With proper planning Hot Dip Galvanizing is a great alternative to paint.
Galvanized skids are ideal for longevity as it pertains to corrosion. From an end user prospective the overall cost of the more frequent routine inspections of painted surfaces vs. galvanized surfaces is a significant cost factor in basing their design decisions as well as the life span of the equipment vs. painted.
From a fabricators perspective Hot Dip Galvanizing (HDG) is less expensive (if done correctly) than the cost of sand blast prime and paint per foot.
There is also the big question of “Can you weld galvanized material?” The answer is yes. The toxic smoke that comes from welding galvanized is from the zinc that was not removed prior to welding. It can safely be removed using other means such as grinding. However, once you remove the zinc coating in that weld area you must replace the zinc with either a cold galvanizing aerosol spray or a brush on zinc. Close attention to customer specifications is needed to ensure what percentage of the structure is allowed to be touched up using one of these methods. It is usual factored on surface per square inch.
Throughout my career I designed or fabricated a multitude of skids that went offshore. Over the past ten years the majority of the offshore market migrated to using HDG skids.
The first issue was finding a vendor with a zinc bath big enough to submerge the entire skid. Cost of transport schedule impact are two pitfalls to avoid when considering getting this process done thru a sub-vendor. Planning is crucial as once you send a fabricated skid off to be galvanized it must be a finished product that requires no additional welding.
The next challenge in planning is providing adequate weep holes and clean flux free welds, the zinc in the HDG process will accumulate in certain areas. Significant deflection in the structural components themselves may require repairs to incorporate the equipment being placed on skid package.
In addition, when we fitting structural beam using cope cuts, often stress cracking can occur due to the flame or plasma cuts used in the coping. Post HDG repairs would be to gouge out the crack, re-weld, then apply Cold Galvanizing.
Often the biggest fear is a customer making changes on final inspection leading to modifications such as additional pipe supports to be welded.
Ultimately, in order to make the HDG work from a fabricators’ perspective a skid design with cut to length materials would be sent to be HDG prior to assembly where instead of welding seams, stainless steel tabs/brackets are used that bolt to the galvanized structure then the tabs/brackets welded together. Similarly, spot weld can be used for the bolted tabs. This approach works well for smaller sized skid packages.
In summation, from a cost stand point can HDG can be quite affective with proper planning.
Design for minimum re-work, handling/re-handling or additional welding to galvanized surfaces. But, use caution, failing to do this and costs can add up quickly.
Eric Aaron is a Project Manager with Vector Systems, Inc. He has over two decades experience developing heavy industrial skid packages and pressure vessels.