Home / Code Calculations
Pressure equipment design, calculated to the code your market accepts.
Vessels, exchangers and pressure-retaining components designed and documented under ASME, European and Canadian rules.
DESIGN CODES
Codes and standards we work to.
Vonmises Engineering performs pressure equipment design and code calculations to the following codes and standards.
Design of equipment and components to any other requested code.
DESIGN MARGINS
Why the same vessel comes out at three different thicknesses.
| Code | Allowable stress basis | Design margin |
|---|---|---|
| ASME VIII-1 | lesser of UTS/3.5 and 2/3*Yield | 3.5 on tensile |
| ASME VIII-2 | lesser of UTS/2.4 and 2/3*Yield | 2.4 on tensile |
| EN 13445 — ferritic | lesser of Rp0.2/1.5 and Rm/2.4 | 2.4 tensile, 1.5 yield |
| EN 13445 — austenitic (A ≥ 30%) | Rp1.0/1.5 | 1.5 on 1.0% proof |
| AD 2000 | K/S, from yield or proof stress at temperature | 1.5 design, 1.05 test |
| PED 2014/68/EU | not a design code — sets essential safety requirements | 1.43 test pressure factor |
Values shown are the general basis for common materials at design temperature. Material class, product form and elevated-temperature or creep service change the governing criterion.
What the numbers mean in practice
EN 13445 generally produces the highest allowable stresses of the three families, and ASME VIII-1 the lowest. Two things drive that gap. Austenitic properties in the European code are based on a 1.0% strain offset rather than ASME’s 0.2%, which runs appreciably higher for stainless grades. And the European allowable is taken as the greater of two values, where ASME takes the lesser.
There is a second, quieter difference: EN 13445 considers ultimate tensile strength only at ambient temperature, while both ASME codes take tensile strength at design temperature. On a hot vessel that matters.
Lower margin is not free. Moving from Div 1 to Div 2 buys wall thickness back, but pays for it in analysis, fabrication tolerance and inspection scope. On a small vessel the saving rarely covers the extra engineering; on a heavy-wall or high-volume item it usually does.
HEAT EXCHANGERS
ASME and TEMA — which one does what.
ASME & TEMA
Many people confuse the roles of ASME and TEMA. Heat exchanger design and construction rules are now explicitly covered in ASME Sec VIII-1 and Sec VIII-2, while TEMA focuses on the specific internal components and operational requirements. TEMA also provides design rules widely used as the basis for expansion joint numerical analysis.
Historically, ASME did not have mandatory rules for designing heat exchangers, and TEMA’s simpler, semi-empirical formulas filled that gap for decades. They worked safely, but ASME eventually developed more rigorous methods.
Beyond calculations, TEMA provides standardised configurations — BEM, AES and the rest — so that buyers and manufacturers instantly recognise the exact type. It also dictates critical details such as tolerances and maintenance guidelines.
In short: TEMA is the best practice for how a heat exchanger should perform and be maintained, while ASME is the law for pressure safety.
Plate exchangers — API 662
Provides requirements and recommendations for the mechanical design, materials selection, fabrication, inspection, testing and preparation for shipment of plate-and-frame heat exchangers for use in petroleum, petrochemical and natural gas industries. Applicable to gasketed, semi-welded and welded plate-and-frame heat exchangers.
PIPING & FITTINGS
Piping and Fittings
We provide piping and fitting design calculations to the requested standards. We have developed our own Excel sheets to perform mechanical calculations for commonly used piping codes.
Most commonly used piping codes
| ASME B31.1 | ASME B31.3 | ASME B31.5 | ASME B31.12 | |
|---|---|---|---|---|
| Application | Boiler external piping | Refineries, chemical, pharmaceutical, pulp and paper, semiconductor, cryogenic | Refrigeration and secondary coolant systems | Hydrogen piping and pipelines |
| Basic allowable | lesser of UTS/3.5 and 2/3*Yield | lesser of UTS/3.0 and 2/3*Yield | as B31.3 basis | B31.3 basis, reduced by a material performance factor |
| Service grading | None — single service | Category D, Normal, Category M, High Pressure, High Purity | Refrigerant service | Part IP industrial piping · Part PL pipelines |
| Examination | Largely fixed by pressure and temperature | Scales with fluid category — from spot checks to 100% | Prescriptive for refrigerant joints | More stringent than B31.3 throughout |
| Design responsibility | Operating company | Explicitly assigned to the Owner | Owner and installer | Owner |
Non-Standard Fittings Designed to ASME Code
Standard-compliant fittings are the straightforward case. Fittings such as valves, measurement devices — thermowells, Coriolis meters and various flow meters — Y strainers, sight glasses and expansion joints can be designed to the B31.3 or B31.1 code. We have developed Excel sheets and also use numerical methods to evaluate non-standard fittings. We can provide pressure–temperature ratings for your non-standard fitting catalogue.
Send us the scope. We’ll tell you what it takes.
A design to review, a calculation to stamp, or a full package prepared to your market’s code — start with a drawing and a datasheet.