In most countries, pressure vessels must be manufactured to a certain code, and in the United States, that code is the Boiler and Pressure Vessel Code (BPVC) from the American Society of Mechanical Engineers (ASME).
The following pressure vessel design guide and resources will help you efficiently optimize your design, before moving on to the actual manufacturing and delivery of a safe and cost-efficient pressure vessel.
TABLE OF CONTENTS:
(Click on a link to jump directly to a section)
Design Processes To Know
SAFETY AND CODES
What Design Standards are Critical to Be Aware of When Designing Pressure Vessels?
The purpose of using design codes is to standardize requirements and to minimize risk for designers, manufacturers, and those working with pressure vessels. As such, codes have been developed over the years using industry experience and best practices.
The rules developed for the design codes represent years of experience. When used, the code requirements can:
- Communicate design requirements
- Utilize know-how and technology
- Keep equipment costs low
- Reduce insurance costs
- Provide rules for the design of equipment adequate for design
conditions determined by others.
ASME BPV Codes
The ASME Boiler and Pressure Vessel Codes are used throughout the world, though they are less common in the UK and the EU. The ASME BPVC is structured into the 12 following sections.
THE 12 SECTIONS OF THE ASME BPV CODE
ASME Section I: Power Boilers
ASME Section VII: Operation of Power Boilers
ASME Sec II: Materials
ASME Section VIII: Pressure Vessels
ASME Section III: Nuclear Fuel Containers
ASME Section IX: Welding and Brazing
ASME Section IV: Heating Boilers
ASME Section X: Fiber Reinforced plastic Pressure Vessels
ASME Section V: Non-Destructive Examination (NDE)
ASME Section XI: Inspection of Nuclear Power Plants
ASME Section VI: Operation of Heating Boilers
ASME Section XII: Transport Tanks
With a focus on pressure vessels, Section VIII is expanded below.
SECTION VIII: PRESSURE VESSEL
Division 1 - 15PSIG to 3000 PSIG
Subsection A, General Requirements:
Subsection B, Fabrication Requirements:
Subsection C, Material Requirements:
Related Article: U-2(g) and Appendix 46 Address ASME Div 1 Gaps
Aspects of ASME’s BPV Code Material Standards
ASME standards for materials are an important factor in calculating a design’s safety. Materials allowed for constructions are listed in Section II, Part D and also in the code of construction (e.g. Section VIII, Division 1). If the code of construction does not include a material listed in Section II, D, the material cannot be used with that code of construction.
The following material properties impact pressure vessel design:
For the most part, ASME BPVC allowable stresses are determined by four things: tensile strength, yield strength, time-dependent properties at higher temperatures (creep), and product form (bolting, welded pipe, etc.).
There is a different safety factor for tensile, yield, and creep. The safety factor for tensile strength varies between the allowable stress tables in Section II, D. For Table 1A, for example, it is 3.5; but for Table 5A it is 2.4.
Additional Material Properties
Other material properties can also be found in Section II, Part D. Yield strength comes from the Y tables. Ultimate Strength comes from the U tables. Modulus of Elasticity comes from the TM tables and Coefficients of Thermal Expansion come from the TE tables.
Other values, such as density and Poisson’s Ratio values, come from Table PRD.
Related Article: ASME 2019 Code Changes include UG-44 Incorporation of Code Case 2901
What Other Design Codes Should I Be Aware of When Fabricating for Global Markets?
While there are several rules developed by countries with recognized technical expertise in the subject, the code that is the most internationally recognized and the most used is Section VIII "Pressure Vessels" of the BPVC of ASME. Other than ASME, the other most commonly used codes for pressure vessels are below:
- Europe: EN-13445
- Germany: A. D. Merkblatt Code
- United Kingdom: PD 5500
- France: CODAP
- China: GB-150
Related Articles:- ASME BPVC 2019 Code Change Gives Design Guidance with Revised U-2(g)
- Comparison of PD 5500, EN 13445, ASME VIII Div 1 & ASME VIII Div 2
How Do I Keep Up With Design Code Changes?
Like many other aspects of this industry, codes are constantly adapting and changing.
It’s important to stay abreast of the latest code releases and to make sure you’re trained on them as well. Not being compliant or unaware of new codes can negatively impact business and result in unplanned scrap and re-work.
In order to review changes in code, you can look at ASME Section VIII, Division 1 under the summary changes. This will highlight any changes made in the code, as well as give the description of the changes. You can also look for the code year designator next to the code.
If you see a number “19,” that means the code was changed in the year 2019, and you can look back in the summary of changes to see what that change was and the record item that was used to manage the change.
If you want to be on top of code changes and not be caught by surprise, it’s helpful to be involved in Committee work. The ASME BPVC meetings are free and open to the public. They offer a balance of interests with different points of view from inspectors, consultants, designers and fabricators. These meetings are an excellent way to learn about code changes before they are published and be involved in the process.
Below are the past code changes:
CEI’s engineering team supports the design and welding industry serving on various code committees including:
- Antonio Howard; Certified Associate Welding Inspector (CAWI)
- Michael Clark; PE
- Tiradej Bunyarattaphantu; Engineer in Training (EIT)
Sometimes, material properties change as well. To find material changes, look in Section II, parts C and D, as well as Section IX. These sections will highlight changes in material, and you can be assured you are abiding by any new material requirements.
DETERMINING PRESSURE VESSEL DESIGN COST ESTIMATION
Since the first step in designing a piece of pressure equipment is choosing the one that is fit for your purpose, it’s important to create a strategy before designing your pressure vessel.
The factors influencing this choice are the function of the object, the location, the nature of the fluid to be stored/processed, the temperature, the operating pressure and the ability to store the volume needed by the process.
What Design Processes Should Be Considered?
Sometimes, a designer needs to consider different methods of pressure vessel design in order to produce an ASME compliant vessel. Two design methods are The Design by Rule (DBR) and The Design by Analysis (DBA).
Design By Rule Method (DBR)
DBR is a typical design methodology and can be located in the ASME Boiler and Pressure Vessel codebooks in Section VIII, Division I and Part 4 for Division 2, as well as other Pressure Vessel References.
Design By Analysis Method (DBA)
DBA method usually incorporates Finite Element Analysis (FEA) that requires additional expertise in the methods of the proposed analysis. ASME BPVC, Section VIII, Part 5 for Division 2 has extensive requirements for using DBA.
Related Article: The 3 Key Aspects of ASME's BPV Code Material Standards
DBR and DBA Combined Method
In many cases, using both DBR and DBA makes life easier for the designer because he/she is able to take advantage of the tools offered by both methods.
The DBR method’s scope may be too limited for all the aspects of a vessel design. In these cases, DBA can be used to supplement the DBR method in order to check aspects such as cycle life and secondary stresses that may not be considered in the DBR method.
How Do You Create a Competitive Advantage When Bidding a Design?
If you want to build in a competitive advantage for your company, it’s important to have the ability to rapidly prototype and quote code-compliant pressure vessel design variations. By looking at design examples quickly, you can offer different options to a client and figure out the best one for their needs.
When quoting a prototype for a client, there are several factors to be taken into consideration, such as loadings, the geography of the installation site, design and operating conditions, upsets, shutdowns, and startups.
Pressure vessels come in several shapes, represented below.
PRESSURE VESSEL DESIGN STANDARDS
The pressure vessel codes, like ASME Section VIII, Division 1, are a set of minimum requirements. They do not cover all possible geometries, loading conditions, etc. It is typically the responsibility of the manufacturer to ensure the vessel is designed properly.
Vessels designed for PED compliance can achieve this by doing a risk analysis. Vessels designed per Section VIII, Division 2 can do this by using the load case case combinations specified in addition to an adequately defined set of loading conditions per a user design specification (UDS); the UDS is the end-user’s responsibility.
Division 1 can be problematic in a lot of these areas as it requires all expected loadings to be considered; but, for the most part, only provides methods for pressure and vacuum (it does not include methods for external loads) and does not mandate a UDS or specific load case combinations. It is critical to account for all loadings, even for a Division 1 vessel.
Proper Material Selection
Choosing the right pressure vessel material is quite literally the foundation of a properly functioning pressure vessel. It is essential for the design engineer to choose the correct material for not only the functionality of the vessel but also for the safety of those using the vessel.
Pressure vessels, depending on requirements, can be made from a variety of materials. Carbon steel and stainless steel might be the most commonly used materials for industrial applications but, between the two there is a vast multitude of alloys and compositions that can be used for pressure vessel construction. Some of these materials are commonly used and others are limited to more specific situations.
Below is a list of pressure vessel materials that are commonly used and why:
Carbon steel possesses a high tensile strength and retains strength at minimal thicknesses.; however it has limited resistance to corrosion, shock, and vibration.
Like carbon steel, stainless steel offers high strength at low thickness and is ideal for tanks and vessels that are exposed to the natural environment (humidity, sunlight, etc.) or high temperatures.
Hastelloy® is a nickel-molybdenum alloy brand that is highly resistant to corrosion and because of the molybdenum it is made stronger at high temperatures.
Incoloy® is relatively easy to fabricate, can be made using the same machines and processes used to make stainless steel, has a high iron content, making it more cost-effective, and is designed for high-temperature applications.
Despite the complexity and associated cost, nickel alloy has much to offer as a pressure vessel material. It provides excellent corrosion resistance, comes in a variety of grades, and protects against thermal expansion. It’s important to note that the manufacturing process for this alloy can be more complex than with other amalgams.
Often considered as an alternative to stainless steel, aluminum is cheaper and much easier to machine than stainless steel. In many instances, labor costs may be higher as some aluminum tank fabrication requires special welding techniques. Its lower density typically means an aluminum pressure vessel is unsuitable for extremely high pressures.
Titanium provides several advantages in salt-water environments. It is resistant to corrosion, maintains strength and rigidity (even at lower thicknesses), facilitates more efficient heat-transfer than many other types of metal, and can maintain its structural properties over long periods of time.
Material Strength and Joint Efficiency
The Joint Efficiency is determined from the quality of the joint design and the degree of examination. Double welded butt joints are considered the highest quality joints and full radiography is, of course, the highest degree of examination. Lower quality joints and lower examination will both result in lower joint efficiency.
Joint efficiency is seen throughout the design formulas in the ASME Section VIII, Divisions 1 and 2. It is basically a multiplier on the material allowable stress, though sometimes it’s use does not make that clear (see 4.3.10 in Section VIII, Division 2 for example).
A high strength material may effectively lose a lot of its strength if the design uses little examination or lower quality joints. However, this may make more sense if the economic risks are more severe to do full or partial radiography (for example) and Type 1 joints; in these cases, more material may just be the more economic choice.
For some design conditions, such as lethal service, the Code requires the designer to specify full radiography. However, even if not required, the designer can specify increased an degree of radiographic examination in order to increase joint efficiency and reduce the required thickness of the vessel wall.
See UW-3 and UW-12 in Section VIII, Division 1 for a better understanding of joint efficiency and its determination.
The main issue with pressure vessel design is staying compliant with ASME Code, which is updated every two years. Keeping up to date on all the changes that occur between code years can be complicated, especially when so much goes into the design process, such as material properties, head and shell design, nozzle reinforcement and weld details. Vessel design software eliminates guesswork and saves time since the changes to the code are built into the software.
An important factor in investing in software is the requirement of the designer to understand how ASME compliant pressure vessel software performs the calculations. Transparent formulas and calculations provide third party reviewers and notified bodies with a much simpler task in confirming the proper diligence was taken in the design.
Multiple code requirements exist, meaning that designers must make decisions that are not explicitly stated in a single code. This means that sections of different codes must be used and how the codes interact must be understood.
An Authorized Inspector must approve the design. A concern may be raised if all calculations are being done by hand. Homegrown tools are tougher to prove in regard to compliance, and inspectors are usually more comfortable with commercially supported ASME compliant pressure vessel software. Even if you’ve been using the same calculation for several years, inspectors still need to be comfortable with the design process used for each design. Proving an acceptable design with in house spreadsheets may be time-consuming and costly for your company.
Due to the critical nature of designing and manufacturing pressure vessels, that are compliant to all relevant codes, it’s vital for manufacturers to have software that simplifies the complexities involved. For thirty years, the engineers at CEI have worked to create the tools and software that are needed to make safe and cost-efficient pressure vessels.
They have delivered comprehensive software tools that are used by industry professionals at all stages of design and manufacturing, starting with the initial stage of quoting a new project by evaluating long-term pressure vessel reliability.
Authorized Inspector Review of Software Calculations
Authorized Inspectors require that the basis of design calculation used is compliant and proven. Because the safety of pressure vessels is so important, ensuring the design meets code is paramount. This can be difficult due to the complex calculations involved in the design process.
Rarely is pressure vessel design done by hand, and at the least, geometry for the required loadings are checked by excel or Mathcad files. While these tools make the designing of a pressure vessel far easier, it’s natural to question whether the software will yield results compliant with ASME Section VIII code. In order to quell these concerns, QA/QC documents will be used to validate the tools and ensure the vessel meets code.
Design Software Tools Have Major Benefits
Selecting a design tool can be a challenge, but it is a very important component of the process. Here are 5 benefits of pressure vessel design software:
A designer or engineer spending their time, to research and implement code changes and new design requirements, is much more expensive than the cost of a subscription to software that will do that for you.
Designers and engineers may move on from your company at any time, meaning their knowledge goes with them. When you purchase software, you gain a consistent platform that is used to track codes and designs.
Access to an external resource, as a second opinion, helps to ensure decisions are consistent with industry best practices and compliant with Code. Furthermore, engineers will have the benefit of consulting an external resource if there is a problem with a calculation.
Without software, research done across various code books is overwhelming as well as time-consuming. With software, this research is always at the ready and reliable.
Authorizing Inspector Familiarity
Inspectors are generally more comfortable with proven software when compared to homegrown spreadsheet macros. Even if you think you’re saving money by not purchasing software, that money may be lost in research, updating in house tools, and rework from mistakes.
Comprehensive Design Catalogs Save Time
Look for a comprehensive collection of pre-built parts, pieces, and material data in the design catalog. This should include pipe, fittings, flanges, structural shapes, etc. This means that rather than starting from a blank sheet and creating everything by hand, you’ll have a design tool with the necessary components available to complete the design.
You can easily drop dimensions and material properties for every component in the design library, which will lessen the work and risk of making a mistake. Once everything is dropped into the library, you won’t have to worry about tediously looking up every aspect in the ASME Code, because everything in the design library will be code compliant.
When selecting ASME pressure vessel design software look for quality control procedures to capture and integrate the latest code revisions. The software should generate easy to read report formats that allow for quick verification in pressure vessel design code. It is a good sign when the software is designed by engineers and welding experts who are active in the development of the standards their software reflects.
It’s important to note that it’s up to the designers and engineers to guarantee a pressure vessel is up to code. While software and tools can aid in the design, ASME Section VIII states:
“The Code neither requires nor prohibits the use of computers for the design or analysis of components constructed to the requirements of the Code.
However, designers and engineers using computer programs for design or analysis are cautioned that they are responsible for all technical assumptions inherent in the programs they use and the application of these programs to their design.”
MANUFACTURING A PRESSURE VESSEL
Listed below are the 3 major benefits of using pressure vessel software for manufacturing:
1. Integration of 3D Modeling Capability
By combining modeling software with ASME code support, engineers can save significant time. Once the designer has confirmed the vessel is code compliant, they can then export the design to modeling software to finish out the necessary detailing.
This connection goes a long way in preventing reentry of dimensional data. Even more crucial is it helps prevent a mismatch of geometries between the drawing used for fabrication and the design calculations. You don’t want your drawing to call out std wall pipe when your design calculations use XXH.
2. Rapid Selection of Material Properties
The material data required to do a design can be quite extensive. You need allowable stress data for every material at every temperature condition to be considered.
In addition, you at least need things like material density, in order to calculate weight and it’s derivative, seismic loading. If you need to consider compressive stress cases or vacuum, then you need a lot of additional data as well.
Now add in the complexity of a change requirement to use different temperatures than originally planned or different materials. The time saved with dynamic updating of material properties is significant.
3. Lowest Cost Design
When designers can quickly address the details of design from an early stage and quickly adjust to required changes, the manufacturer can offer a more competitive bid and fabricate vessels with the least potential for rework.
Upon completion of vessel construction, there are three pressure tests you'll need to be aware of:
A Hydrostatic Test is a pressure test that fills the pressure vessel with water while removing the air and pressurizing the system up to 1.3 times the designed pressure limit (adjusted for differences in the design state and the test state). Hydro tests are beneficial because once it’s completed, designers know if the vessel can handle the pressure that it’s designed to withstand.
In addition, it is considered safer than a pneumatic test. The downside, is that vessels designed for gas service may have to have additional considerations put in place, just to handle the water weight during this test.
A Pneumatic Test is a pressure test that uses a gas and pressurizes the system up to 1.1 times the designed pressure limit (adjusted for differences in the design state and the test state). Pneumatic tests are intended for special cases where a hydro test is not feasible for the vessel in question and they require some additional considerations.
A Charpy Impact Test is a high strain-rate test that requires a weighted pendulum to swing from a set height hitting a standard notched part. The results of the impact test measures the energy absorbed by the part during the impact, testing the strength of the part. The Charpy test is also referred to as the Charpy V-notch test. This test is not typically performed on the vessel itself; but instead is performed on the materials of construction.
Related Article: Do Pressure Vessel Design Codes Require Charpy Impact Test?
ASME Stamp Requires Compliance for Design, Manufacturing, & Installation
Authorized Inspection Design & Manufacturing
A fundamental principle is that the ASME Stamped pressure vessel must receive an inspection by an authorized “third party" during all stages to verify compliance with the applicable requirements of the Code.
A signature by an authorized third party, certifying that the object has been manufactured in accordance with the requirements thereof, is a key step for the acceptance of boilers and pressure vessels, especially by several bodies involved in the legalization process.
Authorized Inspection of Installation
Besides inspecting pressure vessels in the stages mentioned above, an inspector representing the jurisdiction of installation may need to approve the installation. . After the equipment has been placed into service, an authorized inspector or a representative of the jurisdiction can periodically inspect the compliance with legal requirements defined by local regulations on boilers and pressure vessels.
In addition to all the requirements, any stamped boiler or pressure vessel must comply with all aspects of the Code, meaning it must be designed, fabricated, and examined by a manufacturer holding an Authorization Certificate issued by ASME.
Even when a pressure vessel is designed per the ASME Code, the equipment, itself, may not be ASME stamped. Equipment that has the ASME stamp is usually associated with a quality level, and, therefore, safety.
ASME stamped equipment requires thorough documentation management and stringent inspection procedures. The stamp and associated processes are generally the requirements of the customer and the jurisdiction of installation, to ensure safety and reduce liability.
PRESSURE VESSEL DESIGN PROCESS
Optimize Your Design Process
It is essential that those involved with pressure vessels and pressure vessel design and manufacture are up to speed with the latest codes, rules, and regulations.
It is also essential that purchasers specify pressure vessel code compliance, and that the end-user operates and maintains the pressure vessel in a safe and intended manner. Safety is paramount since it lowers cost, reduces insurance and above all, saves lives.
Much has been said about software license models. A one-time purchase seems easy, but as time passes, software needs to be updated. With a subscription model, you’re always assured of the latest revision of the software, and the latest code changes are included.
The tools that you select work better when you have superior support. If your support person is a phone call or chatbot away, that will help to improve your business and problem resolution time.
By choosing the best material for your project, educating yourself on the appropriate codes, assembling your pressure vessel to industry standards, and using the correct software, the manufacturing of pressure vessels can be a safe and efficient process.
If you are in need of ASME compliant pressure vessel software consider using CEI’s DesignCalcs software and Finglow software. Designed by engineers for engineers, DesignCalcs and Finglow ensures all of your designs are up to the latest codes. With the design library, you can save time and have pressure vessel designs ready for an audit and stamp test.
If you need any more information feel free to reach out to our pressure vessel software experts here at CEI.