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Glossary of double seam defects

Knowing what to look for – and how to describe it – is key when it comes to identifying and preventing double seam can defects. Our glossary of common issues is designed to help your seam testing process run as efficiently as possible.  

Common beverage can seam defects


This defect most commonly occurs in the can body just under the seam, although it can appear anywhere, and is an obvious twisting or crumpling of the metal that appears after the double seam is completed.  


Also sometimes known as scoring, creasing is the name for tiny dents below the radius of the lid’s hook where the contact has been made with the can wall. This is a seam defect most commonly found in aluminum beverage cans with a thin neck.   


Noticeable by a scalloped effect along the seam’s bottom, a droop occurs when a small part of the double seam overhangs the bottom.  

False Seam

This defect can be hard to spot – from the outside it looks as though the seam has been completed. However, it occurs when the end and body are not hooked together, but when each are folded over against themselves and compressed. 

Low Free Space

Not always visible to the eye, this defect occurs when the seam is too tightly rolled, during the 2nd operation. The seam may look mangled, or the defect may be found using testing equipment like an End Profile Analyzer. 

Long Seam

An overly long seam can be hard to spot, but it causes weakness in the integrity of the seal. It has a number of causes, including damages with worn tooling or an incorrect roll profile. Find out more about how to measure double seams.  


Obvious to the naked eye, this is a defect caused when the flanges of the lid and the can are not properly aligned and amalgamated during the seaming process.  


When a double seam is not tight enough, the process can be incomplete, creating a spinner effect. It is normally caused by the seaming chuck slipping on the end of the can body. 

Split Seam 

Also known as a clam shell, a split seam is a serious visual defect that can be seen around the double seam itself. It can be caused by a too high or tight 2nd operation, excessive sealing compound, or too high lifter pressure.  


Similar to a droop, this is a sharp protuberance that can occur anywhere around the seam. 


Most common in aluminum cans, wooling (also known as silvering) refers to the shaving of material from the cover or can body flange during seaming. Small flakes of metal can be seen around the seam after the seaming process.  

Get the lowdown on important elements of the canning and testing process with our can guidebook or find out more about can inspection processes to cut down on potential beverage can defects. Whether you’re using visual inspection equipment or traditional seam inspection instruments, we can help to protect your production lines. 

Diagnose and fix your seam issues

If you’re struggling to find a way to pin down issues with your seaming process, the  Industrial Physics’ SEAM Doctor system could help. This handy toolkit, offers all our seaming know-how to help you get to the root cause of any problems – it uses a unique machine-learning algorithm to determine the most likely cause(s) of your seam defect(s). Find out more about the SEAM Doctor system 

Expert double seam can testing

If you’d like help and advice in setting up or adjusting a seam testing solution, you can chat to our knowledgeable team. We have more than 50 years of experience in beverage packaging testing and are experts in everything from enamel rating to end buckle testing. Find out more by getting in touch today