Corrosion, Failure Analysis and Materials Selection Specialists

 

 

 

 

 

Corrosion Testing / Failure Analysis

 

 

 

Corrosion Testing

Failure Analysis

Field Investigations

Litigation

Metallography

Technical Papers

CTL Profile

Pricing & Policies

Contact CTL

Quality Assurance

Return to Failure Analysis Case Histories

Mechanical Fatigue of Aluminum Antenna

ENVIRONMENT:

Atmospheric - High Winds

EQUIPMENT:

Antenna mounted on top of a tower
MATERIAL: Aluminum

FAILURE:

Mechanical Fatigue - Vortex Shedding
 

The upper portion of an antenna consists of a 2" schedule 40 type 6061-T6 aluminum pipe 22 feet long. The antenna is supported at the bottom only. The supports are mounted on top of a tower.

The location of the failure was at a " drilled hole in one wall of the pipe, Figure 1. The pipe snapped in two pieces, and the site of final breakage occurred at a tear directly opposite from the hole. Microscopic examination revealed a ductile fracture. No evidence of corrosive attack was found, Figure 2.

Vortex Shedding is a stress related failure caused by the cyclic oscillation of a vertical cylinder by wind. The point of failure is in close proximity to a "node", or a fixed point that does not move during oscillation.

Corrective action may be performed by shot or bead preening the pipe surface, particularly at locations on the pipe which will be fixed points after antenna assembly.

 
Figure 1. Fractured Aluminum Pipe (0.55X Original Magnification) Figure 2. Fractured Surface of Pipe, no evidence of corrosion.

Site Index

Site Copyright 1995 - 2007, All Rights Reserved,

Corrosion Testing Laboratories, Inc.

60 Blue Hen Drive

Newark, Delaware USA 19713

Phone: 1-302-454-8200

Fax: 1-302-454-8204

web@corrosionlab.com