ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (2024)

Topics: Blog Pressure Vessel Design

ASME standards for materials are a critical requirement for calculating a design’s safety factor. Materials allowable for use in various applications are covered by their relevant code.

Section II, Part D, of the ASME BPV code. Section II, D tables 1A, 1B, and 3 provide allowable stress data for use in Section 1 (Power Boilers), Section III (Nuclear), Section VIII, Division 1 (Pressure Vessels), and Section XII (Transport Tanks).

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (1)

Material lines listed for use in Section VIII, Division 1; the lines that are good for Section VIII, Division 1 are explicitly marked. Table 1A covers ferrous materials, table 1B covers non-ferrous materials, and table 3 covers bolting material.

In the following, CEI provides an overview of how various material properties impact your pressure vessel design. Concentrating on 3 key aspects;

  1. Allowable Stress
  2. Additional Material Properties
  3. Safety Factor

Screenshots are from CEI’s DesignCalcs, pressure vessel design software. Learn more about using DesignCalcs to reduce design errors and save time on your next design.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (2)

Allowable Stress

ASME Standards Section VIII, Division 1

The allowable stresses are determined by safety factor criteria listed in the appendices in the back of the Section II, D. For the most part, this is determined by four things: the tensile strength, the yield strength, the time dependent properties at higher temperatures (creep), and the product form (bolting, plate, etc). The discussion of creep and time dependent properties is going to be left out of this article; however, if you are looking in SC II, D, and you see an allowable stress that is italicized, that is a value that is governed by creep.

For tensile strength, the code requires a safety factor of 3.5 for non-bolting and 4 or 5 for bolting. In addition, if the product form is welded tube or pipe, a joint efficiency factor of 0.85 is typically applied. This can be seen by several of the notes in the stress tables.

For yield strength, the safety factor in most cases is a ⅔ multiplier, with the joint efficiency factor of 0.85 applied in the same case as for tensile; in some cases a higher value of 90% yield may be used instead of the ⅔ value. The safety factor on yield strength for bolting material is a ⅔ multiplier or a ¼ multiplier. The lines allowing 90% of yield will include a G5 material note.

An allowable stress is determined at several temperature increments up to the allowed maximum temperature. At each of these increments, the allowable is determined based on the ultimate tensile stress, the yield stress, and the creep data. The lowest of the three governs. See Mandatory Appendices 1 and 2 in ASME BPV Section II, Part D, for more information.

ASME Standards Section VIII, Division 2

ASME BPV Section VIII, Division 2, uses a much smaller safety factor on tensile strength than Division 1 does. The safety factor is 2.4 instead of 3.5 for non-bolting (see Mandatory Appendix 10 in SC II, Part D). Note G6 in Table 5A indicates an 85% multiplier like we see for Division 1 allowables, even though the Appendix itself does not spell it out. The yield allowable criteria is the same and the bolting allowables are still from Table 3 (for design by rule).

Allowable Stress Example 1: SA-516 Gr 70 Customary for SC8D1

Allowable stress (S, psi) in 2013 is on page 22, line 6
Yield strength (Sy, psi) in 2013 is on page 578, line 30
Ultimate tensile strength (Su, psi) in 2013 is on page 488, line 8

At 250 degrees S = min(2/3*34200 or 70000/3.5) = 20000 psi

At 650 degrees S = min(2/3*28200 or 70000/3.5) = 18800 psi

At 1000 degrees S is governed by creep data and is 2500 psi; this is less than 2/3*22600 and 69100/3.5

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (3)

Allowable Stress Example 2: SA-249 TP316, High (90% yield basis) Metric for SC8D1

Allowable stress (S, MPa) in 2013 is on page 78, line 9
Yield strength (Sy, MPa) in 2013 is on page 638, line 17
Ultimate tensile strength (Su, MPa) in 2013 is on page 512, line 17.

At 150 degrees S = min(0.9*0.85*161 or 0.85*516/3.5) = 123.17 MPa, which is higher than the listed allowable of 117 MPa. The allowable at this temperature exceeds the listed SF requirements.

At 250 degrees S = min(0.9*0.85*139 or 0.85*502/3.5) = 106.34 MPa, which is very close to the listed allowable of 107 MPa.

At 375 degrees S = min(0.9*0.85*125 or 0.85*495/3.5) = 95.63 MPa, which is very close to the listed allowable of 95.7 MPa.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (4)

Additional Material Properties

Yield Strength

The Yield Strength primarily comes from the Y tables in Section II, Part D. DesignCalcs uses fairly strict criteria when attempting to match an allowable stress line from Tables 1A, 1B, and 3 to a yield line in the Y tables. These criteria include matching on aspects such as min yield strength, spec, and nominal composition.

Sometimes, however, a match using these criteria cannot be made. In these cases, DesignCalcs will follow the steps provided in ASME Section VIII, Division 1, UG-28(c)(2) Step 3, using the material’s listed external pressure chart. If a Y table match cannot be made and the external pressure chart method cannot be used,the yield will be listed as zero for all temperatures.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (5)

Ultimate Strength

The Ultimate Strength comes from the U tables in Section II, Part D. Similar criteria to finding a yield match are used to find an ultimate strength match for an allowable stress line.

If a match from the U-tables cannot be used, DesignCalcs employs a conservative method to find the ultimate strength values; in this case, it is assumed that the tensile strength governs the allowable stress and it is solved for in reverse order. If neither option works, the ultimate strength values will be listed as zero for all temperatures.

Other Values

The density and Poisson’s Ratio valuescome directly from Table PRD in SC II, Part D. All materials that are in the shipping data for DesignCalcs have both. Having a weight of zero is not a conservative assumption most of the time.

The Modulus of Elasticity (MoE) primarily comes from the TM tables in SC II, Part D, and DesignCalcs will use the criteria in these tables to assign MoE values to the allowable stress lines. However, when a clear match cannot be made, a backup method is employed. The external pressure charts (figure form as opposed to table form) include a MoE value at various temperatures. DesignCalcs will grab the MoE from the external pressure chart when it cannot find a TM table match. If neither option works, the MoE values will be zero.

The Mean Coefficient of Thermal Expansion data comes from SC II, Part D TE tables column B. There is not a backup method for this property and it is only used in a few calculations at the moment. Those calculations include calculating a sliding saddle slot length and the differential thermal expansion in a fixed tube exchanger.

Related Article:

Additional Properties Example 1:

This material will back solve for ultimate strength, if necessary, and will get its MoE values from external pressure chart CS-3 as needed.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (6)

Additional Properties Example 2:

This material will back solve for ultimate strength, if necessary, and will get its MoE and Yield Strength values from external pressure chart NFA-12 as needed.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (7)

The designer still needs more flexibility. DesignCalcs provides this with custom materials and manual entry options.

Safety Factor

Previous years of ASME Standards BPV Section VIII, Division 1, used a safety factor of 4 on tensile strength instead of 3.5. Until recently, this safety factor of 4 was still in place for the design of certain DOT vessels. This discrepancy can be handled in DesignCalcs in one of several ways.

The user may set a vessel safety factor of 4 instead of 3.5. In this case the allowable stress will be calculated using 4 instead of 3.5 in equations shown in the examples above; as a safety measure, we do not allow the calculated allowable stress to be more than the allowable stress form the ASME codebook. If instead the designer wishes to use their own values for the 4:1 safety factor, or they wish to use a different safety factor on yield or whatever the criteria may be, the designer may either manually input the values in the component form for each instance or they can create a custom material.

This same approach can be used for materials that are not yet in Section II, Part D, but are included in a materials code case like Code Cases 2402-1 and 2403. It is important to remember that not all jurisdictions will accept code cases; they may also be harder to get accepted by the customer requesting the bid.

More information about custom materials may be found in ourhelp files.

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (8)

ASME Section VIII BPV Code & the Pressure Vessel Safety Factor (2024)


What is the safety factor for ASME Section 8? ›

ASME Standards Section VIII, Division 1

For tensile strength, the code requires a safety factor of 3.5 for non-bolting and 4 or 5 for bolting. In addition, if the product form is welded tube or pipe, a joint efficiency factor of 0.85 is typically applied.

What is ASME BPV Code Section VIII? ›

ASME Code Section VIII highlights construction code for design, manufacturing, inspection, and testing of pressure vessels and covers. It also outlines mandatory requirements, special prohibitions, and non-mandatory guidance for materials, certification, and pressure relief.

How do you calculate the factor of safety of a pressure vessel? ›

Factor of safety=Ultimate Load (Strength)/Allowable Load (Stress) As understood from the above equation the allowable stress is always less than the ultimate failure stress. Hence, the factor of safety is always greater than 1.

What is Section VIII of the boiler and pressure vessel code? ›

This Division of Section VIII provides requirements applicable to the design, fabrication, inspection, testing, and certification of pressure vessels operating at either internal or external pressures exceeding 15 psig. Such pressure vessels may be fired or unfired.

What is an acceptable safety factor? ›

A usually applied Safety Factor is 1.5, but for pressurized fuselage it is 2.0, and for main landing gear structures it is often 1.25. In some cases it is impractical or impossible for a part to meet the "standard" design factor.

What is the minimum safety factor? ›

A FoS of 1 means that a structure or component will fail exactly when it reaches the design load, and cannot support any additional load. Structures or components with FoS < 1 are not viable; basically, 1 is the minimum.

What is ASME Section VIII summary? ›

ASME Section VIII of the code is dedicated to pressure vessels. It gives detailed requirements for the design, fabrication, testing, inspection, and certification of both fired and unfired pressure vessels.

What qualifies as an ASME pressure vessel? ›

Generally, a pressure vessel is a storage tank or vessel that has been designed to operate at pressures above 15 p.s.i.g. Recent inspections of pressure vessels have shown that there are a considerable number of cracked and damaged vessels in workplaces.

What does ASME BPVC stand for? ›

What is the ASME Boiler and Pressure Vessel Code? The ASME Boiler and Pressure Vessel Code, abbreviated to ASME BPVC, is the largest standard developed by the American Society of Mechanical Engineers.

Can factor of safety be less than 1? ›

The factor of safety is the ratio of the allowable stress to the actual stress: A factor of safety of 1 represents that the stress is at the allowable limit. A factor of safety of less than 1 represents likely failure. A factor of safety of greater than 1 represents how much the stress is within the allowable limit.

How do you calculate safety factor? ›

The Factor of Safety of the structure is defined as F = C/D and failure is assumed to occur when F is less than unity.

What is the design pressure for ASME VIII? ›

Pressure ranges in ASME Sec VIII code: Pressure range starts from 15 PSI to 3000 PSI can be designed as per ASME Sec VIII Division 1. Pressure range starts from 3000 PSI to 10,000 PSI can be designed as per ASME Sec VIII Division 2.

What is the ASME Code and why is it important to the pressure vessel design? ›

What is the ASME pressure vessel inspection code? A leading standard for pressure equipment and components worldwide, the ASME Boiler and Pressure Vessel Code (ASME Code) provides requirements for manufacturer certification and quality assurance.

What are ASME VIII Division 2 requirements? ›

Requirements for an ASME Section VIII, Division 2 UDS – Part 1 of...
  • A) Installation Site. ...
  • B) Vessel Identification. ...
  • C) Vessel configuration and controlling dimensions. ...
  • D) Design Conditions. ...
  • E) Operating Conditions. ...
  • F) Design Fatigue Life. ...
  • G) Materials of Construction. ...
  • H) Loads and Load Cases.
Jul 26, 2013

What does a safety factor of 5 to 1 mean? ›

Safety Factor Meaning

It is commonly stated as a ratio, such as 5:1. This means that the wire rope can hold five times their Safe Work Load (SWL) before it will break. So, if a 5:1 wire rope's SWL is 10,000 lbs., the safety factor is 50,000 lbs. However, you would never want to place a load near 50,000 lbs.

Can factor of safety be more than 2? ›

Whereas the value of the safety factor is derived from actual load requirement and how much actual load a body can withstand. For example, if the design factor value for critical automotive components is two. These components should have a minimum FOS equal to or more than 2.

What does a 2 to 1 safety factor mean? ›

A study of gripping strength found a huge range in gripping ability. When considering safety factors, if a rescuer can only hold 30 pounds of force and the force exiting a belay device has 15 pounds of force, the system safety factor is only 2:1 regardless of the strength of the equipment.

What is a 4 to 1 safety factor? ›

In the section covering leaf chain, the Machinery Directive states that the minimum safety factor when lifting a weight should be 4:1. In other words, the leaf chain should be able to lift four times the maximum weight it will be lifting in its working life.

Why do we need partial safety factor? ›

Partial safety factors are used to take account of: possible unfavourable deviations of the characteristic values. possible inaccurate modelling of the characteristic values. uncertainties in the assessment of the effects of actions, geometric properties and resistance model.

What is critical safety factor? ›

The identification of the critical safety factors which are categorized in four main groups consists of safety approach, safety engineering, safety management and safety on construction site will enable appropriate allocation of limited resources.

What is ASME safety standard? ›

ASME standards and safety codes are intended to enhance public safety and offer best practices and applicable regulations within specific industries and jurisdictions. ASME standards are accredited as meeting the criteria of the American National Standards Institute (ANSI).

What is the difference between ASME Section 8 Division 1 and 2? ›

ASME Section VIII, Division 2 is intended for purpose-specific vessels with a defined fixed location. Another major difference between the Division 1 and Division 2 lies in failure theory. While Division 1 is based on normal stress theory, Division 2 is based on maximum distortion energy (Von Mises).

Why is ASME code important? ›

ASME code doesn't just indicate the accuracy, performance and efficiency of pressure vessels, it also ensures that during production of pressure vessels in industries, high level of caution and safety is followed to protect the workers from any kind of dangerous situation.

What is the minimum pressure for pressure vessel? ›

A minimum pressure rating (usually 5.104 N/m2) is used to differentiate pressure vessels from low-pressure tanks. Pressure vessels are designed to meet requirements specified by a team of mechanical engineers, thermodynamics engineers, and process engineers.

What PSI is an ASME pressure vessel? ›

What is the minimum design pressure requiring an ASME label? Design pressures exceeding 15 psig are generally ASME labeled and considered ASME pressure vessels.

How do you find the maximum allowable working pressure for a pressure vessel? ›

MAWP Calculations - Calculate MAWP per locations with variou standard formulas.
  1. MAWP summary for a location.
  2. Cylindrical shells Inside Radius P=SEt/R+0.6t.
  3. Cylindrical shells Inside Radius Division 2 P=SEln((t/R)+1)
  4. Cylindrical shells Outside Radius P=SEt/R-0.4t.

What is the purpose of pressure vessel Code? ›

The ASME Boiler and Pressure Vessel Code (BPVC) is the standard that regulates the design and construction of boilers and pressure vessels.

What is ASME BPV Code Section I? ›

This Section provides requirements for all methods of construction of power, electric, and miniature boilers; high temperature water boilers, heat recovery steam generators, and certain fired pressure vessels to be used in stationary service; and power boilers used in locomotive, portable, and traction service.

Do all pressure vessels need to be certified? ›

The rules of this division cover most pressure vessels that operate below 3,000 psi. In order to be able to manufacture a pressure vessel under this section of the BPVC, your pressure vessel fabricator must be certified by ASME to apply the U certification mark.

What could be happen if the factor of safety is less than design limit? ›

If the factor of safety is less than the limit, you can increase the stability against sliding by using a key lock, as shown in Fig. 8.14.

What does factor of safety depend on? ›

The safety factor depends on the materials and use of an item. Different industries have varying ideas on what FoS should be required. Although there is some ambiguity regarding safety factors, there are some general guidelines across multiple verticals.

What is factor safety ratio? ›

A. tensile stress to working stress.

Why do we calculate factor of safety? ›

A factor of safety increases the safety of people and reduces the risk of failure of a product. When it comes to safety equipment and fall protection, the factor of safety is extremely important. If a structure fails there is a risk of injury and death as well as a company's financial loss.

How is factor calculated? ›

In multiplication, factors are the integers that are multiplied together to find other integers. For example, 6 × 5 = 30. In this example, 6 and 5 are the factors of 30.

What is the maximum factor of safety? ›

Factor of Safety Equation

For a structure to be considered safe, its factor of safety must be greater than 1. A factor of safety that is equal to 1 means that the structure's maximum strength or capacity is equal to its determined design load. This means that the structure would fail if any additional load was applied.

How do you calculate allowable pressure? ›

It is helpful in determining the maximum pressure capacity a pipe can safely withstand. The formula is expressed as P=2St/D, where: P. pressure, psig.

How do you calculate design pressure from operating pressure for a vessel? ›

To calculate the design pressure, first one need to know operating pressure of the system, which is determine by process engineer. Then one need to established maximum operating pressure. Which is as per the rule is MOP = 105% of OP ( P>20 bar) or OP+1 bar (P<20 bar).

What is the determining factor of the pressure rating of the fitting? ›

The pressure rating is affected by the temperature of the service also; the higher the process temperature, the less pressure can be handled by the pipe, fitting and valve body. ANSI Standard B16. 34 is used to determine the pressure temperature relationship, as well as applicable wall thickness and end connections.

What is the most important safety device on a pressure vessel? ›

Pressure reducing or pressure control valves are necessary. Safety valve should be connected nearest (close) to the vessel. It should not be connected where pulsating pressure fluctuates.

What are the parameters should have to be consider before the design of pressure vessel? ›

The critical design parameters for calculating the specification of a pressure vessel are design pressure, maximum allowable working pressure, design temperature, maximum allowable stress, joint efficiency, and corrosion allowance.

Are ASME standards mandatory? ›

ASME cannot force any manufacturer, inspector, or installer to follow ASME standards. Their use is voluntary. Standards become mandatory when they have been incorporated into a business contract or incorporated into regulations.

What is the ASME B31 3 piping code safety factor? ›

Power Piping code ASME B31. 1 uses a maximum SIF of 2.0 for reducers while pipe stress calculation. ASME B31. 3 uses a factor of safety of 3; relatively lower than ASME B31.

What are the pressure limits for ASME Section VIII Div 1? ›

Pressure ranges in ASME Sec VIII code: Pressure range starts from 15 PSI to 3000 PSI can be designed as per ASME Sec VIII Division 1. Pressure range starts from 3000 PSI to 10,000 PSI can be designed as per ASME Sec VIII Division 2.

What is the current ASME standard? ›

5 is a standard published by the American Society of Mechanical Engineers (ASME) to establish rules, symbols, definitions, requirements, defaults, and recommended practices for stating and interpreting Geometric Dimensions and Tolerances (GD&T).

Is ASME a standard or code? ›

ASME is the leading international developer of codes and standards, hereafter referred to as standards, associated with the art, science, and practice of mechanical engineering. ASME is the globally recognized, trusted source of consensus standards since 1884.

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