Why a Spring Failed: A Manufacturer's Guide to Diagnosing Fatigue, Corrosion & Overload

A spring failing in the field is rarely a mystery once you actually look at it — the failure mode almost always points straight back to its cause. Here's how we think through it when a customer sends us a broken part.

Fatigue failure

is the most common cause, and it looks distinctive: a clean, often granular fracture surface, usually at a point of maximum stress — the transition where a hook meets the coil body in an extension spring, for example, or a specific coil in a compression spring under repeated cyclic load. Fatigue happens gradually. Every load cycle creates microscopic stress at that point, and eventually a crack initiates and propagates until the remaining material can't hold the load. If you're seeing fatigue failures earlier than expected, the usual culprits are wire diameter undersized for the actual cyclic load, a stress-concentrating design detail like a sharp hook bend radius, or a material grade selected for static load rather than genuine cycle life. This is exactly why we ask about cycle life, not just peak load, when a customer specifies a new spring — our spring design guide covers this distinction in more detail.

Corrosion failure

looks completely different — pitting, rust staining, or a rough, oxidized surface rather than a clean fracture. This is a material selection problem almost every time. Standard spring steel, even zinc plated, will corrode in humid, coastal or washdown environments given enough time and enough breaks in the coating. Once corrosion pits the wire surface, those pits become new stress concentration points, and what looks like a corrosion failure often finishes as a fatigue failure at the pit site. We cover the practical differences between spring steel and stainless grades in our spring steel grades guide.

Overload failure

is the simplest to diagnose — visible permanent deformation, a spring that's taken a set and no longer returns to its free length, or in severe cases, a single catastrophic break. This usually means the spring saw a load beyond what it was specified for. One design detail worth knowing: for extension spring applications where occasional overload is a real risk, a drawbar spring adds a built-in hard stop that prevents this exact failure mode.

If you're troubleshooting a real failure, the physical evidence usually tells you which of these three you're dealing with before any calculation does. Send us photos of the failure point and your original specification, and we can generally narrow it down from there.