How to Increase Flexibility in Piping Systems

Stress and flexibility analysis—also known as stress analysis—is a fundamental discipline in piping system design. Its purpose is to assess whether a pipeline can withstand loads imposed by internal, external, or combined conditions without compromising the system’s integrity.

A piping system must have sufficient flexibility to absorb both thermal expansion and contraction, as well as movements induced by supports and connected equipment. Otherwise, undesirable effects may occur, such as:

• Structural failure of the pipe or its supports
• Leaks at joints or connecting elements
• Damage to nozzles, flanges, or connected equipment

Since this analysis requires a significant investment of engineering hours, not all lines are formally evaluated. Only those considered critical—based on specific project-defined criteria—are analyzed.

When a system lacks the necessary flexibility to absorb thermal displacements, the designer must implement solutions to reduce its rigidity, either through geometric modifications or the use of specialized mechanical devices.

How can flexibility be increased?

Mathematically, for an ideal spring, stiffness is expressed using Hooke’s Law:
F = k ⋅ ΔL

Where:

• F is the applied force
• k is the stiffness constant (N/m)
• ΔL is the axial deformation

This simplified model helps understand structural stiffness and its influence on mechanical response. Based on this equation, reducing the stiffness k and increasing flexibility means allowing larger displacements ΔL under applied loads.

In practical terms, there are two key strategies to increase piping system flexibility: geometric modifications and the use of expansion joints.

Figure 1. Representation of ways to increase the flexibility of a system

1. Geometric Modifications: Changing Direction

One of the most effective and economical ways to increase flexibility is by altering the geometry of the system—especially the direction of piping routes. This technique involves changing the original layout by introducing bends, elbows, or diversions that help absorb thermal and mechanical stresses.

System flexibility depends on multiple factors:

• Geometric configuration

• Pipe diameter and thickness

• Number and type of fittings

• Type of supports and constraints

When these directional changes aren’t enough, expansion loops or offsets are added to increase displacement absorption capacity through additional geometric modifications.

Figure 8. Illustration of pipe models with geometric changes

2. Expansion Joints: Specialized Mechanical Solutions

Expansion joints are mechanical devices designed to absorb axial, radial, or lateral movements in piping systems. Although they provide compact and effective solutions, their use must be carefully assessed due to cost, installation complexity, and failure risk.

When to use expansion joints:

• When space limitations prevent geometric solutions

• When directional changes negatively impact process performance (e.g., pressure drop, heat loss)

• To isolate sensitive equipment (pumps, turbines, compressors) from vibrations or unwanted loads

When to avoid them:

• In severe cyclic conditions

• Where significant torsional moments exist

• In systems with toxic or hazardous fluids (require protective covers)

• In services with solidification risk (e.g., molten sulfur)

Proper expansion joint selection must be based on specific process parameters, such as temperature, pressure, fluid type, displacement direction, connection type, and presence of suspended solids. The Expansion Joint Manufacturers Association (EJMA) guidelines should be followed for this purpose.

Types of Expansion Joints:

• Simple joint: absorbs axial displacement; must be installed between anchors capable of resisting thrust forces

• Pressure-balanced joint: balances axial force due to internal pressure; ideal for protecting rotating equipment

• Tie rod joint: absorbs lateral displacement; installed perpendicular to the least flexible direction

Figure 11. Simple expansion joints

Figure 12. Pressure-balanced expansion joints

Figure 13. Expansion joint with rigid rods

The key to a safe and efficient and safe piping system lies in intelligent flexibility management, combining geometric and mechanical solutions based on process conditions and environmental constraints.