Galvanising Structural Steelwork

Liquid Metal Assisted Cracking (LMAC) can occur when steel components come in to contact with molten zinc. This form of cracking is uncommon but if it is not detected and repaired it can have extremely serious consequences on the performance of the structure. It is generally agreed that there are three main prerequisites for LMAC to occur. These are:

• Stress level
• Material Susceptibility
• Liquid Metal

Although the relative importance and the inter-relationship between these issues in increasing the risk of LMAC are largely unknown there is strong evidence to suggest that careful consideration of these issues with respect to the following activities can reduce the risk of LMAC:

• Design and detailing
• Type and quality of steel
• Quality of fabrication
• The Galvanizing process

This publication provides practical guidance to clients, specifiers and engineers on each of these topics to identify circumstances where any increased risk of LMAC can be ameliorated.

A post galvanized inspection regime is also suggested as a pragmatic approach to reducing the potential consequences of LMAC. It is recommended that the Engineer should specify 100% visual inspection after galvanizing for all structural steelwork that is to be utilised in building construction. In the event some LMAC cracks are found non-destructive testing (NDT) using Magnetic Particle Inspection (MPI) is recommended to determine the extent of cracking. Finally a welding repair procedure is described for repairing most cracks in a galvanized component. This involves removing the zinc from around the area to be welded, repairing the crack and restoring the protective coating with a zinc rich paint or similar system.

By following the guidance given in this publication and by committing a modest amount of attention to detail at each stage of the construction process the chances of LMAC occurring can be substantially reduced.

ISBN 0 85073 048 1
20 pp,  A4 paperback,
September 2005
UK Price: £15.00, EU/Overseas: £18.00, Outside EU: £21.00. BCSA Members get a 25% discount i.e. £11.25)