DIS-TRAN Steel Blog

What You Need To Know About Weathering Steel Hardware Assembly

Posted by Brooke Barone on Oct 8, 2013 10:25:00 AM

Last week we focused on the importance of pairing suitable galvanized hardware together, so what about weathering steel hardware? 

One of the main things to recognize when using weathering steel hardware is that there are many limitations. There aren’t as many different bolt grades available, as well as fewer hardware pairing options.

So what’s the difference in weathering verses galvanized steel?

Well, galvanized steel involves applying a protective zinc coating to steel to prevent corrosion, while weathering steel also provides a protective coating, but the steel is allowed to rust in order to form the protective coating.

weathering steel structures

Another key thing to remember is that galvanized hardware should not be paired with weathering steel structures because galvanized steel is sacrificial by nature, meaning it will spread from the galvanized piece to the adjacent, unprotected steel, weakening the coating of the galvanized piece.   

Some hardware is not available in weathering steel, but there is the option of using stainless steel (if the particular hardware is available in stainless steel). For example, a lock washer, which is locking device, does not come in weathering steel, but is available in stainless steel. The reason stainless steel can be used with weathering steel is because there is no coating and won’t negatively affect the weathering steel.

Bolt- headed and externally threaded fastener designed to be assembled with a nut.

Nut- An internally threaded product intended for use on external or male screw threads such as a headed bolt or a stud for the purpose of tightening or assembling two or more components.

Locking Device- a device used in conjunction with a fastener in order to positively lock the fastener, so that the fastener cannot work loose from vibrations.

Stud- a non-headed fastener.

Also, something else to point out is that you don’t typically see weathering steel in substations, but more in transmission and distribution. Weathering steel has a special patina, which if not careful when placing in an environment that has both wet and dry cycles, could continue to corrode and not stabilize.

There are weathering steel hardware options in ASTM A325 and A449 bolts, but not for A307, A394, A193-B7 and A36. For all thread studs, there are equivalents that can be substituted for the lower strength galvanized bolts. A490 bolt has the option of weathering, as well as black steel, and is an extremely high strength bolt, which is a good option as an equivalent to the galvanized A193-B7 bolt.

It’s also valuable to know the limitations with weathering steel hardware because there are no low strength nuts or square nuts, so a heavy hex nut would be used. Another limitation to note is that M.F. Locknuts are not readily available, and palnuts don’t exist in weathering steel. Feel free to browse our website for futher product and service information. www.distransteel.com


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Tags: astm a325 bolts, heavy hex bolt, square nuts and bolts, steel hardware assembly, stainless steel flat washer, astm a449, astm a193 b7 threaded rod, all thread bolt

The Insider's Guide to Steel Hardware Assembly

Posted by Brooke Barone on Sep 27, 2013 9:43:00 AM

I heard this quote once about “the perfect couple,” and I think it could relate to different circumstances: “Perfect is not when two people are together. It’s when you’re both different but in a way, you complete each other.”

You’re probably scratching your head wondering how in the world assembly hardware relates to “the perfect couple.” Well, don’t worry, this isn’t a blog about 5 Ways to Save Your Relationship, but it is important to know that when it comes to assembly hardware, while they have their different roles, the right hardware needs to be paired with the right bolt.

Just like knowing if you’re compatible or not with someone, you should know which pairings are suitable when either ordering or supplying assembly hardware for steel structures. If the bolt and nut don’t match up in accordance with ASTM standards, you could run into strength problems, requirements issues or over match hardware when it is unnecessary. A low strength nut shouldn’t be paired with a high strength bolt because it would take away the strength of the bolt. In other words, the connection is only as strong as its weakest part. For example, if an A325 high strength bolt is specified for a connection, then you want to make sure the recommended nut and flat washer is supplied to match the A325 bolt’s loading capacity. The same applies if you pair a high strength nut with a low strength bolt, you’ll run into overkill.

In this situation, you end up paying for a more expensive nut when there may have been a more economical option without compromising the loading capacity of the bolt. In the ASTM A563 standard specification for carbon and alloy steel nuts, there is a good nut compatibility chart that shows which nuts are recommended for most bolts. This is also provided in our offer at the bottom of the page, which also includes locking devices and other pertinent information, like available bolt diameters and lengths. This can be helpful when sizing the bolts and selecting the proper locking device because some locking devices aren’t available in larger diameters.

**Just because the bolt you are ordering comes in that size, it doesn’t guarantee that the locking device you selected also comes in that size.

Common terms defined:

Bolt- headed and externally threaded fastener designed to be assembled with a nut.

Nut- An internally threaded product intended for use on external or male screw threads such as a headed bolt or a stud for the purpose of tightening or assembling two or more components.

Locking Device- a device used in conjunction with a fastener in order to positively lock the fastener, so that the fastener cannot work loose from vibrations. 

bolt assembly

One of the more common bolts used is the ASTM A325 Type 1 bolt (galvanized). The ASTM A325 specification covers two types of heat treated heavy hex bolts with starting tensile strength of 120 ksi for sizes 1.0 in. and less, and 105 ksi for sizes over 1.0 to 1.5 in. These bolts are used in steel connections, and the bolts are then classified by “type” based on their chemistry.

For the A325 bolt, Type 1 is described as a medium carbon, carbon buron or medium carbon alloy steel. If your project consists of galvanized steel, then you’ll need to order an A325 Type 1 bolt that is zinc coated…and of course it doesn’t stop there. When ordering these bolts, the supplier also needs to know size (including diameter), threaded pitch, bolt length, length of threads, etc. From there, if the bolt and corresponding hardware is ordered as an assembly, the ASTM A325 specification requires a ROCAP test (Rotational Capacity Test). A ROCAP test essentially tests the capaability between the bolt and nut of certain heat lots.

And just to add, for the A325 bolts, the nuts need to be A563-DH because this nut automatically comes lubricated, which is required in the ROCAP test. (Note: You may be able to get an A194-2H nut lubricated; check with your bolt supplier.) In the instance that you need custom thread lengths, A449 bolts are suitable to use in the place of A325.

Some other commonly used bolts in the utility industry include A307, A394 and A36. These bolts are low to mid strength and are galvanized. They are suitable with A563-A hex or square nut (same grades), or a USS washer (F884). To supply a heavy hex nut or hardened flat washer with these type bolts would be over matching. You can supply higher strength nuts and washers with these bolts; however it’s not as economical and doesn’t provide any extra benefits.

For connections that require a bolt with a higher tensile strength than an A325 bolt, an A193-B7 is a suitable option.  These come as fully threaded studs, and require an A194-2H nut.

So, just as important as it is to choose the right match, it’s critical to know what hardware is suitable, as well as their pairings. That’s also where your bolt supplier or fabricator can come in and service you better.


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Tags: bolt assembly, astm a325 bolts, flange connections, lightning mast, heavy hex bolt, square nuts and bolts, tensile strength bolts, steel hardware assembly

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