examination of critical centrifugal fans and blowers

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Engineering Design Guide: GBHE-EDG-MAC-2220

Examination of Critical Centrifugal Fans and Blowers Information contained in this publication or as otherwise supplied to Users is believed to be accurate and correct at time of going to press, and is given in good faith, but it is for the User to satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no warranty as to the fitness of this information for any particular purpose and any implied warranty or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented by law. GBHE accepts no liability resulting from reliance on this information. Freedom under Patent, Copyright and Designs cannot be assumed.



Engineering Design Guide: Examination of Critical Centrifugal Fans And Blowers

CONTENTS SECTION 0 INTRODUCTION/PURPOSE 2

0.1 Reasons for Critical Classification of Arduous Duty Fans < 500 kW 2

0.2 Reasons for Critical Classification of Arduous Duty Fans > 500 kW 2

0.3 Critical Classification for High Substance Hazard Reasons

0.4 Centrifugal Blowers 2 0.5 General Purpose Fans 3

1 SCOPE 3 2 FIELD OF APPLICATION 3 3 DEFINITIONS 3 4 PRINCIPLES 4 5 CONDITION MONITORING 4



6 EXAMINATION 4

6.1 Impeller 5

6.2 Shaft and Sleeves 5 6.3 Bearings 5

7 ADDITIONAL EXAMINATION REQUIREMENTS FOR

ALL FANS DEEMED CRITICAL FOR HIGH PROCESS SUBSTANCE HAZARD REASONS 7

7.1 Casing 7

7.2 Dynamic Seals 7



APPENDICES A EXAMINATION LOGIC DIAGRAM DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE



0 INTRODUCTION/PURPOSE GBH Enterprises categorizes fans Into Arduous and General Purpose (non-arduous) duties according to various criteria as defined in the appropriate specifications below: GBHE-EDS-MAC-1809: The Design & Construction of Steel Centrifugal

Fans Operating on Arduous Duties. GBHE-EDS-MAC-1810: General Purpose Fans GBHE-EDP-MAC-6601 requires the Identification and registration of Critical Machines Systems. Included amongst these are Arduous Duty fans as defined in GBHE-EDS-MAC-1809 and also those fans and blowers deemed Critical for high substance hazard reasons. This Guide is intended to assist the Specialist Engineer In the verification of the design of Critical fans and blowers as required by GBHE-EDP-MAC-3604 and in the preparation of the necessary Schemes of Examination. 0.1 Reasons for Critical Classification of Arduous Duty Fans < 500 kW In this category, the concern is failure of the Impeller due to overstressing. The boundary between arduous duty and non-arduous duty is defined by a line on a graph of impeller tip speed v. Impeller shape factor (see Figure 1 in GBHE-EDS-MAC-1809. This approximates to the maximum stress levels acceptable In normal' carbon steel materials. For other criteria for Arduous Duty Fans see GBHE-EDS-MAC-1809, Clause F.2. Other possible failure modes. E.g. shaft couplings, etc, would not result In a Critical classification. Design Verification in this case will confine itself to ensuring that the Impeller is adequately designed for the duty and that manufacture and testing were in accordance With GBHE-EDS-MAC-1809. Similarly the subsequent Scheme of Examination will also confine itself to maintaining the Integrity of the Impeller.



0.2 Reasons for Critical Classification of Arduous Duty Fans > 500 kW In this category, the concern is both the failure of the impeller as in 0.1, and any other failure that could release significant kinetic energy. As a result, the Design Verification Will need to look at the wider mechanical issues Including drives, couplings, bearings, shafts, etc, as well as those specified In 0.1, above. In either of these cases, any Scheme of Examination which required the routine stripping and detailed Inspection of parts would seem to be inappropriate unless deterioration is expected. Instrument protection (e.g. vibration, bearing temperatures) and routine condition monitoring would be more appropriate. 0.3 Critical Classification for High Substance Hazard Reasons Arduous Duty fans and General Purpose fans are considered during classification according to GBHE-EDP-MAC-3602 against the various criteria. Sub clauses 0.1 and 0.2 above relate to mechanical hazards. If, however, the concern is loss of containment of a high hazard substance, then Design Verification needs to address additional aspects, such as Integrity of the casing welds and shaft dynamic seals (see 6.3 (b) and 6.5). 0.4 Centrifugal Blowers Centrifugal blowers should be considered as Arduous Duty fans for the purpose of this Guide. 0.5 General Purpose Fans General Purpose fans cannot be > 500 kW. They can only be deemed Critical for high substance hazard reasons. In the future it is envisaged, however that for all such duties Arduous Duty fans designed and constructed to GBHE-EDS-MAC-1809 would be specified. Where steel construction is adequate (see 0.3 above).



1 SCOPE This Guide addresses itself to the mechanical integrity of the fan/blower, in particular of the impeller, for Arduous Duty fans < 500 kW as 0.1 above, and of additional items for Arduous Duty fans > 500 kW as 0.2 above. Also additional requirements are necessary for all fans deemed Critical for high substance hazard reasons as 0.3 above. The manufacturer's maintenance instructions should be adhered to In the renewing, rebalancing, reassembling and setting up of all components within the complete fan/blower system and that such work will be carried out by suitably trained personnel. 2 FIELD OF APPLICATION This Engineering Guide is for use by Specialist Engineers involved In the Design Verification of Critical centrifugal fans and blowers, and for general reference by machines engineers and also for use by works based engineers. Specific Schemes of Examination may be produced from the information presented. 3 DEFINITIONS For the purposes of this Guide. the following definitions apply: Critical Machine A Critical Machine System IS a machine system which has System been assessed to present an unacceptable hazard if the

machine or its protective system should fall. and where failure or malfunction could lead to danger of life. Significant harm to any person or to the environment.

Examination Examination means a careful and critical scrutiny of a

Registered Critical Machine by an authorized person to assess its actual condition and whether it is safe to use for the period up to the next Examination. An Examination may be 'thorough' or 'intermediate'. All examinations are 'thorough' unless specifically described as 'intermediate'.



Level 1 audits These are regular routine workplace audits undertaken by local plant teams.

Scheme of A Scheme of Examination defines the extent, nature Examination preparatory work and frequency of Examinations. With the exception of terms used as proper nouns or titles. those terms with initial capital letters which appear in this document and are not defined above are defined in the Glossary of Engineering Terms. 4 PRINCIPLES As a general principle, it IS recommended that the frequency of thorough Examinations is minimized commensurate with maintaining the integrity of the machine system. To this end, the use of correctly targeted conditioning monitoring is of prime importance. In addition work associated with intermediate Examinations should be minimized, again commensurate with maintaining the integrity of the machine system. If deterioration in service is not expected, e.g. due to erosion/corrosion, then the period between thorough Examinations could be fairly long. The Implementation of condition monitoring is key In this respect (see Clause 6 for more details). 5 CONDITION MONITORING Either continuous or routine periodic condition monitoring as appropriate, should be instigated for all Critical fans and blowers. The following key Items should be considered for monitoring, but (a) should be monitored as a minimum:" (a) Bearing vibration; horizontal, vertical and axial; (b) Bearing temperature; (c) Bearing lube oil pressure, if applicable.



Log sheets should be provided to operating personnel which clearly indicate the normal reading as a standard together with all maximum and minimum values. The sheets should also provide guidance on actions to be taken at certain levels. A lubrication schedule should be available and adhered to rigorously. An oil analysis program should be considered. Level l audits should be In place to provide the necessary check that the system is working. 6 EXAMINATION A Scheme of Examination for a specific critical fan/blower should be based on the following guidelines. and the approach to be adopted should be In stages. (a) Stage 1 Condition Monitoring Implementation of condition monitoring should commence within 3 months of the fan being classified as a Critical Machine System. The Initial readings should be compared with the expected normal readings. As an example, for vibration levels, the manufacturer's data should be checked, but for general guidance, fans should conform to as 4675 Class A quality Judgment or the Good Quality Judgment of ISO 3945 (I.e. 2.8 mm/s RMS). Corresponding alarm and trip settings are suggested:- Normal 2.8 mm/s RMS Alarm 10 mm/s RMS Trip 18 mm/s RMS Depending how the various readings compare then different lines of action may be necessary. See the Examination Logic Diagram (Appendix A).



Further information on Vibration Monitoring can be obtained from GBHE-EDG-MAC-4506. (b) Stage 2 Intermediate Examination With the fan shut down and isolated the unit should be disassembled, as appropriate, cleaned and inspected in-situ as thoroughly as possible In accordance with the relevant sub-clauses, 6.1 to 6.3 inclusive. For example, all that may be required to be done is an in-situ rebalancing to the specified quality grade of the rotating assembly after cleaning. Checks after start up should then establish that vibration levels are satisfactory. If so, the machine can run and condition monitoring and trend analysis should continue. (c) Stage 3 Thorough Examination If possible this should be carried out in-situ but if this is not possible, the rotating Assembly should be removed from the casing and transported to a workshop environment. The impeller should only be withdrawn from the shaft and any keys and half coupling removed when deemed necessary by examination. If this is necessary all items should be thoroughly cleaned to allow examination which should include: 6.1 Impeller This sub clause applies to all Critical Arduous Duty fans and Critical General Purpose fans. (a) Visual inspection and dimensional checking of the backplate. blades, eye-

ring, shrouds for signs of erosion/corrosion, and surface cracks, deformation, etc.

(b) 100% MPT (or DPT if non-magnetic) of all fillet and butt welds.

Radiography of butt welds should be considered if the MPT or DPT indicate possible defects.

(c) Ultrasonic thickness checks of hollow section blades, on fans on

erosive/abrasive duties. The following sub-clauses (6.2 and 6.3) apply to Arduous Duty fans > 500 kW.



6.2 Shaft and Sleeves (a) Visual inspection and dimensional checking of the shaft, including the

journal areas or sleeves for bearings and seals, and changes in section, etc.

(b) 100% MPT (or DPT if non-magnetic), to stress raisers. E.g. keyways,

thread undercuts, changes of section, dowel holes etc. 6.3 Bearings During service just prior to shutdown, the condition of the bearings may be ascertained by audible means, by measuring the temperature and by examining the lubricant. In addition portable vibration monitors may be used where permanent monitors are not fitted. (See Clauses 4 and 5 above.) 6.3.1 Rolling Element Bearings I Radial and Thrust) (a) The rings, cage, rolling elements and other parts of the bearing

arrangement should be thoroughly cleaned using a suitable solvent. (b) They should be then visually inspected for evidence of wear or fatigue of

the tracks, elements and cages and dimensionally checked including Internal clearance, if practicable.

Comparing the bearing 1.10 life with the known service period should assist in the decision whether to re-use the existing bearings or to replace by new ones.

Note: It is imperative that any new bearings fitted are to the correct specification with The appropriate internal clearance and they are from an approved manufacturer (see GBHE-EDS-MAC-1806). (c) After cleaning and inspection, bearings to be re-used should be oiled or

greased immediately using the appropriate in-service lubricant to prevent corrosion which can be rapid.



6.3.2 Plain Journal Bearings (a) These should be removed cleaned and visually inspected for signs of

wear or particle embedment. (b) The bores of the Journals should be dimensionally checked to ensure they

are within design limits. (c) Bearings should be replaced as deemed necessary from the above

actions. Bearings to be re-used should be Oiled or greased using the appropriate in-service lubricant.

6.3.3 Tilting Pad Radial and Thrust Bearings (a) These should be removed, cleaned and Visually inspected. (b) The tilting pads should be individually checked for freedom of movement. (c) The pads/other components or whole units should be replaced as deemed

necessary from the above actions. Items to be re-used should be re-oiled using the in-service lubricant. Individual pads should not be changed.

6.3.4 Fixed Taper Land Thrust Bearings (a) These should be removed and cleaned. (b) By visual inspection the taper lands should be checked for loss of metal

due to wear for signs of surface corrosion/erosion and for deposition. (c) The oil gullies between the taper land wedges and the oil flow control

weirs should be checked. (d) The shaft mating collar should also be Visually examined to check its

condition. (e) The bearings should be replaced as deemed necessary from the visual

inspection. For further detailed information on bearings see GBHE-EDS-MAC-1806. Bearing a arrangements for Machines.



7 ADDITIONAL EXAMINATION REQUIREMENTS FOR ALL FANS DEEMED CRITICAL FOR HIGH PROCESS SUBSTANCE HAZARD REASONS

7.1 Casing (a) After removal of the fan rotating assembly. the Interior of the casing

should be thoroughly cleaned and visually Inspected. (b) All important structural and sealing welds should be subjected to 100%

MPT (or DPT If non-magnetic). 7.2 Dynamic Seals During service just prior to shutdown the condition of the seal should be assessed for ingress/egress of gas, oil, moisture etc. where practicable. Seals should be removed thoroughly cleaned and visually Inspected with particular attention being paid to mechanical seal rotating and stationary faces, condition of springs, other components, labyrinths, Integrity of buffer systems, and all auxiliary dynamic and static seals.



APPENDIX A EXAMINATION LOGIC DIAGRAM