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Nationwide Boiler Steamlines Newsletter: Available Now!

Nationwide Boiler's first Steamlines Newsletter of 2021 is out and available for viewing! Read up on the latest happenings at Nationwide, industry news, technical tips, and more, including... 

A SOLUTION TO STEAM SUPPLIER OUTAGES
Nationwide has nearly 55 years of experience responding to emergency needs, and there is no doubt that we are able and ready to dispatch equipment in a moments notice. What may come as a surprise to some is that unplanned and emergency rentals make up a smaller portion of our business than planned outages. And at times, rental boilers are used for process steam when the outage is planned by the steam supplier next door.

REMOTE WORK: IS IT THE FUTURE?
Since the pandemic forced many companies (including NBI) to move to a temporary remote work model, some corporations like Google, Dropbox, Facebook, and Salesforce are going all in with remote work as a permanent way of business. But is remote work for everyone, and is it the future? Hear from our President & CEO, Larry Day, for his take on the matter.

GETTING TO KNOW OUR STORAGE YARDS
Nationwide Boiler has a purpose built rental fleet featuring firetube and watertube boilers, mobile steam plants, and boiler auxiliary equipment. Partnering with multiple distinguished companies in our industry for the storage & maintenance of this equipment allows us to offer a quick and cost effective solution when a temporary steam need arises.

CALIFORNIA EMISSION RULE UPDATES
More changes are upon us here in California, and at Nationwide Boiler we make it a priority to stay abreast of AQMD emission rulings that will affect our customer base. The three areas of focus at this point are the South Coast AQMD, San Joaquin Valley APCD, and San Diego APCD.

REP SPOTLIGHT: COMBUSTION SYSTEMS, INC.
With headquarters in Indianapolis, IN, Combustion Systems, Inc. (CSI) is the exclusive Nationwide Boiler representative covering the territories of Indiana, Illinois, and most of Wisconsin. Check out this edition of our representative spotlight to learn more.  

NEW RENTAL BOILERS FOR THE FLEET
With over 100 rental boilers currently in our inventory, we still find the need to add new units to fill in the gaps, replace sold equipment, or to boost our numbers for equipment that is often in high demand. Learn about some of the new equipment currently being built for our rental fleet.

View this current edition and past editions of our Steamlines Newsletter, on our website now!

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Proper Sizing and Installation Tips - Safety Valves

The safety valve is one of the most important safety mechanisms in a steam system. Not only are they required by code, but most importantly, safety valves provide a measure of safety for plant operators and for the equipment.

The American Society of Mechanical Engineers (ASME) governs the code that establishes the requirements for safety valves, therefore it key that all plant personnel are familiar with current codes that apply to their system.

We found the following sizing guidelines and installation tips listed in Process Heating Magazine and thought the information would be useful to pass on. We hope that this enhances your knowledge and understanding of safety valves.

Sizing Guidelines

The two major considerations for safety valves are proper sizing and correct installation. The following tips address safety valve sizing.

  • It is suggested that the setpoint selected for the safety valve provide a differential of at least 20 percent between operating and set steam pressures.

  • When considering installation of a safety valve downstream of a steam pressure control valve, the total capacity of the safety valve at the setpoint must exceed the steam control valve's maximum flow capacity (the largest orifice available from that manufacturer) if the steam valve were to fail to open. The inlet steam pressure to the valve must be calculated at the maximum safety valve setting of the steam supply source, not the nominal operating pressure.

  • It is important not to oversize a safety valve. Bigger is not better in this case because a larger-than-required valve could cause chatter, leakage and premature failure.

  • Many times, a single safety valve is not possible due to high capacity, physical limitations or economic considerations. An acceptable alternative is to employ multiple safety valves on the same system. The valves should be of the same setpoint and the capacities must be equal to or greater than the rating of the equipment. Additionally, the vent pipe must be sized to account for the venting capacity of all of the safety valves fully opening at the same time.

  • The set pressure of the safety valve should be set at or below the maximum allowable working pressure (MAWP) of the component with the lowest setpoint in the system. This includes steam boilers, pressure vessels and equipment, and piping systems. In other words, if two components on the same system are rated at different pressures, the safety device protecting both of these devices must be set at the lower of the two ratings.


Installation

Once sizing has been properly determined, proper installation is the next crucial step to ensure safety. There are several points to consider when installing the safety valve.

  • The steam system must be clean and free of any dirt or sediment before commissioning the steam system with a safety valve.

  • The safety valve must be mounted vertically with the valve's spindle in the vertical position.

  • The inlet steam piping to the safety valve must be equal to or larger than the safety valve inlet connection.

  • There should be no intervening shutoff valves located between the safety valve inlet and the steam component that could permit the safety valve to be isolated from the system.

  • Drains or vent openings on the safety valve should not be plugged or capped. They are on the safety valve for a reason.

  • Safety valves are set, sealed and certified to prevent tampering. If the wire seal is broken, the valve is unsafe and should not be used. Contact the supplier immediately.

  • For multiple safety valve installations using a single connection, the internal cross-sectional area of the inlet shall be equal to the combined inlet areas of all the safety valves.

  • All safety valves should use a drip pan elbow on the outlet. The drip pan elbow changes the outlet of the safety device from horizontal to vertical. Installation of the drip pan elbow has its own guidelines, which should be researched and addressed to meet the needs of each application.

  • Never attach the vent discharge piping directly to the safety valve. This would place undue stress and weight on the valve body. Also, the safety valve vent pipe may not touch the drip pan elbow.

  • The drains on the drip pan elbows are to direct condensed vapor and rain safely away to the drain. Do not plug these openings.

  • Steam will not escape from the drip pan elbow if the vent line is sized correctly.


Vent Piping

There also are some important considerations when it comes to the vent piping of the safety valve and the steam system.

  • The diameter of the vent pipe must be equal to or greater than the safety valve outlet.

  • The vent line should be sized so that back pressure is not placed on the drip pan elbow.

  • The length of the vent pipe should be minimized where possible.

  • The discharge outlet of the vent pipe should be piped to the closest location where free discharge of the safety device will not pose a safety hazard to personnel. For a roof-line termination, the vent should be no less than 7' above roof line. The top of the vent line should be cut at a 45° angle to dissipate the discharge thrust of the steam, prevent capping of the pipe and to visually signify that it is a safety valve vent line.

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Recent comment in this post
Guest — james w
some interesting points in here, well laid out.
Thursday, 20 August 2009 01:21
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