Skip to main content

CROSS Safety Report

Liquid metal assisted cracking

Report ID: 49 Published: 1 November 2006 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.


Large cracks appeared down the sides of gusset welds after a truss was erected on site.

Key Learning Outcomes

For civil and structural design engineers:

  • Be aware that liquid metal assisted cracking can occur if due attention is not paid to the design, fabrication, galvanising and inspection processes of susceptible assemblies

Full Report

Find out more about the Full Report

This section contains the Full Report submitted to CROSS and describes the reporter’s concerns or experiences. However, the text has been edited for clarity, and identifiable details have been removed to ensure anonymity and confidentiality. If you would like to know more about our secure reporting process, or submit a report yourself, please visit the reporting to CROSS-UK page.


Another reporter had to advise on a large timber grillage system that had been connected at the nodes with steel connectors formed of a central bar (about 100mm diameter) fitted with radial gussets welded on to it. The whole assembly was then galvanised. The trusses were erected on site, but during erection it was noted that there were large cracks down the sides of the gusset welds into the parent body of the bar. Fortunately, this was spotted before it was too late, nevertheless, the whole truss system had to be dismantled for safety reasons.

The reporter’s firm took expert advice to establish the cause of cracking and the consensus was that it had occurred in the galvanising bath and that it was Liquid Metal Assisted Cracking (LMAC). It looked likely that the cracks had been masked by zinc so were not visibly detected until the structure had been erected and tension applied across the crack surface. The nodes were remade with tougher steel and the cracking did not re-occur.

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

BCSA document 40/05 emphasises that LMAC is a rare phenomenon. However, it can occur if due attention is not paid to the design, fabrication, galvanising and inspection processes of susceptible assemblies. It is apparent that not all designers are yet familiar with the guidance.

Submit a report

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.