Hydrochloric Acid Resistant Centrifugal Fan

Overview

Hydrochloric acid is a non-oxidising acid carrying aggressive chloride ions, so material selection is tied to non-metallic solutions. Carbon steel and 316L both fail through chloride pitting, and a fan for this duty is built in PP, PVC, FRP or PVDF according to acid concentration and temperature.

Material Selection by Medium Conditions

The aggressiveness of hydrochloric acid varies strongly with concentration and temperature. Dilute acid is the more aggressive case, while chlorides remain a pitting risk even at higher concentration.

Location	Material / process	Basis
Impeller	PP or PVDF moulded / welded impeller	Suits ambient to 60 C; PVDF covers higher temperature
Casing	FRP hand lay-up or welded PVC sheet	Easy to form in large and irregular shapes
Shaft	316L sheathed in PP or PVDF, or titanium	Keeps metal out of contact with acid vapour
Sealing	PTFE lip seal or mechanical seal	Stops acid vapour escaping along the shaft
Metal parts	Epoxy or vinyl ester coating	Isolates bolts, base frame and fasteners

Manufacturing Controls

Location	Material / process	Basis
Welding procedure	Consumables and parameters qualified per material	Ensures weld strength and tightness
Weld inspection	Visual plus spark or penetrant testing	Locates leakage points
Fasteners	Polypropylene or sheathed 316L bolts	Prevents fasteners corroding first
Drain and wash	Drain and wash connections at the casing low point	Allows acid residue to be removed
Motor isolation	Corrosion resistant baffle between motor and casing	Protects motor insulation

Applications

Applications include chemical reaction off gas, pickling tank exhaust, electroplating acid mist, hydrochloric acid tank breathing and laboratory ventilation.

Where chlorine or hypochlorous acid is also present, attack increases further and the material has to be re-assessed for the mixed medium.

Concentration and temperature should be mandatory entries in the technical agreement, and material allowance should be provided where concentration fluctuates.

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 3854	Barcol hardness test for reinforced plastics	Hardness acceptance of FRP parts
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

Please provide acid concentration, medium temperature, dust load and air flow. Size and motor power are calculated for the actual duty.

FAQ

Why is 316L not used for hydrochloric acid?

Chloride ions break down the passive film of stainless steel and cause pitting and crevice corrosion, so 316L normally perforates quickly. Non-metallic materials such as PP, PVC, FRP and PVDF are used instead, or titanium and zirconium where a metal is required.

How do I choose between PP and FRP?

Below 60 C with mainly moulded parts, PP is more economical. For large casings, irregular shapes or higher stiffness, FRP hand lay-up is easier to form. The two are often combined.

How is the maintenance interval set?

Estimate from concentration, temperature and continuous running hours, then correct it during the first year using wall thickness and weld inspection. Impeller roots and welds deserve particular attention.

Related pages: Anti-corrosion fan range  PP plastic fan  Rubber and plastic lined fan