Boiler Blog | Nationwide Boiler Inc.

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.

Nationwide Boiler Inc. is pleased to announce the signing of Le Groupe Simoneau Inc. as its new Eastern Canadian Representative for the rental and sale of Nationwide's extensive product line. Le Groupe Simoneau specializes in the manufacturing of a complete line of boilers and supplies boiler tubes and accessories in Canada for the industrial, institutional and commercial markets. Their specialized team of experienced field service staff provides the complete assembly and installation of boilers, in addition to boiler repair and refurbishment.

Please read the full press release for additional information.

The Western Regional Boiler Association Conference will take place March 15-17th at the Hilton Eugene & Conference Center in Eugene, Oregon. Nationwide Boiler's Rental Manager, Michael Medina, will be attending the show and he will be on site to answer questions pertaining to Emergency Contingency Planning and temporary boiler solutions.

Nationwide Boiler's presentation, Guidelines for Preparing for a Temporary Steam Plant, was presented during last year's conference and it provided attendees with a general overview of what's required when renting a boiler and what stages of planning are necessary when renting boilers. If you are interested in obtaining a copy of this presentation, please contact us at info@nationwideboiler.com, or come and visit us at the conference. You can also download Nationwide's free Emergency Preparedness Guide to ensure that your facility's contingency plan is in place and ready, should an emergency arise.

At Nationwide Boiler, we are constantly looking for new opportunities for growth and enhanced relationships with reputable manufacturers. We are thrilled to announce our most recent partnership with Webster Combustion Technology, representing their boiler-burner line in Central and Northern California. This new relationship will allow Nationwide to offer customers an efficient and cost-effective burner as a retrofit or a part of a new package boiler system.

Webster Combustion has been in business since the 1920's, manufacturing multi-fuel burners for commercial heating, process steam, and drying applications. Majority of their burners are utilized in boiler assemblies. Webster burners offer multiple fuel flexibility, high efficiency, low emissions, and high turndown capabilities. Their product line will complement Nationwide Boiler's product offerings very well, providing a quality solution for our customers in California.

For more information, check out our latest press release!