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Unscheduled plant outages, no matter what the cause, result in increased costs and loss revenue. As plants continue to reduce personnel and maintenance budgets, the likeliness of an equipment failure is more and more common. Below are just a few guidelines for effectively managing your plant equipment, while utilizing limited resources:

Know your equipment's age.

Replacing or upgrading obsolete, aging or high maintenance equipment before it fails can prevent serious failures in the future. Obtain and file a record of all your major pieces of equipment. Note when the equipment was acquired, built and record any maintenance items performed. You may also want to take pictures of your equipment, including any serial numbers and nameplates. In addition, be on the lookout for new equipment models that have been re-designed with technological upgrades that may result in immediate cost savings (decreases in energy consumptions or increases in efficiencies). You may received an immediate cost savings or rebate.

Continually train your operators and plant personnel.

Human error is bound to happen, but these errors can be drastically reduced by continual training. Training comes in all forms and it does not necessarily have to be formal, classroom type lectures. Utilizing check-off lists for routine tasks is an easy and low cost method to ensure that all critical task are carried out, no matter how small. Also, promote common maintenance reminders through the use of signage.

Develop a schedule.

Scheduling major inspections and repairs at the same time helps to minimize unscheduled outages and makes the most of a schedule.  Take advantage of that time to conduct anything else that needs repaired, inspected or replaced. Overall, having a plan in place makes it easy to be proactive in your planning and scheduling of people and resources.

Do you have additional guidelines you would like to share? Let us know.
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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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In order for your boiler to operate at peak efficiency, it is important that the correct balance of fuel and combustion air is achieved. Air and fuel ratios are controlled through linkages, fans, dampers and the increase or decrease of gas pressure. Gas pressure is controlled through a pressure regulator and a fan controls the volume of combustion air.
If there are any problems with the fan, more energy may be introduced into the system, causing decreased efficiency. To help ensure that your equipment is running at its peak performance, please review the common fan problems below.

Fan Capacity/Pressure is Below Rating:

  1. Dampers or variable inlet vanes are not adjusted properly

  2. Fan inlet or outlet conditions are impaired

  3. Multiple air leaks within the system

  4. Damage sustained to the blower wheel

  5. Direction of rotation is incorrect


Fan Vibration:

  1. Worn bearings

  2. Unstable foundation

  3. Foreign material in the fan causing an imbalance

  4. Misalignment of bearings, couplings, wheel or v-belt drive

  5. Damaged wheel or motor

  6. Bent shaft

  7. Worn coupling

  8. Loose dampers or variable inlet vanes

  9. Speed too high or incorrect fan rotation

  10. Vibration to fan transmitted from another source

  11. Uneven blade wear

  12. Loose or broken bolts or set screws


Overheated Bearings:

  1. Improper lubrication

  2. Poor alignment

  3. Damaged wheel or driver

  4. Bent shaft

  5. Abnormal end thrust

  6. Dirt in bearings

  7. Improper belt tension


Overload on Driver:

  1. Speed too high

  2. Direction of rotation is incorrect

  3. Bent shaft

  4. Poor alignment

  5. Improper lubrication

  6. Wheel wedging or binding on fan housing

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The winter season is here and for many users affected by freezing temperatures it is critical that the boiler unit is properly protected. Nationwide Boiler recommends the following in order to ensure that your unit continues to operate while facing freezing conditions.

  1. Enclose both the front and rear of the boiler area and use an external heat source to minimize freezing conditions.

  2. Install heat tracing with insulation to protect exposed stagnant water lines.

  3. Utilize an appropriate heat tracing method (electric or steam tracing) to all of your main lines and piping components. This includes the following lines which should be heat traced regardless if the boiler is in operation or not (in freezing conditions): sensing lines (steam drum to CMR, high steam and steam gauge), auxiliary low-water-cut-off, water column and level control blowdown. Depending on the length of piping runs, the main and continuous blowdown should also be heat traced.

  4. In addition to heat tracing on stagnant sensing lines, drain the lines and fill them with a 50/50 (water/glycol) solution, making sure to re-connect the line.

  5. When an extended boiler down time is expected, completely drain the boiler and stagnant water lines.


The above are recommendations, however, use sound engineering judgment calls when there are concerns of possible freeze damage to the equipment. Call us if you have any further questions at 1-800-227-1966.

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