This paper reports the optimal use of control zones to achieve required uniformity of temperature distribution in local post weld heat treatment of welds in 9% Cr heat-resistant large pipe system. In this research, local PWHT tests on temperature distribution with different control zones were carried out on 9%Cr steel pipes (OD710 mm × 35 mm and OD575 mm × 35 mm), which was further used for the development of the thermal analysis of the post weld heat treatment model via ABAQUS. The research results revealed:1) the effect of number of control zone on the uniformity of temperature distribution;2) the effect of size of pipe diameter on the circumferential temperature and the through-thickness temperature gradients. This article discusses the possible reasons for the temperature difference at various positions of the pipe caused by the air flow inside the pipe with different control zones. Based on the obtained results, a practical method was designed for the selection the number of circumferential control zones on 9%Cr heat-resistant steel pipeline according to the required degree of temperature distribution uniformity. This paper contributes to the specific knowledge and the generic methodology.

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