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Safe operation of flameproof motors in explosive atmospheres

25 February 2019

Maintenance and inspection of flameproof motors is critical to ensure safe operation. Pedro Maia offers advice on keeping them in good working order.

Flameproof motors are widely used across many industries that feature explosive atmospheres. Standards such as IEC 60079-17 specify the correct design and definition of components that should be utilized. This standard also offers good advice about maintenance plans in order to maintain certification. Flameproof motors require routine inspection and careful maintenance, otherwise there can be serious ramifications. 

The correct functional operation of hazardous area equipment requires regular inspections which should be performed by skilled personnel and, if necessary, subsequent maintenance and repair works. IEC 60079-17 specifies the need for up-to-date documentation and qualified staff, and defines inspection tables for Ex-marked equipment. For example, daily checks are recommended for noise levels of the complete motor, as well as noise and vibration levels of the bearings. Weekly tasks include bearing lubrication and checking the coupling alignment, while annual checks include the re-fastening of bolts, measuring the insulation resistance of the stator and rotor, and cleaning the inside of the terminal box.

Cleanliness is a big issue. Motors should be free from dust, dirt and oil, which can be removed using soft brushes, clean cotton rags or jets of compressed air. However, the cleaning operation cannot be performed if a potentially explosive atmosphere is present at the time.
 
Lubrication 
It is well documented that bearings are one of the most common causes of failure in electrical motors. As a consequence, correct lubrication is important to maximise bearing life and ensure low-noise and low-temperature operation. 

The lubrication of bearings must be made respecting the quantities and intervals stated on the motor nameplate and documentation; using too much grease can cause overheating and leakage into the motor’s windings. It is also important to apply a grease which is compatible with that supplied by the motor manufacturer. Using an incompatible grease may mean that it offers different viscosity and performance, potentially reducing bearing life. 

Ensure repair procedures deliver maintain compliance: Carefully implemented repair procedures can have a big impact on motor operation and machine uptime. Again IEC 60079-19 gives guidance on the practical methods of repairing equipment and defines procedures to maintain compliance in line with product certification.  

IEC 60079-19 states that repair facilities shall operate a Quality Management System (QMS) and appoint a responsible person with authority and technical knowledge of explosion protection standards. In addition, repair facilities need to be informed regarding equipment certificates, special conditions of use, and all necessary information from the equipment manufacturer. This includes information relative to previous repairs or modifications. 

The documentation dossier may include drawings, technical specifications, operating conditions and dismantling and assembly instructions, for example. Records of inspections and of any jobs performed on a flameproof motor need to be retained by the repair facility.  

Ensure flameproof joint repairs respect manufacturer’s documentation: Common faults include damaged or corroded flameproof joints which may be repaired by means of material addition and machining following the methods approved in IEC 60079-19. However, the resultant joint gap must respect the manufacturer’s documentation. If this documentation is not available, guidance can be found in IEC 60079-19.

  
In accordance with the same standard, repaired or overhauled equipment must be marked with a relevant symbol, applicable standards, the name of the repairer and the date of repair. The symbol will either be the letter ‘R’ in a square box, which indicates repair in accordance with certificate documentation and the manufacturer’s specification, or the letter ‘R’ in an inverted triangle, which indicates repair in accordance with type-of-protection standards but not certificate documentation. 

In cases of systems that after repair do not comply with certificate documentation or type-of-protection standards, the original manufacturer’s label should be removed or altered to give clear indication that the equipment is not compliant. If a supplementary certificate cannot be obtained, the equipment is not in a suitable condition for use in an explosive atmosphere. 

Should any repair procedures require spare parts, these should be obtained directly from the manufacturer wherever possible. In the case of bolt replacement, they must be of the same type, diameter and with at least the same tensile strength as specified by the motor manufacturer. 

The correct maintenance of flameproof motors is crucial to assure the safety of personnel and plant in hazardous areas. Respecting the recommendations, manufacturer documentation and industry standards can make the difference between a unit that offers an operating life devoid of problems, and the occurrence of heavy vibration and noise that leads to damage and failure.

Following carefully prepared maintenance plans with periodic inspection and monitoring will help to predict potential faults and permit end users to take actions that minimise the risks and allow for preventive repairs. These repairs must be registered and documented to permit the tracing of modifications to the certified equipment, preferably respecting manufacturer documentation. Finally, the correct marking of the repair procedures is mandatory and permits inspection teams to access the conformity of installed equipment, granting that the safety of the hazardous area is maintained.

Pedro Maia is coordinator of research, development and certification at WEG.


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