36C26320Q0104-002.pdf

The United States Department of Veterans Affairs

VHA Boiler and Associated Plant Safety Device Testing Manual

Fifth Edition

By Thomas Burch David F. Dyer

Glennon Maples

BEI, LLC

P.O. Box 2255 Auburn, Alabama 36831-2255

December 2018

PURPOSE

This document was prepared for use in training and conducting safety reviews for the United States Department of Veterans Affairs.

Fifth Edition, 2018 revision Copyright 2018.

Thomas Burch, David Dyer, and Glennon Maples Published by: BEI, LLC P.O. Box 2255 Auburn, Alabama 36831-2255

Table of Contents

1. INTRODUCTION

1.1 OBJECTIVE

1.2 BACKGROUND INFORMATION

1.3 REQUIREMENTS FOR SAFETY TESTING

1.4 NOMENCLATURE

1.5 PREPARATION OF SYSTEM FOR SAFETY TESTING

2. WATER LEVEL CONTROL

2.1 LOW WATER CUTOFFS

2.2 LOW WATER ALARM

2.3 HIGH WATER ALARM

2.4 OVERFLOW DRAIN SYSTEM

3. PRESSURE CONTAINMENT

3.1 STEAM SAFETY VALVES

3.2 RELIEF VALVES

3.3 HIGH STEAM PRESSURE LIMIT SWITCHES

3.4 HYDROSTATIC TESTING

4. FUEL TRAIN SAFETY DEVICES .......................................... …………..22

4.1 LOW PRESSURE FUEL CUTOFF SWITCH…

4.2 HIGH PRESSURE FUEL CUTOFF SWITCH

4.3 VENTING BETWEEN AUTOMATIC GAS SHUTOFF VALVES

4.4 LEAK TEST OF AUTOMATIC FUEL SHUT OFF VALVES

4.5 OIL ATOMIZING MEDIA SWITCHES

4.6 AUTOMATIC FUEL SHUTOFF VALVE PROOF OF CLOSURE SWITCH . 27

5. BURNER AND AIR TRAIN SAFETY DEVICES

5.1 THE FLAME SCANNER

5.2 LOW FIRE PROVING SWITCH

5.3 COMBUSTION AIR PRESSURE SWITCH

5.4 PURGE AIR FLOW PROVING SWITCH

5.5 BURNER POSITION SWITCH

5.6 FORCED DRAFT MOTOR INTERLOCK

5.7 FURNACE PRESSURE INTERLOCK

5.8 OUTLET DAMPER POSITION INTERLOCK

5.9 FORCED DRAFT DAMPER WIDE OPEN PRE-PURGE PROVING

SWITCH

5.10 PRE-PURGE AND POST-PURGE TIMERS

5.11 IGNITER TIMER AND MAIN FLAME IGNITION TIMER

5.12 AUTOMATIC FUEL SHUTOFF VALVE CLOSURE TIME5

AFTER MAIN FLAME FAILURE………………………………..… ……35

5.13 AUTOMATIC FUEL SHUTOFF VALVE CLOSURE TIME

AFTER IGNITION FLAME FAILURE……………………………….…36

5.14 MINIMUM PILOT FLAME TEST

5.15 CONTROL AIR PRESSURE INTERLOCK

5.16 FLUE GAS RE-CIRCULATION DAMPER SET FOR PRE-PURGE

5.17 LOW FLUE GAS OXYGEN LEVEL INTERLOCK……………………….…38

5.18 INTERLOCK OF OUTSIDE AIR DAMPER WITH BURNER

MANAGEMENT SYSTEM………………………………………….………. 39

Appendix A STEP BY STEP TEST PROCEDURES Appendix A.1 INTRODUCTION Appendix A.2 Assumptions for Test Procedures………………………… 40 Appendix A.3 BASIC INFORMATION Checklist for High Water Alarm on Condensate Tank (HWACT) Checklist for Low Water Alarm on Condensate Tank (LWACT) Checklist for High Water Alarm on Deaerator Tank (HWADT) Checklist for Low Water Alarm on Deaerator Tank (LWADT) Checklist for Deaerator Overflow Drain System (DAODS)……………….46 Checklist for Deaerator Safety Valve (DASV) Checklist for Safety Valve Following PRV (SVFPRV) - Deaerator Checklist for Safety Valve Following PRV (SVFPRV) - Other Checklist for Liquid Relief Valve on Oil Pump Set (LRVOPS) Checklist for Liquid Relief Valve on Economizer (LRVE) Checklist for Control Air Pressure Interlock (CAPI) Checklist for Propane Pilot Backup System Checklist for Carbon Monoxide and Combustible Gas Alarms in the Boiler Plant………………………………………………..…………………….54 Checklist for Outside Air Damper Alarm (OADA) Checklist for Low Water Alarm and Cutoffs on Boiler

(LWA/LWCO/ALWCO)

Checklist for High Water Alarm on Boiler (HWAB) Checklist for Recycle and Non-Recycle Boiler Steam Pressure Limit Switches (RBSPLS & NRBPLS)…………………………………………………..58 Checklist for Steam Safety Valves on Boiler (SVB) Checklist for Low Fuel Gas Pressure Cutoff Switch (LFGPCS) Checklist for High Fuel Gas Pressure Cutoff Switch (HFGPCS) Checklist for Automatic Fuel Gas Shutoff Valves and Solenoid Vent Valve Seat Leakage (AFGSOV & AFGSVV) - Main Gas………………..63 Checklist for Automatic Pilot Fuel Gas Shutoff Valves and Solenoid Vent Valve Seat Leakage (APFGSOV & APFGSVV) – Pilot Line ...….65 Checklist for Proof of Closure on Automatic Fuel Shutoff Valves (POC-AFGSOV)- Natural Gas………………………………………….……67 Checklist for Flame Scanner-for main flame out (FSMFO)……………….68 Checklist for Flame Scanner Not Sensing Igniter Spark (FSNSIS) Checklist for Igniter Timing (IT) Checklist for Main Flame Ignition Timing (MFIT) Checklist for Pre-Purge and Post-Purge Timing (PPT) Checklist for Low-Fire Proving Switch (LFPS) Checklist for Forced Draft Damper Wide-Open Pre-Purge Proving Switch (FDDWOPS)…………………………...………………...……………74

Checklist for Combustion Air Pressure Switch (CAPS) Variable Speed Fan………………….………….…………………………….75 Checklist for Combustion Air Pressure Switch (CAPS) Constant Speed Fan…………………………………….……………………..76

Checklist for Purge Airflow Proving Switch (PAPS) Checklist for Forced Draft Motor Interlock Switches (FDMIS) Checklist for Outlet Stack Damper Position Interlock Switch (OSDPI) 79 Checklist for Furnace Pressure Interlock (FPI) Checklist for Low Pilot Fuel Gas Pressure Cutoff Switch (LPFGPCS) Checklist for Flue Gas Recirculation Damper Interlock (FGRDI) Checklist for Low Flue Gas Oxygen Level Interlock (LFGOLI) Checklist for Low Fuel Oil Pressure Cutoff Switch (LFOPCS) Checklist for High Fuel Oil Pressure Cutoff Switch (HFOPCS) Checklist for Low Atomizing Media Pressure Switch (LAMPS)………….86 Checklist for Low Atomizing Media Differential Pressure Switch

(LAMDPS)

Checklist for Low Atomizing Media Flow Switch (LAMFS) Checklist for Automatic Fuel Oil Shutoff Valves (AFOSV) - for Seat Leakage Checklist for Proof of Closure on Automatic Fuel Oil Shutoff Valves

(POC-AFOSV)………………..…..………………………………………..…….90

Checklist for Oil Burner Position Switch (OBPS)

Checklist for Emergency Stop/Panic Buttons (ESPB)…………….……… 92

Appendix B Additional Safety Device Test Procedures for Hot Water Boilers………………………………………………………………………… 93 Appendix B.1 Introduction……………………………………………………….93 Appendix B.2 Assumptions For Test Procedures……………………………93 Checklist for Low Water Cutouts (LWCOHW and ALWCOHW)……… 94 Checklist for Liquid Relief Valves……………………………………………… 95 Checklist For High Water Temperature Switch……………………………. 96 Checklist for Flow Switch (FS)………………………………………………… .97 Appendix C Water Treatment Checklist Appendix D General Plant Safety & Reliability Appendix E Typical Equipment Used in Boiler Safety Testing…….. 102 Appendix F Comments on Each Individual Safety Test…………...……106

1. INTRODUCTION

1.1 OBJECTIVE

This manual represents a minimum standard for boiler and associated plant safety device testing. The purpose of this manual is to support the development of an individual boiler and associated plant safety device testing program for your specific facility as required by the VA. The text presents a concise and thorough treatment of boiler safety as applied to automatically-fired gas and oil, heating and process boilers and boiler support equipment servicing healthcare facilities. The text includes a description of each boiler safety device, how it works, what happens if it doesn’t work, what its purpose is, and how to test the device. The safety devices are organized by categories in four chapters: Water Level Control, Pressure Containment, Fuel Train Safety Devices, and Burner and Air Train Safety Devices. Appendix A provides detailed step by step procedures for testing every device covered for steam boilers and many of those devices required for hot water boilers. Devices not applicable to hot water boilers are noted in Appendix A. Appendix B contains 4 test procedures that are specific for hot water boilers. Appendices A and B can be used as a checklist and guide for safety testing and as a template for developing a site specific test procedure. It is important to understand that the VA directive calls for each facility to develop a written, site specific safety testing procedure. Some boilers will not include all of these devices as is explained in Appendix A.

The text does not replace existing standards. It succinctly states the main import of the standards. The final guide to safety should include all applicable standards. However, the testing envisioned in this text is generally more rigorous than current industrial practice or standards. In situations that may arise where adherence to this manual would adversely affect the operation of the boiler, special authority may be requested to deviate from the manual through the Director, OCAMES (10NAS).

1.2 BACKGROUND INFORMATION

One must understand that the use of the term “boiler” may refer to the system that includes the generation of steam, hot water, or hot oil. There are many safety devices such as level alarms, safety valves, relief valves, etc. that are found on the components involved in the distribution and use of steam. The safety checks are necessary and must be conducted on all devices in the system in order to ensure that the system is safe.

It is important that one has the manufacturer’s manuals and wiring diagrams and on all equipment to be tested before beginning the tests described herein and have a customized testing procedure specific to the boiler plant.

1.3 REQUIREMENTS FOR SAFETY TESTING

1.3.1 Properly test and analyze each safety device to determine VA Compliance

There are three questions that the person conducting the safety test must be able to answer affirmatively for a safety device to be VA compliant. IN THE TEST

PROCEDURES GIVEN IN APPENDICES A AND B, THIS SET OF QUESTIONS IS

CALLED THE “3 QUESTION CRITERIA”. IT IS SUCCINTLY STATED IN THE BOX

ON THE NEXT PAGE.

If any of the three questions are not answered affirmatively for a safety device, the device in question FAILS to be VA compliant. If there is a failure of any safety device that can’t be fixed immediately, the boiler must be removed from service or an Interim Safety Measure (ISM) developed, approved, and instituted until the repair is completed. In this situation the Medical Center Director must be notified of the situation.

THE 3 QUESTION CRITERIA

1. Is the correct device installed?

• A device approved by the VA that meets all VA requirements and standards

• The device is in the right location as defined by VA requirements and standards

• The device is set up to accommodate testing

• Any valve isolating the device is lockable only in open position

• If the device is a switch, it must open when it actuates.

• Any signal used in process control cannot be used as an input to a safety system.

• Independent safety control includes the fact that the safety control must be located in an enclosure that contains no other type of control.

• Any shunt on low water cutoffs (bypass switch) must be a non-latching device. No other shunts are allowed.

• The use of a snubber, dampener, pneumatic accumulator or other such device to dampen the pressure provided to a safety switch or gage used in testing the switch is not VA compliant.

2. Does the device activate at the proper set point that is in accordance with the criteria for the set point as defined herein and VA standards?

3. Does the device produce the proper result for its intended purpose (i.e. device must result in actions defined herein)?

1.3.2 REQUIRED CERTIFICATIONS FOR EACH SAFETY DEVICE TEST REPORT

A VA compliant test report will contain the following certification on the first page following the cover page of the report.

I certify that I have properly tested all applicable safety devices listed in this report for boiler #______and its associated equipment and I certify that all of these tests confirm that every device tested “passed” as defined by the following question: Did the device fail or pass the 3 question criteria?

PRINTED NAME SIGNATURE DATE

Position Title Company

OR

I certify that I have properly tested all applicable safety devices listed in this report for boiler #______ and its associated equipment and I certify that some of these tests failed as defined by the following question: Did the device fail or pass the 3 question criteria? More details of these failures are given in Appendix F (Comments on each individual test)

PRINTED NAME SIGNATURE DATE

Position Title Company

1.3.3 Confirming That All Devices Actually Function for Intended Purpose In testing any safety device, it is paramount that the testing procedure verifies compliance with the three requirements listed above.

1.3.4 Lockable Valve Requirements

In order to facilitate testing of some types of safety devices, it is sometimes necessary to temporarily isolate the safety device and provide test ports by means of manual valves. However, these modifications cannot be allowed to increase risk by locking out a safety device during normal operation and must clearly indicate test and normal position. Any such manual valve that could isolate a safety device from its normal operating circuit must be lockable and the lock must be lockable only in the correct operating position. It is most important that in normal operation the valve is actually locked.

1.3.5 Confirming That Jumpers Are Removed and Valves Properly Locked In many cases in order to test a device, it will be necessary to either electrically jumper (bypass) a device or to valve out the device. The safety testing personnel should only carry a fixed number of jumpers and should make sure that at the end of a test that all jumpers being used are accounted for and that all lockable valves are locked in their correct position.

1.3.6 Adherence to Electrical Safety

The VA complies with the NFPA 70E Electrical Code. In executing the safety procedures described herein, it is sometimes necessary to open an electrical panel with a voltage sufficient to require various levels of protection. No personnel should perform such operations without being qualified with the proper training and gear. While this requirement will not be listed for each safety test, it must be understood that all personnel must rigidly adhere to the requirements of NFPA 70E.

1.4 NOMENCLATURE

AFOSV Automatic Fuel Oil Shutoff Valves ALWCO Auxiliary Low Water Cutoff on steam boilers ALWCOHW Auxiliary Low Water Cutoff on Hot Water Boilers APFGSOV Automatic Pilot Fuel Gas Shutoff Valves APFGSVV Automatic Pilot Fuel Gas Solenoid Vent Valve AMSOV Atomizing Media Shut Off Valve CAPI Control Air Pressure Interlock CAPS Combustion Air Pressure Switch DA Deaerator DAODS Deaerator Overflow Drain System DASV Deaerator Safety Valve ESPB Emergency Stop/Panic Button FDDWOPS Forced Draft Damper Wide-Open Pre-Purge Proving Switch FDMIS Forced Draft Motor Interlock Switches FGRDI Flue Gas Recirculation Damper Interlock AFGSOV Automatic Fuel Gas Shutoff Valves and Solenoid Vent Valve AFGSVV Automatic Fuel Gas Shutoff Solenoid Vent Valve FPI Furnace Pressure Interlock FS Flow Switch on Hot Water Boilers FSMFO Flame Scanner-for main flame out FSNSIS Flame Scanner Not Sensing Igniter Spark HFGPCS High Fuel Gas Pressure Cutoff Switch HFOPCS High Fuel Oil Pressure Cutoff Switch HWAB High Water Alarm on Boiler HWACT High Water Alarm on Condensate Tank HWTS High Water Temperature Switch on Hot Water Boiler HWADT High Water Alarm on Deaerator Tank IT Igniter Timing LAMDPS Low Atomizing Media Differential Pressure Switch

LAMFS Low Atomizing Media Flow Switch LAMPS Low Atomizing Media Pressure Switch LFGOLI Low Flue Gas Oxygen Level Interlock LFGPCS Low Fuel Gas Pressure Cutoff Switch LFOPCS Low Fuel Oil Pressure Cutoff Switch LFPS Low-Fire Proving Switch LPFGPCS Low Pilot Fuel Gas Pressure Cutoff Switch LRVE Liquid Relief Valve on Economizer LRVE\HW Liquid Relief Valve on Hot Water Boiler LRVOPS Liquid Relief Valve on Oil Pump Set LWA Low Water Alarm LWACT Low Water Alarm on Condensate Tank LWADT Low Water Alarm on Deaerator Tank LWCO Low Water Cutoff on Steam Boiler LWCOHW Low Water Cutoff on Hot Water Boiler MFIT Main Flame Ignition Timing MV Manual Valve NRBSPLS Non-Recycle Boiler Steam Pressure Limit Switch OADA Outside Air Damper Alarm OBPS Oil Burner Position Switch OSDPI Outlet Stack Damper Position Interlock Switch PAPS Purge Airflow Proving Switch POC_AFOSV Proof of Closure on Automatic Fuel Oil Shutoff Valves POC-AFGSOV Proof of Closure on Automatic Fuel Shutoff Valves PPT Pre-Purge and Post-Purge Timing PRV Pressure Reducing Valve RBSPLS Recycle Boiler Steam Pressure Limit Switch SVB Steam Safety Valves on Boiler SVFPRV Safety Valve Following PRV

TP Test Port

1.5 PREPARATION OF SYSTEM FOR SAFETY TESTING

The normal boiler installation does not generally allow easy access and control for testing. Safety testing is an ongoing activity for safe boiler plant operation. In this section a discussion is given of system design considerations that will allow easy testing.

The discussion is organized around classes of different safety devices. For detailed drawings illustrating an appropriate test setup for each device, refer to the safety testing procedures given in the Appendices A and B. A list of test equipment that is satisfactory for conducting the safety tests is given in Appendix E. The list is an example but many other comparable instruments could be utilized.

1.5.1 Setup for testing a Steam Safety Valve Following a PRV

In order to test a safety valve following a PRV, a manual isolation valve must be installed downstream of the safety valve so that the valve can be tested without raising the pressure on the system downstream of the valve. (See Figure 1.1)

Figure 1.1 Example of Steam Safety Valve Following a PRV

1.5.2 Setup for testing a Combustion Air Pressure Switch, Purge Air Proving Switch, Furnace Pressure Interlock, Control Air Pressure Interlock, High Fuel Gas Pressure Cutoff Switch, High Fuel Oil Pressure Cutoff Switch, Low Fuel Gas Pressure Cutoff Switch, and Low Fuel Oil Pressure Cutoff Switch.

In order to test these switches, it is necessary to be able to temporarily isolate these switches from the normal pressure source and either increase or decrease the pressure applied to the switch using the test port in order to determine the switch trip point. At the same time the piping must be such that the actual pressure that the switch senses can also be measured. The arrangement is pictorially shown in Figures 1.2 for the case of a Combustion Air Pressure Switch. The other switches listed above should be set up in a similar manner as indicated in the respective test procedures in Appendix A.

Figure 1.2 Combustion Air Pressure Switch (CAPS) Setup

1.5.3 Setup for Leak Checking Oil and Gas Block Valves and Gas Bleed Vent Valve In order to easily test for leaks in the block valves, a test port (TP) and calibrated pressure gage must be available both in the line between the valves and downstream of

LWA

HWA (PROBE)

BUTTERFLY VALVE

SOLENOID ACTUATED

OVERFLOW PROBE

Steam

Makeup / Condensate

Vent

10 Psig 500-1000 lb/hr

Vac Breaker

Overflow

To Boiler

DASV

SVFPRV

Vent

DA TANK

PRV

Bypass Valve

MV

TP

Inlet

Outlet

Inlet

Vanes Vanes

Outlet

Lock TP

TP

CAPS

Open the second valve. Also in the case of gas, a lockable manual valve downstream of the solenoid bleed vent valve is required. A port and pressure gage in the line between the solenoid valve and lockable manual valve is also needed as shown in Figure 1.3. Note, there are two test ports (TP) for determining normal operating pressures and one test port (TP) for testing the automatic fuel gas vent valve for leaks. This arrangement is schematically shown for natural gas in Figure 1.3. The arrangement for testing the automatic fuel oil valves is the same with the exception the vent line is absent with its attendant test arrangement as shown in the test procedure for oil leaks in Appendix A.

(Note that some boiler manufacturers do include a liquid relief valve between the two automatic fuel shut off valves. If this relief valve is included it must be tested.)

Figure 1.3 Test setup for leak testing the two Automatic Fuel Gas Shut Off

Valves and the Automatic Fuel Gas Vent Valve

1.5.4 Setup for Checking Dangerous Gas Detection System for the Building Sample gas with a level of CO and combustibles equal to the sensor set points should be available with a means to supply the gas to the sensor per the manufacturers test procedures.

1.5.5 Setup for Checking the Deaerator Overflow System and Oil Liquid Relief Valve A sight glass with turbine wheel should be installed downstream of the valve in order to visually confirm that flow exists. The oil liquid relief valve also requires a pressure gage at the pump discharge.

1.5.6 Setup for Checking Proof of Closure Switches, Low Fire Proving Switches, Force Draft Damper Vane Interlock, Outlet Stack Damper Interlock, Recycle Steam Pressure Switch, Non-recycle Pressure Switch, and Recirculation Damper Interlock It is necessary to electrically isolate or jumper these switches for testing. Although not necessary, it may be convenient to have the two electrical leads from each of these switches wired into an electrical control panel where it is easy to either remove one lead from the terminal block to isolate the switch or to jumper across the two leads to simulate a switch in the closed position.

LFGPCS

HFGPCS

LOCK OPEN

C N

O

LO

R

T

FL

W O

LFGPCS AFGSOV

PRV

BLOCK AND BLEED SYSTEM

MV

Main Gas Line

HFGPCS

AFGSOV

TP

TP

TP

TP

AFGSVV MV

CONTROL

FUEL FLOW

LOCK OPEN

1.5.7 Setup for Low Water Cutoffs

A low water cutoff can be treated in the same way as those switches in section 1.5.6. It is more convenient to have independent, non-latching shunt test switches (Momentary bypass switch) for isolating the two low water cutoffs for steam boilers and hot water boilers that are fitted with two low water cutoffs. This shunt test switch is required for each low water cutoff by VA standards for boilers fitted with two low water cutoffs.

1.5.8 Setup for Hydrostatic Testing

In order to hydrostatically test any device, it is necessary that valves are available to isolate the device, a test port is available to apply the test pressure, and a pressure gage is available to monitor the pressure in the device (See Figure 1.4 as an example).

All devices that could be damaged by the test pressure must be removed or properly isolated prior to conducting the hydrostatic testing. If it is desired to use a hydrostatic test pressure above the pressure at which the safety valve or liquid relief valve opens, it is necessary to remove the valves and blank off the opening.

Figure 1.4 Hydro Testing

In from DA

Drain

Economizer

MV

MV

MV

TP

LRVE

View Port Boiler Feedwater

2 WATER LEVEL CONTROL

2.1 LOW WATER CUTOFFS

2.1.1 Description

A low water cutoff is a device that causes the automatic fuel safety shutoff valves to close if the water level in the boiler drops below a pre-set safe level. Low water causes about 50 percent of all boiler incidents. Low water can cause the boiler to overheat which could lead to the failure of the pressure vessel with enormous potential damage (explosion). Two low-water cutoffs are required for steam boilers while hot water boilers are required to have at least one low water cutoff. Low-water cutoffs operate either on a “float” system or electrode system (probe) for steam boilers. Any low water cutoff for hot water boilers must be a probe. In the float system there is a pipe connection to the boiler high and low connection points. Between these connection points there is a vertical section containing a volume sufficient to house the float. If the water level falls below a prescribed level, the falling float will cause a switch to actuate causing the automatic fuel valves to close. (See Figure 2.1)

Figure 2.1 Low Water Cutoff

In the electrode system, there is a similar piping arrangement as in the float system.

Probes extend vertically downward into the vertical pipe connecting the piping to the high and low boiler connection points or for hot water boilers directly into the boiler.

The electrodes are located at the bottom of the probe and are used to measure the conductivity of the media in which the electrodes are immersed. The conductivity of water is much higher than steam. Hence, if the water level drops below the probe, a drastic change in conductivity occurs. This change is used in an electrical circuit to cause the automatic fuel shut-off valves to close. Most safety codes require at least one float system be included to protect against low water for steam boilers. This is shown in Figure 2.1. The VA requires one float and one probe for steam boilers. True redundancy requires that the low water cutoffs be in two separate piping arrangements as shown. Placing both low water cutoffs in a single piping arrangement could lead to a

LWCO

FLOAT

FLOAT

SHUNT

LWCO

PROBE

SHUNT

PROBE

situation in which blockage in the piping arrangement renders both level control safety devices useless.

Some low-water cutoffs are provided with non-latching “shunt” test switches by which the low water cutoff switch is bypassed. A non-latching shunt test switch means that the test switch must be manually held open in order to bypass the low water cutoff switch.

The VA requires individual shunt test switches for both low water cutoffs for steam boilers. Operators can use the shunt test switch in “testing” each low-water cutoff by simply by-passing one low water cutoff by holding in the other low water cutoff shunt test switch and allowing the active low-water cutoff to shut down the boiler. This procedure is then repeated for the other low water cutoff. Operators electrically check the low water cutoff using this method.

A boiler control system should never allow the boiler to automatically restart after a low-water cutoff has actuated to stop boiler operation and all trip points must occur with water clearly in the sight glass.

A detailed step by step test procedure is given in Appendix A for steam boilers and Appendix B for hot water boilers.

2.1.2 Consequences of Low Water Cutoff Failure

If the low water cutoffs both fail, the boiler would then be fired with no water in the boiler. This will cause the metal temperatures to rise rapidly and the metal strength to be significantly decreased. In fire tube boilers the main Morrison tube typically collapses which could allow steam onto the boiler fireside. The steam pressure has been known to blow the ends out of the boiler through concrete block walls a distance of hundreds of feet. Similar catastrophes could occur in water tube boilers.

2.1.3 Testing a Low Water Cutoff

Low-water cutoffs must be tested in a mode in which they fail. Testing is basically done by allowing the water level to lower in a “slow drain”. In order to be in a realistic mode, one must not follow a procedure that actuates the cutoff by rapidly blowing off a volume of water from the water column containing the switch. This is very important in testing a float type cutoff. The rate of decrease in water level is required to be a maximum of 1 inch/minute.

A detailed step by step test procedure is given in Appendix A for steam boilers and Appendix B for hot water boilers.

2.2 LOW WATER ALARM

2.2.1 Description

The low water alarm provides audible and visual warnings that the water level is approaching a dangerously low level. These alarms are based either on a conductivity probe or float as described in the previous section. These alarms are required on the steam boiler, deaerator, and condensate receiver tanks. On the boiler, the low water alarm must be set to activate before either of the low water level cutoff switches shuts off the boiler. On the deaerator and condensate receiver tanks, the alarm is the only indication of a low water problem. On these devices the setting should be above 1/3rd of the tank diameter and with visible water in the sight glass. The alarm should not be set so high that it causes excessive alarm activation. Of course lack of water in the deaerator or condensate receiver will quickly result in loss of water to the boiler with the problems described in the section of low water level control.

2.2.2 Consequence of Water Level Alarm Failure

Low water in a condensate or deaerator tank is a precursor to low water failure in a steam boiler with the problems described above. There is also the hazard of damage to a condensate transfer or boiler feed pump from running dry. A low water alarm on a boiler is a warning to operators of an impending potential problem of a “boil out” of water.

2.2.3 Testing Low Water Alarms

This alarm is tested by causing a drop in water level in the vessel being tested. The alarm should activate at the desired set point (the set point must be above the level at which the first low water cutout activates, at a level allowing operators time to restore the proper level, and visible in the appropriate sight glass).

A step by step procedure is given in Appendix A for three situations: steam boilers, deaerators, and condensate tanks.

2.3 HIGH WATER ALARM

2.3.1 Description

A high water alarm is required on a steam boiler, deaerator, and condensate tanks to aid in preventing overfilling. Due to the failure rate of float type devices used for this purpose, high water alarms must always be conductivity probe type devices for VA compliance.

2.3.2 Consequence of High Water Alarm Failure

High water in a condensate tank could lead to backup of condensate in condensate lines. High water in a deaerator will result in poor deaeration but also leads to violent shaking of the vessel. High water in a steam boiler could result in pushing liquid into the steam line. Slugs of water in the steam system can move at high velocity due to the motive force of steam causing water hammer. Water hammer can cause valves and other fittings to explode and steam piping to rupture. Death and injury from these events is a regular occurrence. This same effect could produce high water levels in the steam supply to a steam powered appliance connected to the system with detrimental effects on the process.

2.3.3 Testing the High Water Alarm

The high water alarm must be tested off-line. Slowly fill the vessel with water, observe the water level in the sight glass, and note the point at which the alarm sounds. Be careful not to overfill the system, above the level at which the alarm should actuate.

A step by step procedure is given in Appendix A for three situations: steam boilers, deaerators, and condensate tanks.

2.4 OVERFLOW DRAIN SYSTEM

2.4.1 Description

Deaerator tanks and condensate storage tanks have overflow systems to prevent overfilling. The deaerator overflow is shown in Figure 2.2. The overflow system on the condensate tank also helps guarantee that the condensate tank remains at atmospheric pressure and consists of a drain line connected to the vessel. The drain line from a deaerator includes a normally closed device that opens if the water level is too high and allows water to drain either to sewer or into the condensate tank. The VA requires that the condensate tank be a pressure vessel with the same basic requirements as the deaerator if the deaerator overflows into the condensate tank. Two different types of overflow control valve systems are allowed for the deaerator.

• An electronic valve which is operated by a conductivity probe indicating that water level is too high.

• An electronic valve which is operated by a differential pressure cell indicating that water level is too high.

The signal used to control makeup water into the deaerator must not be used to control the overflow valve.

Figure 2.2 Overflow Drain System

2.4.2 Consequence of Overflow Drain Failure

The consequence of an overflow drain failure is the same as that discussed in section 2.3.2.

LWA

HWA (PROBE)

BUTTERFLY VALVE

SOLENOID ACTUATED

OVERFLOW PROBE

Steam

Makeup / Condensate

Vent

10 Psig 500-1000 lb/hr

Vac Breaker

Overflow

To Boiler

DASV

SVFPRV

Vent

DA TANK

PRV

Bypass Valve

MV

2.4.3 Testing the Overflow Drain System on a Deaerator

The purpose of the test is to determine if the system is capable of draining water from the deaerator at a rate equal to or greater than the maximum potential supply of water to the deaerator. The system can be tested with the deaerator out of service (steam valved out and feedwater pumps off). To test the drain system, fill the deaerator with water at a rate equivalent to the maximum rate that could possibly be supplied to the deaerator. Observe the water level in the sight glass. Use the sight glass to confirm that the drain system is capable of maintaining the water level at the drain level.

A step by step procedure is given in Appendix A.

3 PRESSURE CONTAINMENT

3.1 STEAM SAFETY VALVES

3.1.1 Description

The steam safety valves are connected to a steam boiler, steam line, or other device that must be protected from over-pressure. Each steam safety valve discharges into a drip pan ell which discharges through a slip joint into an oversized vent pipe that extends to outside the building. By utilizing drip pan ells, there is no direct connection between the vent pipe and the safety valve so that there is no stress imposed on the safety valve from the thermal expansion of the vent pipe. Additionally any liquid that accumulates due to condensation, drains and does not impact relief capacity. Correct installation includes leaving about a one-inch gap between the drip pan and the bottom of the vent pipe. Steam safety valves must be present on a steam boiler, deaerator, any pressurized condensate receiver, and at all points in steam lines just downstream of any pressure-reducing valves. Each safety valve must have a dedicated separate vent line and drain (See Figure 3.1). Properly designed redundant safety systems for this extremely important safety device allow the system to prevent a boiler explosion even if one of the safety valves and/or vent system fails. All steam safety valves must be lifted by steam pressure.

Figure 3.1 Boiler Safety Valves

3.1.2 Consequences of a Steam Safety Valve Failure

Steam safety valves are the last line of defense against the over-pressurization of a steam boiler or steam system components. If these valves fail along with all the other measures designed to prevent over-pressurization, a violent explosion could occur.

Such an explosion could damage buildings and injure or kill people within several hundred feet of the boiler or system component.

3.1.3 Checking a Steam Safety Valve

The steam safety valves are checked by closing the main steam stop and allowing pressure to build up (The recycle and non-recycle switches are bypassed) until the safety lifts. By continuing firing the boiler in high fire all the safeties should be able to be tested.

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Some authorities recommend doing all steam safety valve testing on a test stand.

However, there is a chance that the valves could be mixed up or damaged in installation so that this test method is not as reliable as testing the valves in situ and is not allowed by the VA to satisfy compliance. Also some authorities check a steam safety valve by lifting the handle by hand. This test does not confirm that the valve opens at its proper setting. It does confirm that the valve can vent steam (is not blocked). Lifting of a safety valve by hand does not meet the VA requirement for compliance. Gagging of a safety valve for test purposes is prohibited and should never be used.

A detailed test procedure is given in Appendix A for three situations: boilers, deaerators, and piping following a PRV station.

3.2 RELIEF VALVES

3.2.1 Description

Relief valves are spring-loaded valves that open if the liquid pressure in the system that they control increases above a pre-set limit. They are similar to safety valves with the exception that they do not exhibit “popping” action or blowdown. (Relief valves do not incorporate the “huddling” chamber found on safety valves). These valves are connected directly to an exhaust pipe that conveys the fluid to the building exterior or storage tank. Three important pieces of equipment requiring relief valves in boiler applications are economizers, hot water boilers, and oil pump sets.

3.2.2 Consequences of a Relief Valve Failure

Failure of a relief valve could lead to a pressure vessel explosion with serious consequences. Failure could also lead to equipment damage due to overheating-e.g. in operation of an oil pump.

3.2.3 Checking a Relief Valve

A testing procedure for the relief valve on an oil pump set and economizer is given in Appendix A. A test procedure for hot water boilers is given in Appendix B.

3.3 HIGH STEAM PRESSURE LIMIT SWITCHES

3.3.1 Description

A steam boiler should be fitted with two, high-steam-pressure-limit switches (HSPLS).

Both switches have the function of causing the two automatic fuel shut off valves to close if a preset pressure limit is exceeded. One switch may be a recycle switch meaning that once the pressure falls below the set point pressure the boiler will automatically restart. The other switch must be a non-recycle switch meaning that it must be manually reset after a pressure excursion above its limit. The pressure setting on the non-recycle switch should be slightly higher than the setting on the recycle switch but lower than the lowest lift pressure for the safety valves. The required differences in the settings described above should be sufficient to allow the boiler to operate without excessive nuisance trips or blowing of safety valves and are enumerated in Appendix A.

3.3.2 Consequences of High Steam Pressure Limit Switch Failure If both HSPLS switches were to fail, the safety valve becomes the last line of defense against a pressure vessel explosion. A tendency of boiler operators is to not worry about the performance of the HSPLS (especially the non-recycle one) because the safety valve is still available to save the operation. This thinking represents the "slippery slope" in safety because true safety relies on redundant measures. In looking at accidents in industry, one can almost always find several unsafe factors that led to the particular accident. Ignoring the first warning escalates the risk.

3.3.3 Checking High Steam Pressure Limit Switches

These switches are checked by closing the main steam valve and firing the boiler until the pressure is elevated to a point that the safety activates. The recycle safety must be jumped in order to test the non-recycle switch.

These tests are described in Appendix A.

3.4 BOILER HYDROSTATIC TESTING

3.4.1 Description

A hydrostatic test is performed on a boiler, deaerator, pressurized condensate receiver and economizer to determine if it is capable of withstanding the potential operating pressure. It is very important to understand that any leak is a sign of weakness in the vessel and should be thoroughly inspected by a professional and properly repaired before the vessel is put back into operation. (These leaks could represent small cracks or metal thinning/corrosion/etc. that is not discernable to the eye).

3.4.2 Consequences of Failure to Hydrostatic Test

If weak spots are present and the vessel is operated, a significant chance exists that a pressure vessel explosion could occur with tremendous loss of property and life. Failure to perform a proper hydrostatic test would allow a weakened vessel to be operated with the associated dangers of such operation.

3.4.3 Performing a Hydrostatic Test

To perform a hydrostatic test, fill the vessel completely full of water below 200 F.

Remove and/or isolate all safety and relief valves. Close all supply and discharge lines.

The boiler must be completely locked and tagged out from all energy sources following OSHA requirements and the fireside opened for inspection. The hydrostatic pressure for the test should be 1.5 times working pressure applied for several hours. The dry side must be checked for any sign of leaks. Any leaks must be professionally evaluated in terms of whether the vessel can be operated safely without repair.

In applying the hydrostatic pressure, care must be exercised not to overpressure the vessel. If the vessel were pressurized above its elastic limit, the vessel would not be fit for further use and should be scrapped!

4 FUEL TRAIN SAFETY DEVICES

4.1 LOW PRESSURE FUEL CUTOFF SWITCH

4.1.1 Description

The low-pressure fuel cutoff switch causes the automatic fuel shutoff valves to close if the fuel pressure is below the lower limit for safe operation. Low pressure fuel cutoff switches are found on the main gas line, main oil line, and pilot gas line. The switch in all three of these applications senses the supply fuel pressure after the pressure regulating valve and upstream of any fuel control valve (See Figure 4.1). For the main oil and gas supply lines, the switch is in continuous operation once the boiler is in the run mode. For the pilot gas supply, the switch operates continuously while the pilot flame is on. A common operational problem with a low pressure cutoff switch occurs due to the PRV allowing a “dip” in fuel pressure on startup. Some facilities have installed a snubber or accumulator between the fuel line and switch to prevent the switch from activating. Snubbers and accumulators are not allowed by VA requirements and standards.

Figure 4.1 Low Pressure Fuel Cutoff

4.1.2 Consequences of Low Pressure Fuel Cutoff Switch Failure Low fuel pressure can result in unstable burning or flameout conditions. When fuel pressure returns to normal, the combustion chamber can overfill with fuel before igniting. This can easily result in combustion explosions that are violent enough to blow the “ends” of the boiler and even through surrounding structures. Extensive property damage, injury, and even death can result.

4.1.3 Checking the Low Pressure Fuel Cutoff Switch

This switch is checked by isolating the switch and slowly venting gas until the switch activates. A step by step test procedure for the low pressure fuel cut out switch for the main gas and main oil supply systems as well as the pilot gas system is given in Appendix A.

4.2 HIGH PRESSURE FUEL GAS CUTOFF SWITCH

4.2.1 Description

The high fuel gas pressure cutoff switch is used to cause the automatic fuel shutoff valves to close if fuel pressure is above a given higher limit for safe operation. These switches are used for both the main gas and main oil fuel supply systems (See Figure 4.2). In both applications the switch should be located after the pressure regulating valve and upstream of the fuel control valve. The switch is in continuous operation once the boiler is in the run mode.

Figure 4.2 High Pressure Fuel Cutoff

4.2.2 Consequences of High Pressure Fuel Cutoff Switch Failure High fuel pressure can cause unstable flame conditions but more importantly it can result in over-firing the boiler. Over-firing can damage burner/boiler materials to the point of meltdown and explosion. The generation of steam can be so intense that a pressure vessel explosion can occur. High fuel pressure can easily occur if a pressure regulator and high-pressure cutoff switch were to fail.

4.2.3 Checking the High Pressure Fuel Cutoff Switch

The switch is checked by isolating the switch and using a hand pump or equivalent device (see Appendix E for equipment list) to raise the pressure until the switch trips out the boiler. A step by step test procedure for the high pressure fuel cut out switch for the main gas and main oil supply systems is given in Appendix A.

4.3 VENTING BETWEEN AUTOMATIC GAS SHUTOFF VALVES

4.3.1 Description

The volume between the automatic fuel gas shutoff valves should be vented to the atmosphere with a system as shown in Figure 4.3 for both the main gas and pilot line automatic shut off valves. While the boiler is running the solenoid valve is shut and gas flows through the two automatic shutoff valves to the burner. When the fuel shut-off valves close, the solenoid valve opens and vents any residual gas in the space between the valve and any leakage of gas through the first automatic shutoff valve.

The purpose of the vent system is to ensure that even if the first automatic shutoff valve leaks, the gas is vented rather than allowed to move through the second automatic fuel-shutoff valve and then into boiler. The vent line must be vented to the atmosphere outside of the building.

Figure 4.3 Gas Train Vent Valve

4.3.2 Consequences of a Failed Vent Valve

Fuel leaks into the boiler are obviously dangerous because if both automatic shut off valves leak, gas would fill the boiler furnace while the boiler is off. Fuel mixed with air is a potentially explosive mixture that with any source of ignition could result in disaster.

On ignition if purging did not adequately vent this gas, a tremendous explosion would result when lighting the burner. This combustion explosion could easily wipe out all property and personnel within several hundred feet of the boiler.

4.3.3 Testing the Gas Train Vent Valve (solenoid valve)

Testing of the vent system includes doing a bubble test with the boiler running by attaching a tube to the test port downstream of the AFGSVV as shown in Figure 4.3 and letting the other tube end be slightly immersed in water with the manual valve above the AFGSVV closed. The other test is to see if the pressure between the two automatic shut off valves goes to zero when the boiler stops running and the manual valve is open.

A detailed step by step procedure to check all these aspects of the vent valve are given in Appendix A.

4.4 LEAK TEST OF AUTOMATIC FUEL SHUT OFF VALVES

4.4.1 Description

A block and bleed system is provided as discussed in section 4.3 to prevent fuel from entering and potentially collecting in the boiler while the boiler is off. This system is used on the main oil and gas supply lines to the burner as well as the pilot gas supply.

(On the main oil supply line a vent is not required. However, some manufacturers do use a vent and if one is provided, it must be equipped for testing and must be tested.)

The two automatic shut off valves used in either case are the means by which the boiler is automatically shut down in case any operating limit is not satisfied. It is essential that these valves do not leak when closed. For both oil and gas, NFPA code requires two automatic shut off valves.

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4.4.2 Consequences of Leaking Automatic Shut Off Valves

If both automatic fuel shut off valves leak and the vent system does not function (in the case of gas), fuel would be introduced into the burner and into the boiler furnace while the boiler is off. This fuel would produce a combustible mixture in the boiler. Fuel leaks into the boiler are obviously dangerous because it allows the presence of a combustible air-fuel mixture that could explode when the fuel is ignited on startup. This combustion explosion could easily wipe out all property and personnel within several hundred feet of the boiler.

4.4.3 Testing the Automatic Fuel Shut Off Valves for Leaks

The testing for leaks can be done when the boiler is off. The test procedure for natural gas is measuring for a leak with a “bubble test”. This method involves connecting a tube to a confined space downstream of the valve being tested with positive pressure on the upstream side of the valve. The tube is placed approximately 1/16th of an inch below a water surface in order to have negligible back pressure. Any leak will show up as a bubble generated in the water at the tube exit. For oil a test port can be provided to visually observe whether oil drains from the test port.

A step by step procedure is given in Appendix A for both oil and gas.

4.5 OIL LOW ATOMIZING MEDIA PRESSURE AND DIFFERENTIAL

PRESSURE/FLOW SWITCHES

4.5.1 Description

An atomizing fluid (compressed air or steam) is usually used to aid in the combustion of the oil fuel (See Figure 4.4). A safety switch is required that shuts the boiler off in case of low atomizing media pressure. This switch measures pressure in the atomizing fluid line immediately after the pressure regulating system and causes the automatic fuel control valves to close if the atomizing pressure falls below its set point. If there is a differential pressure regulator, the sensor must be located upstream of that regulator.

In some cases where air is used to atomize, no atomizing media differential pressure switch is used. For this case only the low atomizing media pressure switch described above is needed. For all other cases, a second switch is needed to help ensure that atomizing media is flowing at a sufficient rate into the burner. For the case in which the atomizing media pressure at the burner is greater than the oil pressure for all firing rates, a differential pressure switch is needed. For the case where the atomizing media is less than oil pressure at some firing rates (“crossover”), a flow switch is required by the VA. The differential pressure switch must be located as shown in the figure. The flow switch must be in the atomizing media line before it enters the burner.

Figure 4.4 Low Atomizing Media and Differential Pressure Switches

(Note Flow switch not shown)

4.5.2 Consequences of Low Atomizing Media Pressure, Inadequate Atomizing Media Differential Pressure or Inadequate Atomizing Media Flow Low atomizing media pressure, low atomizing media differential pressure or low atomizing media flow could cause poor combustion leading to the production of carbon monoxide, flame instability, and possible combustion explosions leading to serious loss of property and injury/death.

4.5.3 Testing the Oil Low Atomizing Media Pressure Switch

The set point on the oil low atomizing pressure switch must not allow the atomizing media pressure to fall below 80% of the regulated pressure upstream of the switch testing is accomplished on-line by slowly lowering the oil atomizing media pressure and observing that the switch operates at the correct set point. If a low atomizing media flow switch is required, the testing is done on line by slowly closing the manual valve in the atomizing media line and observing the atomizing media pressure at point that the switch shuts off the boiler. The switch must shut off the boiler at a atomizing media pressure lower than 80% of the regulated pressure up stream of the switch.

4.5.4. Testing the Low Atomizing Media Differential Pressure Switch The set point on the oil low atomizing media differential pressure switch must not allow the atomizing media differential pressure to fall below 80% of the minimum differential pressure seen by the switch from low fire to high fire.