Hydrofluoric acid—also known as HF acid or hydrogen fluoride—is a strong acid found in some refinery alkylation processes along with specialized chemical processes. DuPont™ Vespel® CR-6100 can help hydrofluoric acid pumps last longer.
Limitations of traditional materials
Traditionally, pump wear parts in hydrofluoric acid pumps are made from Monel, which is very good for corrosion resistance. The downside of this arrangement is that both rotating and stationary wear components need to be made from Monel, requiring large clearances at the wear rings to avoid pump seizure. These large clearances compromise the mechanical seal life, exposing the seal to higher vibration and larger shaft deflections.
Hydrofluoric acid also tends to form crystalline deposits. Several plants using hydrofluoric acid have reported pumps being seized due to crystalline deposits accumulating while the pump is in stand-by, ultimately eliminating the clearance at the wear rings. When Operations tries to switch to the spare pump, it proves to be unavailable.
Upgrading stationary Monel Rings To Composite Materials
The way to upgrade your hydrofluoric acid pumps is to install DuPont™ Vespel® CR-6100 stationary wear rings and continue using Monel rotating rings. This small change essentially eliminates the risk of seizure between Monel parts and allows tighter clearances at the wear rings.
Vespel® CR-6100 is a composite material made from oriented carbon fibers and Teflon® PFA resin, resulting in broad chemical resistance combined, excellent dimensional stability, and a temperature range from cryogenic to 260⁰C (500⁰F). Vespel® CR-6100 has been used in a wide range of hydrofluoric acid services for more than 10 years with excellent results.
Because Vespel® CR-6100 is non-seizing, wear ring and bushing clearances can be reduced to 50% of the API minimum values for metal rings. The reduced clearance increases the hydraulic forces which stabilize the pump rotor. With a more stable rotor, shaft deflection is reduced, vibration is reduced, and seals and bearings will last longer. Furthermore, even if crystalline deposits build up when the pump is in stand-by, it is unlikely they will cause the pump to seize at start up.
The end result of this upgrade is greater reliability and availability. Life cycle costs will be lower with fewer repairs and avoiding seizures of the Monel parts. Contact Boulden today to learn more about Vespel® CR-6100 and Boulden’s B-Series composite materials.