General Introduction

In modern coal-fired power plant, there are four crucial steam distribution lines which are now formally referred to as “covered piping systems(CPS)”. The CPS systems include NPS 4 and larger of the main steam, hot reheat steam, cold reheat steam, and boiler feedwater piping systems. They can be classified as subcritical, critical, supercritical, or ultra-supercritical according to the working temperature and working pressure of the boiler. All the 4 steam lines shall be designed & constructed in accordance with ASME B31.1 Power Piping and ASME BPVC Section I Power Boilers with general requirements of long service life and maximum reliability. Considering the high-temperature & high-pressure working conditions, creep strength enhanced ferritic steel shall be chosen as the main material of steam lines. These piping materials generally include ASTM A335 P11, P22, P91, P92, P122 seamless pipes; fittings manufactured to ASTM A234 WP11, WP22, WP91, WP92; flanges and forgings manufactured to ASTM A182 F11, F22, F91, F92, etc. European standard EN 10216-2 can also be referenced.

Four Crucial Steam Lines of Coal-Fired Power Plants

The main steam line refers to the two pipelines constructed between the outlet header of the superheater and the interface of the high-pressure stop valve of the turbine. The hot reheat steam line generally refers to the two pipelines constructed between the outlet header of the reheater and the intermediate-pressure stop valve of the turbine. The cold reheat steam line generally refers to the two pipelines constructed between the venting valve of high-pressure cylinder of the turbine and the inlet header of the reheater. Finally, the boiler feedwater piping system refers to the pipeline between the feedwater pump outlet and the inlet header of the economizer.

Conventional Design-Temperatures and Design-Pressures

Power	Main Steam		Hot Reheat Steam		Cold Reheat Steam		Feed Water Piping
MW	Pressure	Temp.	Pressure	Temp.	Pressure	Temp.	Pressure	Temp.
	MPa	°C	MPa	°C	MPa	°C	MPa	°C
300 *A	17.5	546	4.80	545	4.80	355	27.3	185
600 *A	17.5	546	4.80	545	4.80	355	32.0	185
600 *B	25.4	576	5.42	573	5.42	342	38.0	193
600 *C	25.0	600	5.70	608	5.70	372	39.0	188
660 *C	27.46	610	6.95	608	7.29	408	34.7	299.1
1000 *C	27.46	610	6.42	608	6.42	472	36.7	303.7

*A: subcritical power unit; *B: supercritical power unit; *C: ultra-supercritical power unit.

Typical Material Selection for Steam Lines

Power Unit			Main Steam	Hot Reheat	Cold Reheat	Feed Water
MW	T/°C	P/MPa
200	540	13.7	ASTM A335 P22 O.D355.5 x 50	ASTM A355 P22 O.D508 x 16~17.5	ST45.8, A106 Gr.B O.D558.8 x 14.2	ST45.8 O.D355.6 x 36~40
300	540	18.2	ASTM A335 P22 I.D368.3 x 83.1~95 ASTM A335 P91 O.D448.3 x 40	ASTM A335 P22 I.D635 x 31~33	ASTM A106 Gr.B O.D802 x 21	ST45.8 O.D406.4 x 55
600	540	18.2	ASTM A335 P22 I.D457 x 103~113 ASTM A335 P91 O.D666.6 x 63.2	ASTM A335 P22 I.D870 x 43	ASTM A106 Gr.C O.D1066.8 x 20.6	ASTM A106 Gr.B O.D350 x 51.5
600 *a	566	24.2	ASTM A335 P91 I.D419.1 x 70 I.D298.5 x 50	ASTM A335 P22 I.D654 x 136.5 ASTM A335 P91 I.D648 x 23 I.D914 x 31	ASTM A106 Gr.C O.D711 x 9 O.D1016 x 27	WB36 O.D508 x 50 O.D355.6 x 40
600 *b	600	25	ASTM A335 P92 I.D292 x 73 I.D406 x 100	ASTM A335 P92 I.D883 x 43 I.D616 x 31	ASTM A335 P22 O.D1016 x 30 O.D711 x 22	WB36 O.D355.6 x 40 O.D508 x 55
1000 *b	600	25	ASTM A335 P92 I.D368 x 92 I.D356 x 94 I.D254 x 68 I.D260 x 66	ASTM A335 P92 I.D749 x 38 I.D527 x 28 I.D686 x 42 I.D495 x 31	ASTM A106 Gr.C O.D1219 x 38 ASTM A335 P11 O.D864 x 27 ASTM A335 P22 O.D1219 x 42 O.D 813 x 30	WB36 O.D660 x 65 O.D610 x 60 O.D660 x 65 O.D457 x 50

*a: supercritical power unit; *b: ultra-supercritical unit.
*All specifications are abstracted from the construction of power plant steam lines we have participated in.