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API Std671， Special Purpose .ouplings for Petroleum .hemicaland Gas IndustryServices， .rdEdition， October 1998
This standard covers the minimum requirements for special purpose couplings intended to transmit power between the rotating shafts of two pieces of refinery equipment. These couplings are designed to accommodateparallel offset， angular misalignment， and axial displacement of the shafts without imposing excessive mechanical loading on the coupled equipment.
ANSI/API Std 67.Vibration，Axial-Position， and Bearing-TemperatureMonitoringSystems， .rdEdition， November 199.
Provides a purchase specification to facilitate the manufacture， procure-ment， installation， andtesting ofvibration， axialposition， and bearingtemperature monitoring systems for petroleum，chemical， and gas industry services. covers the minimum requirements for monitoring radial shaft vibration， casingvibration， shaft axial position， and bearing temperatures. It outlines a standardized monitoring system and covers requirements forhardware (sensors and instruments)， installation， testing， and arrangement. Standard 678 has been incorporated into this edition of standard 670. This iswell-documented， standard， and widely used in all industries.
Application of the Mechanical Standards to the Gas Turbine
An examination of the above standards as they apply to the gas turbine and its auxiliaries are further examined in this section. The ASME B 133.2basic gas turbines and the API standard616， gas turbines for thepetroleum，chemical， and gas industry services are intended to cover the minimum specifications necessary to maintain a high degree of reliability in an open-cycle gas turbine for mechanical drive， generatordrive， or hot-gas genera-tion. The standard also covers the necessary auxiliary requirements directly or indirectly by referring to other listed standards.
The standards define terms used in the industry and describe the basicdesign of the unit. It deals with thecasing， rotors andshafts， wheels andblades， combustors， seals，bearings， critical speeds， pipe connections andauxiliarypiping， mounting plates， weather-proofing， and acoustical treat-ment.
The specifications call preferably for a two-bearing construction. Two-bearingconstruction is desirable in single-shaft units， as a three-bearing configuration can causeconsiderable trouble， especially when the center bearing in the hot zone develops alignment problems. The preferable casing is a horizontally split unit with easy visual access to the compressor andturbine， permitting field balancing planes without removal of the major casing components. The stationary blades should be easily removable with-out removing the rotor.
A requirement of the standards is that the fundamental natural frequencyof the blade should be at least two times the maximum continuousspeed， and at least 10% away from the passing frequencies of any stationary parts. Experience has shown that the natural frequency should be at least four times the maximum continuous speed. care should be exercised on units where there is a great change in the number of blades between stages.
A controversial requirement of the specifications is that rotating blades or labyrinths for shrouded rotating blades be designed for slight rubbing. Aslight rubbing of the labyrinths is usually acceptable， but excessive rubbing can lead to major problems. New gas turbines use ..squealer blades.. somemanufacturers suggest using ceramic tips， but whatever is done， great careshould be exercised， or blade failure and housing damage may occur.
Labyrinth seals should be used at all external points， and sealing pressures should be kept close to atmospheric. The bearings can be either rolling element bearings usually used in aero-derivative gas turbines and hydro-dynamic bearings used in the heavier frame type gas turbines. In the areaof hydrodynamics bearings， tilting pad bearings arerecommended， since they are less susceptible to oil whirl and can better handle misalignment problems.
　
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