OISD RP - 126
Amended edition
FOR RESTRICTED
CIRUCULATION
No.
SPECIFIC MAINTENANCE PRACTICES
FOR ROTATING EQUIPMENT
OISD RECOMMENDED PRACTICE 126
First Edition, August 1990
Amended edition, August, 1999
Oil Industry Safety Directorate
Government of India
Ministry of Petroleum & Natural Gas
OISD RP - 126
First Edition, August 1990
Amended edition, August, 1999
FOR RESTRICTED
CIRCULATION
NO.
SPECIFIC MAINTENANCE PRACTICES
FOR ROTATING EQUIPMENT
Prepared by
COMMITTEE ON
INSPECTION OF ROTATING EQUIPMENT
OIL INDUSTRY SAFETY DIRECTORATE
2ND FLOOR, “KAILASH”
26, KASTURBA GANDHI MARG
NEW DELHI - 110 001.
NOTE
OISD publications are prepared for use in the Oil and gas industry under Ministry of Petroleum and Natural Gas. These are the properties of Ministry of Petroleum and Natural Gas and shall not be reproduced or copied and loaned or exhibited to others without written consent from OISD.
Though every effort has been made to assure the accuracy and reliability of data contained in these documents, OISD hereby expressly disclaims any liability or responsibility for loss or damage resulting from their use.
These documents are intended only to supplement and not replace the prevailing statutory requirements.
Note 1 in superscript indicates the modification/ changes/addition based on the amendments approved in the 17th Safety Council meeting held in July, 1999.
FOREWORD
The Oil Industry in India is 100 years old. Because of various collaboration agreements, a variety of international codes, standards and practices have been in vogue. Standardisation in design philosophies and operating and maintenance practices at a national level was hardly in existence. This, coupled with feed back from some serious accidents that occurred in the recent past in India and abroad, emphasized the need for the industry to review the existing state of art in designing, operating and maintaining oil and gas installations.
With this in view, the then Ministry of Petroleum & Natural Gas, in 1986, constituted a Safety Council assisted by Oil Industry Safety Directorate (OISD), staffed from within the industry, in formulating and implementing a series of self regulatory measures aimed at removing obsolescence, standardising and upgrading the existing standards to ensure safe operations. Accordingly, OISD constituted a number of Functional Committees of experts nominated from the industry to draw up standards and guidelines on various subjects.
The present document on “Specific Maintenance Practices of Rotating Equipment” has been prepared by the Functional Committee on “Inspection of Rotating Equipment”. This document is based on the accumulated knowledge and experience of industry members and the various national and international codes and practices. This document is meant to be used as a supplement and not as a replacement for existing codes and practices. It shall be borne in mind that no standard can be a substitute for judgment of a responsible qualified maintenance Engineer. Suggestions are invited from the users, after it is put into practice, to improve the document further.
Suggestions for amendments to this document should be addressed to the Co-ordinator, Committee on “Inspection of Rotating Equipment”, Oil Industry Safety Directorate, 2nd Floor, “Kailash”, 26, Kasturba Gandhi Marg, New Delhi-110 001.
FUNCTIONAL COMMITTEE
ON
INSPECTION AND MAINTENANCE OF
ROTARY EQUIPMENTS
List of Members
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Name Designation & Position in
Organisation Committee
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1. Sh. K. Gopalakrishanan Sr.Maint.Mgr.CRL Leader
2. Sh.B.P. Sinha Chief Project MGR-MRL Member
3. Sh.Chotey Lal Chief Engineer ONGC Member
4. Sh.R.C. Chaudhary Office Engr.MGR BPCL Member
5. Sh.K.M. Bansal Chief Maint. MGR. IOC Member
6. Sh.Ehsan Uddin Director OISD Member
7. Sh.R.M.N. Marar Jt.Director OISD Member Co-ordinator.
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In addition to the above, several other experts from the industry contributed in the preparation, review and finalisation of this Recommended Practices.
SPECIFIC MAINTEANCE PRACTICES
FOR ROTATING EQUIPMENT
CONTENTS
SECTION PAGE NO.
1.0 Alignment Systems and Procedures
1.1 Scope
1.2 System Survey
1.3 Planning
1.4 Cold Alignment
1.4 Hot Alignment
1.6 Alignment Tolerance
2.0 Balancing
2.1 Scope
2.2 General
2.3 Selection of Number of Balancing Plane
2.4 Balancing Tolerances
3.0 Lubrication System
3.1 Scope
3.2 Functions of Lubricants
3.3 Types of Lubricants
4.0 Preservation of Spare Parts
4.1 Scope
4.2 General
4.3 Preservation of High Value Item
4.4 Preservation Procedure for Other Spare Parts
4.5 Preservation of Bearings
5.0 References
Appendix I
General Safety Precautions
SPECIFIC MAINTENANCE PRACTICES FOR ROTATING EQUIPMENT
1.0 ALIGNMENT SYSTEMS AND PROCEDURES
1.1 SCOPE
This section covers the standard alignment systems and procedures for rotating machinery, precautions to be taken before carrying out the alignment and general alignment guidelines.
1.2 SYSTEM SURVEY
Many steps vital to good machinery alignment should be taken well ahead of the actual ‘cold alignment’. Some of the items, which warrant specific attention, are as follows:
1.2.1 PIPING
A Visual inspection of piping is vital. The following checks should be carried out:
a) Whether the piping is installed in apparent agreement with the design criteria and is complete in all respects as per the drawing.
b) Whether proper placement and adjustment of guides, anchors and supports have been done, whether proper adjustment of tie bolts on expansion joints, correct positioning of hangers have been carried out, whether make up of flanges with gaskets in place have been completed and the bolts tightened.
c) Whether the system is in order so that post alignment piping modifications will not nullify the alignment effort.
d) Nomenclature with flow direction on pipes shall be given. Note 1
1.2.2 Grouting
Grouting should be checked to be sure it is complete and satisfactory.
1.2.3 Foundation bolts
Foundation bolts should be checked for tightness.
1.2.4 Shim packs
Shims are vital link between the machine and foundation. All shim packs should be removed at every machine support just prior to alignment. If the shims have burrs, rust etc. these should be removed and shims without rust, wrinkles, burs, hammer marks and dirt should be used. Use as few shims as possible and replace many thin shims with fewer shims of greater thickness. Stainless steel shims minimise alignment problems associated with shim deterioration.
1.2.5 Checking for Misalignment
Misalignment should be checked in the following manner. A dial indicator should be mounted on the machine support with the indicator stem resting on the sole plate. Watch the indicator as the hold-down bolts are loosened. If movement of the indicator is more than 0.025 to 0.05 mm, it is an indication of a problem that must be defined and eliminated. Remove the shim pack and check with feeler gauges to be certain the machine support is parallel with the sole plate. If not, regrout, re-machine the support or prepare tapered shims.
1.2.6 Checking the Causing for distortion
Test for gross distortion of casing can be made when shim packs are checked in the following manner:
a) With three supports tightened down, remove the shim pack from the fourth support.
b) Determine the total thickness of the shim pack and record the dimension.
c) Using feeler gauges, determine the distance from the sole plate to the machine support. Measure the dimension.
d) Subtract the feeler gauge dimension from the shim pack thickness. This is the total deflection of the machine casing with no support at the corner being checked.
e) Repeat the procedure at each of the four supports and compare the deflection of each. Gross differences in deflections at any of the four supports is an indication of probable casing distortion.
1.2.7 Checking for piping strain
Piping strain is seldom detectable by visual observation. However, gross problems can be detected by the following tests. Following the check of casing distortion, place dial indicators on the machine to monitor both vertical and horizontal movement of the casing or shaft. Loosen all the hold down bolts. If the machine moves more than the average observed when checking individual supports, it is obviously the result of an external force, i.e. the piping.
1.2.8 Bearings
Ensure that the bearings are properly installed in the machines and they are lubricated. Also check the bearing covers for proper tightening.
1.3 PLANNING
Alignment program should be properly planned in order to achieve good results within minimum time. Plans should include:
a) Determination of the desired placement of the shafts (cold settings) considering anticipated thermal growth of the various components. Definition of movement of shafts within bearing clearances, hydraulic loading and any other factors expected to produce relative movement of shaft center when the machines are operated.
b) Determining the sequence of alignment for multi unit trains. For two component trains determine which of the two machines is to be moved.
c) Selecting a specific method for determining relative shaft positions.
d) Deciding on tolerances for theoretical cold alignment settings.
e) Ensuring the quality of alignment bracket, dial indicators and shims required for alignment.
f) Making provisions for permanent recording of alignment data.
g) Ensuring that jack bolts are provided and they are free for moving the machine for alignment.
1.4 COLD ALIGNMENT
The term ‘cold alignment’ refers to the position of a machine’s shaft center line relative to the shaft center line of a connected machine, with both machines in a non operating or ‘cold condition. Cold alignment is normally the only check made to directly determine the relative position of the two shafts. Results of the check form the basis for determining shaft alignment during operation.
The face and rim method and the reverse indicator method are commonly used for accurately measuring the shaft alignment between machinery. In the face and rim method, a face (axial) measurement and a rim (radial) measurement determine the angle and position respectively of one shaft relative to another. The reverse indicator method uses two rim measurements, one from each coupling to locate one shaft center line relative to the other. Both the face and rim measurements are to be taken with dial indicators.
The face and rim method of alignment can be carried out by using a single dial indicator for taking the face reading or using two dial indicators for taking the face readings. The use of two dial indicators for taking face readings eliminates the effect of axial movement of the shafts during alignment. Procedure for carrying out the alignment using three dial indicators is as follows:
1.4.1 Alignment measuring procedure -Three dial method
The normal method of alignment measurement for turbomachinery is by using an apparatus with three dial indicators as shown in fig 1. The dial indicator with its axis in a radial direction measures the radial misalignment of the shafts. The two dial indicators with their axis in an axial direction measures the axial misalignment of the shafts. Normally the heaviest or the most centrally placed machine is made the reference for alignment.
1.4.2 Reading of the radial misalignment
Zero the radial indicator in correspondence to the vertical plane as indicated in the figure. Rotate the shaft in the operational direction of rotation and note the gauge readings at 900 intervals. Interpret the readings as positive if the dial indicator rod re-enters its appropriate place and negative if it does not. The readings are to be taken at least twice and ensure that the indicator operates with the rod at half stroke. It is advisable, especially for couplings with spacers, to recheck by moving the apparatus with the indicators from one shaft to the other.
The value of the misalignment in the vertical plane is rv=b/2 where b is the reading effected on the dial indicator after a rotation of 1800. Such are the values read after a rotation of 900 (W) and 2700 (Z) that their algebraic addition coincides, with the measurement taken after 180oC , i.e. b =W + Z (approx.), while their algebraic semi difference indicates the radial misalignment in the horizontal plane, i.e. values of W’, Z’ and ‘b’, must be considered with their sign.
1.4.3 Readings of the axial misalignment
The axial misalignment of the shafts (angular misalignment of the coupling) is read by means of two offset indicators of 1800 and zeroed to their initial position. For taking the reading of axial misalignment use the two vertically aligned indicators. Zero the indicators. Then rotate both shafts and record the measurements read on the dial indicators for each misplacement of 900 as indicated in figure 4.
Supposing that the two comparators are installed on the flange of the P Shaft (with the indicator button bearing on the flange of the Q shaft) and that the readings are made looking at the unit from left to right, we have the value of the axial misalignment in the vertical plane “av as av = d-g/2. If “av” is negative, the flanges appear open downwards and if av is positive flanges appear open upwards. The value of the axial misalignment angle in the vertical plane is obtained through
tg < v = av/o
The value of the axial misalignment in the horizontal plane as will be
ao = (c-o) --(F-h)
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2
If “ao” is negative flanges appear open leftwards. If “ao” is positive flanges appear open rightwards. The value of the axial misalignment angle in the horizontal plane “L” is obtained through tg < O = ao/o. Values of c,d,e,f,g and h must be considered with their sign.
1.4.4 Alignment correction procedure
First perform the correction of axial alignment on the vertical plane. It can be corrected by verifying the height of the shims placed underneath the support plates of the machine. As shown in figures the shims to be removed from underneath of the external support is obtained as follows:
S= av.L
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o
To correct the vertical radial misalignment, lift and lower the machine and without changing its angular position, insert or withdraw a shim from each support plate of the machine feet.
To correct the axial and radial misalignment on a horizontal plane, it is sufficient to horizontally move the machine by turning the set screws of the machine.
1.5 HOT ALIGNMENT
Alignment of machineries changes from ambient to operating conditions. Correction for this can be done in two ways:
a) By calculating the thermal growth of individual machineries and giving allowances for it in the cold alignment.
b) By shutting down a machine which had been allowed to stabilise at temperature, installing dial indicators and taking measurements.