Hydrogen Damage - Environmental Degradation of Metals - page 465

conditions during welding. The use of an appropriate preheat before welding
and a postweld heat treatment are also recommended. For titanium, zirco-
nium, and their alloys, inert gas shielding during welding is required to mini-
mize hydrogen pickup.

7. Oxygen addition . An addition of 0.4-0.7 vol % oxygen effectively inhibits

the embrittlement of steels in gaseous hydrogen environments. However,
such additions are not effective to prevent cracking in hydrogen sulfide gas
environments.

Hydrogen attack can be minimized by the following measures:

1. Material selection . Carbide-forming elements, such as chromium and molyb-

denum, increase the resistance of steel to hydrogen attack. Steels containing
0.5 Mo or, preferably, 1-2.25 Cr and Mo are recommended for use in hydro-
gen atmospheres at high temperatures. Since increased carbon content de-
creases the resistance of steel to hydrogen attack, the carbon content should
be low.
Stainless steels, particularly austenitic stainless steels, are immune to hy-
drogen attack. However, atomic hydrogen will diffuse through these steels
when used as thin cladding material and the nonresistant substrate steel may
be prone to attack.

2. Use of Nelson Curves . Nelson curves (Fig. 8.14) provide the operating limits

of various steels in high-temperature, high-pressure hydrogen service. The
curves are based on long-term refinery experience rather than on laboratory
studies. The curves are revised periodically by the American Petroleum Insti-
tute and the latest data should be consulted for the proper selection of steel.

REFERENCES

1. W. H. Johnson, Iron , Vol. 1, pp. 291 and 452-453, 1873.

2. G. G. Hancock and H. H. Johnson, Trans. Met. Soc. AIME , Vol. 236, pp. 513-516,

1966.

3. G. A. Nelson and R. T. Effinger, Welding J ., Vol. 34, pp. 125-215, 1955.

4. I. M. Berstein, R. Garber, and G. M. Pressouyre, Effect of hydrogen on the behavior

of materials, in Proc. of International Conference , TMS-AIME, New York, 1976,
p. 39.

5. R. M. Latanision and H. Oppenhauser, Met. Trans. A ., Vol. 5, p. 483, 1974.

6. S. P. Lynch and N. E. Ryan, Hydrogen in metals, Proc. of 2nd International Con-

gress , Paris, June 1977; Pergamon Press, Oxford, 1978, Paper 3D12.

7. G. A. Nelson, Proc. Am. Petrol Inst ., Vol. 29MIII, pp. 163-174, 1949.

8. G. M. Pressouyre, Met. Trans. A , Vol. 10A, p. 1571, 1979.

9. C. A. Zapffe and C. E. Sims, Trans. AIME , Vol. 145, pp. 225-261, 1941.

10. J. K. Tien, Effect of Hydrogen on the Behaviour of Materials , A. W. Thomson and

I. M. Bernstein, (eds.), Met. Soc. AIME, New York, 1975, p. 309.