asme safety valve code quotation

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 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.

The other advantage of POPRV’s is that whether a snap-acting or modulating pilot is used, the presence of superimposed back pressure does not affect the opening pressure when the valve is in service. This is unlike direct spring safety relief valves, which require expensive and fragile bellows to protect against backpressure.

The modern POPRV can be used confidently in ASME Section VIII applications. POPRV’s provide a leak-free system operation very close to the PRV set pressure. A non-flowing pilot design assures that the POPRV will relief consistently within code tolerances even in “dirty” service applications, thus lower cost of ownership. Since process pressure is used to provide sealing force, a lighter unit weight and smaller size results in a lower cost of installation. POPRV’s provide advanced, reliable, and efficient overpressure protection, utilizing a product technology designed for a wide range of ASME Section VIII applications.

The primary role of a safety relief valve is to prevent over-pressure situations in pressurized vessels or systems. If the tank’s relief valve fails, it can lead to an accident that destroys property, life, or landscape.

The National Board of  Boiler and Pressure Vessel Inspectors is one of the governing bodies for the testing and/or repair of ASME Safety Relief Valves.

You, as the owner of the valve, can test it, but it must be done in accordance with the National Board Inspection Code and your state’s and/or local regulations.

Based on the National Board Code, which bases their inspection intervals on what type of service the valve is used for, the following intervals are suggested:

Also, keep in mind that this piping should be oriented so that no liquid relieved through this piping can flow back and rest on the ASME safety relief valve’s outlet port.

The ASME relief valves are set to fully open at its “set” pressure but will begin to partially open before then – normally at 10% below its set pressure.

If your valve is allowed to do this, trash and/or corrosion can set in over time which could prevent the valve from either closing completely or from fully opening, either of which is not a favorable solution.

The improper installation of pressure relief devices can have dire consequences, causing unnecessary safety risks, and delaying operations while they are replaced or repaired. PRVs are typically one of the last lines of defense in an upset condition. To ensure that PRVs relieve and flow properly, the ASME and the National Board certify all PRV assembly programs, testing facilities, and even technicians. When you see marks and symbols on your pressure relief devices, it means that your device is certified safe because it came from a National Board and/or ASME certified organization.

The five symbols in the above graphic above are issued by the ASME and National Board. There are others, and you may see a few different variations from time to time. Each of them denotes a specific certification:

ASME Boiler and Pressure Vessel Code Certificate of Authorization Program The American Society of Mechanical Engineers offers Certificates of Authorization for the construction of new pressure-retaining equipment to various sections of the ASME Boiler and Pressure Vessel Code – Section I; IV; VIII, Divisions 1, 2, & 3; X; and XII. A

The ASME Single Certification mark indicates that an organization has followed all aspects of the ASME codes and standards, meeting all requirements of the Conformity Assessment certification program. The ASME certification mark is stamped onto devices, paired with one of 8 designators from the National Board: V, UV, UV3, UD, HV, NV, TV, depending on which program they’ve completed. For example, at Vinson Process Controls, we are UV Assembly certified, meaning we successfully completed the National Board’s UV Assembly certification program. Because we are a certified PRV assembler, our customers know that the pressure relief devices they receive from us are compliant with the ASME Boiler and Pressure Vessel Codes (BPVCs). The mark for a UV assembly certified company has the ASME single certification mark paired with the UV designator from the national board.

The simple answer? Safety. However, there’s a bit more to safety than you might think. In order to ensure safe operation, organizations like the ASME and National Board set firm standards and require the completion of specific programs to attain certification. These programs are rigorous, and the UV Assembly Program is no exception.  It’s designed to be very stringent, as it ensures consistency in the capabilities and functionality of all components in the PRV assembly process. Ideally, a PRV should be procured from a certified assembler that is also able to test and repair the device if necessary. Unfortunately, this is a tall order that not all suppliers are able to.

Vinson Process Controls has the capabilities and credentials required to assemble, test and repair pressure relief devices. In order to better serve our customers, we earned the certifications for the UV (assembly program), VR (valve repair) and T/O (testing only) certifications from the ASME and the National Board. We take the guesswork out of PRV procuring and maintenance so that our customers can relax and reap the benefits.

As a UV-certified assembler, Vinson has invested in stocking Anderson Greenwood™ and Crosby™ relief valves for faster lead times. We have a wide range of options for our customers, including same-day service, when required.  The vast majority of Vinson’s relief valve inventory is in the portable 81P valves and pilot operated valves. Apart from the combined inventory we share with Emerson, we also have access to shared inventory across all 21 of Emerson’s Impact Partners. We are proud to say that all valves assembled in our Carrolton Valve Center have met or exceeded expected shipping dates.

In addition to faster lead times, our customers can maintain confidence that the products shipping from Vinson are of the samequality as those shipping directly from Emerson’s factory. The ASME, the National Board and Emerson audit all shops, quality control processes, techniques, and valves, before and after awarding certifications.  Vinson will continue to receive audits to ensure that we are meeting or exceeding expectations over time. Our adhesion to our quality control manual means that all valves assembled by Vinson have the same factory warranty as if they were assembled in Emerson’s production line.

As a part of the Emerson Impact Partner Network, Vinson is one of the primary points of contact for direct sales of Anderson Greenwood™ and Crosby™. We are a certified UV assembler, also offering valve repair and testing services. We can offer you quotes for both repair and replacement options.  Because of this unique status, Vinson can offer competitive pricing.

Vinson is proud to be an ASME and National Board UV and VR certified supplier. We are excited about our ability to offer our customers flexible delivery and quality products, all at a competitive rate. Our partnership with Emerson™ and the Emerson Impact Partner network enables us to provide continued support for our clients, no matter the complexity of their application needs. Contact us for assistance with your next project. We’re here to help and we’d love to hear from you!

ASME safety valves are used across several applications including low-pressure and high-pressure boilers, process equipment, and air, gas, and vapor equipment. We have multiple products in a range of configurations and material construction that meet ASME Class I, IV, and VIII.

**Update to this article, June 7, 2022 : If you found this article helpful, here is a link to another article I recently found that does a nice job explaining the topic: ENGINEERS BEWARE: API vs ASME Relief Valve Orifice Size – Petro Chem Engineering (petrochemengg.com)

NOTE: this article is written to an audience that is familiar with PSVs, PSV sizing, and API and ASME standards at a basic level. I initially wrote this article in early 2017, and due to some great input and questions made significant revisions to increase clarity in mid-2018. I hope it is helpful to you, please send me a message with any comments/questions!

If you"ve ever sized/selected a Pressure Safety-Relief Valve (PSV) using vendor sizing programs or good-old hand calculations, you"ve probably run into a very strange anomaly: Why does a PSV orifice size change between American Petroleum Institute (API) and American Society of Mechanical Engineers (ASME) data sets? What is an "effective" orifice area? How do I know which standard to use when selecting a PSV?

Usually, this issue is one of curiosity and doesn"t affect the end result of what valve is chosen. Common practice is to default to API sizing equations and parameters, and only use ASME data sets for situations outside of the API letter-designations. But what if I told you that approach is likely causing you to oversize about 10% of your PSVs and their respective piping systems?

Most of the time simply using API data sets is fine. And I should note that this is a conservative approach, so you won’t make a mistake doing this. But did you know that PSVs are certified to ASME capacities, not API? And did you know those ASME capacities are nearly always higher than the API ones? I’m guessing you don’t, because there are very few resources available that speak to this topic. I’ve found it common for engineers to understand API 520 quite well, but have a very limited working knowledge of how the ASME BPVC comes into play.

Too often, we leave that third part out of the process, and simply calculate relief loads and select valves using API techniques, without ever checking our selection against certified ASME data. Proper application of these standards is the first key point of this article:

Initial sizing and valve selection is done using API equations, and final valve selection and certification is done using ASME-certified coefficients and capacities.

When sizing a PSV, the sizing equations are always API 520. When a PSV is certified, it is always certified to ASME BPVC (whether one “selects” ASME certification or not!) It"s important to remember that the ASME BPVC is the "code", the standard to which we must design. API 520/526 are "recommended practices" which were developed to give engineers a tool to meet the ASME requirements. Another way to look at it: ASME BPVC sets the goal, API 520/526 provide the instructions, and ASME has the final say.

The BPVC is an enormous code, and not reviewed in detail here. On the subject of PSVs, it basically says that a PSV must be capable of relieving the required load, and it must be tested in a specific manner to be certified to do so. If a valve is tested per the specific directions in the BPVC, it will be ASME certified and receive an ASME UV stamp.

NOTE: when specifying a PSV for a pressure vessel, it"s important to always specify that the UV stamp is required. There are times when a non-code PSV is acceptable, but that is outside the scope of this article.

The first thing API does is attempt to standardize physical PSV sizes and design, and it does so in API RP 526, which is targeted at PSV manufacturers. API provides pre-defined valve sizes, with letter designations D through T (API 526). It also defines other details directed toward valve manufacturers (such as temperature ratings). All of this is intended as minimum design standards, and manufacturers are free to exceed these parameters as they wish.

The second thing API does is provide standardized equations and parameters to use when trying to figure out just what size of a PSV one needs for a particular scenario. The equations account for design parameters that ASME doesn"t speak to, such as specific fluid properties, backpressures, critical flow, two-phase flow, and many other aspects of fluid dynamics that will affect the ability of a particular valve to relieve a required load.

API sizing equations are by nature theoretical, standardized, and use default or "dummy" values for several sizing parameters that may or may not reflect the actual values for any specific valve.

API RP 520 very clearly talks about this, and emphasizes that the intended use of its equations is to determine a preliminary valve size, which should be verified with actual data. API intends PSV sizing to be a two-step process, but we are often unaware of this because we (gasp) don’t read the full standard, and/or rely solely on vendor sizing software that hides the iteration from us. See API 520, part 1, section 5.2 for further explanation.

When valves are built, they are built to the API RP 526 standard, however, as one might imagine, when valves are actually tested and certified, the results don’t match up identically to the theoretical values that were calculated. This is where API and ASME intersect; we switch from calculations (API) which were used as a basis to design the valve, to actual empirical data (ASME) to certify the valve. When a valve manufacturer gets the UV code stamp that certifies the valve orifice size and capacity, it is based on actual test results, not API sizing standards. And ASME (which came first) does not have tiered letter designations. The typical D, E, F, etc. sizes we refer to are strictly an API tool, and ASME’s capacity certifications are completely independent of them!

2. They test the final product according to ASME BPVC, and get a result that equates to an effective orifice area of 4.90in2. This is its ASME effective area.

3. A third-party Engineer (you), trying to select a PSV, runs a sizing calculation using API 520 equations on ABC Valve Company"s sizing software, gets a result that requires 4.66in2 to relieve the load, and is now thoroughly confused on what size valve to select.

If one selects the API data set on the sizing software in this example, it will automatically eliminate N-orifice valves as an option, and bump the user up to a P-orifice. However, if one simply selects the ASME data set, the N-orifice valve magically reappears as an option. How can this be? Will the N-orifice work or not?

The short answer is yes, it is certified to an actual area of 4.90in2. So the “N” orifice for this specific PSV will work, and is certified to do so, in this application. Remember: use API to get you close, and ASME to confirm the final answer.

Digest that for a moment. If you’ve sized and purchased more than a dozen PSVs, chances are you have inadvertently selected a PSV a full size larger than you needed to, in a situation much like our example, simply because you chose a PSV based on its API “rating” rather than its real, certified, stamped ASME rating. If that was a small valve, impact was probably nil. But what if this happened on a valve that resulted in selecting a 8x10 PSV when you could have used a 6x8?

If you’re like me, that answer isn’t very satisfying. Why on earth is this so confusing? How can you simply hit a button on the sizing program and a different size of valve is suddenly acceptable? The key lies how the main coefficient of discharge, Kd, is handled, and how capacities are determined.

There are several K values used in API calculations, all of which have generic values defined in API 520 that can be used for preliminary sizing. These are the numbers used in initial sizing calculations to get us close, then (if we do this correctly) replaced with the actual/tested/empirical/ASME values when we get a certified valve. Remember, anytime you hear “certified” or “stamped”, think ASME.

Let’s take the numbers from the example above, which came from an attempt to size a valve for liquid relief. API says to use a value of Kd=0.65 for liquid relief. If one uses the API data set on the vendor software, then the calculation stops here, and you get a required area of 4.66in2. When you select a valve, you’re comparing that to the API effective (actual) area of an N orifice, which is 4.34 in2, which is obviously too small and you’d logically step up to a P orifice. However….

Remember that the API N-orifice area is just the benchmark, a minimum requirement, and may or may not (most likely not) reflect the actual area of a real-life PSV. Once a valve is selected, all of those K values and capacities should be replaced with actual ASME-certified K values, also determined by testing, that are specific to each valve model, and the calculations performed again.

Normally, ASME-certified K-values are smaller than the API dummy values, driving up the required orifice area. So valve manufacturers have to over-design their valves to make up for it, resulting in ASME-certified areas and capacities that typically exceed the benchmark API ones. The end result of all this?

It (almost) all boils down to one sneaky little sentence in the ASME BPVC which mandates a 10% safety factor on the empirically-determined Kd that “de-rates” the valve (see ASME BPVC Section VIII, UG-131.e.2). This tidbit seems to be a little-known fact that is key to proper PSV sizing and selection, because as engineers we often pile safety factors upon each other and oversize our equipment. I cannot highlight this enough:

I mentioned above that ASME K values are nearly always lower than API values, due to this 10% de-rating. The PSV in our example scenario has a determined Kd of 0.73, which is adjusted down by 10% for a final AMSE Kd of 0.66, slightly higher than the dummy API value (that just means that this particular valve proved it could do about 11% better than the minimum theoretical flow calculated by API when it was tested). So, for our valve in question, the Required ASME area is slightly less than the API area. This is atypical, but not unheard of, and again points to the importance of checking the ASME ratings of any valve you select, and comparing against the API benchmarks.

But that’s not the whole picture. For our example, the net effect of the ASME Kd is basically nothing. So how is it the ASME capacity is higher? This brings us to the last key concept:

When you choose to use the ASME data on a specific valve, it’s not just the Kd sizing factor that changes; the actual orifice area and therefore the capacity of the valve also adjusts to empirical, certified values. You can generally expect both values to increase over the API values.

Why is this? Simply that any given real-world valve is usually over-designed so that it will meet and exceed the required minimum capacity of its corresponding API size. What a simple concept, but so often overlooked by engineers!

Back to our example scenario: even though the ASME Kd, and hence required area, adjustment had a negligible effect, the actual ASME orifice area, and hence capacity, is significantly higher than the listed API area and capacity for an N-orifice. Below is a summary:API N Orifice: 4.340 in2

*Note: this is data from a real case; the specific PSV make/model is omitted. Did you catch the result? The actual, certified capacity of this valve is nearly 13% higher than the generic N-orifice valve, and that includes its 10% safety factor!

With this adjusted orifice area, we can compare to the ASME certified area (which is always going to be larger than the API area), and we have our final answer for the valve size. Often this will not result in a different choice of valve, but sometimes, as in the example case, it will allow us to use a valve with an API letter designation that did not appear large enough based on its API effective area. This can save time and money for our plants by preventing over-sizing valves, leading to smaller piping systems to support them. And remember, the ASME values are empirical and have a 10% safety factor built in, so we don’t need to worry about cutting the design too close; the conservatism is already built in to the method. We can choose the Brand X N-orifice valve and sleep well at night!

Avoid simply defaulting to the API data set for the final “rating” or data sheet when selecting a PSV. Use API sizing calculations as they are intended: for preliminary valve selection. Then switch to the ASME data set. This will often (but not always, remember, it"s valve-specific) result in two differences:

2. A required orifice area that is greater than the one calculated by API. This is also ok, and is usually due to the 10% de-rating on Kd that ASME requires.

Closing notes: PSV sizing and selection is a big topic, and this article only addresses one issue. I have chosen to omit specific code references and quotations in an attempt to make this a general guideline that is useful for most engineers, not an interpretation of the codes. Many tangent issues can spin off from this article; I will be happy to help with any questions it may generate. Please email me any comments or suggestions, I welcome all input.

Kingston Model 115 ASME Code Soft Seat Safety Valves are constructed of brass with a Viton seal and positive stop for a bubble-tight seal. This valve is equipped with a pull ring for manual testing. Internal construction and performance are the same as Model 114 differing only by the pull ring. The Kingston Model 115 ASME Code Soft Seat Safety Valve, like every Kingston Safety Valve, is set and tested at factory for quality and dependability. The Kingston Model 115 ASME Code Soft Seat Safety Valve is approved in Massachusetts and Washington DC and is stamped with UV & NB symbols. Registered in all Canadian provinces and territories.

Bell & Gossett cast iron and bronze body ASME Safety Relief Valves are engineered in accordance with the requirements of Section IV of the ASME Boiler & Pressure Vessel Code for Heating Boilers, and their capacities are certified by the National Board of Boiler and Pressure Vessel Inspectors. B&G diaphragm operated cast iron, and diaphragm-assist operated bronze ASME Safety Relief Valves, are designed to protect fired and unfired hot water vessels against overpressure conditions.

Bell & Gossett diaphragm operated cast iron and diaphragm-assist operated bronze ASME Safety Relief Valves are designed to protect fired and unfired hot water pressure vessels against over-pressure conditions. These valves feature a unique failsafe disc with sufficient area to permit the valves to maintain their safety relief function in the event of a diaphragm rupture. These valves are designed, manufactured, tested and labeled in accordance with the requirements of Section IV of the ASME Boiler and Pressure Vessel code. They are offered in a wide range of capacities to permit a close match with the boiler output rating.

Kingston Model 114 ASME Code Soft Seat Safety Valves are constructed of brass with a Viton seal and positive stop for a bubble-tight seal. This valve is also equipped with a protective stem cover and manual test lever. Internal construction and performance are the same as Model 115 differing only by the test lever.  The Kingston Model 114 ASME Code Soft Seat Safety Valve, like every Kingston Safety Valve, is set and tested at factory for quality and dependability.  The Kingston Model 114 ASME Code Soft Seat Safety Valve is approved in Massachusetts and Washington DC and is stamped with UV & NB symbols. Registered in all Canadian provinces and territories.