ASME Code Section 8 Content:

See following Fig; it shows ASME Code Section 8 Content:

This section is divided into three Subsections, Mandatory Appendices, and Nonmandatory Appendices.

Subsection A consists of Part UG, covering the general requirements applicable to all pressure vessels.

Subsection B covers specific requirements that are applicable to the various methods used in the fabrication of pressure vessels.

It consists of Parts UW, UF, and UB dealing with welded, forged, and brazed methods, respectively.

Subsection C covers specific requirements applicable to the several classes of materials used in pressure vessel construction.

It consists of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon and low alloy steels, nonferrous metals, high alloy steels, cast iron, clad and lined material, cast ductile iron, ferritic steels with properties enhanced by heat treatment, layered construction, and low temperature materials, respectively.

For example, if you need to manufacture a pressure vessel with SA 516 Gr.70 material (Carbon Steel), then you need to meet the marked items in above Fig.

Please note that ASME Code Section 8, does not provide you fabrication tolerances except for misalignment and weld reinforcement.

For example, for nozzle orientation, projection, elevation and other required tolerances there are no values in the code, and you may refer to pressure vessel handbooks for such information.

Review the Pressure Vessel Dimension Inspection article for such tolerances.

If you review the ASME Forward statement it clearly says The Code does not address all aspects of construction activities, and those aspects which are not specifically addressed should not be cons

In continuing it says, The Code is not a handbook and cannot replace education, experience, and the use of engineering judgments.

For example, ASME Code Section 8 Div 1 in UG-28 mandates all loading to be considered in pressure vessel design, but the method for calculation of all of them has not been addressed.

For example, the formula for wind or earthquakes is not provided in the ASME Code Section 8, and these items and other similar loading considerations need to be designed by using the information provided in the pressure vessel handbooks.

For ASME pressure vessel manufacture certification, as well as Authorized Inspection Agency certification, Review the Pressure Vessel Certification article.

We Provide TPI Inspection Services in Most Industrial Areas Around the Globe. Click Here for More Information

What is the Summary of Important Points in ASME Code Section 8 ?

1. ASME Code Section 8 edition is issued once every 3 years and addenda, once a year both on July 1st. Edition and addenda become effective on the 1st of January of next year (i.e., 6 months after issue).

2. Thickness of cylindrical shell t = PR/(SE-0.6P) + C

3. Longitudinal weld is more critical because it is subjected to double the stress than Circ. Weld.

4. Weld joint categories A, B, C, D are based on joint locations in the vessel and stress levels encountered. Weld Types (type 1, 2, 3, etc.) describe the weld itself.

5. Depths of 2:1 Ellip. and hemisph. heads are D/4 and D/2 respectively. (D= Head diameter.)

6. Weld Joint categories:

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.

7. 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)

8. For full penetration welds (type 1):

Joint efficiency, E = 100%, 85%, 70%

(For the radiography = Full, Spot, Nil respectively)

9. Radiography marking on name plates (typically for Type-1 welds)

RT-1: (E=1) All butt welds full length radiography

RT-2: (E=1.0) All Cat. A Butt welds Full length, Cat B, spot

RT-3: (E=0.85) Spot radiography of both Cat A and B welds

RT-4: (E=0.7) Partial/No radiography

10. For Welded Heads for E=1, all welds within the head require full length radiography (since they are all Cat. A welds)

11. For seamless heads, E=1, If a) head to shell weld is fully radiographed (if Cat. A), and at least spot radiographed (if Cat. B)

12. Compared to Cylindrical shell, thickness of 2:1 Ellipsoidal head is approx. same as shell, Hemisph. head approx. half and Torisph head is 77% higher.

13. MAWP is calculated for: Working condition (Hot & Corroded). Vessel MAWP is always taken at the Top of the Vessel and is lowest of all part MAWPs adjusted for static pressure.

14. Hydro-Test is Standard Pressure test on Completed Vessels.

Hyd. Test Pr. = 1.3 x MAWP x stress ratio

Insp. Pressure (hydro) = test pr. / 1.3

Min. Test temp. = MDMT + 30F

Max. Inspection temp. = 120F

15. Pneumatic test is performed if hydro is not possible due to design or process reasons. Prior to the test, NDT as per UW-50 is mandatory.

Pneumatic test pressure = 1.1 x MAWP x stress ratio, Pressure should be increased in steps (Total 6).

1st step 50% of test pressure

2nd to 6 step 10% of test pressure

Insp. Pr. (pneumatic) = test pressure /1.1

16. Pressure gauge range should be about twice the test pressure. However, in any case it shall not be lower than 1.5 times and not higher than 4 times the test pressure.

17. Vessel MAWP represents the maximum safe pressure holding capacity of the vessel. Vessel MAWP is measured at top-most point and is lowest of vessel part MAWPs, adjusted for hydrostatic head.

18. For vertical vessels, hydrostatic pressure caused due to liquid with specific gravity = 1, 1ft of height = 0.43 psig. Or 1 mtr of height = 0.1 Bar

19. Total pressure at any point of Vertical vessel is given by:

Total Pr. = Vessel MAWP + h x 0.433.

(h = height from top in ft.)

20. If part MAWP and elevations are known, Vessel MAWP can be calculated by the deducting hydrostatic head from part MAWP.

21. Ext. Pressure is worked out on basis of Geometric factor A (which depends on L/Do and Do/t ratios) and factor B (depends on A, )

Allowable Ext. Pressure, Pa = 4B/(3(Do/t))

22. For values of A falling to the left of material line in the material chart:

Pa = 2AE/(3(Do/t))

23. Name plate shows The Code stamping, MAWP, design temp., MDMT, and Extent of Radiography.

24. ASME materials (SA) shall be used for code stamped vessel fabrication instead of ASTM (A) materials.

25. Reinforcement pad is not required, if the size of finished opening is (UG 36)

Not exceeding 2-3/8 for all thicknesses of vessel

Not exceeding 3-, if vessel thickness is 3/8

26. Reinforcement pad with OD = 2d and thk = vessel thk is always safe (d = diameter of finished opening)

27. Reinforcement limit along vessel wall = 2d

28. Reinforcement limit normal to vessel wall = smaller of 2.5 t or 2.5 tn

29. In reinforcement pad calculations, credit can be taken for area available in shell and nozzle.

30. Fillet weld throat dimension = 0.707 x leg of weld

31. Adequacy of weld sizes shall be checked as required by UW-16. The nozzles construction shall be one of the Code acceptable types.

32. The maximum permitted ovality tolerance (D max D min) shall not exceed 1% of nominal diameter of vessel. If there is opening, then the tolerance can be increased by 2% x d (d = diameter of opening) if measurement is taken within a distance of d from axis of opening.

33. The mismatch tolerances and the maximum allowable weld reinforcement is more strict on longitudinal welds compared to circumferential welds (UW-35).

34. Principle of reinforcement:

Area removed = Area compensated.

Compensation area shall be within reinforcement limits.

35. For use as pressure parts, the plates shall be fully identified. Maximum permitted under tolerance on plates is 0.01 (0.3 mm) or 6% of ordered thickness, whichever is less.

36. All welding (including tack, seal, etc.) shall be done using qualified procedures and welders.

37. Mandatory full radiography in ASME Code Section 8 is required for all welding with thickness exceeding Table UCS-57, and also for lethal service vessels and unfired boilers with Design Pr. More than 50 psig.

38. PWHT is ASME Code Section 8 requirement if thickness exceeds those given in tables UCS-56 (given in notes under the tables). These tables also give min. PWHT temperature and min. holding time (soaking period) based on P-Nos. and thickness respectively.

39. For Furnace PWHT in ASME Code Section 8 , Loading Temperature shall not exceed 800F, heating rate 400 deg F/hr/inch of thickness, cooling rate 500F /hr/inch of thickness. Still air cooling permitted below 800F. During soaking period, temp difference between hottest and coldest part shall not exceed 150F.

40. Minimum overlap for PWHT in multiple heats = 5 ft.

41. For the ASME Code Section 8 impact test requirement, UCS 66 curve. If MDMT-thickness combination falls on or above the curve, impact testing is exempted. Additional exemptions are given as per UG-20(f) and UCS=68 (c).