As an experienced and expert repair shop for a wide range of hydraulic and pneumatic equipment, we often get asked about fastener grades for various pieces of equipment. At first glance, this may not seem like such an important question, but hydraulic systems are typically used in extremely rugged and harsh environments and hardware failures can be costly in terms of both time and money.
Operators who experience frequent equipment failures, especially for such critical components as bolted pump flanges may be the victim of hardware that’s simply not meeting their specs. For example, some repair shops may be using SAE Grade 5 hardware when they should be using Grade 8. In some cases, this may be a simple case of “ignorance is bliss” and the repair mechanic may not realize there’s a significant difference between the two grades’ performance. With that in mind, let’s take a look at why it’s important to use Grade 8 hardware to meet your specs.
A bolt is not just a bolt.
SAE grades really do have a meaning and purpose. They basically tell you how strong a fastener is. But it’s actually a little more complicated than that because there are different strengths to consider:
- Yield strength, which indicates when a bolt is beginning to deform and determines performance limits.
- Proof strength, which is about 90 percent of yield strength.
- Ultimate tensile strength, which indicates the capacity of the fastener to resist loads tending to elongate and pull it apart.
- Shear strength which represents how hard it is to break a fastener – this is different than tensile strength. The difference is tensile is about pulling apart, shear about breaking.
Some technicians might argue that Grade 8 fasteners are more brittle than Grade 5, but in most cases, the Grade 5 bolt will have reached its ultimate load and failed before a Grade 8 bolt even begins to yield or stretch, making the brittle argument inconsequential.
Toughness is another important factor in ensuring that specs are met. The higher the hardness number (Brinell or Rockwell) the tougher the fastener material. Based on a Rockwell rating, Grade 8 fasteners (C-33-39) are tougher than Grade 5’s (C25-34).
So to sum up, if you’re experiencing too many failures with your hydraulic or pneumatic systems due to fastener problems, it might be the hardware grade. Even if the manufacturer’s spec calls for Grade 5 fasteners, they often spec parts that meet safety regs, but may fail when worked hard – and what hydraulic system owner doesn’t work their systems hard? To be sure, the little extra cost involved in upgrading to Grade 8 hardware can not only meet your specs, but save you money in the long run.