F593 Frequently Asked Questions

Is an intergranular test required on F593 bolts? 

Yes, intergranular testing is required on F593 bolts. This test evaluates the material to make sure there is no intergranular corrosion or cracking. Any corrosion or cracking can significantly reduce the strength of the material.  

This kind of corrosion can happen during the forging and heat-treating phase of the manufacturing process. This test can be performed many ways with the most common being subjecting the bolt to corrosive environments and conditions and then inspecting the bolt to ensure there is no cracking or corrosion happening.  

What are the primary differences between A193 stainless bolts and F593 stainless bolts? 

The main difference between these two specifications is that A193 bolts are specialized and designed specifically to be used in high-temperature high-pressure applications. F593 bolts are more of a general-purpose stainless-steel fastener. 

Another difference between these grades of bolts is the thread pitch. Per the ASTM specifications, A193 bolts must be 8-pitch when the diameter is larger than 1” unless otherwise specified. With F593 bolts the pitch is to always be UNC. 

Why are my F593 bolts or F594 nuts rusting? 

There are two reasons this could be happening. Firstly, there could be contamination from equipment that is used to make other carbon steel products. This could cause some iron deposits to be left on the stainless bolts that would rust over time. This is only a cosmetic problem and will not affect the bolt’s mechanical or chemical properties. 

The other reason your bolts and nuts are rusting is the bolts weren’t made correctly. An important step during the manufacturing process is solution annealing the bolts. This is the process of realigning the grain structure and restoring the corrosion-resistant properties of the bolt. Skipping this step leaves the bolts vulnerable to corrosion. 

What is the compatible grade of washers for F593 bolts? 

Per the ASTM specification, SS304 or SS316 washers are to be used for F593 bolts. In order to decide to use SS304 or SS316 washers depends on the alloy group that is being used.  

What is the difference between F593 Alloy Group 1 bolts and Alloy Group 2 bolts? 

These are the two most common alloy groups. The difference between these two groups is the steel used to manufacture the bolts. Alloy group 1 uses SS304 and alloy group 2 uses SS316.  

Each of these grades of stainless steel has different chemical compositions and properties. SS304 is most used in buildings and infrastructure. SS316 has a higher corrosion resistance and is commonly used in harsher environments that are exposed to chemicals, salt water, and acids.