1. Lack of Stress Analysis for Various Loads:

Insufficient stress analysis and inadequate piping flexibility can lead to excessive loads on the system, ultimately causing failure. Piping systems are subjected to various types of loads, including primary loads like hoop stress, secondary loads such as thermal load or displacement, sustained loads, occasional loads, and reaction or impact forces. Each of these loads affects the system’s performance, and if not properly analyzed and managed, they can lead to system failure. Below are the common loads that occur in piping systems and can cause failure if not adequately analyzed and maintained.

1.1 Principal Piping Stresses: Fluid pressure within a pipe creates three primary types of stress:

• Longitudinal (Axial) Stress (δa): This stress acts along the length of the pipe. In the case of a pipe sealed with caps at both ends, the longitudinal stress is exerted toward the fittings, potentially causing the fittings to detach or push the pipe ends outward.
• Circumferential (Hoop) Stress (δh): This stress acts outward, around the pipe’s circumference. It is the most significant stress and can cause the pipe to split along its length, especially under high pressure.
• Radial Stress (δr): Radial stress is exerted away from the pipe’s central axis, extending outward toward the pipe wall. It is the least significant of the three types of stress.

Among these three types of stresses, hoop stress has the largest effect followed by axial stress and radial stress being the smallest.
Principal or primary stresses are typically force-driven, meaning they are caused by external forces such as gravity, internal pressure, spring load, pressure safety valve operation, and water hammering. These forces can exert significant stress on piping systems, making it crucial to account for them during the design and analysis phases to ensure the system’s integrity and avoid potential failure.

1.2 Principal Piping Stresses: Sustained loads are caused by internal pressure and the weight of the piping components, including valves, flanges, and fluid, as well as additional factors like thermal insulation or snow in colder climates. These loads primarily create longitudinal or axial stress (δa) from fluid pressure. If not properly managed with adequate pipe supports, sustained loads can lead to piping failure or collapse.

1.3 Sustained Load: Sustained loads are caused by internal pressure and the weight of the piping components, including valves, flanges, and fluid, as well as additional factors like thermal insulation or snow in colder climates. These loads primarily create longitudinal or axial stress (δa) from fluid pressure. If not properly managed with adequate pipe supports, sustained loads can lead to piping failure or collapse.

• Earthquake and Blast Load: Forces generated by seismic events or explosions.
• Wind Load: Caused by sudden air movement. If not accounted for in the design, it can lead to piping failure or damage to facilities.

1.4 Displacement Stress: Displacement stress is a secondary load, like thermal stress, that fluctuates between hot and cold conditions. As the temperature changes, the allowable stress (Sc and Sh) also changes. This can cause failure if the material is exposed to a single excessive hot load or repeated cycles that exceed the allowable stress range (SA).
Thermal expansion is a type of displacement stress that usually occurs with temperature fluctuations in the piping system and if the system is not flexible enough to handle these changes then it causes a leakage or pipe failure.

1.5 Piping Reaction Forces: Reaction forces in piping can result from pressure safety valves, slug flow, and water hammering. These forces, classified as dynamic loads by ASME B31.3, can cause vibration and potential damage to the piping system.

• Pressure Safety/Relief Valve Reaction Force: When the safety valve opens, it generates reaction forces due to back-pressure and sudden impulses, particularly in gas services with high velocity and pressure. Proper pipe support is essential to manage these forces.
• Slug Flow Reaction Force: Slug flow, a mixture of gas and liquid, causes vibration and load fluctuations, negatively affecting the piping system and potentially shutting down the process.
• Water Hammering Load: Water hammering occurs from rapid changes in flow rate, such as valve operation or pump cycling, creating pressure surges that can damage the piping.

2. Corrosion:

Corrosion is a chemical reaction where metals return to their natural state, often leading to material degradation and pipe fragility. The main types of corrosion affecting piping systems include:

• Uniform Corrosion: Caused by exposure to moisture and oxygen, resulting in rust.
• Galvanic Corrosion: Occurs when dissimilar metals interact, accelerating corrosion at the joint.
• Pitting and Crevice Corrosion: Common in environments with acidic or chloride-containing fluids, leading to localized, deep pits.

Corrosion can weaken pipes, making them prone to breakage. To mitigate corrosion risks, material selection, coatings, and cathodic protection are essential preventative measures.

3. Water Hammering:

High velocity or pressure in piping systems can lead to water hammer, a phenomenon where abrupt changes in flow generate pressure waves that strike valves and pipe walls, causing loud rattling sounds and potentially damaging pipe supports, valves, and the pipes themselves. This occurs when fast-moving fluid is suddenly stopped, creating stress on the pipe walls. When a valve closes quickly, it interrupts the flow, causing water or gas to change direction, and the energy from this disruption has nowhere to go but back into the pipe walls and surrounding components, generating pressure waves. Frequent water hammer events weaken joints and fittings, leading to leaks or fractures, and in severe cases, the intense pressure fluctuations can cause pipes to burst.

4. Flange Connection Issues and Gasket Failures:

Flanges are key components in connecting pipes, valves, pumps, and other equipment in a piping system. They are typically welded or screwed to the pipe, with flanged joints formed by bolting two flanges together and placing a gasket between them to create a seal. Piping system failure and leakage can result from several factors, including poor material selection, corrosion, improper design,
poor machining or corrosion of the flange face, inadequate gasket selection, and improper installation or alignment. Most of the failures are linked to installation issues like gasket misalignment and insufficient bolt load.

5. Movement and Vibration:

Piping systems need to be stable, and movement and vibration in piping systems can lead to failure due to several factors. External forces like earthquakes and ground settlement can cause pipes to shift, leading to misalignment and fractures. Operational vibrations from equipment such as compressors and pumps, along with flow-induced turbulence, can generate mechanical stresses that cause the pipes to vibrate, potentially leading to fatigue and failure. Over time, these vibrations increase stress on the piping, which can initiate cracks, wear through fretting, and lead to eventual failure.