Level Displacers

IPE Engineering Practice IPE-EP-12-1-16

Document number: IPE-EP-12-1-16 · Section: 12 — Instruments and Controls

SCOPE

Displacer type liquid level instruments shall be supplied in strict accordance with the attached Data Sheets, this Practice, and the referenced standards and publications.
Where special features or improvements over the Practice are required as determined by the Owner, or Owner’s Engineer, these shall be specified on the Instrument Data Sheets and shall be adhered to by the vendor.
Any deviation from this Practice must be approved by the procedure described in EP 1–1–3.
A revision bar indicates all changes made to this Revision.

2.0 REFERENCES

The following codes and standards shall be considered as part of this Practice. All documents shall be the latest editions in force on the date of issuance of this Practice.

STANDARDS AND PUBLICATIONS

IPE Engineering Practices
EP 1–1–3 Deviations to IPE Engineering Practices EP 5–2–2 Flanges, Gaskets and Bolting EP 12–1–1 Control Systems EP 12–1–2 Supplemental Requirements for Control Systems EP 12–1–16 DS Level Displacers Data Sheet
ASME
B 1.20.1 Pipe Threads General Purpose (Inch) B 16.5 Pipe Flanges and Flanged Fittings B 31.3 Chemical Plant and Petroleum Refinery Piping
ISA Standard
S50.1 Compatibility of Analog Signals for Electronic Industrial Process Instruments
NEMA
ICS 6 Enclosures for Industrials Controls and Systems
NFPA
70 National Electrical Code

DEFINITIONS

Inspector - A Inflection Point Engineering, LLC appointed engineer or inspector.
Manufacturer - The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a manufacturer by a contractor or the Owner. An indirect order is one issued to a manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.
Owner - Inflection Point Engineering, LLC.
Owner’s Engineer - A Inflection Point Engineering, LLC appointed engineer.

DESIGN AND MATERIALS

General
The equipment shall consist of a displacer element responding to changes in liquid level and actuating a pneumatic or electronic instrument external to the displacement element by means of a torque tube or similar device. The instrument shall be designed for either control, transmission, or both as specified on the Instrument Data Sheet.
Each component of the equipment shall be suitable for the specified process conditions.
The dimensions and rating of flanges shall conform to EP 5–2–2.
Design and fabrication shall be in accordance with manufacturer’s standards for the design conditions given on individual Instrument Data Sheets. The pressure/temperature rating of the chamber shall be equivalent to the specified flange rating.
All threaded connections shall be tapered and shall conform to ASME B1.20.1.
Design and materials not specified shall be in accordance with the manufacturer’s standards suitable for the operating and design conditions specified on the Instrument Data Sheets.
Rotatable heads are required on all external displacers. Minimum flange rating and size shall be 2 inch 300# RF. All external displacers shall have a bottom drain and top vent.
Displacement Elements and Suspension Rods
Displacer elements shall be of the lengths specified on the Instrument Data Sheets.
Displacer elements shall be 300 series stainless steel as a minimum. The vendor shall notify the purchases of the suitability of various materials for the specified service. Use of other materials shall be approved by the Owner’s Engineer.
Torque Tube Housings, and Displacement and Mechanism Chambers
External units shall be furnished with displacement chambers and mechanisms chambers. Mechanism chambers shall be fully rotatable for all but top and bottom connected types. Process connections for the displacement chambers shall be as specified on the individual Instrument Data Sheet. When the lower connection is a side connection, a 3/4 inch NPT internally threaded pipe connection with pipe plug shall be provided for bottom draining. Displacement chamber shall be of flanged construction for easy float removal.

Mechanism chambers for internal units shall be furnished with a flange of the specified size and rating for connection to the vessel.
Torque tube housings shall be isolated from the pneumatic or electronic mechanisms by a positive sealing arrangement. ”Pressure-tight” bearings, stuffing boxes, or other packed devices shall not be used.
Unless otherwise specified, torque tube housing and displacement and mechanism chambers shall be of carbon steel in accordance with the manufacturer’s standard for the operating and design conditions.
Finned extensions shall be furnished when required to meet the maximum operating temperature.
Pneumatic Transmitters and Controllers - Mechanisms
The Pneumatic mechanisms shall be enclosed within a weatherproof case. Air supply and output connections shall be internally threaded (NPT) and of minimum size NPS 1/4.
Cases shall be furnished right or left hand mounted as specified on the Instrument Data Sheets. The case of a right hand unit shall be to the right of the displacement element when viewed from the front of the case.
When the instrument is specified for both transmitting and controlling, an individual air pilot mechanism for each function shall be furnished.
Control mechanisms shall incorporate proportional action adjustable from 10% to at least 100% of the range of calibration without reset action. Controllers should be specified with proportional and integral action.
The proportional band for controllers shall be readily adjustable.
Transmitters and controllers shall be furnished with indicating pressure gauges for both air supply and output.
Single and dual pilots shall be furnished with combination reducing valve and air filter sets with internal relief integrally mounted and piped by the manufacturer. Air sets shall be designed for operation on air supply of 60 to 100 psig. Dual pilots shall have one common air set with isolating valves.
Instruments with one pilot mechanically linked and the other set through pneumatic transmission shall be furnished with two isolating valves: one in the air supply line to the control pilot; and one in the transmitted air line to the control pilot.
Electronic Transmitters
Transmitters shall be the two wire type providing an isolated 4 to 20 mA signal while operating from a remote power supply of nominal 24 VDC (actual 23 to 32.7 V). The detailed requirements are type 2U in accordance with ISA S50.1.
Transmitters shall be adjustable span types calibrated for the full displacer length and the operating specific gravity shown on the instrument Data Sheets.
Span and zero adjustments on electronic transmitters shall not interact.

Screw terminals for electrical connections are required and shall be identified to indicate polarity, ground connections, test connections and any other pertinent information.
Electrical conduit connections shall be internally threaded 1/2 inch NPT.
Electronic transmitter shall meet the National Electrical Code (NEC) area classification requirements of Class 1, Groups D,C, and D. However, minimum case rating shall be NEMA Type 4 in accordance with NEMA ICS 6.
Electronic transmitter output error shall not exceed 0.5% of the calibrated range for RFI in the range of 27 to 500 MHz for a field strength of 30 volts per meter or less.

PERFORMANCE

General

Each instrument shall be capable of meeting the performance requirements of the following sections when the installation, operation, and maintenance of the instrument has been in accordance with the manufacturer’s submitted instructions, and the equipment has been subjected to exposure of the displacement element to fluids of the densities specified on the Instrument Data Sheets.

Accuracy

Transmitter accuracy shall be equal to or better than 1.0% of calibrated span over the specified range.

Repeatability

Transmitter repeatability shall be equal to or better than 1.0% of calibrated span for pneumatic transmitters, and 0.2% calibrated span for electronic transmitters.

Supply Voltage Sensitivity

Electronic transmitter output signal shall not change more than 0.01% of sensing element span per 1 volt change in supply voltage.

6.0 INSTRUCTIONS FOR DATA SHEET

The following numbers correspond to the line numbers on the Data Sheet.

1.	Show tag number
2.	Refers to process service or application
3.	Give line number or process area
4.	Material of chamber and/or mounting flange
5.	For float specify top or side of vessel connection. For displacer in a chamber specify upper, then lower connection; such as side-side, side-bottom, top-bottom. Give flange size and rating or NPT size.
6.	Same as 5
7.	Refers to position of instrument case when viewing the front of the case relative to the chamber; the case is either to the left, right, or top.
8.	On displacer instruments specify if case is to be rotatable with respect to the chamber. This only applies if there is one or more side connections.

9.	Orientation of control with respect to displacer chamber.
10.	Cooling extension
13.	Specify float diameter or displacer length. The displacer length is also the range.
14.	Insertion depth applied to side mounted or internal displacers. It is the mounting flange to the center of the displacer.
15.	The displacer extension is measured from the face of the mounting flange to the top of the
16.	Includes rod displacer. This dimension is required only for top of vessel mounted instruments.
17–19.	Refer to manufacturer’s standard materials or special materials.
20.	Transmitter, controller, switch, etc.
21.	Air pressure or electrical signal output of transmitter or controller.
22.	P: Proportional
	Pn: Narrow band proportional
	PI: Proportional plus integral (reset)
23.	Differential if controller on/off must specify differential adjustment or fixed. State adjustable range or fixed amount.
24.	Increase (direct action) or Decrease (reverse Action).
25.	Remote, or integral.
26.	Electrical classification of housing. NEMA number
27.	Air pressure or voltage. (60 psig, 24 VDC)
29.	Used only for interface application.
30.	Used for all services
31.	Specific gravities at operating temperature.
32.	Operating and max pressure, or vacuum
33.	For cryogenic service, give minimum temperature
36.	Airset assumed mounted to case.
37.-45.
45.	Manufacturer
47.	Model number of entire assembly.

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