The 9% nickel steel plates are widely used for the construction of cryogenic LNG pressure vessels. Usually, they shall be manufactured in accordance with ASME SA-353/ ASTM A353 in double normalized and tempered (NNT) condition, or ASME SA553/ ASTM A553 Type I in quenched and tempered (QT) condition. The fatigue properties and S-N curves for 9% nickel alloy steel are investigated in this article.

Fig-1 illustrates the stress-number of cycles of failure (S-N) curves for 9% nickel steel specimens, which are furnished in QT or NNT condition, with standard smooth (un-notched) or V-notched surface, respectively. It is concluded that 9% nickel steel is very notch sensitive. Even minor flaws at the surface may reduce the fatigue strength drastically. The test shall be conducted in accordance with ASTM E466.

The low cycle reciprocating beam (strain-controlled) fatigue tests are conducted for 9% nickel alloy steel specimens at 3 different temperatures. The S-N curves are shown in Fig-2. This test shall be performed in accordance with ASTM E606.

The plastic-fatigue behavior of 9% nickel steel in double normalized and tempered and quenched and tempered condition are investigated respectively. As shown in Fig-3, the degree of plastic strain is plotted against cycles to failure.