Materials for Carbon Steel Pressure Vessels Subject to Sulfide Stress Cracking

Vessels in sour service should meet the requirements of NACE MR-01-75 as well as the additional requirements of this specification.

1. Shell and Heads

Shell and head material for vessels designed for H2S service should be normalized SA-516-70. The normalizing temperature should not exceed 17500F (9540C).

  1. The hot forming temperature for normalized material should not exceed the normalizing temperature unless the material is re-normalized after hot forming.
  2. Cold formed components should be re-normalized.

Unspecified elements, i.e., Copper, Nickel, Chromium, Molybdenum, Vanadium, Titanium and Columbium, in SA-516-70 material, should conform to the limitations of ASTM A20/A20M Paragraph 7, Table 1.

Corrosion allowance on shell and fittings should be a minimum of 0.125" (3 mm).

Plate should conform to the following chemistry limits:

  • CEq = 0.43 max. [CEq = C + Mn/6 + (Cu + Ni)/15 + (Cr + Mo + V)/5]
  • S = 0.002 wt. % max.
  • P = 0.008 wt. % max.
  • Nb + V = 0.020 wt.% max.

2. Support and Miscellaneous Parts

Vessel supports and non-pressure parts should be fabricated from material complying with ASTM A285 Grade C as a minimum.

ASTM A36 material may be used for structural plates, shapes, and beams.

3. Forgings

Forging material should be in accordance with ASTM A105 [1-1/2 inch (38 mm) and smaller] or ASTM A234 WPR [2 inches (50 mm) and larger], normalized.

4. Pipe

Pipe should be Grade B seamless and in accordance with ASTM A106, normalized.

5. Fittings

Pipe fittings such as weld ells, weld caps, weld reducers, etc., should be SA-234 Grade B or Company approved equal, normalized.

6. Couplings

Threaded connections should not be permitted.

7. Internal Bolting

Bolting material should be SA-193-B7M with SA-194-2HM nuts.

8. Postweld Heat Treatment

Vessels in sour service should be postweld heat treated.

9. Hardness

All carbon steel pressure-containing components, including weld metal and heat affected zones, should not exceed BHN 200, unless otherwise specified by the component's ASTM material specification.

10. Weld Procedure Qualification

Test welds should be made with the lowest weld heat input that will be used in vessel construction, including fillet attachments.

Each weld procedure test should include two micro-hardness traverses of the weld and weld heat affected zones made on a polished cross section of the weldments.

  1. Each hardness traverse should be located 2 mm below the surface of the weld toe.
  2. No hardness reading should exceed HV 248.

11. Internal Coating

Vessels should be internally coated with a product suitable for sour service.

Tags: Sulfide Cracking Stress SSC