boiler safety valve regulations factory

Boiler explosions have been responsible for widespread damage to companies throughout the years, and that’s why today’s boilers are equipped with safety valves and/or relief valves. Boiler safety valves are designed to prevent excess pressure, which is usually responsible for those devastating explosions. That said, to ensure that boiler safety valves are working properly and providing adequate protection, they must meet regulatory specifications and require ongoing maintenance and periodic testing. Without these precautions, malfunctioning safety valves may fail, resulting in potentially disastrous consequences.

Boiler safety valves are activated by upstream pressure. If the pressure exceeds a defined threshold, the valve activates and automatically releases pressure. Typically used for gas or vapor service, boiler safety valves pop fully open once a pressure threshold is reached and remain open until the boiler pressure reaches a pre-defined, safe lower pressure.

Boiler relief valves serve the same purpose – automatically lowering boiler pressure – but they function a bit differently than safety valves. A relief valve doesn’t open fully when pressure exceeds a defined threshold; instead, it opens gradually when the pressure threshold is exceeded and closes gradually until the lower, safe threshold is reached. Boiler relief valves are typically used for liquid service.

There are also devices known as “safety relief valves” which have the characteristics of both types discussed above. Safety relief valves can be used for either liquid or gas or vapor service.

Nameplates must be fastened securely and permanently to the safety valve and remain readable throughout the lifespan of the valve, so durability is key.

The National Board of Boiler and Pressure Vessel Inspectors offers guidance and recommendations on boiler and pressure vessel safety rules and regulations. However, most individual states set forth their own rules and regulations, and while they may be similar across states, it’s important to ensure that your boiler safety valves meet all state and local regulatory requirements.

The National Board published NB-131, Recommended Boiler and Pressure Vessel Safety Legislation, and NB-132, Recommended Administrative Boiler and Pressure Vessel Safety Rules and Regulationsin order to provide guidance and encourage the development of crucial safety laws in jurisdictions that currently have no laws in place for the “proper construction, installation, inspection, operation, maintenance, alterations, and repairs” necessary to protect workers and the public from dangerous boiler and pressure vessel explosions that may occur without these safeguards in place.

The documents are meant to be used as a guide for developing local laws and regulations and also may be used to update a jurisdiction’s existing requirements. As such, they’re intended to be modifiable to meet any jurisdiction’s local conditions.

The American Society of Mechanical Engineers (ASME) governs the code that establishes guidelines and requirements for safety valves. Note that it’s up to plant personnel to familiarize themselves with the requirements and understand which parts of the code apply to specific parts of the plant’s steam systems.

High steam capacity requirements, physical or economic constraints may make the use of a single safety valve impossible. In these cases, using multiple safety valves on the same system is considered an acceptable practice, provided that proper sizing and installation requirements are met – including an appropriately sized vent pipe that accounts for the total steam venting capacity of all valves when open at the same time.

The lowest rating (MAWP or maximum allowable working pressure) should always be used among all safety devices within a system, including boilers, pressure vessels, and equipment piping systems, to determine the safety valve set pressure.

Avoid isolating safety valves from the system, such as by installing intervening shut-off valves located between the steam component or system and the inlet.

Contact the valve supplier immediately for any safety valve with a broken wire seal, as this indicates that the valve is unsafe for use. Safety valves are sealed and certified in order to prevent tampering that can prevent proper function.

Avoid attaching vent discharge piping directly to a safety valve, which may place unnecessary weight and additional stress on the valve, altering the set pressure.

As a design engineer responsible for developing and specifying boilers, dryers, furnaces, heaters, ovens and other industrial heating equipment, you face a daunting labyrinth of standards and industry regulations. Regulatory bodies sound a bit like alphabet soup, with acronyms like UL, FM, CSA, UR, AGA, ASME, ANSI, IRI, CE and NFPA tossed about. This article will help explain a common task for many thermal processing equipment specifiers: meeting the requirements of key codes — including Underwriters Laboratories (UL), Factory Mutual Insurers (FM) and the National Fire Protection Association (NFPA) — for safety valve equipment used in process heating applications.

Key to designing safety into your fuel train configurations are familiar technologies such as safety shutoff valves and vent valves as well as visual-indication mechanisms and proof-of-closure switches.

Your design skills come into play with how you take advantage of the wide range of products available. You can mix and match solenoid and safety shutoff valves — within designs from catalytic reactors to multi-zone furnaces — to create easily installed, cost-effective solutions that comply with all necessary standards. (See table.)

Make sure, however, that you start with a good grasp of valve element fundamentals. For example, examining a proof-of-closure (POC) switch underlines how reliably modern valves can ensure combustion safety. The POC unit provides an electrical contact interlocked with the controller safety circuit. In a typical design, the switch is located at the bottom of the valve, positioned to trace the stroke of the valve disc. When the disc seal reaches the fully closed position, it triggers the mechanism to push down on the contact, closing it and triggering the unit’s visual indicator to show open or closed status. As a result, the operator can act with full confidence in situations where it is critical that a safety valve be safely closed.

To provide ease of installation, many users prefer valves with modular capabilities. For example, to reduce mounting complexity, you can choose modular gas safety shut-off valves — combining a solenoid valve with an electrohydraulic motorized valve for a compact double-valve footprint, a slow-open feature and high flow rates. An accompanying actuator can provide on/off or high/low/off firing rates as well as visual indication and proof of closure for compliance with most industry standards.

Also, you may want to look for valves that include useful features such as pipe taps, which can facilitate accurate pressure readings and leakage testing.

Knowing your valve choices — and how they meet given codes and standards — can reduce the time required for design and production while facilitating compliance. This results in safer, more efficient and cost-effective heating process installations.

(a) Each power boiler, nuclear boiler, and high temperature water boiler shall have safety valves or pressure relieving devices constructed, stamped and installed in accordance with the applicable section of the Code, except:

(2) Upon written request by the employer, the Division may permit three-way two-port valves to be installed under two safety valves, each with the required relieving capacity, provided they are so installed that both safety valves cannot be closed off from the boiler at the same time and provided the three-way valve will permit at least full flow to the safety valve in service at all time.

(b) The user shall maintain all pressure relieving devices in good operating condition. Where the valves cannot be tested in service, the user shall maintain and make available to the inspector records showing the test dates and set pressure for such valves.

3. Change without regulatory effect inserting "(a)" immediately preceding the first paragraph and "(b)" immediately preceding the fourth paragraph, filed 1-24-91 pursuant to section 100, Title 1, California Code of Regulations (Register 91, No. 7).

Years ago, it was not uncommon to read news about tragic boiler explosions, sometimes resulting in mass destruction. Today, boilers are equipped with important safety devises to help protect against these types of catastrophes. Let’s take a look at the most critical of these devices: the safety valve.

The safety valve is one of the most important safety devices in a steam system. Safety valves provide a measure of security for plant operators and equipment from over pressure conditions. The main function of a safety valve is to relieve pressure. It is located on the boiler steam drum, and will automatically open when the pressure of the inlet side of the valve increases past the preset pressure. All boilers are required by ASME code to have at least one safety valve, dependent upon the maximum flow capacity (MFC) of the boiler. The total capacity of the safety valve at the set point must exceed the steam control valve’s MFC if the steam valve were to fail to open. In most cases, two safety valves per boiler are required, and a third may be needed if they do not exceed the MFC.

There are three main parts to the safety valve: nozzle, disc, and spring. Pressurized steam enters the valve through the nozzle and is then threaded to the boiler. The disc is the lid to the nozzle, which opens or closes depending on the pressure coming from the boiler. The spring is the pressure controller.

As a boiler starts to over pressure, the nozzle will start to receive a higher pressure coming from the inlet side of the valve, and will start to sound like it is simmering. When the pressure becomes higher than the predetermined pressure of the spring, the disc will start to lift and release the steam, creating a “pop” sound. After it has released and the steam and pressure drops below the set pressure of the valve, the spring will close the disc. Once the safety valve has popped, it is important to check the valve to make sure it is not damaged and is working properly.

A safety valve is usually referred to as the last line of safety defense. Without safety valves, the boiler can exceed it’s maximum allowable working pressure (MAWP) and not only damage equipment, but also injure or kill plant operators that are close by. Many variables can cause a safety valve on a boiler to lift, such as a compressed air or electrical power failure to control instrumentation, or an imbalance of feedwater rate caused by an inadvertently shut or open isolation valve.

Once a safety valve has lifted, it is important to do a complete boiler inspection and confirm that there are no other boiler servicing issues. A safety valve should only do its job once; safety valves should not lift continuously. Lastly, it is important to have the safety valves fully repaired, cleaned and recertified with a National Board valve repair (VR) stamp as required by local code or jurisdiction. Safety valves are a critical component in a steam system, and must be maintained.

All of Nationwide Boiler’s rental boilers include on to two safety valves depending on the size; one set at design pressure and the other set slightly higher than design. By request, we can reset the safeties to a lower pressure if the application requires it. In addition, the valves are thoroughly checked after every rental and before going out to a new customer, and they are replaced and re-certified as needed.

Safety valves are required by code and insurers. Therefore, it is important to have good, up-to-date records of all safety valves in the steam system. With today’s readily available technology, a database should be developed containing all the relative information of all safety devices in a facility. The safety valve database should be reviewed on a periodic basis depending on plant standards, insurance company recommendations and the local, state or federal government requirements.

The code that establishes the requirements for safety valves is governed by the American Society of Mechanical Engineers (ASME). Through its committees, ASME has published and continues to update the Boiler and Pressure Vessel codes for safety valves. It is the responsibility of plant personnel, primarily the steam team, to know which codes apply to the different parts of the steam system.

In the United States, the major considerations for safety valves are proper sizing, followed by correct installation. A partial listing of sizing and installation highlights is listed below.

• When considering a safety valve downstream of a steam pressure control valve, the total capacity of the safety valve at the set point must exceed the steam control valve’s maximum flow capacity (largest orifice available) if the steam valve were to fail 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 method is to employ multiple safety valves on the same system. The valves should be of the same set point 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 the safety valves fully opening at the same time

• The set pressure of the safety valve shall be set at or below the Maximum Allowable Working Pressure (MAWP) of the component with the lowest set point in the system. This includes but is not limited to 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.

• There shall be no intervening shut-off valves located between the safety valve inlet and the steam component that could permit the safety valve to be isolated from the system

• 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. Install the drip pan according to manufacturer guidelines

• 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 7ft above roof line. The top of the vent line should be cut at a 45-degree 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.

The proper selection, installation and use of safety valves requires a complete understanding of ASME code and any additional requirements adopted by insurance companies or the local jurisdictional authority.

As soon as mankind was able to boil water to create steam, the necessity of the safety device became evident. As long as 2000 years ago, the Chinese were using cauldrons with hinged lids to allow (relatively) safer production of steam. At the beginning of the 14th century, chemists used conical plugs and later, compressed springs to act as safety devices on pressurised vessels.

Early in the 19th century, boiler explosions on ships and locomotives frequently resulted from faulty safety devices, which led to the development of the first safety relief valves.

In 1848, Charles Retchie invented the accumulation chamber, which increases the compression surface within the safety valve allowing it to open rapidly within a narrow overpressure margin.

Today, most steam users are compelled by local health and safety regulations to ensure that their plant and processes incorporate safety devices and precautions, which ensure that dangerous conditions are prevented.

The principle type of device used to prevent overpressure in plant is the safety or safety relief valve. The safety valve operates by releasing a volume of fluid from within the plant when a predetermined maximum pressure is reached, thereby reducing the excess pressure in a safe manner. As the safety valve may be the only remaining device to prevent catastrophic failure under overpressure conditions, it is important that any such device is capable of operating at all times and under all possible conditions.

Safety valves should be installed wherever the maximum allowable working pressure (MAWP) of a system or pressure-containing vessel is likely to be exceeded. In steam systems, safety valves are typically used for boiler overpressure protection and other applications such as downstream of pressure reducing controls. Although their primary role is for safety, safety valves are also used in process operations to prevent product damage due to excess pressure. Pressure excess can be generated in a number of different situations, including:

The terms ‘safety valve’ and ‘safety relief valve’ are generic terms to describe many varieties of pressure relief devices that are designed to prevent excessive internal fluid pressure build-up. A wide range of different valves is available for many different applications and performance criteria.

In most national standards, specific definitions are given for the terms associated with safety and safety relief valves. There are several notable differences between the terminology used in the USA and Europe. One of the most important differences is that a valve referred to as a ‘safety valve’ in Europe is referred to as a ‘safety relief valve’ or ‘pressure relief valve’ in the USA. In addition, the term ‘safety valve’ in the USA generally refers specifically to the full-lift type of safety valve used in Europe.

Pressure relief valve- A spring-loaded pressure relief valve which is designed to open to relieve excess pressure and to reclose and prevent the further flow of fluid after normal conditions have been restored. It is characterised by a rapid-opening ‘pop’ action or by opening in a manner generally proportional to the increase in pressure over the opening pressure. It may be used for either compressible or incompressible fluids, depending on design, adjustment, or application.

Safety valves are primarily used with compressible gases and in particular for steam and air services. However, they can also be used for process type applications where they may be needed to protect the plant or to prevent spoilage of the product being processed.

Relief valve - A pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure.

Relief valves are commonly used in liquid systems, especially for lower capacities and thermal expansion duty. They can also be used on pumped systems as pressure overspill devices.

Safety relief valve - A pressure relief valve characterised by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application, and which may be used either for liquid or compressible fluid.

In general, the safety relief valve will perform as a safety valve when used in a compressible gas system, but it will open in proportion to the overpressure when used in liquid systems, as would a relief valve.

Safety valve- A valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored.

The Pressure Safety Valve Inspection article provides you information about inspection of pressure safety valve and pressure safety valve test in manufacturing shop as well as in operational plants.

Your pressure safety valve is a direct spring-loaded pressure-relief valve that is opened by the static pressure upstream of the valve and characterized by rapid opening or pop action.

Your construction code for pressure safety valve is API Standard 526 and covers the minimum requirements for design, materials, fabrication, inspection, testing, and commissioning.

These are:API Recommended Practice 520 for Sizing and SelectionAPI Recommended practice 521 Guideline for Pressure Relieving and Depressing SystemsAPI Recommended Practice 527 Seat Tightness of Pressure Relief Valves

For example in the state of Minnesota the ASME Code application and stamping for pressure vessel and boiler is mandatory which “U” and “S” symbols are designated for stamping on the nameplate.

For example if there is pressure vessel need to be installed in the state of Minnesota then the pressure vessel nameplate shall be U stamped and pressure vessel safety valve shall be UV stamped.

National Board Inspection Code (NBIC) have own certification scheme for pressure safety valves and using NB symbol. The NBIC code book for this certification is NB 18.

There are some other standards and codes which are used in pressure safety valve such as:ASME PTC 25 for pressure relief devices which majorly is used for assessment of testing facility and apparatus for safety valvesBS EN ISO 4126-1, 4126-2 and 4126-3 which is construction standard similar to API STD 526.

This API RP 527 might be used in conjunction of API RP 576 as testing procedure for seat tightness testing of pressure safety valve for periodical servicing and inspection.

These are only important points or summery of points for pressure safety valve in-service inspection and should not be assumed as pressure safety valve inspection procedure.

Pressure safety valve inspection procedure is comprehensive document which need to cover inspection methods to be employed, equipment and material to be used, qualification of inspection personnel involved and the sequence of the inspection activities as minimum.

You may use following content as summery of points for Pressure Safety Valve Inspection in operational plantDetermination pressure safety valve inspection interval based API STD 510 and API RP 576 requirementsInspection of inlet and outlet piping after pressure safety valve removal for any foulingInspection of pressure safety valve charge and discharge nozzles for possible deposit and corrosion productsTaking care for proper handling of pressure safety valves from unit to the valve shop. The detail of handling and transportation instruction is provided in API RP 576.Controlling of seals for being intact when the valves arrived to the valve shop.Making as received POP test and recording the relieving pressure.

If the POP pressure is higher than the set pressure the test need to be repeated and if in the second effort it was near to the set pressure it is because of deposit.If in the second effort it was not opened near to the set pressure either it was set wrongly or it was changed during the operationIf the pressure safety valve was not opened in 150% of set pressure it should be considered as stuck shut.If the pressure safety valve was opened below the set pressure the spring is weakenedMaking external visual inspection on pressure safety valve after POP test. The test need contain following item as minimum;the flanges for pitting and roughness

Making body wall thickness measurementDismantling of pressure safety valve if the result of as received POP test was not satisfactoryMaking detail and comprehensive visual and dimensional inspection on the dismantled valve parts (after cleaning)Making special attention to the dismantled valves seating surfaces inspection e.g. disk and seat for roughness, wear and damage which might cause valve leakage in serviceReplacing the damaged parts in dismantled valves based manufacture recommendation and API RP 576 requirementsMaking precise setting of the pressure safety valve after reassembly based manufacture recommendation or NB-18 requirements

Making at least two POP test after setting and making sure the deviation from set pressure is not more than 2 psi for valves with set pressure equal or less than 70 psi or 3% for valves with set pressure higher than 70 psiMaking valve tightness test for leakage purpose after approval of the setting pressure and POP tests. The test method and acceptance criteria must be according to the API RP 576.The API RP 527 also can be used for pressure safety valve tightness test.Recording and maintaining the inspection and testing results.

When it comes to understanding pressure relief valve testing requirements, there’s a lot of information out there, but not all of it seems conclusive. If you’re new to pressure relief valves or are getting started in a new industry, it can be tough to decipher what testing requirements your facility needs to meet.

It’s good to keep in mind that every industry and region has unique pressure relief valve testing requirements. Your facility may be required to just bench test pressure relief valves every five years, or you may have to test valves every year, but bench test and repair valves every three to five years. There is a large variance in the testing requirements for pressure relief and safety valves depending on your industry and your region. That said, there are a few general testing requirements we can look at to start with.

The National Board Inspection Code, created by the National Board of Boiler and Pressure Valve Inspectors, makes the following recommendations on the frequency of testing for safety and pressure relief valves, depending on the temperature, psi, and function of your boiler:

High-pressure steam boilers greater than 15 psi and less than 400 psi should be manually checked every 6 months and pressure tested annually to verify nameplate set pressure.

High-pressure steam boilers greater than 400 psi should be pressure tested to verify nameplate set pressure every three years, or as determined by operating experience as verified by testing history.

High-temperature hot water boilers operating at greater than 160 psi and/or 250° F should be pressure tested annually to verify nameplate set pressure.

It’s important to remember that these are general pressure valve testing recommendations. For specific requirements, you’ll have to verify your unique jurisdictional and industry code requirements. See the resources below for more information.

The National Board Inspection Code is an industry-recognized name offering quality information on pressure relief valve testing requirements. Here, you’ll find a wealth of information and testing best practices.

The ASME is another organization setting pressure relief valve testing requirements, and offering the necessary training engineers need to test and understand the testing procedures for pressure relief valves. In addition to testing requirements and standards, the ASME offers a variety of online courses on pressure relief valves, from fabrication and proper installation to inspection and repair.

For specific testing standards, it’s best to check with your industry and your regional jurisdiction. Pressure relief valve testing requirements can vary by state or region and are most often industry-specific. Check your industry’s standards, and check local code requirements to ensure your facility is adhering to the most relevant pressure relief valve testing requirements.

When you’re looking for the pressure relief valve testing requirements relevant to your facility, it’s important to understand the different testing methods that are available to you. It’s likely that regardless of your industry if you have safety and pressure relief valves in use at your facility, you’ll have to bench test those valves at least every five years.

In addition to those bench tests, though, you’ll also have to perform manual or on-site pressure relief valve testing. Here’s a quick look at the three most common pressure relief valve testing methods you’ll see when researching pressure relief valve testing requirements:

The most commonly mandated form of pressure relief valve testing, bench testing is unique in that it requires you completely shut down your facility’s system and remove all pressure relief valves. The valves are then transported to a lab where they are tested and repaired as necessary. Tested valves are then re-installed in your system.

Bench testing is the most involved method of pressure relief valve testing, but as this is how valves are tested when they’re manufactured, the industry considers this to be the most thorough testing method.

Inline testing is another accurate pressure relief valve testing method that doesn’t require the removal of valves or facility downtime. With inline safety relief valve testing equipment, a trained technician can test valves in the system to calculate the real setpoint of a valve in the system.

While inline testing cannot take the place of mandated bench testing, it is a more efficient form of testing for other regular testing requirements. Inline pressure relief valve testing is the ideal choice for any required testing that does not have to be bench testing, as it eliminates the need for downtime while still providing exceptionally accurate results.

Some pressure relief valve testing requirements will call for regular manual testing for freedom of operation. This is a basic test that can be done on-site. To complete an operated-in-place test, the test lever on the valve is manually activated. This test functions to ensure that the valve can open and shut tightly, but it does not verify at what pressure the valve opens and shuts. This is a test that may be required quarterly or bi-annually, to ensure the most basic functionality of safety relief valves.

Pressure relief valve testing is necessary for any facility with safety relief and pressure relief valves. For more information about the equipment you need for pressure relief valve testing, the profitability of certain testing methods, and more, head to the AccuTEST blog. There, you’ll find a variety of resources on everything from implementing inline safety relief valve testing to minimizing plant downtime.

If your company requires regular pressure relief valve testing, you might be interested in AccuTEST’s high-tech equipment. Offering inline testing with accurate, repeatable results, our system is the best on the market. See how our equipment works in real-time — schedule a live webinar demo today.