Stress relieved welds in positive expulsion fuel tanks with rolling metal diaphragms

A method of forming a metallic positive expulsion fuel tank, the method comprising:

• forming a first hemispherical shell having a first circumferential edge;
• forming a metallic cylinder having a first circumferential edge and a second circumferential edge;
• welding the first circumferential edge of the metallic cylinder to the first circumferential edge of the first hemispherical shell along the first circumferential edge of the first hemispherical shell and the first circumferential edge of the metallic cylinder to form a first weld seam;
• forming a hemispherical rolling metal diaphragm having a first circumferential edge;
• attaching the hemispherical rolling metal diaphragm to the metallic cylinder along the first circumferential edge of the diaphragm and the second circumferential edge of the metallic cylinder;
• forming a second hemispherical shell having a first circumferential edge;
• welding the first circumferential edge of the second hemispherical shell to the second circumferential edge of the cylinder along the first circumferential edge of the second hemispherical shell and the second circumferential edge of the metallic cylinder to form a second weld seam and a container with two interior chambers separated by the hemispherical rolling metal diaphragm;
• attaching a pressurized gas inlet fixture to the first hemispherical shell;
• attaching a fuel outlet fixture to the second hemispherical shell;
• and
• performing a localized post-weld stress relief heat treatment on the first and second weld seams in which heating of the metallic positive expulsion fuel tank is confined to a distance of 2 inches (5.08 cm) from the first weld seam and a distance of 2 inches (5.08 cm) from the second weld seam such that stresses in the first and second weld seams are relieved and the rolling metal diaphragm is unaffected by the localized post-weld stress relief heat treatment.