Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Weld Slag

Last updated: October 31, 2018

What Does Weld Slag Mean?

Weld slag is a nonmetallic byproduct of certain types of welding processes. Weld slag is formed when the flux used in the welding process solidifies after the welding has been performed. The weld slag is a combination of the flux and the impurities or atmospheric gases that combined with the flux during welding. Without the flux and resultant slag, oxidation of the weld would occur.


Corrosionpedia Explains Weld Slag

Weld slag is found in a variety of welding processes. Examples of these include submerged arc welding, shielded metal arc welding (SMAW), electroslag welding and flux cored arc welding (FCAW). Both gas shielded flux cored arc welding and self-shielded flux cored arc welding have slag. The thickness of the weld slag layer is determined by the type and amount of flux.

A weld slag inclusion is a common discontinuity with the above-mentioned welding processes. Slag inclusions occur when the molten slag does not solidify on the exterior surface of the weld. Weld slag inclusions can be caused by improper welding technique, improper flux or improperly handled flux.

A weld slag inclusion can cause corrosion of the weld. The contact of the two different materials (the weld and the slag) may result in rapid oxidation. Slag inclusions can also form crevices that allow for a higher corrosion rate.


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