scope:

General

This Standard specifies requirements and gives recommendations for sealing systems for centrifugal and rotary pumps used in petroleum, natural gas, and chemical industries. It has been written mainly for hazardous, flammable and/or toxic services where a greater degree of reliability is required for the improvement of equipment availability, the reduction of both emissions to the atmosphere and life cycle sealing costs. It covers seals for shaft diameters from 20 mm (0,75 in.) to 110 mm (4,3 in.). This Standard also applies to seal spare parts and can be referred to for the upgrading of existing equipment. The seal configurations covered by this Standard can be classified into three categories (1, 2 and 3), three types (A, B and C) and three arrangements (1, 2 and 3). Further, Arrangement 2 and 3 seals can be in three orientations: "face-to-back", "back-to-back" and "face-to-face". These categories, types, arrangements and orientations are defined in 1.2 and illustrated in Figures 2 through 6.

NOTE Figure 1 places all these concepts in one diagram. It is a comprehensive way to look at the relationships of these concepts.

Seal categories, types and arrangements

There are three seal categories, as follows:

1) Category 1 seals are intended for use in non-ISO 13709 seal chambers, preferably meeting the dimensional requirements of ANSI/ASME B73.1, ANSI/ASME B73.2 and ISO 3069 Type C seal chamber dimensions and their application is limited to seal chamber temperatures from − 40°C (− 40°F) to 260°C (500°F) and absolute pressures up to 22 bar (315 psi).

2) Category 2 seals are intended for use in seal chambers meeting the chamber envelope dimensional requirements of ISO 13709. Their application is limited to seal chamber temperatures from − 40°C (− 40°F) to 400°C (750°F) and absolute pressures up to 42 bar (615 psi).

3) Category 3 provides the most rigorously tested and documented seal design. It is required that the entire seal cartridge is qualification tested as an assembly in the required fluid in accordance with clause 10 and are provided with all the data requirements specified in clause 11. They meet the seal chamber envelope requirements of ISO 13709 (or equal). Their application is limited to seal chamber temperatures from − 40°C (− 40°F) to 400°C (750°F) and absolute pressures up to 42 bar (615 psi).

A summary of the main seal category differences is given in clause 11 and annex A.

Temperatures and pressures outside the ranges, or which involve fluids not included in annex A, may require engineering and seal selection guidance other than provided in this Standard.

There are three seal types, as follows:

1) Type A seal is a balanced, inside-mounted, cartridge design, pusher seal with multiple springs and in which the flexible element rotates. Secondary sealing elements are elastomeric O-rings;

2) Type B seal is a balanced, inside-mounted, cartridge design, non-pusher (bellows) seal in which the flexible element rotates. Secondary sealing elements are elastomeric O-rings; and

3) Type C seal is a balanced, inside-mounted, cartridge design, non-pusher (metal bellows) seal in which the flexible element is stationary. Secondary sealing elements are flexible graphite.

Type A and Type B are for temperatures up to 176°C (350°F); and a stationary flexible element is a data sheet selection. Type C seals are for high temperatures up to 400°C (750°F); a rotating flexible element is a data sheet selection.

There are three seal arrangements, as follows:

1) Arrangement 1: Seal configurations having one seal per cartridge assembly;

2) Arrangement 2: Seal configuration having two seals per cartridge assembly, with the space between the seals at a pressure less than the seal chamber pressure.

3) Arrangement 3: Seal configurations having two seals per cartridge assembly, utilizing an externally supplied barrier fluid at a pressure greater than the seal chamber pressure.

New technology designs and sealing methods are also considered, as follows:

1) Contacting wet seals "CW": Seal design where the mating faces are not designed to intentionally create aerodynamic or hydrodynamic forces to sustain a specific separation gap (refer to definitions);

2) Non-contacting seals (whether wet or dry) "NC": Seal design where the mating faces are designed to intentionally create aerodynamic or hydrodynamic separating forces to sustain a specific separation gap; (refer to definitions) and

3) Containment seals (whether contacting or non-contacting) "CS": Seal design with one flexible element, seal ring and mating ring mounted in the containment seal chamber.

Figure 1 places all these concepts in one diagram. It is a comprehensive way to look at the relationships of all these concepts.

Finally, Arrangement 2 and Arrangement 3 seals can be in the following three orientations:

1) Face-to-back (old tandem terminology): a dual seal in which one mating ring is mounted between the two flexible elements and one flexible element is mounted between the two mating seal rings;

2) Back-to-back: a dual seal in which both of the flexible elements are mounted between the mating seal rings; and

3) Face-to-face: a dual seal in which both of the mating seal rings are mounted between the flexible elements.

Objectives

Shaft sealing systems conforming to this Standard are intended to meet the following objectives:

1) All seals should operate continuously for 25,000 h without replacement;

2) Containment seals should run for at least 25 000 h (wet or dry seals) at any containment seal chamber pressure equal to or less than the seal leakage pressure switch setting [not to exceed a gauge pressure of 0,7 bar (10 psi)] and for at least 8 h at the full seal chamber conditions;

3) All seals should operate for 25,000 h while complying with local emissions regulations, or 1 000 ml/m³ (1 000 ppm vol) as measured by the EPA Method 21, whichever is more stringent.

Specifying and/or purchasing a sealing system

The data sheet (annex F) shall be used to convey purchasing requirements. Default requirements are identified therein that allow the purchaser to specify a seal with minimum information. The minimum data required on the data sheet to obtain budgetary pricing on a sealing system is expressed in the seal code (annex J). This assumes all standard defaults (construction features and materials). The minimum information required on the data sheet to purchase a seal with assurance that the selection will satisfy the objectives of 1.3 is the pump data, fluid data and seal specification.