Standard Technical Features of BTG System for Supercritical 660 ...

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Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Units18.1.3 Material selectionThe material used for power cycle piping shall be equal to or better than thefollowing unless specified otherwise:Design metal temperatureMateriali) Upto & including 400 0 C Carbon steel to ASME SA-106 Gr. B/Cor SA 210 Gr. C or equivalent.ii) Upto & including 550 0 C Alloy steel to ASME SA-335: P-11, P-12,P-22, P-91 or equivalent.iii) Upto & including 605 0 C Alloy steel ASME SA-335/213:P-91, P-92 or equivalent.iv) Above 605 0 C Austenitic stainless steel, P-92, Super304H, TP347H or equivalent.18.1.4 Pipe wall thicknessi) Pipe wall thickness calculation shall be made on the basis of procedureand formula given in ASME B 31.1. Stress values of piping materialfor calculation shall be selected from tables given in ASME B 31.1.Thickness, thus calculated shall be checked as per IBR formula (whereapplicable) and the more stringent of the two shall then be selected. Inany case the thickness selected shall not be less than the standardthickness specified in ANSI B 36.10. In such cases where thicknesscalculated does not fall in the standard range of thickness as given inANSI B 36.10, ID/OD controlled pipes as per ASA-530 shall also beacceptable.ii)iii)iv)The selected pipe thickness shall not be less than Sch.80 for alloy steel& carbon steel pipes of sizes 50 NB & below. The selected thicknessfor SS pipes shall not be less than Sch.40S of ANSI B36.19.For the piping systems likely to be subjected to two phase flow, i.e.down stream of control valves on heater drain lines etc. and for thelength of piping which is required for the proper mixing of spray waterat downstream of de-superheater, the selected thickness shall not beless than Sch.40 for pipe sizes above 50 NB but below 300 NB andSch. STD for pipe sizes 300 NB and above.To account for losses due to corrosion, erosion etc. during the plantservice life, an allowance of 1.6 mm/0.75 mm shall be considered inthe minimum wall thickness calculation of pipes as per ASMEB31.1/IBR respectively.18.1.5 Layouti) All high points in piping system shall be provided with vents. All lowpoints shall be provided with drains. Provisions of drains on steampiping shall be as per ASME code TDP-1. Drain lines shall beadequately sized so as to clear condensate in the line and prevent waterhammer and damage to turbine due to water induction.173
Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsii)iii)All piping shall be sloped towards the system low point such that slopeis maintained in both hot and cold condition.The pipe routing shall be such that a clear head room of not less than2.2 m above the walkways/ working area is available.18.1.6 Stress/ dynamic analysisi) Flexibility and stress analysis for various piping systems shall becarried out by the contractor as per the requirement of ANSI B 31.1.Analysis results shall satisfy the following:a) Calculated stresses in the piping system shall be within theallowable limits stipulated in ASME B 31.1 as well as IBR forpiping under the purview of IBR.b) Calculated forces and moments on equipment nozzles/TP shallnot be more than the allowable loading provided by equipmentmanufacturer(s). Flexibility analysis shall also calculate thedeflections in all directions (translational and rotational) toenable design and selection of hanger/support system.c) Besides the flexibility analysis, steam hammer analysis/ dynamicanalysis shall also to be performed wherever required to study theeffects of fast closure of steam admission valves and safety valveblowing. Requirements of additional restraints/ snubbers to takecare of these effects shall be established, and such restraints/snubbers shall be provided. The effects of seismic and wind loadsand adequate support to take care of the same shall be provided.ii)Cold pulling shall not be used and piping systems shall be so designedthat there will be no requirement of cold pull for meeting allowablereaction/ stress values.18.1.7 Specifications for piping and fittingsAlloy SteelCarbon Steeli) Pipesa) Material X20 Cr. Mo V 121 toDIN 17175ORASTM A335 Gr.P91ASTM 106 Gr. B/ Gr. C(ASTM 106 Gr. C for BFDand CRH design parametersORwith ASTM A335 P36/ WBASTM A335 Gr.P22 36 as alternate material forORASTM A335 Gr.P11 BFD design parameters)ORASTM A691 2-1/4 ASTM A 672 Gr. B60Cr. Class 22 CLASS-12/22(See Note below) (See Note below)b) Construction Seamless (See Note below)174
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