Introduction to ASME Sec. VIII Div. I and II Code: ASME Section VIII Div. I and II are codes used for the design of Pressure vessels. This Code contains guidelines rules and regulation requirements for pressure vessels as follows:
- Design
- Materials
- Fabrication
- Examinations
- Inspection
- Testing
- Certifications
- Safety
- Restrictions
These requirements mentioned may be mandatory or non-mandatory.
ASME Sec VIII Division 1 vs ASME Sec VIII Division 2
ASME Sec VIII Div. I and II codes seem the same, but they contain some key differences which we will discuss in this article.
| Content | ASME Sec VIII Div I | ASME Sec VIII Div II |
| Design Method | Div. I use the design-by-rule approach | Div. II uses the design-by-analysis approach |
| Design Factor | Design Factor 3.0 is used for the stress (Tensile and Yields) and temperature considerations | In the case of Div. II Class I consider design factor 3.0, whereas in the case of Div. II Class II considers design factor 2.4 for the stress (Tensile and Yield) and temperature considerations. |
| Pressure Range | Pressure upto 3000 PSIG | Pressure ranges from 600 PSIG or higher (but lesser than 10000 PSIG) |
| Design Calculation | Simpler Calculation required | The descriptive calculation is required |
| Design Theory (for failure) | Standard stress theory is used | Maximum distortion energy (von mises criteria) is utilized |
| Testing: Material and Impact | Some restriction on the material and impact testing is required until unless exempted or stated.
Refer to clause UG 20, UCS 66/67 for broad exemption. |
More restrictions on the material.
Impact testing criteria remain the same as in ASME SEC VIII DIV. I |
| NDE (Non-Destructive Examination) requirements | NDE requirements exemption is possible by increasing the design factor. | NDE requirements become more stringent.
In this code Radiographic, dye penetrant, ultrasonic, and magnetic particle test is largely used. |
| Experimental Stress analysis | In normal cases, no requirement for experimental Stress analysis | Experimental Stress analysis is introduced and may be subject to requirements. |
| Welding and fabrication | Different types of weld options (Including butt weld and others) | Butt weld and high penetration (Including Non – Pressure attachment welds) welds are preferred. |
| Fatigue analysis | Fatigue analysis is not mandatory. | AD-160 is used for fatigue analysis. |
| Hydrostatic test pressure | The hydrostatic test pressure is 1.3 times of design pressure. | The hydrostatic test pressure is 1.25 times of design pressure. |
| Hydrotest Stress Calculation | Hydrotest Stress is not limited up to a specific limit and partial penetration welds are allowed. | Calculation of Hydrotest Stress is a mandatory requirement and welds of full penetration are required. |
| Material Cost | High material cost | Lower material cost |
| Allowable stress value at design temperature (same for both cases) | Lower which means a higher design margin. | Higher which means lower design margin. |
| Shell Thickness at design pressure (same for both cases) | Thicker | Thinner |
| Equations for Thickness calculation at minimum design pressure | t = PD/2S -1.2P | t = D/2{Exp (P/S) – 1} |
| Vessels produced annually (Nos.) | Larger | Lower |
| Manufacturers | Manufacturers have to submit data reports along with declaration compliance. | Data report, design certifying report (Specification and code) Compliance. |
| Code stamping and Marking | U code stamp with marking as W, B, P; RES, L, DF, UB, HT & RT |
U2 Code stamping with marking HT |