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  • What Causes Steam Coils to Fail?


    Steam coils are a cost effective way to heat air. Costly premature failures can occur for a number of reasons, which leads to the purchase and installation of replacement steam coils. Usually this occurs at inopportune times and can lead to emergency service and overtime. Here are the five primary reasons steam coils fail:

    1. Erosion

    Over time, internal erosion can take place inside the coil at tubes and headers. This erosion is caused by two factors, poor steam quality and internal steam velocity.

    Steam quality (or dryness fraction) is defined as the percentage of gaseous steam in a pound of steam. The more liquid it contains, the worse the quality. Some steam boiler manufacturers will guaranty steam with a quality of 99.5%. That's 99.5% steam and 0.5% liquid, usually in the form of very small droplets. Though it may leave the boiler very dry, by the time it gets to the point of use, like a steam coil, it may have degraded to 80% dry or worse. If you could see inside the piping, you might see a fog traveling down the pipe with a stream of condensate running down the bottom of the pipe. Poor planning, poor piping practices, and/or failed steam traps are typical causes for steam quality degradation.

    Once these droplets enter the steam coil, they literally wear out the metal parts that are in their path, just like a sand blaster. If the coils are not designed well, the internal steam velocities can be high, making this situation worse.

    We at Campbell-Sevey have developed solutions for poor steam quality and can design steam coils around acceptable internal steam velocities to lengthen coil life.

    2. Corrosion

    When non-condensable gasses are allowed to remain inside steam coils, oxidation and carbonic acid corrosion can occur. Carbonic acid forms when carbon dioxide dissolves in water (condensate). The cooler the condensate and/or the higher the steam pressure, the worse the effect. Localized pH's of 3 are possible, which is quite acidic and dissolves the pressure containing metals of the coil. Pin-hole leaks start to develop over time. The use of thermostatic air vents and proper piping is critical to the removal of these gasses.

    3. Freezing

    Why does freezing occur? Steam in the coil turns to water (condensate) as it gives up heat. Once condensate is formed it must exit the coil before the freezing air on the finned side can extract enough additional heat from the water to turn it to ice. Unfortunately, installers and designers sometimes fail to recognize the factors which cause condensate to remain in the coil.

    Freezing occurs when condensate isn’t allowed to drain with freezing air temperatures blowing across the face of the coil. Proper steam coil installation planning, piping, trapping, and condensate return are critical for freeze prevention.

    4. Improper Coil Selection

    Not every coil is designed to work with every system. Sometimes the coil is not designed for the performance, and sometimes the coil is not designed for the duty. Conventional copper tube coils are usually adequate for low pressure steam commercial heating installations; however, industrial heating and process applications demand the most rugged possible coil construction.

    Adding additional surface area beyond what is required is not always the best solution. This can lead to decreased steam pressures in the coil and possibly unnecessary cooling of condensate, causing corrosion.

    For most coil replacements, Campbell-Sevey's field technicians first identify what caused the failure and then work with the design staff and our manufacturers to determine the best approach to increase the performance and life of the coil.

    5. Improper Installation

    If you have the right coil, but it isn't installed properly it is destined to fail. Here are several of the most common installation issues that occur:

    • The Coil is Not Pitched Toward the Return Main

    Since gravity is a main force used to drain condensate, pitching the coil toward the return main can be critical factor in getting the condensate out quickly.

    • No Vacuum Breaker Installed 

    Without a vacuum breaker, modulation of the steam valve causes a vacuum to form, so that the pressure in the coil is less than the pressure in the condensate main. Condensate will not drain, so the coil will begin to flood. This can cause freezing, corrosion, and/or water hammer.

    • There is Either No Drip Leg or a Drip Leg of Insufficient Height 

    When the steam control valve modulates sufficiently, the only available pressure to force condensate past the strainer and trap is the static head of the condensate in the drip leg. A short drip leg may reduce the trap capacity to the extent that the trap cannot keep up with the condensate loading, so flooding takes place.

    • Insufficient Trap Capacityor Wrong Trap is Used 

    Knowing that much of the time there is only head pressure to remove condensate, the steam trap orifice size selection becomes critical. It must be of sufficient size to remove all condensate generated by the coil, plus safety factor, at the pressure differential determined by the drip leg. The maximum operating pressure rating of the steam trap must be determined by the safety relief valve set pressure of the steam supplying the coil. If either of these factors is not taken into account, the wrong trap could be installed and the coil could fail.

    Selecting the proper steam trap style is also important to ensure that that the coil operates at peak performance. We offer and stock many steam trap styles and will recommend the proper style for your application,

    • The Condensate Return Line Rises Above the Steam Trap Outlet

    Some system designers contend that condensate will be lifted by steam pressure. While this may be true at the full load conditions, at part load conditions not enough pressure exists at the steam trap to lift condensate. The result is coil flooding with condensate.

    Consult with Campbell-Sevey

    For proper operation, all steam coils require additional equipment, such as control valves, steam traps, thermostatic air vents and vacuum breakers that will increase the performance and the life of the coil. When combined with the proper equipment and correct installation your coils can last for many years. At Campbell-Sevey, our experts understand the interplay among these pieces of equipment and how each affects the others. We size them all, we select them all, and we show you how they should be installed. We look at the past failures and use that information to make recommendations for improvements for the future. We look upstream and downstream of the coil, from steam supply to condensate return, to make recommendations to increase overall system efficiency and effectiveness. We understand these 5 pitfalls and how to avoid them.

    Both Industrial heating and process applications demand the most rugged possible coil construction. Campbell-Sevey offers a wide selection of coil construction and materials from light duty comfort heating to heavy industrial and utility grade and we have the expertise to know when to use each type.

    Consult with the steam, air and water experts at Campbell-Sevey to choose the right equipment for your steam coil applications.

  • Armstrong Acquires Veris Flow Measurement Instruments

    It's hard to manage what you can't measure. That's why Armstrong International has expanded its portfolio of intelligent system solutions through the acquisition of Veris, Incorporated, a leader in accurate and reliable flow measurement technology for gas, steam and hot water applications. 

    Veris has more than 25 years experience in designing and manufacturing flow measurement instruments. It's two primary measurement tools are Verabar® and Accelabar®.

    Verabar provides the most accurate, reliable technology for measuring gas, liquid and steam as well as the lowest operating and installation costs. View this Verabar video demonstration to see how it works. 

    Accelabar is a new and unique flow meter that provides superior performance in challenging applications. It combines two differential pressure technologies to produce high accuracy and low velocity flow rates at turndowns tested up to 65:1 with no straight run requirements. See this video on how Accelabar works.

    To learn more about these products or to see what type of flow measure technology would be best for your system, contact the team at Campbell-Sevey.

  • NB-27: A Guide for Blowoff or Blowdown Vessels


    Guide to Blowoff Vessels

    The treatment of boiler feedwater is an integral part of boiler operation, used to control scaling, corrosion, and deposits. Boiler feedwater treatment often leads to the formation of solid particles that are initially suspended in the boiler water. Solids concentrated in boiler water tend to promote foaming and scaling with a resultant loss of heat transfer which may result in overheating of the boiler tubes. Solids also may settle to the bottom of the boiler to form sludge. “Blowing off” part of the boiler water is a means of removing solids from the water while controlling boiler water levels. (It is common for the terms “blowdown” and “blowoff” to be used interchangeably.)

    The primary function of the blowoff system is to provide a safe means of controlling boiler blowoff water. This includes reduction in both pressure and temperature to limits acceptable for safe discharge into a sewer, drain system, or other area. The usual practice, therefore, is to discharge the water into a vented vessel where it may be allowed to cool, or mixed with cold water to reduce the temperature and pressure to acceptable discharge levels.

    The National Board of Boiler and Pressure Vessel Inspectors issued this Guide for Blowoff Vessels. The publication is intended to provide design information and guidance for boiler blowoff systems.

    It does not address details for all possible arrangements of boiler blowoff equipment. If the design of boiler blowoff equipment is not covered in this publication, guidance should be obtained from both a competent engineering firm and the inspection authority of the jurisdiction in which the equipment is to be installed.

    If you have further questions, contact the team at Campbell-Sevey

     

     

     

  • Test Your Knowledge: Which Piece Doesn't Belong? And What Is Missing?


     

    When it comes to configuring steam systems there are a number of factors to consider to determine what parts are needed and where they should be placed.

    In the sketch above, can you spot:

    • Which piece of equipment shown is not recommended?
    • Which two major pieces of equipment are missing?

    Know the answers? If not, here they are:


     

    Answer #1 - Quick opening solenoid valves are not recommended for steam service due to the potential for water hammer and thermal shock, both of which decrease the longevity of equipment and can lead to safety issues.

    Answer #2 - The two major pieces are a safety value and a vacuum breaker. A safety valve is required downstream of the pressure reducing valve by section VIII of ASME code. As we describe in our previously posted article on vacuum breakers, a vacuum breaker is recommended downstream of the coil and above the steam trap for complete condensate drainage under all operating conditions.

    Questions about your system? Contact Campbell-Sevey for answers and best practices.

     

  • To Avoid Boiler Combustion Problems, Supply Fresh Air

    Operating any boiler properly depends on the systems that support and connect to it. These include, but are not limited to: 

    • Boiler room fresh air supply
    • Flue gas exhaust system
    • Fuel delivery system
    • Power distribution grid
    • Steam or hot water distribution system.

    The starting point in any combustion system is the supply of fresh air. To avoid serious combustion problems, the boiler must have an adequate supply of fresh air and a supply system that does not affect the boiler's operation.

    HOW MUCH AIR IS REQUIRED? 

    In general, the following formulas have been developed to determine the amount of air required for any boiler room with a package firetube boiler firing gas or oil fuels.

    1. Combustion Air = HP* x 8 CFM/HP = 
    2. Ventilation Air = HP* x 2 CFM/HP = 
    3. Total Air Required = HP* x 10 CFM/HP =

    *HP refers to the total maximum boiler HP located in the boiler room. The above calculations are adequate for installations up to 1000 feet above sea level (fasl). For installation above 1000 fasl, add 3% additional air for each 1000 fasl (or portion thereof) to allow for the density change in air at higher altitudes.

    WHAT SIZE OF OPENING TO THE OUTSIDE IS REQUIRED IN A BOILER ROOM? 

    boiler room air supplyThe size of the fresh air inlet openings and their location are very important. There should be a minimum of two permanent air supply openings in the outer walls of the boiler room. Whenever possible, they should be at opposite ends of the boiler room and no higher than seven feet above the floor. This will promote thorough mixing with the air already in the boiler room, proper cooling of the boilers and tempering of potentially colder outside air prior to its entering the burner for combustion.

    The air inlets should be provided with some type of weather protection, but they should never be covered with a fine mesh wire screen. This type of covering results in poor air flow characteristics and is subject to clogging by dust, dirt, paper and other small items.

    To determine the net free open area of the opening, divide the total CFM required in the boiler room by the allowable velocity at the opening (see table below).

    ACCEPTABLE AIR VELOCITIES IN BOILER ROOM
    0-7 ft. above floor 250 FPM
    Above 7 ft. high 500 FPM
    When sizing an opening to the outside, it should be a minimum of one square foot.

    Care should be taken to ensure that no water, oil or steam lines are run in the direct path of cold fresh air entering from any of the outside air opening. Heated heavy oil lines should be protected from cold air and they should be electrically or steam heat traced and insulated.


    WHAT ABOUT AIR DUCTING? 

    In some applications the boiler room is located in a building such that it has no outside walls. Many of these applications do not have sufficient excess makeup air in the factory to allow for combustion air requirements. In these cases there are two solutions:

    • Ducting fresh air to the boiler room. Where this is required, the general rules for the size of wall opening for fresh outside air can be used. The duct size to the outside and its free open area inlet must never be smaller than the wall opening in the boiler room. In addition, the pressure drop through the duct at maximum flow must never exceed 0.05" w.c.
    • Ducting fresh air directly to the boiler. In general, this method of air supply should be avoided whenever possible. The disadvantages of this type of system far exceed any perceived advantages. If used, the ducting becomes a part of the boiler system and can effect the stability of combustion due to varying weather conditions, wind direction and velocity, humidity and temperature. An outside temperature variation of -10EF in the winter to 80EF in the summer (many areas of the country are wider) can cause a burner adjusted for 15% excess air combustion on the coldest winter day to be 5% short of air on a warm day. This can lead to massive CO production, soot formation, plus unstable and unsafe combustion.

    If direct ducting must be used, we suggest the following minimum steps be followed:

    1. Each boiler has its own, completely separate fresh air ducting and exhaust stack. Shared air supplies and exhaust stacks will lead to combustion problems and unsafe operating conditions.
    2. Boilers directly connected to fresh outside air ducts must be checked for proper combustion adjustment and operation every three months by a certified package firetube boiler specialist.
    3. The duct work supplying the fresh air to the boiler must be sized so that it has a maximum pressure drop at maximum flow of 0.05"wc.
    4. The fresh air supply duct should have an electric, hot water, or steam heater to temper cold outside air to at least 50EF.
    5. If the application is utilizing a low emission with flue gas recirculation, do not use direct ducted outside air. The potential problems associated with a standard burner are intensified with a low emission burner.

    SAMPLE CALCULATIONS 

    Determine the net free open area of the boiler room supply openings for one 300 HP boiler and one 800 HP boiler, both in the same boiler room. Boiler room located 1800 fasl and its direct outside air inlets are to be five feet above the floor level.

    Total maximum HP = 300 + 800 = 1,100 HP
    Total air required = (1,100) (10) = 11,000 CFM
    Altitude correction = (11,000 CFM) (1.03) = 11,330 CFM

    11,330
    Net free open area required = = 45.32 sq. ft.
    250

    The boiler room will require a minimum of two fresh air opening of 22.66 sq. ft. (45.32 sq. ft ) 2) net free open area. NOTE: For all applications, the above is a general minimum requirement for fresh air supply. Always consult local codes which may supersede the above recommendations.

    Information from Johnston Boiler Company.

  • Steam Table: Properties of Saturated Steam

    Here is a table on the Properties of Saturated Steam for you to refer to as needed. View it here or click to download the pdf.

  • Knowledge Center: See our Video Demos of How Steam Traps Work

    Most of you know that steam traps are used to discharge condensate and non condensable gases with a negligible consumption or loss of livesteam. Most steam traps are nothing more than automatic valves. They open, close or modulate automatically.

    However there are several different types all performing unique functions. In the CS Knowledge Center we highlight six different traps and show how they work. The traps include: balanced-pressure thermostatic, float and thermostatic, inverted bucket, thermodynamic disc, TVS 800, and two bolt steam trap connector blocks.


    Most of you know that steam traps are used to discharge condensate and non condensable gases with a negligible consumption or loss of livesteam. Most steam traps are nothing more than automatic valves. They open, close or modulate automatically.


    However there are several different types all performing unique functions. In the CS Knowledge Center we highlight six different traps and show how they work. The traps include:
    balanced-pressure thermostatic, float and thermostatic, inverted bucket, thermodynamic disc, TVS 800, and two bolt steam trap connector blocks.


    Check our instructional videos of how various steam traps work.

    Most of you know that steam traps are used to discharge condensate and non condensable gases with a negligible consumption or loss of livesteam. Most steam traps are nothing more than automatic valves. They open, close or modulate automatically.  

     

    However there are several different types all performing unique functions. In the CS Knowledge Center we highlight six different traps and show how they work. The traps include: 

    balanced-pressure thermostatic, float and thermostatic, inverted bucket, thermodynamic disc, TVS 800, and two bolt steam trap connector blocks.
  • Campbell-Sevey Welcomes Tyler Rechtzigel to our Sales Team

    We are excited to announce the addition of Tyler Rechtzigel to our team. Educated at Dunwoody College of Technology, Tyler comes to us with 6 years experience in Combustion Systems and Controls (Production, Health and Institutional burners and controls) and 3 years experience in Commercial HVAC.

    "I chose Campbell-Sevey because of their great reputation throughout the industry," said Tyler. "I look forward to utilizing my knowledge in the mechanical trades and working with the rest of the team to provide solutions for clients."

    With Tyler's background in sales, design, project management, service coordination and estimation, along with his experience in the field, he a great asset to our team. Welcome aboard.




  • Check out our New Website and Knowledge Center

    New website features extensive knowledge center of steam, air and water product videos, educational tips, and manuals.

    We are proud to announce the launch of our newly updated website -www.Campbell-Sevey.com. The new site and brand image more accurately depicts Campbell-Sevey's services and product lines.

    The website provides detailed information on the key industries we serve and the steam, air and water products and services we provide including utility systems studies and steam/hot water boiler products.

    The most extensive addition is the CS Knowledge Center. "We have a highly trained team that has worked with every kind of system application and field-tested every component", said Brian Ross, Campbell-Sevey CEO. "Within the Knowledge Exchange we share our insight into products, systems, and best practices."

    The Knowledge Center features numerous manuals, literature, submittal drawings, and education videos for use by plant managers, architects, contractors, and operations engineers.


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Products We Carry

GENERATION
  • Hot Water Boilers
  • Watertube Steam Boilers
  • Firetube Steam Boilers
  • Deaerators
  • Heat Recovery Steam Generators (HRSG’s)
  • Automatic Recirculation Valves
  • Economizers
  • Gas-Fired Water Heaters
  • Gas-Fired Humidifiers
  • Boiler/Generator Flue Stacks
  • Continuous Emissions Monitors (CEMS)
DISTRIBUTION
  • Pressure Reducing Valves
  • Safety and Relief Valves
  • Control Valves
  • Pressure Independent Control Valves
  • Expansion Joints, Guides, Anchors
  • Flash Tanks
  • Flow Meters
  • Balancing Valves
  • Check Valves
  • Separators
  • Pumps
  • Pressure Booster Systems
  • Piston Valves
UTILIZATION
  • Heating/Cooling Coils
  • Plate and Frame Heat Exchangers
  • Shell and Tube Exchangers
  • Water Heaters
  • Steam Humidifiers
  • Vacuum Systems
  • Condensers
  • Steam Traps
  • Wireless Steam Trap Monitors
  • Tube Bundles
  • Direct Gas-Fired Space Heaters
  • Direct Gas-Fired Make-Up Air Units
  • Unit Heaters
  • Strainers
  • Air Vents
  • Liquid Drainers
  • Heat Transfer Packages
  • Digital Water Mixing Valves
  • Air Cooled Condensers/Dry Coolers
  • Steam Filters
RETURN
  • Electric Condensate Pumps
  • Steam/Air-Powered Condensate Pumps
  • Packaged Condensate Pump Skids