A telescopic crane boom section intended to form part of a telescopically extensible crane boom, the crane boom section having an elongated main body in the form of a straight tubular beam formed by one single bent metal sheet and consisting of several wall portions (W1-W12) which are distributed about a longitudinal centre axis of the tubular beam and connected to each other via bending corners formed in the metal sheet, wherein: - opposite longitudinal edges of the metal sheet are joined to each other by a welding joint extending in the longitudinal direction of the tubular beam ; - the tubular beam has a vertical plane of symmetry as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam; - a neutral layer of the tubular beam extends across a first lateral wall portion (W1) on a first side of the vertical plane of symmetry and across an opposite second lateral wall portion (W2) on an opposite side of the vertical plane of symmetry ; - the tubular beam has a planar upper wall portion (W3) at its top, wherein this upper wall portion (W3) is perpendicular to the vertical plane of symmetry and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W4-W7); - the tubular beam has a planar lower wall portion (W8) at its bottom, wherein this lower wall portion (W8) is perpendicular to the vertical plane of symmetry and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W9-W12); characterized in: - that the welding joint is located at an upper edge or lower edge of one of said first and second lateral wall portions (W1, W2); and - that each one of said first and second lateral wall portions (W1, W2) has a length (L) that is 5-45% of the height (H) of the tubular beam , as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam . - opposite longitudinal edges of the metal sheet are joined to each other by a welding joint extending in the longitudinal direction of the tubular beam ; - the tubular beam has a vertical plane of symmetry as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam; - a neutral layer of the tubular beam extends across a first lateral wall portion (W1) on a first side of the vertical plane of symmetry and across an opposite second lateral wall portion (W2) on an opposite side of the vertical plane of symmetry ; - the tubular beam has a planar upper wall portion (W3) at its top, wherein this upper wall portion (W3) is perpendicular to the vertical plane of symmetry and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W4-W7); - the tubular beam has a planar lower wall portion (W8) at its bottom, wherein this lower wall portion (W8) is perpendicular to the vertical plane of symmetry and is connected to each one of said first and second lateral wall portions (W1, W2) via one or more intermediate wall portions (W9-W12); - that the welding joint is located at an upper edge or lower edge of one of said first and second lateral wall portions (W1, W2); and - that each one of said first and second lateral wall portions (W1, W2) has a length (L) that is 5-45% of the height (H) of the tubular beam , as seen in a cross-section perpendicular to the longitudinal centre axis of the tubular beam . <EOS>