Selection of Control Valves

COMPLETE REVISION March 2003

Process Industry Practices Process Control

PIP PCCCV001 Selection of Control Valves

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES In an effort to minimize the cost of process industry facilities, this Practice has been prepared from the technical requirements in the existing standards of major industrial users, contractors, or standards organizations. By harmonizing these technical requirements into a single set of Practices, administrative, application, and engineering costs to both the purchaser and the manufacturer should be reduced. While this Practice is expected to incorporate the majority of requirements of most users, individual applications may involve requirements that will be appended to and take precedence over this Practice. Determinations concerning fitness for purpose and particular matters or application of the Practice to particular project or engineering situations should not be made solely on information contained in these materials. The use of trade names from time to time should not be viewed as an expression of preference but rather recognized as normal usage in the trade. Other brands having the same specifications are equally correct and may be substituted for those named. All Practices or guidelines are intended to be consistent with applicable laws and regulations including OSHA requirements. To the extent these Practices or guidelines should conflict with OSHA or other applicable laws or regulations, such laws or regulations must be followed. Consult an appropriate professional before applying or acting on any material contained in or suggested by the Practice.

This Practice is subject to revision at any time by the responsible Function Team and will be reviewed every 5 years. This Practice will be revised, reaffirmed, or withdrawn. Information on whether this Practice has been revised may be found at www.pip.org.

© Process Industry Practices (PIP), Construction Industry Institute, The University of Texas at Austin, 3925 West Braker Lane (R4500), Austin, Texas 78759. PIP member companies and subscribers may copy this Practice for their internal use. Changes, overlays, addenda, or modifications of any kind are not permitted within any PIP Practice without the express written authorization of PIP.

PIP will not consider requests for interpretations (inquiries) for this Practice. PRINTING HISTORY October 1995 Issued March 2003 Complete Revision Not printed with State funds

COMPLETE REVISION March 2003

Process Industry Practices Process Control

PIP PCCCV001 Selection of Control Valves Table of Contents 1. Introduction................................. 2 1.1 Purpose ............................................. 2 1.2 Scope................................................. 2

2. References .................................. 2

9.2 Pressure-Drop Determination for Nonpumped Systems ...................... 14 9.3 Pressure-Drop Determination for Pumped Systems............................. 15 9.4 Secondary Control Valves ............... 15 9.5 Operating Range ............................. 15

2.1 Process Industry Practices ................ 2 2.2 Industry Codes and Standards .......... 2 2.3 Government Regulations ................... 3

10. Noise Considerations .............. 15

3. Definitions ................................... 4

11. Actuator .................................... 17

4. Body - General ............................ 5 5. Globe Valves ............................... 7 6. Rotary Valves.............................. 9 7. Trim............................................ 10 8. Bonnet ....................................... 11 8.1 8.2 8.3 8.4

General ............................................ 11 Gaskets............................................ 12 Packing ............................................ 12 Bolting .............................................. 13

11.1 11.2 11.3 11.4

General ............................................ 17 Diaphragm Actuator......................... 19 Piston and Vane Actuators .............. 20 Volume Tank ................................... 20

12. Positioner/Current-to-Pneumatic Transducer (I/P)........................ 21 13. Accessories .............................. 21 13.1 Handwheel Operator........................ 21 13.2 Limit Switches and Solenoid Valves 22

14. Marking, Identification, and Nameplate ................................. 23

9. Sizing Considerations.............. 14 9.1 General ............................................ 14

Process Industry Practices

Page 1 of 24

PIP PCCCV001 Selection of Control Valves

1.

COMPLETE REVISION March 2003

Introduction 1.1

Purpose This Practice provides designers and vendors the requirements for the selection and sizing of control valves.

1.2

Scope This Practice specifies requirements for selection and sizing of pneumatically actuated control valves, including requirements for body, bonnet, trim, actuator, accessories, and noise considerations. This Practice, along with a completed PIP PCSCV001, PIP PCECV001, and the individual control valve data sheets (i.e., ISA20 or equivalent), defines the minimum requirements for selection, materials, construction, and installation of control valves. This Practice does not cover requirements for motor-operated valves, on-off valves intended for emergency isolation, or valves with hydraulic actuators. Comment: The intention is that the owner will fill out the PIP PCSCV001 control valve specification sheet to define company and location generic requirements for control valves. This document is a complete revision of PIP PCCCV001, and therefore, revision markings are not provided.

2.

References Applicable requirements in the latest edition (or the edition indicated) of the following standards shall be considered an integral part of this Practice. Short titles will be used herein when appropriate. The owner shall be informed if portions of this Practice do not comply with referenced codes, standards, and regulations. 2.1

Process Industry Practices (PIP) – PIP PCECV001 - Guidelines for Application of Control Valves – PIP PCSCV001 - Specification of Control Valves – PIP PCSIP001 - Instrument Piping and Tubing Systems Specifications

2.2

Industry Codes and Standards • American Society for Mechanical Engineers (ASME) – Boiler and Pressure Vessel Code, Section VIII, Division 1 – ASME B16.5 - Pipe Flanges and Flanged Fittings – ASME B31.3 - Process Piping • Fluid Controls Institute Inc. (FCI) – ANSI/FCI 70-2- Control Valve Seat Leakage

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Process Industry Practices

COMPLETE REVISION March 2003

PIP PCCCV001 Selection of Control Valves

• The Instrumentation, Systems, and Automation Society (ISA) – ISA20 - Specification Forms for Process Measurement and Control Instruments, Primary Elements, and Control Valves – ISA75.03 - Face-to-Face Dimensions for Integral Flanged Globe-Style Control Valve Bodies (ANSI Classes 125, 150, 250, 300, and 600) – ANSI/ISA75.04 - Face-to-Face Dimensions for Flangeless Control Valves (ANSI Classes 150, 300, and 600) – ANSI/ISA75.05.01 - Control Valve Terminology – ANSI/ISA 75.08 - Installed Face-to-Face Dimensions for Flanged Clamp or Pinch Valves – ISA 75.08.04 - Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves (Class 4500) – ISA 75.08.07 - Face-to-Face Dimensions for Separable Flanged Globe-Style Control Valves (ANSI Classes 150, 300, and 600) – ANSI/ISA 75.15 - Face-to-Face Dimensions for Buttweld-End Globe-Style Control Valves (ANSI Classes 150, 300, 600, 900, 1500, and 2500) – ANSI/ISA 75.16 - Face-to-Face Dimensions for Flanged Globe-Style Control Valve Bodies (ANSI Classes 900, 1500, and 2500) – ISA 75.17 - Control Valve Aerodynamic Noise Prediction – ANSI/ISA 75.22 - Face-to-Centerline Dimensions for Flanged Globe-Style Angle Control Valve Bodies (ANSI Classes 150, 300, and 600) • International Electrotechnical Commission (IEC) – IEC 60534-8-3 - Industrial-Process Control Valves, Part 8, Noise Considerations, Section 8: Control Valve Aerodynamic Noise Prediction Method – IEC 60534-8-4 - Industrial Process Control Valves, Part 8, Noise Considerations, Section 8: Prediction of Noise Generated by Hydrodynamic Flow 2.3

Government Regulations • U. S. Environmental Protection Agency (EPA) Code of Federal Regulations (CFR) – EPA 40 CFR, Part 60, Appendix A, Attachment 1, Reference Method 21 Determination of Volatile Organic Compound Leaks – EPA 40 CFR, Part 61 - Monitoring Requirements – EPA 40 CFR, Part 63, Subpart H - National Emissions Standard for Organic Hazardous Air Pollutants from Synthetic Organic Chemical Manufacturing Industry Equipment Leaks • U. S. Occupational Safety and Health Administration (OSHA) – OSHA 1910.95 - Occupational Noise Exposure

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PIP PCCCV001 Selection of Control Valves

3.

COMPLETE REVISION March 2003

Definitions The following terms and their definitions are derived from ANSI/ISA75.05.01: ball valve: a valve with a rotary motion closure member consisting of a full ball or a segmented ball butterfly valve: a valve with a circular body and a rotary motion disk closure member, pivotally supported by its stem closure member: the movable part of the valve that is positioned in the flow path to modulate the rate of flow through the valve. Examples include the plug for a plug valve, the disk for a butterfly valve, and the ball for a ball valve. eccentric rotary disk: a spherical segment in a rotary motion valve that is not concentric with the disk shaft and moves into the seat when closing equal percentage characteristic: an inherent flow characteristic, which, for equal increments of rated travel, will ideally give equal percentage changes of the existing flow coefficient (Cv) flangeless control valve: a valve without integral line flanges, which is installed by bolting between companion flanges, with a set of bolts, or studs, generally extending through the companion flanges full ball: a closure member having a complete spherical surface with a flow passage through it. The flow passage may be round, contoured, or otherwise modified to yield a desired flow characteristic. globe body: a valve body distinguished by a globular-shaped cavity around the port region, wherein the closure member motion is linear and normal to the plane of the port lugged body: a thin annular section body with lug protrusions on the outside diameter of the body, having end surfaces mounted between the pipeline flanges or attached to the end of the pipeline without any additional flange or retaining parts, using either through bolting and/or tapped holes plug valve: a valve with a closure member that may be cylindrical, conical, or a spherical segment segmented ball: a closure member that is a segment of a spherical surface, which may have one edge contoured to yield a desired flow characteristic travel: the movement of the closure member from the closed position to an intermediate or the rated full open position wafer body: A thin annular section butterfly body having end surfaces located between the piping flanges and clamped there by bolts extending from flange to flange

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March 2003

4.

Body - General 4.1

Material, end connections, pressure rating, gaskets, and packing of valve body shall, as a minimum, conform to the applicable piping specification. The materials engineer shall approve any deviation from the piping specification. Comment: Special alloy bodies that differ from the piping specification may be required in conditions such as high temperature, severe erosion/corrosion, or critical applications such as oxygen.

4.2

Valves shall not be cast iron. Carbon steel shall be the minimally acceptable material on control valve bodies.

4.3

Control valves in flashing water service require harden body material such as 5 Cr-1/2 Mo.

4.4

Ratio of nominal pipe size to body size shall not be greater than 2:1.

4.5

Valves 1 inch and larger shall not be screwed.

4.6

Valves with welded end connections shall be approved by the owner. Comment: Welded valves are often used in high-pressure steam applications and in high-temperature applications.

4.7

Flanged connections shall be required in the following services: •

Flammable, toxic, or lethal services

•

Services above 400ºF

•

Where subject to deep thermal cycling

•

Where steam pressure is greater than 50 psig

•

Where fire-safe design is required

4.8

Control valve body size shall not exceed the line size.

4.9

Body sizes 1-1/4, 2-1/2, 3-1/2, 5, or higher odd numbers shall not be used. If valve calculations indicate a requirement for such sizes, reduced trim shall be used in standard size valve bodies, i.e., NPS 3 valve with 2-1/2-inch trim.

4.10

Face-to-face dimensions of valve body shall conform to ISA standards in accordance with the following Table 1: Table 1 - Valve Body Face-to-Face Dimensions Body Style Globe-style with integral flanges Globe-style with separable flanges Flangeless Buttweld-end globe Globe-style angle flanges

4.11

ISA Standard ISA75.03 or ANSI/ISA75.16 depending on ANSI class rating ISA75.08.07 ISA75.04 ISA75.08.04 or ANSI/ISA 75.15 depending on ANSI class rating ISA75.22

Flanged connections shall be raised face (RF), conforming to ASME B16.5.

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4.12

Flanges with tag welds or flanges with partial penetration welding are not acceptable.

4.13

Flangeless valves shall have centering means (e.g., lugs, holes, or equivalent) to ensure proper alignment of valve and gasket. Valve body gasket surface areas shall be the same as that of the mating flanges.

4.14

Separable flanges must be approved by the owner. The manufacture shall supply a permanent, yellow tag on the valves with separable flanges that can rotate when the bolts are loosened. The tag shall be inscribed with the following statement: “Warning - This valve has separable flanges and may rotate when bolts are loosened. The actuator must be supported before loosening the bolts.”

4.15

If separable flanges are specified, the flange-retaining ring shall be zinc-plated or shall be made of stainless steel.

4.16

Welding procedures, performance of welders, and welding operators shall meet the requirements of ASME B31.3.

4.17

Only valves in critical applications that require minimum leakage shall have ANSI Class VI seat leakage rating. Valves with this seat leakage rating shall be submitted to the owner for approval before they are incorporated into the design.

4.18

Flow direction, where applicable, shall be permanently marked on the valve body.

4.19

Mechanically linked valves shall not be used for split process flows in lieu of threeway valves.

4.20

Severe service valves (e.g., globe or angle with hardened trim, specially designed multi-hole/path cavitation trim, or noise abatement trim) shall be used for applications where conventional valves (globe, ball, butterfly, etc.) are not appropriate because of loss of control characteristics over time. Examples of conditions where severe service valves shall be considered are as follows: •

Liquid valves Cavitation potential exists: (P1-P2)/(P1-Pv) > 0.6 Application is a flashing service: (P2 < Pv)

•

Gas valves (P1-P2)/P1 > 0.5 where P1 is the upstream pressure; P2 is the downstream pressure; Pv is the vapor pressure of the process fluid at flowing temperature.

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4.21

5.

PIP PCCCV001 Selection of Control Valves

Severe service valves shall be used in the following service applications: •

Intermittent letdown (e.g., high-noise, errosive service) in daily service

•

Recirculation in daily service where cavitation is predicted

•

Where high vibration and/or high noise is expected from the application

•

Where history of valve failures or need for severe service trim exists

Globe Valves 5.1

Globe valves are acceptable for all applications and pressure classes listed in Table 2, as follows.

Process Industry Practices

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PIP PCCCV001 Selection of Control Valves

March 2003

Table 2 - Acceptable Applications for Valve Body Types Body Type (Note 1)

Process Characteristic A.

Globe (Angle)

Wafer Eccentric Disc

Rotary E-Disc / Segmental Ball

Ball and Plug

M,S,O

---

M,O

M,S,O

S,O

= 300

M,S,O

---

M,O

M,S,O

S,O

Globe (Straight)

= 150

Process Gas or Liquid

1. Clean service (liquid - no cavitation or flashing) (Note 4) B.

Valve ANSI Flange Rating (Note 2)

= 600

M,S,O

---

---

M,S,O

---

> 900

M,S,O

---

---

---

---

= 150

M,S,O

M

---

---

---

= 300

M,S,O

M

---

---

---

Process Liquid

1. Clean service (cavitation or flashing condition) 2. Suspended solids (erosive) (Note 3)

3. Corrosive

4. Viscous or nonerosive slurry

= 600

M,S,O

M

---

---

---

> 900

M,S,O

M

---

---

---

= 150

---

M,S

---

M,S (Note 6)

S,O (Note 7)

= 300

---

M,S

---

M,S (Note 6)

S,O (Note 7)

= 600

---

M,S

---

M,S (Note 6)

---

> 900

---

M,S

---

---

---

= 150

M,S,O

---

---

M,S,O

M,S,O (Note 8)

= 300

M,S,O

---

---

M,S,O

M,S,O (Note 8)

= 600

M,S,O

---

---

M,S,O

---

> 900

M,S,O

---

---

---

---

= 150

---

---

---

M,S,O

M,S,O

= 300

---

---

---

M,S,O

M,S,O

= 600

---

---

---

M,S,O

---

> 900

---

---

---

---

---

Notes: 1. "M" indicates valves that are acceptable for modulating service; "S" indicates valves that are acceptable for shutdown service; "O" indicates valves that are acceptable for on/off service. 2. The ANSI flange rating relates to the pipe flanges for flangeless valves. 3. Valve selection for nonerosive suspended solids service is the same as that for process gas or liquid (A1). 4. Utility (steam, air, water) valve selection is the same as that for process gas or liquid (A1 and B1). 5. Control valves used in streams that have a combination of the above process characteristics or process characteristics not listed shall be selected according to project requirements. 6. Valve must be installed in accordance with the manufacturer's recommendation. 7. Full port valves only. 8. Plug valves are acceptable in corrosive service. Ball valves are not typically available in corrosionresistant materials.

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PIP PCCCV001 Selection of Control Valves

March 2003

5.2

Single-seated globe valves are required unless otherwise approved by the owner.

5.3

Cage guiding shall not be used in applications with suspended solids. Globe valves shall be used for high-pressure-drop applications, low-flow applications, clean liquid and gas service applications (corrosive and non-corrosive), and clean liquid service, particularly where cavitation, flashing, or noise are design considerations.

5.4

Globe valves with split bodies shall not be used unless otherwise approved by the owner.

5.5

To reduce the exit velocity of the valve and to dissipate energy, control valve bodies in the following applications shall be no smaller than one size less than line size. Comment: The proper reduced trim size must also be specified in these severe service applications: •

To reduce the valve body liquid flow velocity below a maximum of 33 ft/sec

•

To reduce the valve body gas/vapor outlet velocity below a maximum of 0.3 Mach

•

When the calculated noise not including special noise trim or other noise reduction methods exceeds the maximum continuous operating noise level entered on PIP PCSCV001 data sheet. Comment: Velocity must be below 0.3 Mach for effective noise treatment.

6.

•

Choked flow services

•

Flashing services

•

Erosive services maximum velocity shall not exceed 20 ft/sec

Rotary Valves 6.1

Rotary valves include all types of ball or plug valves (e.g., ball, segmented ball) and butterfly valves (e.g., eccentric disk). Rotary valves are acceptable for all applications and pressure classes listed in Table 2.

6.2

Rotary valves in applications where cavitation or high-noise conditions are present require approval by owner. These applications normally use a globe valve.

6.3

Flangeless valves shall have centering guides to ensure proper alignment of valve and gasket.

6.4

Flangeless and wafer-style valves shall not be used in toxic and/or highly corrosive services.

6.5

Flangeless valves that exceed a body width of 5-1/2 inches shall be subject to owner approval. Lugged body flanges shall be through-bolted. Threaded lugged flanges require owner approval.

6.6

Unless otherwise specified, the valve shaft shall be oriented in the horizontal plane.

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PIP PCCCV001 Selection of Control Valves

6.7

COMPLETE REVISION March 2003

Rotary valves shall be designed such that a mechanical failure will not expel the shaft of the stem from the valve body. Comment: When the stem breaks and is expelled from the valve, a leak path develops that is equal to the cross section of the stem. This failure scenario has caused considerable damage to plants. Since maintenance may remove the actuator while under pressure, the preferred mechanism to retain the stem should be independent of the actuator. If the actuator is used to retain the stem, the valve shall have a tag that states this possibility as a warning statement.

7.

6.8

The actuator end of the valve stem shall be the spline or keyed design. Shear pins are not acceptable. Shafts shall be made of one piece. The shear safety factor shall be a minimum of 150% at the specified shutoff-pressure-drop condition. The valve stem bearing shall be designed to prevent the stem guide bushing from rotating in the valve body. Bearing material shall be selected to prevent galling of the bearing or valve stem.

6.9

The valve shaft bearing shall be designed to prevent the shaft guide bushing from rotating in the valve body.

6.10

Bearing material shall be selected to prevent galling of the bearing or valve shaft and to operate at the maximum and minimum process temperatures.

6.11

The valve disk and shaft for lined, carbon steel, and stainless steel valves shall be made of stainless steel. Other trim parts shall also be made of stainless steel, as a minimum, or of material that meets the process requirements.

6.12

Because the disk in wafer-style valves may project beyond the valve body during part of the disk rotation, clearance shall be maintained between the disk and the pipe wall, particularly if the pipe is of heavy wall construction.

Trim 7.1

For maximum allowable control valve seat leakage, refer to PIP PCSCV001 control valve specification sheet. On individual valves, the maximum allowable seat leakage ANSI/FCI 70-2 Class shall be stated on the individual control valve data sheet.

7.2

Control valves that must provide a tight shutoff (TSO) shall be an ANSI/FCI 70-2 Class V or better. The actual leakage rate shall be communicated to the process engineer for approval. Comment: This requirement does not pertain to isolation valves and safety valves. Leakage requirement for these valves must be defined individually by process requirements.

7.3

Because of close tolerances between the cage and plug, cage trim valves shall be used only in clean liquid, vapor, or gas service.

7.4

Cage-guided trim in dirty services shall be subject to owner approval.

7.5

Trim shall be 13 Cr (400 series SS) as a minimum for control valves with cageguided design and for other valves where such metallurgy is of standard construction.

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7.6

Trim for valves in services that contain erosive or solids-bearing fluids shall be hardened with a minimum hardness of 38 Rockwell C.

7.7

Trim material shall meet the requirements of Table 3 as a minimum. Table 3 Hardened Trim Applications Flowing dP psid 0-100 100-200 200-400 500-600 600-800 800-up

Gases 1 1 1 1 1 1

Steam 2 2 2 3 3 3

Water 1 4 4 4 4 4

HC Liquids 1 2 4 4 4 4

1 = Manufacture’s standard valve trim (316 or 400 series stainless minimum) 2 = 400 series stainless minimum 3 = Stellite trim (alloy 6 or 316/alloy 6 overlay for the seat ring and plug) 4 = Standard trim 400 series stainless or hard-faced stellite unless valve is cavitating or flashing. • If cavitating, use anti-cavitating trim or harden trim according to the manufacturer’s recommendation. • If flashing, use harden trim (stellite, 440C, or Colmonoy® 6)

7.8

Valve stem and plug shall be pinned and welded or be of a one-piece design.

7.9

Threaded trim parts, except seat rings, shall be pinned or spot-welded to supplement the threaded attachment.

7.10

In erosive or corrosive services, self-flushing valves shall be preferred instead of permanent flushing connections built into the control valve.

7.11

Permanent flushing connections shall be subject to owner approval.

7.12

Valves that require cavitation or noise trim shall be submitted to the owner for approval. Do not use small passage cavitation/noise trim on processes that contain particulates, solids, or plugging material. Comment: To avoid plugging, conical strainers shall be considered for installation upstream of valves with anti-noise or anti-cavitation trim.

7.13

8.

If operating temperature exceeds 700°F, guide post areas and rings shall be hardfaced stellite or equivalent.

Bonnet 8.1

General 8.1.1

The bonnet shall have a bolted design.

8.1.2

Extended or finned bonnet shall be used for service temperatures below 0°F and above 750°F.

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Comment:

8.1.3 8.2

8.3

Extended bonnets may be avoided in processes above 400°F and below 750°F if graphite-based or other high-temperature packing is used.

Bonnet bolts shall not be used to attach actuators or mounting brackets.

Gaskets 8.2.1

Default bonnet gasket material shall be as specified on the PIP PCSCV001 control valve specification sheet.

8.2.2

Bonnet gasket shall be compatible with the process, the maximum temperature, and maximum pressure. The gasket material shall be in compliance with the piping specification.

8.2.3

Gaskets containing asbestos are unacceptable.

8.2.4

If the valve is required to be fire safe, the following materials are considered fire safe: •

Metal gaskets

•

Flexible graphite gaskets

Packing 8.3.1.

Packing material shall be compatible with piping specification. 8.3.1.1 Packing shall not require lubrication. 8.3.1.2 The cooling effects from use of an extended bonnet shall not be taken into account when selecting the packing. 8.3.1.3 Packing material containing asbestos is unacceptable. 8.3.1.4 For applications in temperatures above 750°F, an extended bonnet shall be used to protect the positioner and actuator from heat. 8.3.1.5 See the PIP PCSCV001 control valve specification sheet for packing type for non-fugitive emission and fugitive emission versus process temperature. 8.3.1.6 Packing shall conform to vendor’s sizing and selection criteria for temperature/pressure curves. The packing material shall be in compliance with the piping specification. 8.3.1.7 For fire-safe applications, graphite-based packing shall be used. 8.3.1.8 Bellow seals shall require owner approval.

8.3.2

Fugitive emissions considerations are as follows: 8.3.2.1 Packing shall limit fugitive emissions. Fugitive emissions of any substance containing more than 5% by weight of volatile hazardous air pollutant as defined in the EPA 40 CFR, Part 63, shall be limited in accordance with the applicable local regulation or limited to a maximum of 500 parts per million, whichever is more stringent.

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8.3.2.2 Determination of leaks and monitoring requirements shall comply with EPA 40 CFR, Parts 60 and 61, respectively. Comment: Methods of meeting the above-mentioned requirement include application of twin packing designs, live-loaded packing, and bellows seals. Bellows seals, while relatively expensive, should be considered for cases in which no leakage across the stem can be tolerated or for cases in which excessive packing friction results in unreasonably large packing friction forces. Comment: Increased emphasis on limiting packing leaks has resulted in the development of new packing materials and methods. Valve vendors are offering increasingly effective designs, and they should be consulted for recommendations on specific fugitive emission control applications. Comment: To meet fugitive emissions, the stem should be finished to a maximum of 8 microinches RMS. Smooth finish assists in reducing fugitive emissions over service life of control valve. 8.3.2.3 Packing design shall be approved by the owner before implementation. 8.3.2.4 Control valves shall be designed, selected, and installed to permit easy access of monitoring packing areas prone to fugitive emissions without removing equipment or devices. 8.3.2.5 PIP PCSCV001 control valve specification sheet, which indicates the testing criteria, identifies whether fire-safe packing is required. 8.4

Bolting 8.4.1

Vendor-recommended bonnet bolts shall be used unless owner specifies differently.

8.4.2

Valve bonnets shall be bolted type with a retained-type gasket.

8.4.3

Plated bolting material shall not be used for pressure-containing parts.

8.4.5

The following valve components shall be 304 or 316 SS minimum: •

Gland studs and nut (e.g., packing bolts)

•

Packing flange and follower

8.4.6

Packing glands and followers shall be bolted for valves larger than 1 inch.

8.4.7

Carbon steel screwed packing followers shall not be acceptable.

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9.

March 2003

Sizing Considerations 9.1

General 9.1.1

Valve-sizing procedure shall address the full range of expected flow conditions. Appropriate differential pressure shall be applied as load changes. Flow equations specified in PIP PCSCV001 control valve specification sheet shall be used.

9.1.2

When sizing a valve, only the characteristcs of the plug shall be considered for an accurate understanding of the plug stroke at the various conditions. A positioner with characterization such as equal percentage may be used on trim with an inherent linear characterization to enhance control.

9.1.3

Linear trim design shall be preferred if pressure drop across valve does not vary more than 20% between maximum flow and minimum flow; i.e., dP(max flow) – dP(min flow)/dP(min flow)<20%. This practice typically achieves an installed linear characteristic. If the linear valve does not have sufficient rangeablilty to meet the minimum and maximum conditions, an equal percentage valve is prefered.

9.1.4

The manufacturer shall be consulted in sizing of a two-phase, liquid-vapor mixture.

9.1.5

Body outlet velocity, defined as the fluid velocity at the discharge flange of a control valve, shall not exceed the following:

9.1.6 9.2

•

0.3 Mach for gas, vapor, and steam services except in vacuum services

•

0.4 Mach for infrequent services (i.e., services for which the control valve is closed for more than 4 hours during an 8-hour shift, including emergency vent and emergency depressurizing services)

•

33 ft/sec for liquid services other than water

•

18 ft/sec for water service

•

20 ft/sec for erosive fluid (e.g., those that contain errosive particles)

Comment:

Oversized control valve bodies with reduced trim may be required to meet these limits.

Comment:

If manufacturer’s plug guiding or construction governs maximum allowable velocities, manufacturer’s recommended lower velocities shall be used.

Final valve sizing shall be confirmed by valve manufacturer and shall be approved by owner.

Pressure-Drop Determination for Nonpumped Systems Control valves shall be sized for a minimum pressure drop of 20% of variable system pressure drop, excluding drop across control valves.

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9.3

9.4

Pressure-Drop Determination for Pumped Systems 9.3.1

The pressure drop shall be adequate to provide control at all process conditions including start-up.

9.3.2

Primary control valves shall have a minimum pressure drop that is the greater of the following: •

15 psi

•

A minimum of 30% of the total system pressure drop (defined as system frictional pipe losses) excluding the pressure drop across the control valve at pump-rated flow

Secondary Control Valves 9.4.1

Secondary control valves (e.g., temperature control valve at inlet to exchanger) shall have a minimum pressure drop that is the greater of the following: •

5 psi

•

20% of exchanger pressure drop in fouled condition at maximum operating flow rate

Comment:

9.5

Operating Range 9.5.1

10.

The “secondary” control valve is defined as the valve that individually controls sub-systems of a major system such as streams to multiple exchangers, streams to multiple heaters, or boilers. Typically, the primary and secondary control valves will be in series with a header or similar configuration. As an example, the main pump discharge feeds into a header via a “primary” control valve, and the flow is split into multiple streams via a “secondary” control valve.

Operating ranges for linear motion and rotary valve types shall comply with the following: •

The Cv of control valve through all conditions shall be sized to operate within 15% through 80% of maximum rated Cv of the control valve.

•

Stem travel/rotation at normal design flow conditions shall be within 40% through 65%.

Noise Considerations 10.1

Noise level produced by control valves shall conform to the limits identified on the in PIP PCSCV001 control valve specification sheet. The noise level is based on 1 meter downstream and 1 meter from the surface of the attached piping. These calculations shall include all process conditions as stated on the data sheet for maximum, normal, and minimum flow.

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Comment: OSHA 1910.95 defines a maximum allowable equivalent noise dose, which is based on the noise level and the length of exposure time to this level during an operating shift. 10.2

Control valve noise calculations shall be performed for all control valves. For aerodynamic noise of gases, steam, or vapor, ISA 75.17 or IEC 60534-8-3 calculations shall be used. For hydrodynamic noise, the vendor method or IEC 60534-8-4 shall be used.

10.3

For the noise calculations to be valid, the maximum valve body exit velocity must be below 0.3 Mach.

10.4

Noise emissions shall not exceed the limits stated on PIP PCSCV001 control valve specification sheet for the following conditions, which are the definitions of terms used in the noise section of PIP PCSCV001 control valve specification sheet: •

Continuous: Operation is for more than 2 hours per shift.

•

Infrequent: Each occurrence is less than 30 minutes in duration. Total cumulative effect of each occurrence shall be less than 2 hours per year (e.g., emergency and relief conditions).

•

Intermittent: Each occurrence is no more than 2 hours per shift or includes startups and shutdowns.

•

Remote: These are areas in which personnel are not normally present during periods of higher noise emission (e.g., tank farm, flare line).

•

Normally attended: These include fence line areas to publicly travel areas, areas bordering residential areas, and normally traveled areas within the plant. More stringent noise criteria may need to be applied to these applications on a case-by-case basis.

10.5

The control valve vendor shall advise the owner if the calculated noise level exceeds the 85 dB(A) value as stated on the PIP PCSCV001 control valve specification sheet.

10.6

Calculated noise level shall not exceed 110 dB(A). The control valve manufacturer shall be consulted to verify that the control valve will perform correctly for the expected duration with no damage at noise greater than 100 dB(A).

10.7

Control valve noise shall be treated at the source except as noted below. The provision of low-noise multipath-multistage trim designs is required because it reduces noise at multiple operating points. Diffusers, baffle plates, and silencers, either inside the valve body or downstream of the valve, shall not be permitted for the following applications: •

Process control/feed regulation

•

Continuous letdown

•

Intermittent letdown in daily service

•

Recirculation in daily service Comment: For other applications, special attention shall be given to the possible limited flow ranges of these devices (i.e., noise reduction

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from these devices is generally reduced at low-flow conditions). Noise generated by diffusers or baffle plates shall be calculated with ISA 75.17 or with IEC 60534-8-3 as a separate system from the valve trim and included in the overall noise source. If a diffuser is being considered, then the noise level shall be calculated at half the design flow. 10.8

11.

Hardened materials in trim design shall be used to assist in prolonging the life of the control valve.

Actuator 11.1

General 11.1.1 Unless otherwise specified, valve actuator shall be pneumatic diaphragmtype or piston-type. Vane and other type actuators may be appropriate for rotary-type valves. Comment:

Use of electric motor or electro-hydraulic actuator may be considered for special applications, particularly if pneumatic power is not available or if very high thrust forces are required.

11.1.2 The actuator shall drive the valve to a safe position on loss of signal or motive power. The actuator shall have an enclosed spring to achieve fail-safe action. Valve failure position shall comply with owner-approved P&IDs and the control valve data sheet. When sizing the spring, the process pressure shall not be considered if this pressure assists in achieving the fail-safe position. Comment:

Using an actuator having an enclosed spring design provides the most reliable fail-safe operating parameter. If fail-safe position cannot be ensured by an enclosed spring, volume tanks may be used with prior owner approval to provide the necessary motive power.

11.1.3 The actuator shall be sized to meet control, shutoff, and leakage class at the minimum instrument air pressure identified on the PIP PCSCV001 control valve specification sheet Comment:

Valves that must shut off against reverse flow shall be identified on the individual control valve data sheet, and the actuator shall be sized appropriately.

11.1.4 PIP PCSCV001 control valve specification sheet identifies the shutoff criteria for valves on the loss of motive force (e.g., air supply) as follows:

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•

The shutoff classification must be met with spring force only. The spring must be sufficient to maintain shutoff classification at maximum delta P on loss of motive force.

•

On loss of motive force, the valve shall return to required end position using spring force only. Air assistance may be used in conjunction

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with spring force to maintain shutoff classification at maximum delta P. •

On loss of motive force the valve shall return to required end position using spring force only. Process pressure assistance may be considered in conjunction with spring force to maintain shutoff classification at maximum delta P.

11.1.5 Sufficient actuator thrusts, tubing diameter, and accessories sizes shall be provided to minimize the dead band, hysteresis, frequency response, and speed of response at all process conditions. 11.1.6 Actuators shall be sized for positioning the closure member against a minimum of the maximum differential pressure at all process conditions unless otherwise specified in PIP PCSCV001. Maximum differential pressure shall be considered the maximum upstream pressure with the control valve fully closed and downstream pressure at atmospheric pressure. If there is a vacuum on the control valve outlet, then the maximum vacuum pressure on the valve outlet shall be used to determine the maximum differential pressure 11.1.7 Valves in services that cause the control valve stem to stick shall have the actuator sized with a 1.25 design factor. 11.1.8 For rotary valve actuator, the vendor shall confirm the breakout torque requirements and the maximum percentage opening limit for stable operation. 11.1.9 The actuator case shall be rated for the maximum available pneumatic supply pressure. 11.1.10 The actuator material of construction shall be the vendor’s standard material. 11.1.11 Valve yokes shall be nodular iron, high-tensile-strength cast iron, or steel unless specified otherwise in the individual control valve data sheet. 11.1.12 Springs, internal parts, fasteners, and hardware shall be resistant to the corrosive effects of the environment. 11.1.13 The actuator exterior shall be painted with the vendor’s standard paint and color, unless specified otherwise. 11.1.14 The sliding stem actuator shall have a valve position indicator that shows position of valve stem against a full travel linear scale. 11.1.15 A travel indicator, graduated in opening percentages, shall be attached to the rotary valve actuator end of the shaft. 11.1.16 The actuator and associated accessories shall be assembled, piped, and mounted on the control valve and aligned, tested, and shipped as a complete unit. 11.1.17 The designer shall coordinate the installation and orientation of valve accessories with the vendor before final assembly and shipment.

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11.1.18 Refer to PIP PCSIP001 for piping and tubing specifications. Tubing shall be sized to meet the required valve stroke response time. 11.1.19 The actuator shall have a permanently attached stainless steel tag. The tag shall be stamped with the vendor’s standard data and the owner’s item number. 11.1.20 The valve vendor shall supply filter or filter/regulator, whichever is applicable according to the control valve data sheet. 11.2

Diaphragm Actuator 11.2.1. Nominal diaphragm spring ranges shall be 3 to 15 psig or 6 to 30 psig. Comment:

Although some applications will allow the use of actuators that stroke over the input range of from 3 to 15 psig, higher diaphragm pressures often will be required. Generally, the valve should be specified to control and provide the necessary shutoff force with a 6- to 30-psig diaphragm pressure range.

11.2.2 If the control valve is not provided with a positioner, instrument air supply shall be regulated in accordance with the following: •

Instrument air supply shall be minimum of 10 psi above spring range (bench set) of actuator.

•

The 10-psi requirement may be increased if additional instrument air supply pressure may reduce actuator size or provide more force to achieve the ANSI-class leakage shutoff requirement.

•

All devices in the instrument air loop for control valve assembly shall be rated/designed for this regulated pressure, including air supply filter, air supply regulator, I/P, diaphragm, actuator housing, and solenoid valves.

•

If 10 psi above spring range exceeds rated/designed pressure of any component, pressure for instrument air shall be regulated at the design pressure of the component having the lowest design pressure.

11.2.3 If the control valve is provided with a positioner, the instrument air supply shall be regulated at a minimum of 5 psig above the actuator-required pressure to achieve fully open or closed positions (e.g., if actuator requires 6-30 psig, then the supply pressure will be set at a minimum of 35 psig). •

All devices in the instrument air loop for control valve assembly shall be rated/designed for 50 psig, including air supply filter, air supply regulator, I/P, positioner, diaphragm, actuator housing, and solenoid valves.

11.2.4 If 50 psig exceeds rated/designed pressure of any component, pressure for instrument air shall be regulated at design pressure of the component that has lowest design pressure.

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11.3

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Piston and Vane Actuators 11.3.1 Piston and vane actuators shall be used in the following situations: •

when valve stem or shaft loading is high

•

where fast valve action response is require

•

where a compact physical installation is required

11.3.2 The actuator shall be designed to meet control and shutoff requirements with the minimum available air supply. 11.3.3 Air exhaust connections shall be oriented and/or equipped to exclude or minimize the entry of water, dirt, and insects. 11.3.4 Valves with piston operators shall be sized at the minimum instrument air pressure stated in PIP PCSCV001 control valve specification sheet. Only a filter shall be provided. 11.3.5 The following shall apply for control valves: •

All devices in the instrument air loop for the control valve assembly shall be rated/designed for instrument air header pressure, including air supply filter (required), positioner, actuator housing, actuator internals, and solenoid valves. Comment:

•

11.4

Typically the I/P requires a separate filter/pressure regulator set at a pressure compatible to the device.

If the instrument air header pressure exceeds the rated/designed pressure of any component (e.g., solenoid valve), the instrument air pressure shall be regulated at the design pressure of the component that has the lowest design pressure.

Volume Tank 11.4.1 Use of volume tank shall be approved by owner. 11.4.2 Volume tank shall be sized to fully stroke the valve through two travel cycles. 11.4.3 If the volume tank, by virtue of size, pressure rating, or local regulation must conform to Part U-1 of Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code, capacity tank shall be ASME Code stamped and be equipped with a pressure relief device. 11.4.4 Volume tank shall be equipped with the proper accessories (tubing, fittings, pressure transmitters, solenoid valves, etc.) to ensure that the valve fails in the safe position. Comment:

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The pressure transmitter is required only if identified on the PIP PCSCV001 control valve specification sheet.

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12.

Positioner/Current-to-Pneumatic Transducer (I/P) 12.1

A positioner shall be used on all valves unless its use would be detrimental to good process control. Local pneumatic loops do not require a positioner.

12.2

The positioner shall be mounted on plates or bosses on the valve dedicated for that purpose.

12.3

The positioner shall be mounted, piped, and aligned by the vendor to provide a complete control valve assembly.

12.4

The positioner shall be equipped with the manufacturer’s standard supply, input, and output gauges unless otherwise specified.

12.5

A positioner bypass shall be provided only if specified by the owner.

12.6

Pneumatic boosters shall be used in conjunction with positioners in applications such as pressure control to achieve the required response time.

12.7

Positioners shall

12.8

12.9

13.

PIP PCCCV001 Selection of Control Valves

•

Use two-wire loop power.

•

Provide pneumatic output signal in which range is as required by actuator.

•

Meet electrical area classification where they are installed.

Digital positioners shall •

Use standard digital communication and 4-20 mA as input signal.

•

Provide diagnostic functions and information through hand-held communicator, laptop computer, or computer console.

Electropneumatic transducers (I/P) shall •

Convert 4 to 20 mA DC electronic signal to 3 to 15 psig output signal.

•

Be configured to be direct acting rather than reverse acting.

•

May be integrally mounted on control valve, with owner approval, if transducers are rated for operating conditions, such as maximum temperature and vibration.

•

Have minimum air flow rating of 0.25 scfm.

•

Meet area classification and NEMA 4X.

Accessories 13.1

Handwheel Operator 13.1.1 Control valves shall have a handwheel operator only if specified by the owner.

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13.1.2 The handwheel operator shall be continuously connected and shall operable through an integral declutching mechanism. Note:

Declutchable means a shaft-mounted worm gear that can be detached from the power of the actuator.

Comment:

Handwheel operator may be side mounted, lockable, or screw or gear driven if accessibility is not a consideration.

13.1.3 The handwheel operator on a rotary valve shall be mounted directly on the shaft, and the clutch shall be installed so that it can be declutchable. 13.1.4 Top-mounted jacks or handwheels shall not be used unless approved by owner. 13.1.5 A valve-to-open direction arrow shall be permanently marked on the handwheel. 13.1.6 Handwheels shall not be used to eliminate block and bypass valves 13.1.7 Handwheels shall not be used as limit stops. Comment: 13.2

When handwheels are used as limit stops, the adjustment can be changed inappropriately.

Limit Switches and Solenoid Valves 13.2.1 General 13.2.1.1 All accessories shall be suitable for the electrical area classification. 13.2.1.2 Solenoid valves and limit switches shall be mounted and tubed by the valve vendor unless directed differently by the owner. For instruments without terminal strips, the valve vendor shall provide a terminal strip and housing. 13.2.2 Limit Switches 13.2.2.1 Unless otherwise specified, limit switches shall be hermetically sealed. 13.2.2.2 Unless otherwise specified, limit switches shall be proximity types. 13.2.2.3 Limit switches shall be enclosed in watertight, dust-proof housings. 13.2.3 Solenoid Valves 13.2.3.1 Solenoid valves shall be rated for continuous duty and shall have a minimum of Class F high-temperature encapsulated coils; Class H coils are preferred. 13.2.3.2 The solenoid coil shall be molded in epoxy. 13.2.3.3 The solenoid coil shall be rated for continuous duty. 13.2.3.4 The solenoid valve for tripping the control valve shall be between the positioner and actuator or in the tubing that provides the motive power to the actuator.

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13.2.3.4 Tripping the solenoid valve shall provide sufficient capacity to exhaust the actuator chamber air volume within the time required to allow the valve to fail in a safe position. If solenoid valve Cv is not sufficient, a “quick exhaust” valve shall be provided that works in “conjunction” with the tripping solenoid valve if needed. 13.2.3.5 If the solenoid valve vent port is open to the atmosphere, it shall have an insect screen. 13.2.3.6 The solenoid valve shall be capable of switching under conditions of maximum and minimum operating differential pressure. 13.2.3.7 Instrument air supply piping must be of adequate size to stroke the valve in the time specified. 13.2.4 Boosters and Quick Exhaust 13.2.4.1 Boosters shall be provided when necessary to achieve the required stroke time. A volume booster shall be used only if approved by owner. 13.2.4.2 Instrument air supply piping to boosters must be of adequate size not to limit the supply to the boosters. The piping size selection must also include drops across filters and regulators. Normally, pipe is used for supplies. Larger pipe may be required for extensive pipe runs. The flow through the boosters must not be restricted. In some cases, connections in the actuators must be enlarged. 13.2.4.3 Conditions may exist making it desirable for the valve to move rapidly in one direction but slower in the other. This can be accomplished by selectively restricting one side of the booster or boosters. 13.2.5 Air Sets and Auxiliary Equipment 13.2.5.1 Air sets that are required at valves shall be rigidly mounted to valve yoke if mounting pads are provided. 13.2.5.2 Pressure gages supplied with positioners that are not enclosed in positioner housing shall have stainless steel cases. 13.2.5.3 If approved by owner, auxiliary solenoid valves, position switches and transmitters, and pneumatic relays associated with control valves may be integrally mounted on control valve. 13.2.5.4 Air sets shall not be supported by pipe nipples from positioners. Air sets for positioners bolted to control valve yoke shall be permitted.

14.

Marking, Identification, and Nameplate 14.1

The direction of flow shall be marked on the valve. The flange rim of three-way valves shall be identified.

14.2

The trim position of rotary valves shall be engraved on the shaft end.

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14.3

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A permanently fastened (e.g., by stainless steel rivets) stainless steel nameplate, showing the following information, shall be provided on each control valve: •

Tag number specified on the individual control valve data sheet

•

Manufacturer’s name, model number, and valve serial number

•

Body material, valve size, and flange rating

•

Trim material, trim size, and Cv

•

Trim characteristic type

•

Stem travel distance in inches

•

Actuator model, size, and bench set and actuator serial number

•

Actuator failure position

•

Actuator maximum allowable case pressure

•

Operating range (air signal to operator with valve under pressure)

•

Bench setting (air signal to operator with no pressure in valve body); applies only to diaphragm-actuated valves

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