Q:  We are trying to move away from zinc plated 12.9 bolts due to hydrogen embrittlement problems and the geomet finish is giving us problems due to the diameter of the screw. As a better solution, we have thought about using Super Duplex screws or Nimonic 80A screws.  I understand that we would achieve tensile strength with both materials and at the same time avoid having to use a coating.

Do you think the solution I propose is correct?

A:  The concept of replacing coated material with a higher performance alloy is a good idea, however both Nimonic 80A and Super Duplex will not have the minimum strength requirements of 12.9 which is  1100MPa  (159KSI) minimum yield strength and 1220MPa (177 KSI) minimum tensile strength.  You could see a material strength comparison table at: https://www.extreme-bolt.com/high-strength-fasteners.html#Metals

From a strength perspective, a material you could consider as a replacement for 12.9 would be 17-4 PH Stainless Steel H900 bolts.  This will have 190KSI min Tensile and 170KSI min Yield.  Learn more at: https://www.extreme-bolt.com/17-4-ph-fasteners-flanges.html

Q: We are in search for a bolt material that can handle sulfuric acid – compatible with 96% H2SO4. The exposure should be low and only on an infrequent basis. Also,  these applications when H2SO4, DI Water is used to flush and clean off the surfaces during any maintenance that occurs inside the platform.

A: Without knowing the temperature of your application it’s impossible to give a firm recommendation as the corrosiveness of the acids is highly dependent on the temperature. However, if you are below 140F Hastelloy C276 bolts would be a robust choice to consider.  See the corrosion curve below (You want to be as far below the 5mpy line as possible.)

Q:  I’m looking to source high temperature nuts, bolts and washers for a marine engine exhaust system with a continuous temperature rating of 600C. Is there a material that can handle the temps and corrosion?

A: Probably the best material you could have at 600C in a marine environment would be Inconel 625 bolts. This material will be immune to sea water and have no issue those temperatures.

Q: We are in need of 3/8″-16 a 1-1/2″ hex head cap screws in material that can withstand 1700° F operating temperature. What would you recommend?

A: A good option to consider would be 310 hex bolts.  This is a high temperature stainless steel that should be good up to 2000F.

Q: We are essentially having issue identifying the highest available high strength stainless steel nylon insert nuts. Is Duplex 2205 the best option?

A: If you are just looking for strength for your lock nut with a nylon insert, one of the highest strength stainless steel’s you could consider would be 17-4 PH (ranging from 136-190KSI)

A286 locknuts are a good option as well with good high temperature stability (130 KSI)

Duplex lock nuts are also much stronger than 316 with about 120KSI tensile strength. Duplex also offers better corrosion resistance. This material is not as strong as A286 or 17-4

Q: I’m looking to purchase some ¼-20 bolts/nuts/washers that will be suitable to fasten metal plate together at 1,300C.  The fasteners need to last at least 4 minutes at this temperature but preferably longer. The load on the bolts will be very low.

A: I think there are a couple fast delivery options.

#1 – Inconel 600.  Although this is limited in long term temp resistance to ~1100 C… The short time at temperature should allow it to perform OK.  I’m sure 4 mins is OK.  You may want to use a high temp anti-seize if these are disassembled often (https://www.extreme-bolt.com/store/anti-seize-lubricant/extreme-anti-seize-lubricant)

#2 – Ceramic.  This material is exceptionally resistant to temperature and will have no problems at 1300C for long durations.  However, ceramic screws are not as strong or tough as metals.

Q: What is the difference between “standard” Inconel 718 and Inconel 718 per AMS 5962

A:  While nothing about Inconel 718 is standard, however the most popular variety of Inconel 718 bolts is per ASTM B637.  For this version of s, the bolts are age hardened to have a minimum tensile strength of 185 KSI and minimum yield of 150 KSI.  Inconel fasteners per AMS 5962 are not only age hardened but they are also cold worked or work strengthened to produce an extremely high minimum tensile strength of 220 KSI.

Q: Why is Aluminum 7075 often used for aircraft?

A: There are many grades of aluminum bolts but those categorized under grade 7075 are specifically used for aerospace and other high stress structural applications that require a combination of strength and extreme light weight.

Grade 7075 can be tempered to different conditions, each providing different levels of strength. Among these tempers is 7075-T6, which is the strongest.  Aluminum 7075-T6 bolts are 1/3 the weight of steel and can offer nearly double the strength-to-weight  ratio of grade 2 titanium.  In addition, they offer good plasticity and high fracture toughness, making it ideal for stress/strain resistance.

Q: How does Aluminum 7075 compare to titanium grade 5?

A: Aluminum 7075 can be tempered to many different strengths. The strongest being T6 which not only offers the highest strength. The primary drawback being that it also has low fracture toughness.

Aluminum 7075-T6 bolts offer more strength than grade 2 titanium, but less than that of grade 5 titanium bolts. The most unique feature of Aluminum 7075 bolts is that they have very low density which gives them higher strength to weight ratio than that of titanium grade 2 and a similar strength to weight ratio to titanium grade 5.