Asme u Stamp - Free download as Powerpoint Presentation (.ppt /.pptx), PDF File (.pdf), Text File (.txt) or view presentation slides online. Flow chart and guideline for acquiring ASME U designation. What is the meaning of U and U2 stamps by ASME for section viii div.1 amp 2 respectively. Means U for what CR4 - The Engineer's Place for News and Discussion ® New Post. The Certificate Holder needs to inform the ASME Conformity Assessment Department at [email protected] of the address change due to postal re-designation including any changes to the building number, street name, zip code, etc. ASME will issue a revised ASME Certificate of Authorization provided the Certificate Holder'/s Authorized Inspection Agency (AIA) of record provides documentation to ASME to support the Certificate Holder'/s request. Where there is no AIA involved in the Certificate Holder.
The ASME Pressure Vessel Joint Efficiencies article provides you with information about pressure vessel joint efficiency requirements and their connection with radiography testing.
You may know Pressure Vessel Joint Efficiencies are linked to the radiography testing grades and there is a concession for full radiography testing as per the UW-11(a) (5) (b) clause which it is a little bit confusing.
This article provides you the ASME pressure vessel joint efficiencies requirements and guidelines for the above clause.
Based on the ASME Code requirement, manufacturers have to mark the type of RT i.e. RT1, RT2, RT3 and RT4 in the pressure vessel name plate and state the same in Pressure Vessel Data Report.
The ASME Training Course is 5 days training course and available online and the student that successfully pass the exam, receive I4I academy certificate with 40 hours training credit.
We have seen many professionals, from inspectors to quality control engineers who are confused between RT1 and RT2, specifically when they see ASME Pressure Vessel Joint Efficiencies for both RT1 and RT2 is the same and equal to 1(E=1).
They say both RT1 and RT2 are categorized in the “Full Radiography” part in UW-11 clause ..
So why are some joints in RT2 radiographed in spots?
We are making spot radiography, but it is categorized in full radiography!!!
So in this 'ASME Pressure Vessel Joint Efficiencies' article we want to answer this question in very simple way, but before this, we need review joint categories and summarize them as below:
Category A:
- All longitudinal welds in shell and nozzles
- All welds in heads, Hemisph-head to shell weld joint
Category B:
- All circumferential welds in shell and nozzles
- Head to shell joint (other than Hemisph.)
Category C and D are flange welds and nozzle attachment welds respectively
Longitudinal welds (Category A) are more critical than Circumferential welds (Category B) because they are under double stress.
This the reason why in different part of ASME code we have stringent rules in category A joint compared to category B joint.
See the following Fig. for joint categories:
Now let's get back to the ASME Pressure Vessel Joint Efficiencies subject, to remove the above confusion about RT1 and RT2.
We need to know:
Asme U Stamp Explained
When and where is there a code requirement for full radiography?
Item 1: All butt welds in vessels used to contain a lethal substance (UW-11(a)).Lethal substances have specific definitions in ASME Code in UW-2 and it is the responsibility of the end user to determine if they ordered a vessel that contains lethal substances.
Item 2: All butt welds in vessels in which the nominal thickness exceeds specified values (UW-11(a). You can find these values in subsection C, in UCS-57, UNF-57, etc. For example, this value for P-No.1 in UCS-57 is 1 ¼ inch.
Item 3: All butt welds in an unfired steam boiler with design pressure > 50 psi (UW-11(a)).
Item 4: All category A and D butt welds in vessel when “Full Radiography” optionally selected from table UW-12(column (a) in this table is selected); and categories B and C which intersect Category A shall meet the spot radiography requirement (UW-11(a) (5) (b)).
The point is this: items 1, 2 and 3 are similar, but item 4 is completely different. In items 1, 2 and 3 it is mandated by code; to do full radiography in all butt welds in vessel so it means it is mandatory for designer to select column (a) in UW-12 table.
But in item 4, there is no mandating rule. A manufacturer with its own decision has chosen to use column (a) in table UW-12 for full radiography.
So here there is a concession or bonus to manufacturers for categories B and C.
What is concept behind this concession or bonus in pressure vessel RT test?
If you review item 1, 2 and 3 one more time, you will see that the pressure vessel RT tests are related to the type of welds and services.
You can see the pressure vessels in these items are critical from a safety point of view, one contains a lethal substance, the other one has a high thickness, which implicates high pressure, and the last one is an unfired steam boiler. But item 4 has no criticality like the other items have.
But you should note all 4 items have been categorized in full radiography clause( U-11(a)), so to differentiate item 1, 2 and 3 from item 4, the RT symbols are used in Code (UG-116).
RT 1: Items 1, 2 and 3, (E=1), All butt welds-full length radiography
RT 2: Item 4 (E=1), Category A and D butt welds full length radiography and category B and C butt welds spot Radiography
RT 3: (E=0.85), Spot radiography butt welds
RT 4: (E=0.7), Partial / No radiography
You need to consider the hemispherical head joint to shell as category A, but ellipsoidal and torispherical head joint to shell as category B;
Do you know why? Why ASME considered the stringent rule for pressure vessel RT test in hemispherical head joint?
It is because this joint is more critical, because the thickness obtained from the formula for hemispherical head approximately would be half of the shell thickness;
It means if the shell thickness is 1 inch, the hemispherical head thickness would be 0.5 inch.
For more detail, you may review the Pressure Vessel Heads article.
ASME Pressure Vessel Joint Efficiencies for welded Heads
For Welded Heads, the joint efficiency of the vessel will be 1(E=1), if all welds within the head's full length are radiographed (since they are all Cat. A welds). See above figure.
ASME Pressure Vessel Joint Efficiencies for Seamless Heads
For seamless heads, the joint efficiency of the vessel will be 1(E=1) if the head to shell weld is fully radiographed for the hemispherical Head (Cat A);
See the following Figure for RT types:
Spot radiographed for ellipsoidal and torispherical heads(Cat. B).
Weld Types:
Here is some clarification about the different type of welds that have specific definitions in ASME Code SEC VIII DIV 1 and related to the pressure vessel RT test.
The concept is to define the different types and then introduce some restriction for using them.
For example, a Type 1 weld is defined as a full penetration weld, typically double welded and Type 2 is welds with backing strips.
So when you go to service restriction for a vessel containing a lethal substance, you see there is a restriction there that says all category A joints shall be weld Type 1 and Category B and C shall be type 1 or type 2.
You should take this point in to account, which is this: the same joint category with different weld types have different joint efficiencies.
Summary of weld types:
Summary of weld types:
Type 1: Full penetration welds (Typically Double welded)
Type 2: Welds with backing strip
Type 3: Single welded partial penetration welds
Type 4, 5 and 6: Various Lap welds (rarely used)
Related Articles
Pressure Vessel Definition, Pressure Vessel Certification, Pressure Vessel Heads, Pressure Vessel Handbook, Spherical Pressure Vessel, Pressure Vessel Plate Material, ASME Code Section 8, ASME Impact Test Requirement, Pressure Vessel RT Test , Vessel Pressure Testing, Third Party Inspection for Pressure Vessel, Inspection and Test Plan for Pressure Vessel
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Have your say about what you just read! Leave me a comment in the box below.Engineering Tips: PSV Sizing and Selection
How understanding API and ASME standards can help prevent over-sizing PSVs and their respective piping systems
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!
The Conundrum
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?
Standards referenced in this article:
- ASME Boiler & Pressure Vessel Code (BPVC), Section VIII
- API Recommended Practice (RP) 520
- API Recommended Practice (RP) 526
ASME and API : To Size or Not to Size
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.
First, let’s clarify the main roles API and ASME play on this subject, and how the standards are intended to be used:
1. API 526 provides basic design criteria for PSVs, and is aimed at manufacturers.
2. API 520 provides detailed methods to a) determine specific required relief loads, and b) select preliminary, generic valve sizes.
Winhex full version download. 3. ASME BPVC governs testing and certification of valves.
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.
ASME BPVC: What are the Rules?
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.
API 526: Standardized Valve Design
Types Of Asme Stamps
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.
API 520: PSV Sizing Equations
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.
The Intersection
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!
An Example
Here is an example scenario where all of this comes to a confusing head:
1. ABC Valve Company builds a valve, aiming at the design specs for an API N orifice, which API says is an effective area of 4.34in2.
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?
A More Detailed Explanation
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?
The ASME-certified capacity of any given valve will nearly always exceed its API capacity.
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:
…by selecting an ASME data set at the final iteration of valve selection, you automatically include a 10% safety factor in your design!
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
- API Calculated Required Area: 4.667 in2
- ASME Calculated Required Area: 4.624 in2
- ASME Certification for Brand X* 4N6: 4.900 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!
Summary
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:
1. An actual orifice area that is greater than the standard API letter-designated orifice area. This is ok; it just means the PSV selected performs slightly better, or is slightly larger, than the minimum design conditions for its API letter designation.
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.
Anytime you are selecting a PSV that is near its API capacity limits, a flag should go off in your head: remember to check the ASME capacity!