Grade 8 vs. A325
Grade 8 vs. A325
(OP)
We are provider of packaged modular energy solutions and we use A325 bolts for skid steel framing (One skid package has about 15% A325 Bolts and 85% Grade 8 used for piping and mechanical equipment). In order to simplify purchasing, handling and storage of bolts we would like to use Grade 8 Bolts instead of A325.
Guidance and counsel would be greatly appreciated.
Thanks,
Ibro V.
Guidance and counsel would be greatly appreciated.
Thanks,
Ibro V.






RE: Grade 8 vs. A325
Could you use A325 all around, also?
RE: Grade 8 vs. A325
If there is no specification or contractual requirements and the physical differences are not a factor, the substitution could make sense. I would still be interested why they were doing it the present way, however.
Regards,
-Mike
RE: Grade 8 vs. A325
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RE: Grade 8 vs. A325
RE: Grade 8 vs. A325
In addition each discipline (Mechanical and Structural in this case) is more comfortable with specifications they are familiar with. Most likely either bolt spec, A325 or Grade 8, would work for the entire project. Which enineer should have to go out of their way to learn the others spec?
In my opinion the Grade 8 bolts should be spec'd for the skid. Their mechanical properties are greater than or equal to A325. More importantly, in a manufacturing environment, use of a single bolt spec will save money while making the QA&QC requirements easier to meet (less specs = less chance of error).
The above notwithstanding I would go with an all welded tubular skid frame as opposed to a bolted arrangement using WF and C sections, clip angled together. The tube steel has much greater torsional strength and overall stiffness with very little cost differance.
RE: Grade 8 vs. A325
RE: Grade 8 vs. A325
-Mike
RE: Grade 8 vs. A325
From AISC’s publication, A Guide to Engineering and Quality Criteria: Common Questions Answered:
Question 6.2.5: Is it acceptable to substitute SAE J429 grades 5 and 8 bolts for ASTM A325 and A490 bolts, respectively?
Answer: No. The strength properties of SAE J429 grade 5 bolts and ASTM A325 bolts are identical; likewise, SAE J429 grade 8 bolts are the strength equivalent of ASTM A490 bolts. These material specifications differ, however, in that ASTM A325 and A490 specify thread length and head size, whereas SAE J429 does not. Additionally, quality assurance and inspection requirements for ASTM A325 and A490 bolts are more stringent.
Since AISC and RCSC specifications call for pretensioned installation for your application (which involves fatigue), I would question whether the SAE fasteners that were installed were properly installed. Also, I’d question if the head size, threading and quality assurance were adequate for the application. Usually, the request to substitute an SAE fastener for A325 or A490 comes because SAE’s are cheaper. Perhaps that gives you the answer right there.
Charles J. Carter
American Institute of Steel Construction
Chicago, IL
Hope this helps.