Hydrofluoric Acid Resistant Centrifugal Fan

Overview

Hydrofluoric acid reacts with glass phases, silica and most metals, so its corrosion behaviour is unlike that of ordinary acids. Glass reinforced plastic and silica-bearing ceramics are attacked by hydrofluoric acid, and the fan wetted parts are made from Monel alloy or PTFE / PVDF lining instead.

Material Selection by Medium Properties

Hydrofluoric acid attacks glass phases and most metals, so silica-bearing materials must be avoided.

Location	Material / process	Basis
Impeller	Monel alloy or PTFE / PVDF lining	Resists hydrogen fluoride and fluoride attack
Casing	Carbon steel or metal frame with PTFE / PVDF lining	No GRP, which would lose its glass fibre
Shaft	Monel or PTFE sheathed shaft	Keeps metal out of contact with acid mist
Sealing	PTFE lip or mechanical seal	Resists hydrofluoric acid and stops leakage
Metal parts	Epoxy or vinyl ester coating	Protects bolts, base frame and non-wetted parts

Lining and Sealing Process

Location	Material / process	Basis
Lining material	PTFE / PVDF lining, no silica-bearing material	Hydrofluoric acid attacks glass phases and silica
Lining anchors	Welded anchors with adhesive bonding	Prevents the lining detaching
Weld inspection	Visual plus penetrant or spark testing	Locates leakage points
Fasteners	Monel or PTFE sheathed bolts	Prevents fasteners corroding first
Wash down	Wash and keep dry when stopped	Limits residue standing time

Applications

Hydrofluoric acid production, fluorochemical tail gas, glass etching, semiconductor cleaning exhaust and metal surface treatment, wherever hydrogen fluoride gases are handled.

Hydrofluoric vapour and fluoride gases become more aggressive when moisture is present, so water ingress and liquid pooling must be avoided.

Where an oxidising acid such as nitric acid is also present, the corrosion behaviour changes and the mixed medium has to be assessed on its actual composition.

Acceptance and Verification

Standard	Title	Purpose
HG/T 20679	Design code for external anti-corrosion of chemical equipment and piping	Anti-corrosion design for chemical media
GB/T 1236	Industrial fans - Performance testing using standardized airways	Air flow, pressure and efficiency testing
ISO 12944-5	Paints and varnishes - Corrosion protection of steel structures by protective paint systems - Part 5	Coating system and durability class
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade
JB/T 10563	General purpose centrifugal fans - Technical specifications	General technical conditions and works acceptance

Please provide the hydrogen fluoride concentration, medium temperature, whether moisture is present and the air flow. Size and motor power are calculated for the actual duty.

FAQ

Why is GRP not used for a hydrofluoric acid fan?

Hydrofluoric acid reacts with the silica in glass fibre and with glass phases, so GRP loses strength; silica-bearing ceramics are attacked in the same way. Monel alloy or PTFE / PVDF lining is used for this duty.

How do I choose between Monel and PTFE lining?

Monel suits anhydrous or low moisture, low temperature hydrogen fluoride and can be made into an integral impeller. Where moisture is present or temperature is higher, PTFE or PVDF lining is usual, and the two are often combined.

How is leakage controlled on a hydrofluoric acid fan?

A PTFE mechanical or lip seal stops acid mist escaping along the shaft, the lining uses welded anchors with adhesive bonding, and penetrant or spark testing locates weld leaks.

Related pages: Anti-corrosion fan range  Rubber and plastic lined fan  F9-19 anti-corrosion centrifugal fan