5　Basic Design

5.1　General Requirements

5.1.1　The equipment（including auxiliaries）shall be designed and constructed for a minimum service life of 20 years and at least 3 years of uninterrupted operation（periodic shutdown is permitted due to replacement of spare parts）.Unless otherwise approved by the purchaser in written form，the products supplied by the vendor shall be within the range of his design and manufacture experiences，and shall have two or more years of proven applications available for at least two trains of the same type operated under the same or similar process conditions.

5.1.2　The vendor shall assume unit responsibility for all equipment and all auxiliary systems included in the scope of the Contract.Unless otherwise specified，the vendor shall assume the technical responsibilities for the proper configuration of the machine train，including compressors，drivers，oil systems，controls and instrumentation，couplings，associated accessories and piping systems.For details about the vendor's scope of supply，refer to Appendix A of this Specification.

5.1.3　Unless otherwise specified，compressors，drivers and their accessories shall be suitable for outdoor startup and continuous operation under specified environment conditions.The compressor shall be suitable for air test running on the field.

5.1.4　Cooling water systems shall be designed based on the utility conditions specified by the purchaser，and shall be provided with provisions for complete venting and drainage.

5.1.5　The minimum temperature rise of the water side for the cooling water system shall be specified by the purchaser based on the utility condition.Unless otherwise specified，the minimum temperature rise of the gas cooler shall be 8℃or greater，and oil cooler shall be 4℃or greater.Other parameters shall comply with 6.1.7 of API Std 618-2007.

5.1.6　Opposed-balanced or opposed compressor is preferred，which shall be directly coupled with low constant speed motor.When variable-speed driver is used，all equipments shall be designed to run safely throughout the operating speed range，up to and including the trip speed.For variable-speed drivers，the vendor shall provide a list of unsafe speeds to the purchaser，and the list shall be in accordance with 6.7 and 7.6.2 of API Std 618-2007.

5.1.7　The design and arrangement of the equipments in the compressor train shall be in accordance with 6.1.8 through 6.1.11，6.1.13，6.1.14 of API Std 618-2007.

5.1.8　Motors，electrical apparatus，electrical components and material shall be applicable to classification of hazardous areas，gas group and temperature group specified in purchaser's data sheets（refer to Appendix B of this Specification）based on GB 3836.14 or IEC standard.If 500，501，502 and 504 of NFPA Std 70-2011 or other standard is used；approval of the purchaser is required.

5.1.9　The purchaser shall specify the equipment's normal operating point and the certified point（no negative tolerance of the capacity）.The vendor shall guarantee the capacity of the specified point with no negative tolerance.The vendor shall submit the positive tolerance between the compressor's rated capacity and the specified capacity.This tolerance shall not be more than 3%.

5.1.10　The vendor shall use the specified values of mass flow，the specified gas composition，and the specified gas conditions to calculate molecular weight，ratio of specific heats（Cp/Cv），compressibility factors（Z）and inlet volume flow（at the suction pulsation suppression device inlet flange）.The vendor shall indicate his values on the data sheet.All equipment and related technical documents and drawing notes，which are provided by the vendor，shall be in SI units.Compressor performance guarantee values shall be given in the proposals.

5.1.11　If any of the compressor cylinders are to be operated partially or fully unloaded for extended periods of time，the vendor shall provide the measures and implementation methods to purge accumulation of lube oil in the compressor cylinders（for example，periodic momentary loading）.

5.1.12　For compressors installed in outdoors（with or without a roof），entirely or partially exposed to the atmosphere，the following measures of protection shall be provided at least：

a）The crankcase shall be enclosed.

b）The distance piece shall be enclosed，and equipped with vent and nitrogen purging connections in accordance with 6.13.1.6 of API Std 618-2007.

c）If winterizing is required，the heating or tracing facilities should include crankcase，oil lines，lubricators and cooling water lines，etc.

d）Cooling water spaces and lines may be drained completely.

5.1.13　If the process unit has the definite requirements that the compressed gas shall not contain any mineral or synthetically lubricant，the compressor cylinders and packings shall be operated on nonlubricated if technically exercisable.If there is no otherwise specified，the lubricator may be provided，the design of piston ring，wear band and packings shall be non-lubricated，and operated on little oil condition.

5.1.14　The compressor shall be designed to safety operation under the trip speed when the discharge pressure approaches the safety relief valve set pressure.And the compressor shall also be able to withstand the effects under a fully loaded shutdown against safety relief valve set pressure.In the case of an electrical motor driver，the compressor train shall be able to withstand the effects of a two-phase short circuit.

5.1.15　The system shall be capable of starting up and shutting down with each stage unloaded.In addition，the vendor shall take one of the following safety measure：

a）All the compressor stages shall be designed to start up and shutdown with fully operating pressure.

b）Equipped with a torque limiting device.

c）Provide interlocks of automatic unloading and ensure that the compressor cannot start-up with load.

5.1.16　The vibration level of the installed，foundation mounted，compressor frame shall not exceed an unfiltered peak velocity of 2.5mm/s and 100μm unfiltered peak to peak vibration.This vibration measurement shall be taken at the bottom of the frame.The vibration of the cylinders mounted to the installed frame shall not exceed 7.5mm/s unfiltered peak velocity.The compressor vendor shall provide all required data to enable the foundation designer to meet these requirements.

5.1.17　The compressor shall also be in accordance with 6.1.18 through 6.1.21，6.1.23，6.1.25，6.1.26 of API Std 618-2007.