2-12.001 May 2011 Low pressure boiler* inspection and maintenance Introduction Even as our society evolves into a more technologically advanced, economically driven environment, many businesses and their facilities still rely upon low-pressure boilers to support building services and manufacturing process applications. However, even with the installation of more sophisticated electronic controls and safety devices, our insureds continue to experience occurring incidents each year where low-pressure boilers cause property damage, personnel injury and extensive loss of business income. Zurich Services Corporation / Risk Services help our insureds with respect to their use and care of such equipment very seriously. We employ qualified Boiler and Pressure Vessel Inspectors (BPVIs) as well as other competent staff who are knowledgeable in the requirements to help protect both personnel and property that can be exposed to harm from the improper or poor operation of this equipment. Once an insured location has been identified having this class of equipment, our BPVIs do perform periodic risk assessments, as required, to help safeguard against sudden and accidental boiler losses. Safe boiler operation not only requires our service, it requires the commitment of the boiler owner to know how to operate this type of equipment properly. We offer the following general information regarding the inspection and maintenance of this equipment's primary safety devices. *A boiler in which steam or vapor is generated at a pressure less than or equal to 15 psig (103.4 kpa gauge)
Pressure relief devices (PRD s) ** The Safety Valve (SV) is the primary safety device installed on any low-pressure boiler to protect it against over pressurization. Manufacturers design and build the SV to relieve all of the pressure the boiler can generate. When a boiler is in operation, the operator or competent person in charge can manually test the SV operation by lifting its test lever. The boiler operating pressure should be at least 75% of the safety valve set pressure when testing the safety valve manually. An alternate method of testing the low-pressure boiler SV is to remove it from the boiler during the annual scheduled maintenance/service period and send it to an ASME (VR)*** accredited testing facility for bench testing and re-certification before re-installation. Either verification test method is acceptable. The boiler owner needs to have this service incorporated into a proper boiler preventative maintenance program to ensure regular testing of this important safety device. ** Commonly referred to as a Safety Valve or Safety Relief Valve depending upon its intended service. *** American Society of Mechanical Engineers, Valve Repair Low Water Fuel Cut-Off (LWFCO) Because low water conditions in a boiler can result in internal damage or even catastrophic failure, the LWFCO is a very important safety device designed to cut off the fuel supply to the boiler in the event a low water condition. Most jurisdictional authorities (State and Provincial) now require that there be two of these devices installed on all low-pressure boilers, one as the primary protection with a secondary backup device. The Primary LWFCO when manually drained will shut off the fuel supply to the boiler, temporarily shut down the boiler air supply fan and start the feedwater pump. Upon closing the drain valve and the water level is returned to normal, the air supply fan will automatically restart to purge the boiler gas side before the fuel firing system will be energized to resume normal operation. A minimum of four boiler gas passage air exchanges is typically required before the automatic fuel valves can be energized to operate. The Secondary LWFCO when manually drained will shut off the fuel supply to the boiler, shut down the boiler air supply fan and the feedwater pump will remain shut off. Only when the manual drain valve is closed and the LWFCO is manually reset, as per the manufacturers operating instructions, will the pre-purge and auto firing sequence resume after the feedwater pump starts to supply the proper water level within the boiler. In both tests an audible alarm at the boiler and a remote alarm sounds (unattended plants) which will have to be reset at the boiler operating panel. Simply open the lower water side drain below the float chamber or probe column. The flame failure should occur almost immediately when the water level drops. Close the drain valve once flame failure is confirmed visually and by alarm. By keeping the inside of the float or column piping and chamber clean, this test will maintain these devices in good operating condition. This manual testing can be done daily or no less than once per week depending upon the critical nature of the steam process and demand. The results are to be logged in the Operators Log Book for review. The benefit from doing this manual test regularly is that you are forcing the water and any sediment out while verifying that the steam and water side piping and connections are not obstructed. If the piping is clear this test should take no more than five seconds. Additionally this effectively tests the automatic function capability of both safety devices. Periodically the water level gauge glass needs to be blown down on the Primary LWFCO device to ensure the gage glass' proper operation. When operating properly, the water level gauge glass should always have a water level between a third and a half of the glass. NOTE: the boiler fuel system should shut down before the water level drops below the lowest visible point in the glass.
Burner operation Flame failure scanner To prevent boiler fireside explosions, the boiler owner/operator must verify that some type of flame-sensing device is in use to ensure that flame conditions are safe on the boiler burner side. In the event of flame failure during operation, the flame-sensing device must be capable of stopping the boiler fuel supply, initiating an alarm and causing an air purge of the boiler fireside passes to remove latent fuel fumes from the boiler's fireside. Check the burner operation and flame pattern regularly and flame failure scanner periodically, preferably at least weekly. In general, listen for unusual noise, check for fuel leaks, check the position of dampers, and look or smell for indications of flue gas leakage. Observe the boiler stack temperature to verify it is within the normal operating range. Follow the boiler manufacturer s guidelines and the ASME CSD-1 Code for burner maintenance and testing of the flame failure scanner. If the burner shows any indications of abnormal operation, contact your boiler service technician. Boiler steam gauge The boiler steam gauge allows the boiler operators to see how much pressure the boiler is generating. Steam gauges should be clearly visible and in good operating condition. The gage shall be connected to the boiler steam space or to its water column or its steam connection. The gage or gage connection shall contain a siphon or equivalent device that will develop and maintain a water seal that will prevent steam from entering the gage tube. The scale on the dial of a steam boiler gage shall be graduated to not less than 29 psig (200 kpa) or more than 58 psig (400 kpa). The travel of the pointer from 0 psig (0 kpa) to 29 psig (200 kpa) pressure shall be at least 3 in. (76 mm). High limit controls Each boiler must have high limit controls installed. These devices will act as a backup control to the normal operating controls. On a low-pressure steam boiler, there will be an Operating Limit Switch set to have the boiler burner fire when the steam pressure drops to a predetermined low set point and then cut off when pressure reaches a predetermined high set point. If steam pressure exceeds the Normal Operating Pressure range of low - high, the High/High Limit Control Switch is designed to send a signal to the boiler controls that will stop fuel flow and cut the boiler off, similar to the flame failure scanner. Have a qualified technician test these devices during any scheduled maintenance period to ensure the proper signals are being received at the normal device set points. Conclusion There are other devices used on low-pressure boilers that are very important to the boiler's safe and efficient operation temperature gauges, pressure gauges, air/fuel supply controls and linkages, fuel shut off valves, strainers, feedwater pump/motor, bearing cooling, isolation valves, main steam outlet valve, manhole and handhole gasket quality, refractory insulation, etc. All of these items have regular inspection and maintenance requirements that are just as important as the inspection and maintenance of the automatic safety devices. They should be maintained routinely with all defects corrected. Care for all of these devices should always be left to a fully qualified boiler operator or service technician trained in the operation and testing of steam boiler equipment. Do not hesitate to contact your Zurich Risk Services Specialist directly or Risk Services General Assistance (416-586-2740) to leave a message. We will have someone contact you within 24 hours. References 1. National Board of Boiler & Pressure Vessel Inspector s Code. 2. ASME Boiler & Pressure Vessel Code, Section VI and CSD-1.
The information in this publication was compiled from sources believed to be reliable for informational purposes only. All sample policies and procedures herein should serve as a guideline, which you can use to create your own policies and procedures. We trust that you will customize these samples to reflect your own operations and believe that these samples may serve as a helpful platform for this endeavor. Any and all information contained herein is not intended to constitute legal advice and accordingly, you should consult with your own attorneys when developing programs and policies. We do not guarantee the accuracy of this information or any results and further assume no liability in connection with this publication and sample policies and procedures, including any information, methods or safety suggestions contained herein. Moreover, Zurich reminds you that this cannot be assumed to contain every acceptable safety and compliance procedure or that additional procedures might not be appropriate under the circumstances The subject matter of this publication is not tied to any specific insurance product nor will adopting these policies and procedures ensure coverage under any insurance policy