Salient point of API 610–Piping stress engineer

Salient point of API 610 a piping stress engineer needs to know

1)     Relevant industry operating experience suggests pumps produced to this International Standard are cost effective

When pumping liquids at conditions exceeding any one of the following:

NOTE For sealless pumps, reference can be made to API Std 685. For heavy duty pump applications in industries other than petroleum, petrochemical and gas processing, reference can be made to ISO 9905.

2)     The equipment (including auxiliaries) covered by this International Standard shall be designed and constructed for a minimum service life of 20 years (excluding normal-wear parts as identified in Table 20) and at least 3 years of uninterrupted operation.

3)     The vendor shall specify on the data sheets the NPSH3 based on water [at a temperature of less than 55 °C (130 °F)] at the rated flow and rated speed. A reduction or correction factor for liquids other than water (such as hydrocarbons) shall not be applied.

The purchaser should consider an appropriate NPSH margin in addition to the NPSH3 specified. An NPSH margin is the NPSH that exists in excess of the pump’s NPSH3. It is usually desirable to have an operating NPSH margin that is sufficient at all flows (from minimum continuous stable flow to maximum expected operating flow) to protect the pump from damage caused by flow recirculation, separation and cavitation.

4)     The arrangement of the equipment, including piping and auxiliaries, shall be developed jointly by the purchaser and the vendor. The arrangement shall provide adequate clearance areas and safe access for

operation and maintenance.

5)     Openings for nozzles and other pressure casing connections shall be standard pipe sizes. Openings of DN 32, DN 65, DN 90, DN 125, DN 175 and DN 225 (NPS 1 1/4, NPS 2 1/2, NPS 3 1/2, NPS 5, NPS 7 and NPS 9) shall not be used.

6)     Suction and discharge nozzles shall be flanged, except those on pumps with forged casings, which shall be flanged or machined and studded. One- and two-stage pumps shall have suction and discharge flanges of equal rating.

7)     Cast iron flanges shall be flat-faced and, except as noted in 6.4.2.4, conform to the dimensional requirements of ISO 7005-2 and the flange finish requirements of ANSI/ASME B16.1 or ANSI/ASME B16.42. PN20 (Class 125) flanges shall have a minimum thickness equal to that of PN40 (Class 250) flanges for sizes DN 200 (NPS 8) and smaller.

8)     The pressure casing shall be designed to

1. a) Operate without leakage or internal contact between rotating and stationary components while subject simultaneously to the MAWP (and maximum operating temperature) and the worst-case combination of twice the allowable nozzle loads of Table 5 applied through each nozzle;
2. b) Withstand the hydrostatic test (see 8.3.2).

NOTE: – The twice-nozzle-load requirement is a pressure-casing design criterion. Allowable nozzle loads for piping designers are the values given in Table 5, which, in addition to pressure casing design, include other factors that affect allowable nozzle loads, such as casing support and baseplate stiffness.

9)     Steel and alloy-steel horizontal pumps and their baseplates, vertical in-line pumps with supports anchored to the foundation, and vertically suspended pumps shall be designed for satisfactory performance if subjected to the forces and moments in Table 5 applied simultaneously to both suction and discharge nozzles in the worst case combination for the pump in question. For horizontal pumps, two effects of nozzle loads are considered: distortion of the pump casing (see 8) and misalignment of the pump and driver shafts (see 7.3.20).

Allowable forces and moments for vertical in-line pumps with supports not anchored to the foundation may be twice the values in Table 5 for side nozzles.

For pump casings constructed of materials other than steel or alloy steel or for pumps with nozzles larger than DN 400 (NPS 16), the vendor shall submit allowable nozzle loads corresponding to the format in Table 5.

10)  Annex F gives methods of qualifying nozzle loads in excess of those in Table 5. The purchaser should be aware that the use of the methods in Annex F can result in a misalignment up to 50 % greater than that based on the loads given in Table 5 and can impact equipment installation criteria. The use of the methods in Annex F requires approval by the purchaser and specific direction to the piping designers for its use.

11)  To minimize misalignment of the pump and driver shafts due to piping load effects, the pump and its baseplate shall be constructed with sufficient structural stiffness to limit displacement of the pump shaft at the drive end of the shaft or at the register fit of the coupling hub to the values shown in Table 13.

Sources:

• Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries, ANSI/API STANDARD 610,ELEVENTH EDITION, SEPTEMBER 2010,ERRATA, JULY 2011