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Block Valve Packing Systems


1.0 Scope

This specification defines the minimum requirements for design, materials, packing arrangements, and installation and testing requirements for rising-stem and quarter-turn valve stem packing systems.

2.0 References

The following documents are considered part of this specification. Use the edition of each referenced document in effect on the date of the publication of this specification.

CFR–U.S. Code of Federal Regulations

40 CFR 60 Standards of Performance for New Stationary Sources

In the event of a conflict among the above listed standards or between the standards and other instructions listed in the specifications and drawing, it should be the Suppliers responsibility to notify the Buyer in writing for a resolution of the conflict prior to starting work.

3.0 Design


Figure 1 – Type 1 Graphite Packing Arrangements



Figure 2 – Type 2 Elastomer-Plastic Packing Arrangements

The packing should be selected to control fugitive emissions in compliance with local environmental regulations.

Packing system selection should be per Table 1 for the service, unless otherwise specified.

Table 1:  Packing System Selection

Service
Fluid Temperature Range Packing Type Styles
Hydrocarbons (including vapors), hydrogen, H2S (including sour water), steam and condensate, organic solvents, caustic, air, inert gases, additives, water (including salt/brackish), ammonia, amines −400°F (−240°C)
to
1000°F (540°C) (1)
Type 1 A, and B1 or B2
Acids, halogens, oxygen and other strong oxidizers −450°F (−268°C)
to
450°F (232°C)
Type 2 (2)(3) C
Notes:
  1. Use over 1000°F (540°C) or colder than −400°F (−240°C) requires approval of the Buyer.
  2. Type 1 packing may be used in services where low concentrations of strong oxidizers exist with approval of the Buyer.
  3. Type 2 packing should not be used in a valve designated to be fire safe, unless a secondary fire safe packing, completely independent of the primary packing, is used and approved by the Buyer. Actual packing temperature should not be less than −80°F (−62°C).

Type 1 packing systems should have an active zinc, passive barium molybdate, or passive phosphorus based corrosion inhibitor, either embedded in each graphite ring or in the form of a surface coat.  Separate zinc washers between packing rings should not be used.  Barium molybdate based corrosion inhibitors should not be used in HF acid services.

Bushings (spacers), not additional rings of packing, should be used to take up excess depth, if any, in the stuffing box.  Bushing material should be either the same nominal chemical composition as the valve body or stem (preferred), or alternatively, 95 percent plus pure carbon bushings with corrosion inhibitor may be used when the bottom of the stuffing box is flat.

Graphite based die-formed rings, braided rings and bushings, should have a minimum carbon content of 95 percent, no more than 100 ppm leachable chloride content, and no more than 1500 ppm sulfur content, and should not contain binders, lubricants, or other additives.

Type 1 end (wiper) rings should be Style A.  The inside (sealing) rings may be either Style B1 or B2 (Style B2 preferred) for infrequently cycled valves, and should be Style B2 for frequently cycled and repacked valves.

Type 1 or Type 2 packing ring cross sections may be other than rectangular if they are supplied as a manufacturer's standard configuration.

Unless otherwise approved by the Buyer, five ring packing sets should be used on API STD 600 and ASME B16.34 gate valves, and other rising stem valves.

Unless otherwise approved by the Buyer, four ring packing sets should be used on all quarter-turn valves (ball, plug and butterfly types) except that for quarter turn valves NPS 1 (25 mm) and smaller, the wiper rings may be eliminated.

Endless die-formed packing rings should be used on all new and shop reconditioned valves.

When tandem packing sets with lantern ring are specified, the lantern ring should be of the same nominal chemistry as the valve body or stem, and should be configured as shown in Figure 3, for all-graphite packing systems unless otherwise specified.  Non-graphite tandem packing sets, if used, should have materials and configuration specified.

Use of live-loaded glands for packing systems should be approved by the Buyer.




Figure 3 - Tandem Graphite Packing with Lantern Ring Arrangement

4.0 Testing

When specified by the Buyer for new or reconditioned valves, a shop packing emission check should be done subsequent to the valve pressure testing, using the following procedure.  The number of valves to be tested should be specified.

  • The packing gland nuts should be loosened and the valve opened but not backseated or turned 90 degrees on 1/4 turn valves.  The area above and below the stuffing box should be dried by air blowing and the stem should be wiped dry.
  • Install valve packing according to the manufacturer's procedures and specifications.
  • The packing gland nuts should be tightened to the packing manufacturer's recommended values, and the stem cycled per the manufacturer's instructions, or at least once, closed to open, but not backseated.
  • The valve body should be pressurized with a light hydrocarbon gas, preferably methane.  Alternatively, a gas containing at least 50, by weight, percent hydrocarbons may be used; that gas must remain in gaseous form at the test pressure and 60°F (15°C).  Test pressure should be specified, with a minimum of 100 psig (690 kPa).
  • Using a VOC (Volatile Organic Compound) detection instrument, the gland area should be sniffed for emissions, to the 40 CFR 60 (Method 21) procedure.  Acceptable emission levels should be specified.



Tags: Block Valve Packing