, tees, reducers and pressure-rated valves.
- Effluent Discharge - bends, reducers, tees and non-return valves.
Materials of Pipes used in Different Units at WWT:
- Primary Treatment - Ductile iron, HDPE or PVC.
- Biological Stage - Inlet/Outlet pipes to sedimentation basins (PVC or HDPE).
- Tertiary Treatment and Filtration - PVC, HDPE for filtered water and chlorine dosing lines.
- Sludge Treatment - Cast Iron, HDPE, or Carbon Steel.
- Effluent Discharge - PVC, HDPE or concrete (for gravity flow).
3. Oil and Gas Transportation: In oil and gas transportation, pipes and fittings are the backbone of the transportation system, carrying crude oil, natural gas, refined products, and process fluids safely over long distances. In the oil and gas industries, various applications span extraction, transportation, refining, and distribution.
Typical Pipe and Fittings Materials (Extraction site):
Pipe material: Carbon steel (API 5L, ASTM A106, A53), SS316, SS304, Duplex/Super Double Steel.
Fittings Materials: Elbows (45°, 90°),
Tees and crosses,
Reducers, Flanges and unions, Couplings, Nipples, caps and plugs.
Typical Pipe and Fittings Materials (Transportation and Storage):
Fittings Materials: Butt-welded fittings,
Insulated fittings, Ball/Gate valves, Pig Launchers/receivers.
Typical Pipe and Fittings Materials (Refining and Petrochemical Processing):
Pipe material: SS304, SS316, Alloy steel (P11, P22, Inconel), PVC, CPVC, PP.
Fluid Friction Effects in Chemical Process Industries:
In chemical engineering plants, an installed piping network facilitates the transportation of fluids and gases, effectively delivering a sufficient mass of materials to the desired reaction in the reactor at a constant flow rate, thereby enabling further chemical reactions. To reduce the corrosion effect on metallic pipelines, most of the industries use SS type of materials in piping design, which not only serves for transportation but also enhances the efficiency of the plant working process without cracking on the surface of the metallic layer. To reduce thermal load, stability on metals by coating the pipes. That directly affects the minimal losses and also covers the surface from damage. According to Mathews 1981, most metals affect shoes' ductility behaviour with certain thermal limits.
The fluid friction in the piping network means quantifying resistance in the pipelines because of a wide range of pressures in the industrial piping network. Those experiences in the pipes, ducts, packed beds, reactors, and heat exchangers. It is s critical factor in design, energy efficiency, and safety.
Frictional losses: The drops in pressure as fluids move due to viscous shear and form drag. It affects pump sizing, energy consumption, and process controllability.
Viscosity: A fluid property that directly influences friction, with higher viscosity with higher frictional losses.
Reynolds number: a dimensionless parameter that characterises flow regimes (laminar, transitional, turbulent) and helps select correlations for friction factors. It is a dimensionless coefficient used in head/pressure drop correlations like Darcy-Weisbach.
L
= length of the pipe
D
= pipe diameter
ρ
= fluid density
v
= average fluid velocity
f
= friction factor (function of Re and roughness)
Moodsy
chart / Colebrook-White equation:
f
= f (Re, ε/D) for turbulent flow in smooth/rough pipes.
For
laminar flow (Re < ~2000), f = 64 /
Re.
Equivalent
roughness or empirical adjustments may be applied to ducts and some fittings.
Components
and sources of friction loss in processes
Straight
pipe segments: primary contributor to pressure drop via
viscous shear, build tiny losses (K-values) that build up to big losses in
fittings, valves, bends, expansions, and contractions.
Reactions
in packed or structured beds: flow distribution and bypassing affect pressure
drop.
Heat
exchangers and surface roughness: fouling increases effective roughness over
time, increasing friction.
Multiphase
flow: gas-liquid or liquid-solid mixtures complicate
friction; slip, emulsions, and phase distribution change effective viscosity.
Design
considerations
Pipe
sizing: balance between minimum sufficient diameter to keep
Re in the desired regime and material/cost constraints.
Pump
selection: ensure net positive suction head (NPSH) availability
and energy efficiency; consider variable-speed drives for part-load efficiency.
Fouling
management: anticipate fouling factors, clean-in-place (CIP) intervals, and
design for ease of cleaning.
Temperature
and viscosity changes: viscosity typically decreases with
temperature; account for process heat integration and viscosity variation in
friction calculations.
Hydrodynamic
modelling: use computational fluid dynamics (CFD) or one-/two-dimensional
models for complex internals; otherwise, rely on standard correlations for
pipes and ducts.
Common
equipment where fluid friction matters
Pipelines
and distribution networks
Heat
exchangers (shell-and-tube, plate): pressure drop across
tubes/plates and fouling resistance
Reactors
with internal coils or baffles
Packed-bed
reactors and distillation columns (radial/axial flow packs, random packings)
Absorbers/strippers
with gas-liquid contactors
Slurry
pipelines and slurry transport lines
Practical
steps for engineers
Collect
fluid properties: density, viscosity (and viscosity as a function of
temperature), phase fractions.
Determine the flow regime by computing Re and anticipating possible transitions due to temperature
or composition changes.
Select
appropriate friction factor correlations: Laminar (f =
64/Re) or Turbulent (Colebrook-White, Haaland, Swamee-Jain, etc.).
Add
minor losses: use K-values for fittings, valves, expansions, contractions; sum
with major losses.
Account
for fouling: include a fouling factor (e.g., in heat transfer and friction
calculations) and plan maintenance.
Validate
with plant data: compare predicted ΔP with measured pressure drops; recalibrate
correlations if needed.
Quick
example (pipe flow)
Given:
2-inch pipe (D = 0.1524 m), length L = 50 m, fluid: water, 25°C, ρ ≈ 997 kg/m³,
μ ≈ 1.0 mPa·s.
Compute
velocity from volumetric flow rate Q (if provided).
Re
= ρvD / μ.
If
Re < 2000, f = 64/Re; else use Colebrook-White with ε/D (pipe roughness for
commercial steel ~0.045 mm).
ΔP
= f (L/D) (ρ v² / 2)
Fouling
and maintenance notes
Over
time, fouling increases the friction factor. Monitor the pressure difference
between heat exchangers and reactors.
Establish
CIP and pigging schedules for pipelines to mitigate buildup.
Use
coatings or smoother internal components where feasible to reduce surface roughness.
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