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Monoflanges and Instrument Manifolds

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Have a question on or need to purchase quality Monoflanges and Instrument Manifolds? Our Sponsors Prochem Pipeline Products  are Experts in this area!
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Jump to the Various Sections of this and other Instrument Fittings and Tubing Pages; Monoflanges and  Instrument Manifolds | Frequently Asked Questions associated with Monoflanges and Instrument Manifolds | Instrument Monoflanges | Instrument Manifolds | Instrument Fitting Technical Information | Gauging Instrument Threads and Fittings | Codes and Standards | Compression Fittings| Excess Flow Valves | Instrument Manifolds, Monoflanges,Valves and Accessories | Tubing Selection

Monoflanges and  Instrument Manifolds

Monoflanges and Instrument Manifolds are used as an alternative to multivalve systems. They have been specifically designed to provide a compact installation for gauge or transmitter instruments. An application where a monoflange is used is in place of other equipment. For example, the instance where instead of having one valve and relying on it to close so that a transmitter can be isolated, two valves are used. A double block and bleed monoflange can be used in place of the two valves. It takes away that need for two valves and reduces it all into one. That is the monoflange has two valves on it, which are closed, and a vent that is opened to reduce the pressure between. It has reduced weight and minimum leak paths providing a higher integrity system. The reduced length of the installation also reduces the risk of damage through vibration.

Monoflange manifolds can be mounted directly onto vertical or horizontal flanged connections, allowing a gauge to be kept in an upright position. Suitable for both primary isolation (double block and bleed) and instrument (block and bleed) duties a Monoflange provides isolation, venting and instrument mounting in a single compact unit. The designs incorporate safety features that limit vibration and reduce the overall height of a gauge installation.

In order to ensure System Integrity one must not lose sight of the fact that Monoflanges and Instrument Manifolds are subject to Process Conditions eg., pressure and temperature, therefore it is important to purchase high quality units. 

Frequently Asked Questions associated with Monoflanges and Instrument Manifolds

What materials are used and why?
The materials generally used in producing a suitable alloy are Carbon, Silicon, Manganese, Chromium, Molybdenum, Nickel and Copper in different proportions to create different mechanical properties, such as tensile strength, depending on the conditions in which they are to be placed. That is, for example, whether the environment is corrosive, hot, wet or changeable etc.

What does NPTF thread stand for?|
NPT thread stands for National Pipe Taper. It refers to the thread that tapers inward to create a better seal. It is recommended that care is taken in regards to the thread tolerances and only the best quality units are purchased to achieve this. It is imperative that any manufacturer has demonstrated quality assurance to a high standard. It is worthwhile ensuring the quality of threads by gauging at least a proportion of the threads to ensure compliance. Also it is recommended that  thread tolerances and gauging should be specified to a tolerance better than the requirements of ASME B1.20.1. ICEweb's compression fittings page has a more detailed explanation of the gauging and tolerance requirements.

What does ASTM/UNS stand for?
ASTM stands for American Society for Testing and Materials.
UNS stands for Universal Numbering System.

What is an OS&Y valve?
An OS&Y valve is an Outside Screw and Yoke valve. It is a part of the piping specification. It has a firesafe outside screw construction.

Why is the Molybdenum content of 316SS 2% minimum in an offshore environment?
The molybdenum content is at a minimum 2% to prevent chloride corrosion.

Why is 303 or 304SS not to be used in an offshore environment?
303 or 304SS is not to be used because their molybdenum content is nil and thus the material is subjected to chloride corrosion.

Is there a maintenance issue when Close Coupled Monoflanges are used? If the Monoflange is installed on a clean, non blocking process then it is not an issue in that access to the tapping point is required very rarely. This is especially so on Fieldbus and HART systems as the transmitter provides a huge amount of diagnostics on-line.  The huge advantage of Close Coupling is that many instrument fittings are no longer required, thus eliminating potential leak failure points. 

Instrument Monoflanges

More Details on Monoflanges - From our sponsor Prochem Pipeline products

Close Coupled Monoflanges - This design incorporates all the integrity features of the convention models, however adds even more safety and cost saving features. The design eliminates the requirement for instrument tube, fittings and threaded connections. Mono Flange Direct, can be provided in a direct mount version or a interface mounting plate can be facilitated if required - From our sponsor Prochem Pipeline products

Installation, Operation and Maintenance of Monoflanges - Comprehensive Information from Anderson and Greenwood

Instrument Manifolds

Comprehensive Catalogue of Instrument Manifold Technical information and specifications - From Anderson and Greenwood - with 162 pages this is a large 6 Meg download. 

Co-Planer Instrument Manifolds Read from page 105 - Anderson Greenwood MC & MT series Integral Manifolds are designed specifically for Rosemount Coplanar style transmitters including Model 3051C, Model 3051P, Model 2024, and the Model 3095 Multivariable transmitters.

Manifold and Isolation Valve Mounting System for Direct Mounting DP Transmitters - The system does not require impulse lines, thereby considerably reducing installation and maintenance costs.

Co-Planer Instrument Manifolds - This technical engineering note from Rosemount gives a good description of the advantages and benefits of these manifolds.

Information on Manifolds 

Instrument Fitting Technical Information

ICEweb’s Instrument Fittings Technical Data Page – This comprehensive page covers just about all the engineering information that you need to know including Design, Interchangability, Installation, Maintenance, Thread Tolerances, Material Selection, Gauging and much more!

Gauging Instrument Threads and Fittings

The following excellent links are compliments of Glastonbury Southern Gage.

Thread and End Connection Identification Guide - a 56 page document from Swagelok.

Great technical information on other products from our sponsors PROCHEM PIPELINE PRODUCTS

INSTRUMENTATION  - Includes information on; 

HYDRAULIC- Includes information on; 

VALVES AND ACTUATORS - Includes information on;

MANUFACTURING - Includes information on; 

PIPING PRODUCTS- Includes information on; 


Welded Duplex Tube - Welded Duplex Tube to: ASTM SA789/A789 UNS S31803/S32205.
Y-Type Strainer