HF Flange Assessments

An HF flange, or HF alky flange, is the external lip of a Hydrofluoric (HF) Alkylation Unit, where pipes and other similar equipment can be connected.

HF flanges are particularly vulnerable to hydrofluoric acid corrosion, which can be extremely hazardous to both employees and equipment. For this reason, these flanges should be monitored closely for potential damage.

Inspecting HF flanges manually can be an incredibly costly; sometimes even more so than replacing them outright. Even so, every HF flange should be inspected at least every 10 years when in main acid service, and every 15 years when in trace acid service.

Phased array ultrasonic testing (PAUT) is an effective nondestructive examination (NDE) technique for inspecting HF flanges and tends to be far more accurate and less costly than more conventional methods. Whatever type of inspection is conducted though, it should be performed in accordance with API 751, which doesn’t require any particular method of inspection.

API RP 751, Safe Operation of HF Alkylation Units, provides guidelines on how to keep HF Alkylation Units running smoothly, and how to prevent corrosion in HF flanges and other related equipment.

Benefits of HF Flange Inspections

Hydrofluoric acid is extremely toxic and can cause serious injury and even death if exposed to plant personnel. Moreover, it is highly corrosive and can damage nearby equipment. Performing regular inspections of HF flanges is an integral part of a facility’s mechanical integrity program and will help ensure your facility continues to operate safely and reliably.

Sentinel’s Hydrofluoric Alkylation Unit Expertise

Sentinel Integrity Solutions offers HF Flange inspections as a part of our comprehensive on stream and turnaround inspection services. Click the button below to contact one of our experts. We will work with you to determine whether or not an HF Flange inspection is the right application to fit your needs.


6606 Miller Road 2
Houston, Texas 77049
Office: (281) 457-2225
Fax: (281) 457-0225


3038 Leopard Street
Corpus Christi, Texas 78408
Office: (361) 887-2014
Fax: (361) 887-2022


1954 West Shore Avenue
Port Allen, Louisiana 70767
Office: (225) 421-8640
Fax: (225) 421-8645