Something that might be viewed as a small, insignificant venting hole on a 10,000 pound steel structure, if not well thought out, could really have an adverse effect on production.
When creating fabrication drawings for galvanized structures, it’s important, as well as valuable, to know proper draining and venting provisions. If adequate venting and draining holes are not provided, it can really have an intangible effect.
5 Problems to Watch Out For:
1. Air pockets can form, causing structures to rust out from the inside
2. Excess galvanizing buildup
3. Lead to longer fabrication times
4. Welded plate can blow out, causing safety concerns
5. Poor coating
It’s hard to put a dollar amount on what happens when a structure either doesn’t have proper venting, or one of the five stated above occurs. It’s usually not too hard to correct if it’s caught up front, but the further it gets in the process and closer to delivery dates, it can really put a stop to production, causing low production numbers and possibly delayed shipping. But working with a trusted steel fabricator, can help avoid these issues.
Some standard shape structures, such as square and rectangular tube columns and beams, are hollow, so provisions need to be made in order to allow galvanizing to easily flow and coat the inside portion of the structure. Tapered tubular structures are also hollow so the same principles can apply with provisions.
Other standard shape structures, like channels, wide flanges and angles are solid, so just the outside receives coating, but keep in mind that air pockets can form without proper drainage, causing excessive galvanizing buildup. For these shapes, you need to watch where stiffeners, connection plates and brackets are welded that could form large pockets of air as the section is dipped into the kettle.
For standard shape and tapered tubular structures, using removable cover plates on the ends of beams is a good option instead of welding solid plates or expanded metal to the ends. This allows for faster flow through the member and more adequate galvanizing, also helping to eliminate buildup.
But ensuring proper venting doesn’t mean place a bunch of holes all over the structure, but rather strategically supply the venting and drainage provisions. For example, if dealing with corners in a square and rectangular tube, slots or holes can be provided near these corners to prevent air pockets from forming, which can decrease the amount of galvanizing coating in the area.
It’s key that along the process, there are people in place who know what to look for or have an eye for knowing what will work when it goes to the galvanizer. If it passes through the line of engineering, detailing, quality control and then is delivered to the galvanizer, modifications can be more costly and difficult.
The more you understand how the member is lifted and dipped in and out of the galvanizing kettle, the better you can locate the venting and draining provisions. As a designer, you are always trying to find the balance of putting enough holes for galvanizing, while not putting too many to impact the structural integrity of the steel member.