Anti-corrosion Explosion Proof Centrifugal Fan

Overview

When the medium is corrosive and flammable at the same time the two requirements often conflict: corrosion resistant non-metallic materials do not conduct, so they can accumulate static, while metal materials with good conductivity may be attacked by the medium. The solution is to give non-metallic parts conductive treatment and a reliable earth.

Material and Protection Configuration

Corrosion resistance sets the material and explosion protection sets the motor and static control, and both have to be resolved on the same drawing.

Location	Combination	Basis
Impeller	PP or PVDF lining, or corrosion resistant stainless steel	Selected from medium corrosivity
Static control	Conductive treatment and earthing of non-metallic parts	Prevents static discharge
Motor	Flameproof Ex d, rating per gas group	Configured per GB 3836.2
Shaft seal	PTFE mechanical seal	Resists corrosion and limits leakage
Fasteners	Sheathed bolts or duplex stainless bolts	Prevents fasteners corroding first

Construction and Safety Measures

Location	Combination	Basis
Equipotential earthing	Metal parts, ducts and base bonded and earthed	Eliminates potential differences
Coating system	System selected by environmental class	Combines corrosion resistance and durability
Bearing monitoring	Temperature and vibration monitored online	Detects abnormal conditions early
Gas detection	Detection suited to the medium on site	Protects maintenance personnel
Maintenance procedure	Shutdown and gas freeing before work	Controls maintenance risk

Applications

Applications include chemical solvent exhaust, pharmaceutical tail gas, paint and printing exhaust and mixed sulphur and solvent bearing streams.

Where the composition fluctuates, the protection level is set by the component with the higher group requirement and the material by the more aggressive component.

Acceptance documentation for this type of duty usually covers both corrosion protection and explosion protection, so the two sets of standards should be listed separately in the technical agreement.

Acceptance and Verification

Standard	Title	Purpose
GB 3836.1	Explosive atmospheres - Part 1: Equipment - General requirements	General design and marking of explosion protected equipment
GB 3836.2	Explosive atmospheres - Part 2: Equipment protected by flameproof enclosure d	Flameproof motor and terminal box
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
GB/T 9239.1 / ISO 21940-11	Mechanical vibration - Balance quality requirements for rigid rotors	Impeller balancing grade

Please provide medium composition and concentration, medium temperature, flammability and air flow. Size and motor power are calculated for the actual duty.

Explosion Protection Marking and Coverage

The explosion proof certificate held for our fans covers the marking Ex db IIC T4 Gb; Ex tb IIIC T130℃ Db, certificate No. SHExC26.0908. It covers both explosive gas atmospheres and combustible dust atmospheres.

Marking	Meaning	Coverage
Ex db	Flameproof, equipment protection level Gb	Zone 1 and Zone 2 gas atmospheres
IIC	Gas group	Covers group IIA, IIB and IIC
T4	Temperature class, surface limit 135℃	Covers T1 through T4
Ex tb IIIC T130℃ Db	Dust protection by enclosure, conductive dust	Zone 21 and Zone 22, covers IIIA, IIIB and IIIC

Temperature class limits are T1 450℃, T2 300℃, T3 200℃, T4 135℃, T5 100℃ and T6 85℃. A device marked T4 has a surface temperature limit of 135℃, so it covers any location that requires T1 to T4.

BT4 Marking Coverage

Required marking	Covered	Note
Ex d IIA T4, Ex d IIB T4, Ex d IIC T4	Covered	IIC is compatible with IIA and IIB; temperature class is T4
Ex db IIB T4 Gb (current designation)	Covered	Same protection type in current standard wording
Ex d IIB T1, T2, T3	Covered	T4 has a lower surface temperature limit and is more restrictive
Ex de IIB T4 (with increased safety e)	Confirm by design	Different protection type; group and temperature alone are not sufficient
Ex ia, Ex ib IIB T4 (intrinsic safety)	Not covered	Intrinsically safe equipment is required
Ex d IIB T5, T6	Not covered	Surface temperature limit is not sufficient
Zone 0 (requires Ga)	Not covered	Gb equipment is intended for Zone 1 and Zone 2

Suitable locations: chemical solvent exhaust, pharmaceutical tail gas and paint or printing exhaust in Zone 1 and Zone 2 where the stream is both corrosive and flammable, together with Zone 21 and Zone 22 where conductive dust is also present.

Applicability of a specific model is subject to the scope of the explosion proof certificate and the equipment nameplate. Site use must also comply with the hazardous area classification and the electrical design documents.

FAQ

Can a plastic impeller be used in an explosion protected area?

Yes, provided the static issue is solved. Non-metallic materials do not conduct, so conductive treatment and reliable earthing are required together with controlled clearance to avoid rubbing, and the protection level still has to be confirmed against the gas group.

How are conflicting corrosion and explosion protection requirements resolved?

It is not a choice between the two: the material follows corrosivity while the motor and static control follow flammability, and conductive treatment resolves the conflict point. If both cannot be met, the process conditions have to be adjusted rather than one requirement being relaxed.

What documentation is normally reviewed at acceptance?

Material certificates and anti-corrosion process documents, type approval documents for the explosion protected equipment, and performance test and balancing reports. Certification for explosion protection is issued by a qualified body and is not issued by the manufacturer.

Related pages: Non-standard fan range Explosion proof fan range Anti-corrosion fan range