Best bolts for Inconel 625 flanges

q: What bolting material should be used with Inconel 625 flanges? We used ASTM A193 Gr B7 however noticing some corrosion issues.

A: This is a very common problem but to answer it accurately, it depends on the environment that your flanges see and also to a certain extent what media is inside the flange.

If we focus on corrosion only, the reason why the media contained by the flange is of concern is there are normally small fugitive emissions. Depending on the corrosiveness of the medial it could certainly attack the B7 bolts given the fact that you are probably are trying to contain a fairly corrosive media by using Inconel 625. Additionally you will accelerate corrosion via galvanic effects if the bolting get wet.

Beyond corrosion, you need to consider the strength of the bolts as well. B7 has a min yield of 105ksi while Inconel 625 has a typical yield of 85ksi. So while Inconel 625 will certainly work as bolting from a corrosion point of view, you need to see if it has enough strength for you pressure rating. If you need higher strength you might want to consider Inconel 718 as it has both excellent strength and corrosion resistant properties.

Best flange for high pressure hydrochloric acid

Q: I have a high pressure application with HCl at fluctuating temperatures. Can you recommend the best flange to provide a safe secure joint?

A: Hands down, the weld neck flange is best for these types of hazardous, high pressure applications. Weld neck flanges are easily identified by their long tapered neck which fits over the pipe providing a secure, reinforced connection. The inside of the flange is bored to match the inside diameter of the pipe in order to ensure there is no restriction in flow and also to prevent turbulence at the joint. The tapered neck provides thicker metal at the flange joint, while the neck smooths down gradually to meet the pipe where it is butt welded to the pipe.

This design helps to transfer stress from the flange to the pipe, as well as diminish stress concentration at the base of the flange connection. Weld neck flanges are ideal for critical applications involving high pressure, sub-zero and elevated temperatures, and in conditions where fluctuations cause pipe expansion/contraction.

Key Feature: Ideal for High Pressure Applications
Advantages:
• Ability to withstand high pressure – since pipe is welded to the neck of the flange, stress is transferred to the pipe.
• The beveled end that, when connected to a pipe, creates a trough for a strong weld.
• Most versatile flange in the ASME stable of flanges.

Disadvantages:
• More advanced welding skill is needed for installation. The inside weld must be smooth to reduce friction and the outside weld must meet code criteria.

Uses
• Severe conditions that include high-pressure, high-cyclic and hazardous fluid applications.
• Fitting-to-fitting fabrication where the flange is welded directly to a fitting, such as an elbow, without the need for a short piece of pipe, as would be required with a slip-on flange.

Best uses for a threaded flange

Q: When do you recommend to use a threaded flange? I need a flange that can be changed easily & frequently.

A: After speaking with the customer, I found out that he has a pilot plant where he will be frequently changing parts. In this case a threaded flange is ideal because they can be frequently changed and reconfigured as they don’t require welding to install. Threaded flanges have a tapered female thread to join the male threads of a pipe in order to create a tight seal.

Benefits of Threaded Flange
1. The main benefit is that that threaded seal eliminates the need for welding.
2. As they do not require welding they save time and money to install.
3. Allow for connections to be made in dangerous, explosive applications where welding is not possible.
4. Useful connection in materials that are difficult to create a successful and strong weld.

Threaded Flange Best Practices
• They are not suitable where high temperatures, cyclic conditions or bending stresses can be potential problems.
• Ideal for where the necessary post weld heat treatment is not possible. Also best for hazardous, flammable or explosive applications where welding is dangerous.
• Ideal to connect small diameter pipes.
• Well suited for pilot processes whose configuration is often changed