Lubricated Air Compressors - Operating and Maintenance Procedures Required to Avoid Fires and Explosions

GBH Enterprises, Ltd.

Engineering Design Guide:
GBHE-EDG-MAC-2234

Lubricated Air Compressors Operating and Maintenance
Procedures Required to Avoid Fires
and Explosions
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.

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Engineering Design Guide:

Lubricated Air Compressors Operating and Maintenance
Procedures Required to Avoid
Fires and Explosions

CONTENTS

SECTION

0

INTRODUCTION/PURPOSE

2

1

SCOPE

2

2

FIELD OF APPLICATION

2

3

DEFINITIONS

2

4

MODEL INSTRUCTIONS FOR OIL LUBRICATED
RECIPROCATING AIR COMPRESSORS

3

4.1

Introduction

3

4.2

Lubricating Oil

3

4.3

Oil consumption

3

4.4

Operating Discharge Temperatures

3

4.5

High Discharge Temperature Trips

3

4.6

External Visual Inspection of Pipework

3

4.7

Routine Removal of Carbon Deposits

3


5

4

5.1

Introduction

4

5.2

Lubricating Oil

4

5.3

Oil Consumption

4

5.4

Oil Change Frequency

4

5.5

Separator Element Change Frequency

4

5.6


4

5.7

6

MODEL INSTRUCTIONS FOR OIL FLOODED ROTARY
COMPRESSOR

High Discharge Temperature Trip

4

LOG SHEETS

5

APPENDICES

A

EXPLANATORY NOTES FOR RECIPROCATING COMPRESSORS

B

EXPLANATORY NOTES FOR OIL FLOODED ROTARY
COMPRESSORS

DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE


0

INTRODUCTION/PURPOSE

In the industry there have been a significant number of fires and explosions in
reciprocating air compressors with cylinder lubrication and oil flooded rotary air
compressors. The cause of these fires and explosions has been, either the
spontaneous ignition of a solid carbonaceous material deposited on the internal
surfaces of the discharge system, or the ignition of a flammable air/oil mixture.
Suitable operating and maintenance procedures would have contributed to the
elimination of these hazards.
The carbonaceous deposit results from the thermal decomposition of the cylinder
lubricating oil at elevated temperatures.
As a result of such incidents, all such compressors will be registered as 'critical
machines systems' (see GBHE-EDP-MAC-6601) and the design and operation
verified. A key part of verification will be to check that the maintenance and
operating instructions provide the information necessary to ensure that fires and
explosions can be prevented. This design guide includes model instructions
which, when completed for the particular installation, will meet this objective.

1

SCOPE

This GBHE Engineering Guide gives advice on the operating and maintenance
procedures required to avoid fires and explosions in lubricated reciprocating air
compressors and oil flooded rotary compressors. Model instructions are provided
for each machine type.
Other safety-related issues, such as pressure relief and guarding, are not
covered by this document..

2

FIELD OF APPLICATION
This Engineering Guide applies to all lubricated air compressors.


3

DEFINITIONS

For the purposes of this Guide, the following definitions apply:
Critical Machines System

Any machines system so designated in the
machines classification review (see GBHEEDP-MAC-6601).

Lubricated (Reciprocating)
Air Compressor

A reciprocating air compressor in which oil is
injected to lubricate the cylinders and valves.

Oil Flooded Rotary Air
Compressor

A rotary air compressor in which oil is used to
cool the air and/or lubricate the
Compression mechanism. Examples are screw and
sliding vane compressors.

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

MODEL INSTRUCTIONS FOR OIL LUBRICATED RECIPROCATING
AIR COMPRESSORS

4.1

Introduction

This compressor has oil lubricated cylinders. Use of the incorrect oil, or operation
with excessively high discharge temperatures, can cause the oil to decompose to
form a carbon-like deposit which builds up on the internal surfaces of the
discharge system. This can ignite if it becomes more than (specify - see
Appendix A Note 1) mm thick and cause a fire or explosion.

4.2

Lubricating Oil

The lubricating oil for the cylinders and crank case shall be (specify code number
- see Appendix A Note 2).


4.3

Oil consumption

The normal oil consumption of the compressor is (specify - see Appendix A Note
3). The actual amount of oil used shall be recorded on the log sheet.
If the consumption increases to (specify) or more, the (specify) should be
informed.
4.4


The normal maximum discharge temperatures are (specify for each stage - see
Appendix A Note 4). The actual discharge temperatures will be affected by
operating conditions and will generally be less than this. The actual temperatures
are displayed (specify where) and should be recorded on the log sheet every
(specify - see Appendix A Note 5). If the normal maximum
temperature(s) are exceeded, inform (specify).
Some of the possible causes of high discharge temperatures are:
(a)

Inadequate intercooler performance

- fouling
- low water flow rate
- high inlet water temperature;

(b)

Inadequate cylinder cooling

- fouling
- low water flow rate
- high inlet water temperature;

(c)

Discharge valves passing ;

(d)

High air inlet filter pressure drop.

4.5

High Discharge Temperature Trips

High discharge temperatures trips are fitted to each stage and are set at (specify
– see Appendix A Note 2).
4.6

External Visual Inspection of Pipework

Any signs of overheating of discharge pipework - e.g. blistered paint, shall be
reported to (specify).


4.7

Routine Removal of Carbon Deposits

Internally inspect the machine discharge ports, discharge pipework and any
vessels up to and including the aftercooler every (specify - see Appendix A Note
6). Remove any carbon deposits by mechanical means.

5

MODEL INSTRUCTIONS FOR OIL FLOODED ROTARY
COMPRESSOR

5.1

Introduction

This compressor is of the oil flooded rotary design. Oil lubricates and cools the
rotating parts and the discharge air. If the oil flow is reduced, or the oil cooler
does not operate correctly, a fire or explosion can occur in the discharge system.

5.2

Lubricating Oil

The oil used in the compressor is (specify - code number - see Appendix B Note
1).

5.3

Oil Consumption

The normal oil consumption of the compressor is (specify - see Appendix B Note
2). The actual amount of oil used shall be recorded on the log sheet. If the oil
consumption increases to (specify) the (specify) should be informed.

5.4

Oil Change Frequency

The compressor oil shall be changed every (specify - see Appendix B Note 3).

5.5

Separator Element Change Frequency

The separator element shall be changed every (specify - see Appendix B Note
4). The resistance to earth of the element shall be checked at this time.
Maximum resistance shall be 100 ohms.


5.6


The normal maximum discharge temperature is (specify - see Appendix B Note
5). The actual discharge temperature will be affected by operating conditions and
will generally be less than this. The temperature should be recorded on the log
sheet every (specify - see Appendix B Note 6). If the normal, maximum
temperature is exceeded, inform (specify).
Some of the possible causes of high discharge temperatures are:
(a)

Low oil level;

(b)

High inlet filter pressure drop;

(c)

Loss of cooling air;

(d)

Fouling of oil cooler;

(e)

High pressure ratio;

(f)

Increased rotor clearance.

5.7

High Discharge Temperature Trip

The high discharge temperature trip is set at (specify - see Appendix B Note 7).
This is tested as part of the routine trip and alarm tests (see Appendix B - Note
7).

6

LOG SHEETS

Log sheets should be designed to both inform and guide the operator as well as
to record operating conditions. The maximum and/or minimum allowable values
for each of the readings should be indicated where appropriate. As a minimum
for both reciprocating and rotary compressors these would include:
(a)

Maximum operating discharge temperatures;

(b)

Maximum oil consumption.

In such cases the log sheet should indicate the appropriate action; e.g. inform
supervisor.

APPENDIX A

EXPLANATORY NOTES FOR RECIPROCATING
COMPRESSORS

Note 1
Spontaneous combustion can occur under the following conditions:

Compressor Discharge Pressure
(barg)

Guidance on maximum allowable
Carbon Deposit Thickness to
avoid spontaneous combustion
(mm)

P < 10
10 P < 30
30 P

3
2
1

Note 2
The crankcase and cylinder oils shall be to the same specification. The following
oils are commonly used in compressors.
The maximum, normal operating and trip temperatures for each stage are the
same and are as listed.

Maximum Temperatures
Discharge Pressure
Oil
P (barg)

Operating
T o (°C)

Trip
T t (°C)

Straight mineral oil
to BS 4475

P 30

T o 140

T t 150

DIN 51 506 VD-L
(e.g. Shell Corena P)

P 30

T o 160

T t 170

30 < P 100

T o 140

T t 150

Others

Consult Machines Section


Note 3
The anticipated normal oil consumption can be either obtained from the
manufacturer or from experience. If consumption increases to 150% of the
normal, an appropriate supervisor/manager should be informed.

Note 4
The normal maximum discharge temperatures for each stage can either be
obtained from the manufacturer or from experience.

Note 5
Discharge temperatures should be recorded at least once per shift.

Note 6
Initially, examine the discharge pipework after six months operation and then
adjust, based on experience.


APPENDIX B

EXPLANATORY NOTES FOR OIL FLOODED ROTARY
COMPRESSORS

Note 1
Use special air compressor oil, e.g. Shell Corena 27 or equivalent, or a turbine oil
to BS 489 : STO32.

Note 2
The anticipated, normal oil consumption can either be obtained from the
manufacturer or from experience. If consumption increases to 150% of the
normal, an appropriate supervisor/manager should be informed.

Note 3
The oil change frequency shall be as recommended by the compressor
manufacturer. This will typically be every 1000 or 2000 h.

Note 4
The separator element change frequency shall be as recommended by the
manufacturer for the conditions in which the compressor is operating. Dusty
environments will increase the frequency. Typically, a separator life of 4000 h
might be expected. A low resistance electrical path is required between the
element and the housing to avoid static build up.

Note 5
The normal maximum discharge temperature can either be obtained from the
manufacturer or from experience.

Note 6
Discharge temperature should be recorded at least once per shift.


Note 7
The high discharge temperature trip setting should be as recommended by the
manufacturer. However, this should not exceed 140°C. The testing procedure for
the trip shall include a time to trip. This time should be established during
commissioning and if any significant change occurs during routine testing the
reasons should be investigated.

DOCUMENTS REFERRED TO IN THIS ENGINEERING GUIDE
This Engineering Guide makes reference to the following documents:
BRITISH STANDARDS
BS 489

Turbine Oils
(referred to in Appendix B Note 1)

BS 4475

Straight Mineral Lubricating Oils
(referred to in Appendix A Note 2)

GBHE ENGINEERING PROCEDURES
GBHE-EDP-MAC-6601

Registration of Machines : Critical Machine Systems

GBHE ENGINEERING GUIDES
Glossary of Engineering Terms (referred to in Clause 3).


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