May 1999

Process Industry PracticesProcess Control

PIP PCCCR001Selection Criteria for Control Regulators

PURPOSE AND USE OF PROCESS INDUSTRY PRACTICES

In an effort to minimize the cost of process industry facilities, this Practice hasbeen prepared from the technical requirements in the existing standards of majorindustrial users, contractors, or standards organizations. By harmonizing these technicalrequirements into a single set of Practices, administrative, application, and engineeringcosts to both the purchaser and the manufacturer should be reduced. While this Practiceis expected to incorporate the majority of requirements of most users, individualapplications may involve requirements that will be appended to and take precedence overthis Practice. Determinations concerning fitness for purpose and particular matters orapplication of the Practice to particular project or engineering situations should not bemade solely on information contained in these materials. The use of trade names fromtime to time should not be viewed as an expression of preference but rather recognized asnormal usage in the trade. Other brands having the same specifications are equallycorrect and may be substituted for those named. All practices or guidelines are intendedto be consistent with applicable laws and regulations including OSHA requirements. Tothe extent these practices or guidelines should conflict with OSHA or other applicablelaws or regulations, such laws or regulations must be followed. Consult an appropriateprofessional before applying or acting on any material contained in or suggested by thePractice.

Process Industry Practices (PIP), Construction Industry Institute, TheUniversity of Texas at Austin, 3208 Red River Street, Suite 300, Austin,Texas 78705. PIP member companies may copy this practice for their internaluse.

Not printed with State funds

May 1999

Process Industry Practices Page 1 of 5

Process Industry PracticesProcess Control

PIP PCCCR001Selection Criteria for Control Regulators

Table of Contents

1. Introduction.................................21.1 Purpose.............................................21.2 Scope................................................2

2. References ..................................22.1 Process Industry Practices (PIP) .......22.2 Industry Codes and Standards...........22.3 Government Regulations...................2

3. Data ..............................................3

4. Applications ................................3

5. Sizing and Selection...................3

6. Construction ...............................3

7. Pressure Protection ...................3

8. Materials of Construction ..........4

9. Installation...................................4

10.Noise............................................5

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1. Introduction

1.1 Purpose

The purpose of this Practice is to provide designers and vendors with requirements forthe selection of control regulators.

1.2 Scope

This Practice specifies requirements for selection of control regulators, applications,sizing, construction, pressure protection, materials of construction, installation, andnoise.

2. References

Applicable requirements in the latest edition (or the edition indicated) of the followingstandards and references shall be considered an integral part of this Practice. Short titles willbe used herein when appropriate.

2.1 Process Industry Practices (PIP)

PIP PCCIP001 - Instrument Piping and Tubing Systems Criteria

PIP PCECR001 - Guidelines for the Selection of Control Regulators

2.2 Industry Codes and Standards

American Society of Mechanical Engineers (ASME)

ASME Boiler and Pressure Vessel Code

Section VIII, Division 1 - Pressure Vessels

American Society for Testing and Materials (ASTM)

ASTM A105 - Carbon Steel Forging for Piping Applications

ASTM A216 - Steel Castings, Carbon, Suitable for Fusion Welding for High-Temperature Service

ASTM A217 - Steel Castings, Martensitic Stainless and Alloy, for Pressure-Containing Parts, Suitable for High-Temperature Service

ASTM A352 - Steel Castings, Ferritic and Martensitic, for Pressure-Containing Parts, Suitable for Low-Temperature Service

ISA

ISA S20.51 - Specification Form for Pressure Control Valves, Pilots andRegulators

2.3 Government Regulations

US Department of Labor, Occupational Safety and Health Administration (OSHA)

OSHA 29 CFR 1910.95 - Occupational Noise Exposure

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3. Data

A data set in electronic or hard copy format shall be provided for each control regulator.Minimum content for the data set is located in ISA S20.51.

4. Applications

Regulators shall not be used in toxic service or where seat leakage would constitute ahazardous condition.

5. Sizing and Selection

5.1 The Manufacturers formulas and tables shall be used to size and select controlregulators.

5.2 Owner approval is required for end connection sizes larger than 1 inch.

5.3 The regulator shall be sized to deliver the full range of regulated flow at no less than20% or no more than 60% open, with no more than 10% droop occurring at maximumflow. Ideally, the regulator should be sized to deliver the normal flow at 50-60% open.(Refer to PIP PCECR001 for a discussion of droop.)

5.4 Consideration shall be given to the possibilities of flashing and cavitation in liquidservice.

5.5 The selection process shall include necessary corrections for the specific gravity of thecontrolled fluid.

6. Construction

6.1 The preferred self-contained regulator shall be spring-loaded with an internal pressure-sensing connection.

6.2 Internal pressure sensing regulators shall be designed such that the regulated pressureis applied directly to the diaphragm through the valve body. Internal pressure sensingregulators shall also be provided without packing boxes.

6.3 Diaphragm loading springs shall be enclosed and readily adjustable. The adjustingdevice shall be provided with a locking mechanism to ensure that the control pointcannot shift or be changed inadvertently.

6.4 The regulator body shall be rated for the maximum upstream and downstreampressure and temperature to which it may be subjected. Where this requirement cannotbe met, provision must be made for appropriate external relief.

7. Pressure Protection

7.1 Whenever possible, the pressure rating of the regulator body, end connections, andspring case shall equal or exceed upstream and downstream conditions with theregulator blocked in against the pressure source and isolated from the load. In some

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instances, the regulator body, case, and end connections may be rated for themaximum expected pressures, but not the internal components. If all parts of theregulator cannot be specified to meet the maximum expected pressure, suitableexternal relief devices shall be installed at appropriate places in the associated piping.

7.2 Where relief is required, a relief device shall be sized to relieve flow resulting from aregulator that has failed fully open, assuming design upstream pressure at the inlet ofthe failed regulator, and relief set pressure (plus allowable overpressure) at theregulator outlet.

7.3 The preferred relief device is a pressure relief valve. Typically, the relief device will belocated in the outlet piping of the protected regulator. Internal relief valves are suitableonly for small diaphragm leaks and will not provide full overpressure protection.

7.4 Pressure regulators used in backpressure control (pressure relief) are not sufficientlypositive in action to provide primary protection for equipment that must meet therequirements of ASME Boiler and Pressure Vessel Code Section VIII, Division 1.

8. Materials of Construction

Regulators shall conform to the requirements of this Section and, whenever possible, bespecified with the Manufacturers standard materials. In general, the valve body and endconnections shall meet or exceed the applicable piping specification.

8.1 Carbon steel body and end connections shall conform to ASTM A105 or ASTM A216specifications for cast or forged carbon steel.

8.2 The spring and diaphragm housing shall be steel or stainless steel.

8.3 Cast iron bodies are not permitted in hydrocarbon service. Cast aluminum is permittedonly in air or nitrogen service.

8.4 Bolts, studs, nut, gaskets, and internal trim shall be the Manufacturers standard,assuming compatible service conditions. Frequently, Manufacturers standard materialoffering for internal trim parts will not be compatible with the piping specification.Accordingly, all process-wetted parts shall be resistant to the corrosive or chemicaleffects of the controlled fluid.

8.5 Nickel-alloy, stainless steel, or low-temperature carbon steel shall be specified forpressure containing parts in services below -20 F.

9. Installation

9.1 Spring-loaded valves and pilots shall be located to minimize the effects of shock andvibration and to facilitate maintenance and setpoint adjustment.

9.2 Pressure gauge taps shall be installed on the upstream and downstream sides of theregulator.

9.3 Steam regulators shall be preceded by a separator and trap. A strainer and/or filter isrequired for any regulator having small ports that would be susceptible to plugging.

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9.4 Regulators judged to be in critical applications shall be equipped with a bypassarrangement that will allow continuous operation if the primary regulator or regulatorsare removed from service. The bypass arrangement shall consist of piping, isolationvalves, and a parallel regulator or regulators having the same capability as the primaryregulator(s).

9.5 Regulators in gas or vapor service shall be installed such that condensate will notaccumulate in the piping between the regulator and the load.

9.6 Internal pressure relief vents shall be piped to a safe location. Atmospheric vents shallbe threaded and equipped with insect screens.

9.7 All external pressure feedback piping (tubing) shall be at least 1/4 inch stainless steel.Pressure sensing connections shall be internally threaded and no smaller than 1/4 inchNPT. External pilots shall be specified with integral filters.

9.8 External pressure feedback taps shall be located to minimize the effects of linepressure drop, velocity changes, and turbulence. A distance of at least 10 pipediameters from the regulator is recommended.

10. Noise

10.1 The Manufacturer shall be consulted if the critical pressure ratio approaches 2:1.

10.2 The calculated noise level shall not exceed 90 dBa. The owner shall be advised if thecalculated noise level exceeds 82 dBa.

10.3 The requirements and guidelines established by OSHA in 29 CFR 1910.95 shall befollowed.