Technical Bolting

API 653, a standard for tank retrofits and repairs, has approved the use of friction stud welding as a repair method. Friction stud welding reduces the risk of igniting flammable vapors and allows for installations on tanks where conventional welding is unachievable. The proposed changes to API 653 include guidelines for friction stud welding, such as qualification requirements, design considerations, safety protocols, and examination procedures. Notably, Section 11.5 covers the use of friction stud welding, while Section 12.1.11 focuses on the examination and testing of friction welded studs.

Friction welding is a solid-state welding process that generates heat through mechanical friction between workpieces, without relying on external heat sources.

With API approval, friction stud welding is recognized as a standardized and safe welding method, delivering exceptional benefits in terms of repair quality and unmatched safety for bolted-on retrofits and repairs of ASTs.

According to API 653 Section 12.1.11, friction welded studs should undergo visual examination and torque testing, adhering to ASME Section IX torque test requirements. Non-destructive examination (NDE) applies to all tank and stud materials.

Friction welding can be used for various repairs and retrofits of tanks and vessels, including but not limited to the following:

1. Installation of studs: Friction stud welding can be employed to install studs on in-service and out-of-service tanks, such as tank shells, roofs, and floating roofs.

2. Structural repairs: Friction welding can be utilized for repairing structural components of tanks and vessels, addressing issues like cracks, corrosion, or damaged sections.

3. Leak repairs: Friction welding can be employed to repair leaks in tanks and vessels by joining or sealing damaged areas.

4. Attachment of components: Friction welding can be used to attach or weld additional components, such as reinforcing plates, brackets, or support structures, to tanks and vessels.

5. Retrofitting: Friction welding can facilitate retrofitting activities, enabling the installation of new equipment, modifications, or upgrades to existing tanks and vessels.

It is important to note that the specific repairs that can be done with friction welding may vary depending on factors such as the condition of the tank or vessel, the type of material involved, and the recommendations of engineering professionals overseeing the repair process.

Forge bonding uses very high pressures to bond instead of high temperatures. A 5/16” stainless steel stud is inserted, and pressure is applied to rotate the stud at very high speeds for a few seconds. A small amount of thermal energy is applied during this process, which softens the two metals to a clay-like consistency.

After the three seconds are up, the metals are fused together. And the bond is so strong, it becomes stronger than either of the two metals involved in the bonding process.

There are a few varieties of steel that are worked on with Forge Bonding, but the most common is carbon steel. And when making the repairs, we will always try to use carbon steel in the repairs that is the same as the parent material.

98% of the studs we put down use a 304 stainless steel, which creates an incredibly strong bond that is immune to the elements. A standard polymer is used to seal the plate against the leak, which fills the pits and helps to planarize if we have to cross a lap joint.
Also, Forge bonding enhances the asset the repair is performed on, which means that the equipment that is repaired is left in better shape than before the leak happened in the first place!

The good news is that a forge bond itself only takes about 3 seconds, plus or minus depending on the temperature of the equipment being worked on. The more time consuming portion is moving and setting up the machine for each bond.

Three sizes of plates are typically worked with – 4 bolt, 8 bolt, and 12 bolt, with 12 bolt being the most common. We estimate on a good day, sixty studs can be put down. So if we happen to be working with 8 bolt plates, you can expect six to eight to be put down in a typical shift.

This is of course affected by things like obstacles and hard to reach areas, but that is to be expected.

Forge Bonding is incredibly safe for a few different reasons.

First, there’s the benefit of being able to eliminate hot work by using this process. And as the industry is becoming more and more safety conscious, the amount of safety gained by eliminating hot work is huge.

Second, the amount of thermal energy used in the bond is very minimal. Truth is, the auto-ignition temperature of most hydrocarbons is in fact exceeded that the bonds are performed on top of. However, the auto-ignition temperature is measured over a 10 minute interval. And according to API practice 2216, if the thermal energy that the hydrocarbon is exposed to is small enough, it takes a much higher temperature to ignite. Considering the bond only takes 3 seconds, a much higher temperature is required, which is never reached.

And Third – the machine used for the bonding process is completely air driven. There’s no electrical hookups required. Plus, the pressure and temperatures are regulated on the machine to ensure maximum safety. There are pneumatic timer counts down the 3 seconds that the bond takes, then shuts off. There’s also redundant timers built in as backup to ensure a smooth process

If you’re going to be implementing a new process, you’ll obviously need some numbers to justify your decision. We understand that.

First, let us tell you that the bonding studs are fully qualified to the ASME codes, section nine.

Second, the torque test performed(where a stack of washers is put on the stud and a nut is torqued on until something gives) fails at 45 foot pounds of force. Code only requires passed 1 foot pound!

Third, when taking a hydraulic press to the stud and pulling, it fails at a whopping 5000 pounds of force! (Which actually rips the base metal out rather than the stud)

As just mentioned, the skill level required for forge bonding does not need to be specialized.

While we can’t guarantee you a price point without looking at your situation, we can say that it is going to cost a heck of a lot less than taking your tanks out of service. If your tank is only 10 feet in diameter, welding might be for you.
Once you get larger than that, forge bonding truly starts to shine.

In Conclusion…

Forge bonding solves a big problem in the marketplace by letting you keep your production going while you make repairs to your equipment. It also lets you make these repairs outside of your turnaround which eases the pressure next time you have to shutdown.