Boiler tubes

Boiler tubes form the water walls, economisers, superheaters and reheaters. Carbon steel tubes to ASTM A192 and A210 are used for water walls and economisers; chrome-moly tubes to ASTM A213 T11, T22 and T91 for superheaters and reheaters as steam temperature rises; and austenitic stainless tubes such as TP304H and TP347H for the hottest superheater sections in high-efficiency boilers.

Main steam and reheat piping – P91

Main steam, hot reheat and header piping in modern plants is typically ASTM A335 P91 pipe, whose creep strength allows much thinner walls than P22, reducing weight and thermal stresses. Cold reheat and lower-temperature lines use P11, P22 or carbon steel. Matching alloy steel pipe fittings (A234 WP91, WP22, WP11) and A182 flanges complete the system. Other grades are on the alloy steel pipes and tubes page.

Stainless 304H and 347H

The H grades of stainless steel have controlled carbon (0.04–0.10%) for guaranteed creep strength at high temperature. TP304H and TP347H tubes are used in the final superheater and reheater stages, where their oxidation resistance and strength exceed those of T91. 347H, stabilised with niobium, resists sensitisation and is often preferred for welded components.

Inside the hottest tubes, steam-side oxidation forms scale that can spall and block tubes or erode turbine parts. Fine-grained and shot-peened versions of 304H and 347H, and higher-alloy grades, are specified in some boilers to reduce this; please give the boiler maker's tube specification with the enquiry so the exact grade and processing can be matched.

Feedwater, condensers and balance of plant

Feedwater heaters use carbon steel or stainless U-tubes; condensers use stainless, duplex or titanium heat exchanger tubes depending on cooling water quality. Boiler feed, condensate and cooling water piping uses carbon steel seamless pipes and stainless steel, with A105 flanges and A234 WPB fittings.

IBR certification

In India, pipes and tubes for boilers and steam lines covered by the Indian Boiler Regulations are supplied with IBR certification when the order requires it, with the mill documents and inspection arranged accordingly. Please state the IBR requirement with the enquiry.

Combined-cycle and HRSG plants

Heat-recovery steam generators in combined-cycle plants have many thin-walled finned tubes and headers in carbon steel, T11, T22 and T91, and see frequent start-stop cycles that cause thermal fatigue. Close control of tube and header material, weld quality and heat treatment matters more than in base-load boilers. Gas turbine auxiliary systems use stainless steel for lube oil and fuel lines and carbon steel for cooling water.

Maintenance and spares

Boiler tube failures are a common cause of forced outages, so power stations keep spare tubes, bends and fittings matched to the original specification, size and grade. For planned overhauls, we can supply cut-to-length tubes, pipe and fittings with IBR certification where required, together with mill test certificates and positive material identification to prevent grade mix-ups between carbon and alloy steels that look the same.

Products for power plants

• Seamless pipes and tubes and welded pipes and tubes
• Flanges and pipe fittings in carbon and alloy steel
• Plates and sheets – A516 and A387
• Round bars and fasteners – B16 and high-temperature bolting

All material is supplied with mill test certificates, with PMI and third-party inspection on request. All industries we serve are on the industries page.