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Ex Special Interest Group Briefing Note: Ex ‘d’ flanges – installation

Author : Harvey T. Dearden, HTS Engineering Group

05 March 2021

The Institute of Measurement and Control Explosive Atmospheres Special Interest Group (Ex-SIG) aims to promote good practice and support continuing professional development in the Ex discipline through a range of activities and publications. The group produces briefing notes to help inform members on key topics. This article is one such briefing note on the installation of Ex ‘d’ flanges.

(Ex-SIG Briefing Notes are first released to members of the SIG before being made publicly available)

It is often assumed that painting of flanges on Ex ‘d’ enclosures is not allowed, but the protection technique does not rely upon the maintenance of a gap; it depends upon the gap not exceeding the dimension specified.

“For flanged joints of other than quick-acting doors or covers, there shall be no intentional gap between the surfaces other than that created by the flatness tolerances of the mating parts.” (Reference IEC 60079-1: 2014 Section 5).

Painting is allowed and should not be identified as a defect.

“Painting (by the user) of a flameproof enclosure after complete assembly is permitted.  The application of grease to the flameproof joint faces will reduce, but not eliminate, the quantity of paint penetrating the gap.” (EEMUA, A Practitioner’s Handbook for Potentially Explosive Atmospheres. Publication 186. Edition 7, 6.5.1.5)

Painting of the joint surfaces themselves is not permitted.

Painting is sometimes discouraged because of the possibility, when a flange is separated, for paint flakes to prevent proper mating of the flange faces when the joint is remade.  It is also for this reason that only non-hardening greases are permitted on flange faces.

Any gap must be less than specified as allowable, to prevent the transmission of gases from an internal explosion in a manner liable to ignite an external atmosphere.  A variety of effects contribute to the cooling of the gases and testing has established the ‘maximum experimental safe gap’ and the acceptable proximity of obstructions and use of weatherproofing tape.

Zone* Gas Group Sub-Division
(*Not the equipment rating)
Minimum Obstruction Distance (applicable to flange joints, not compliant threaded joints)
IIA
10mm
IIB
30mm
IIC
40mm

Non-hardening grease-bearing tape may (per the above EEMUA guide 4.4.4.6) be applied (in a single layer with a short overlap) as follows:

Zone* Gas Group Sub-Division
(*Not the equipment rating)
Stipulation
IIA
Allowed
IIB
Allowed if maximum gap between the joint surfaces does not exceed 0.1mm irrespective of the flange width.
IIC
NOT allowed

New tape should be applied whenever the existing tape is disturbed.

This document is distributed by the Ex-SIG as an information service to the SIG membership. No guarantee is made by the institute or the author(s) concerning the accuracy, reliability or completeness of the information provided. This document should not be construed as providing advice. Readers should satisfy themselves of the applicability of the information provided. Readers make use of the information provided at their own risk.


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