Abstract: During field installation, the 12Cr2Mo steel pipes provided by a plant were found to have transverse cracks on the inner surface of them. Investigation tells us such kind of cracks exist commonly in these steel pipes. We examined and analyzed these cracks and for the purpose of avoiding them in the future, proposed that the method of direct rolling should be adopted for the pipes of this specification, and suggested pipe manufactures should perform ultrasonic inspection for both transverse and longitudinal defects.in HP boiler pipes.