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API STD 681:2010 pdf download

API STD 681:2010 pdf download.Liquid Ring Vacuum Pumps and Compressors for Petroleum, Chemical, and Gas Industry Services. Pipe threads shall be taper threads conforming to
ANSI B1.20.l.
2.3.4 For flammable and toxic service the threaded connection shall be seal welded; however, seal welding is not permitted on cast iron equipment, for instrument connections, or where disassembly is required for maintenance. Seal-welded joints shall bc in accordance with ASME
B 31.3.
2.3.5 Connections welded to the casing shall meet the material requirements of the casing, including impact values, rather than the requirements of the connected piping (see and
2.3.6 Openings for NPS 1¼, 2½, 3½, 5, 7, and 9 shall not be used.
2.3.7 Tapped openings not connected to piping shall be plugged with solid plugs furnished in accordance with ASME B 16.11. As a minimum, these plugs shall meet the material requirements of the casing. Plugs that may later require removal shall be of corrosion resistant material. A lubricant that meets the proper tcmperaturc specification shall be used on all threaded connections. Tape shall not be applied to threads of plugs inserted into oil passages. Plastic plugs are not permitted.
2.3.8 Flanges shall conform to ASME B 16.1, B 16.5, or
B 16.42 as applicable, except as specified in through Cast iron flanges shall he flat-faced. Flat-faced flanges wIth full raised-face thickness are acceptable on casings other than cast iron. Flanges that are thicker or have a larger outside diameter than that required by ASME B 16.5 or B 16.47 Series “B” are acceptable. Connections other than those covered by ASME B 16.5, B 16.47 Series “B” require the purchaser’s approval. Unlcss otherwise specified, mating parts for these nonstandard flanges shall be furnished by the vendor.
2.3.9 Machined and studded connections shall conform to the facing and drilling requirements of ASME B 16.1, B 16.5, or B 16.42. Studs and nuts shall be furnished installed. The first one and one half threads at both ends of each stud shall be removed. Connections larger than those covered by ASME shall meet the requirements of
2.3.10 All of the purchaser’s connections shall be accessible for disassembly without the machine being moved.
2.3.11 Casings shall be provided with a vent connection unless they are self-venting by the arrangement of the piping.
2.3.12 Casings shall be provided with sufficient drains to ensure complete drainage.
2.3.13 Welded branches of one inch nominal size or less shall be reinforced by gusset plates or otherwise adequately supported to avoid a fatigue failure at the point of attachment, particularly where a valve or other mass is supported from the branch.
2.4 External Forces and Moments
The manufacturer shall spccify the maximum allowable external forces and moments that the compressor or vacuum pump casing will withstand. These shall be at least equal to the values calculated in accordance with NEMA SM-23. The allowable forces and moments shall be shown on thc ouline drawing.
2.5 Rotating Elements
2.5.1 Rotating assemblies shall he designed to be stiff cnough to prevent contact between the rotor and the casing when operating a the maximum allowable differential pressure for all possible operating conditions. Calculated deflection of the shaft at the seals shall not exceed 50 micrometers (0.002 inches).
2.5.2 The impeller shall be either secured to the shaft by an interference fit or keyed, and be capable of transmitting a torque not less than 2.5 times that required for any specified duty, and provided with an arrangement for positive axial location.
2.5.3 Solid rotors are preferred. Hollow rotors wiH be acceptable only if furnished in compliance with one of the requirements specified in or The rotor is continuously self-venting. The rotor is provided with a plug to allow complete venting of any accumulated gas before beginning any maintenance activity.
2.5.4 Shafts shall be made of one piece, forged steel or hot rolled bar stock and be of ample size to transmit the maximum torque required under any specified operating conditions and to withstand continuously all stresses resulting from supported weights, thrusts, and starting, including direct-on-line motor starting.
2.5.5 Shafts shall be provided with renewable shaft.


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