{"id":766,"date":"2026-08-17T12:36:41","date_gmt":"2026-08-17T07:06:41","guid":{"rendered":"https:\/\/www.mbmtubes.com\/blog\/?p=766"},"modified":"2026-07-31T12:40:40","modified_gmt":"2026-07-31T07:10:40","slug":"tp347-vs-tp347h-seamless-tubes","status":"publish","type":"post","link":"https:\/\/www.mbmtubes.com\/blog\/tp347-vs-tp347h-seamless-tubes\/","title":{"rendered":"TP347 vs TP347H Seamless Tubes: Understanding the Differences"},"content":{"rendered":"

Demand for stabilized austenitic seamless tubing has climbed alongside higher operating temperatures across refineries and power plants. <\/span>TP 347 stainless steel<\/b><\/a> and its higher carbon variant, TP347H, dominate that space. Governed by ASTM A213 and ASTM A312 specifications, both niobium-stabilized grades share adjacent UNS designations (S34700 and S34709) but differ in their carbon content. This article provides a comparison of composition, mechanical behavior, applications, and the factors that decide the selection between TP247 and TP347H.<\/span><\/p>\n

TP347 vs TP347H Seamless Tubes: Quick Comparison<\/b><\/h2>\n

Procurement teams evaluating quotes often require a high-level summary before reviewing detailed metallurgical specifications. The table sets both grades side by side across the properties that shape purchase decisions, from carbon range to service duty.<\/span><\/p>\n\n\n\n\n\n\n\n\n\n\n
Property<\/b><\/td>\nTP347<\/b><\/td>\nTP347H<\/b><\/td>\n<\/tr>\n
Carbon Content<\/span><\/td>\n0.08% max<\/span><\/td>\n0.04% to 0.10%<\/span><\/td>\n<\/tr>\n
Chromium & Nickel<\/span><\/td>\n17.0 to 20.0% Cr, 9.0 to 13.0% Ni<\/span><\/td>\n17.0 to 20.0% Cr, 9.0 to 13.0% Ni<\/span><\/td>\n<\/tr>\n
High-Temperature Strength<\/span><\/td>\nAdequate up to 538\u00b0C<\/span><\/td>\nHigher allowable stress above 538\u00b0C<\/span><\/td>\n<\/tr>\n
Creep Resistance<\/span><\/td>\nModerate, grain size uncontrolled<\/span><\/td>\nStronger, coarse grain extends life<\/span><\/td>\n<\/tr>\n
Weldability<\/span><\/td>\nWider heat input window<\/span><\/td>\nTighter interpass control needed<\/span><\/td>\n<\/tr>\n
Oxidation Resistance<\/span><\/td>\nScaling resistant to 870\u00b0C<\/span><\/td>\nScaling resistant to 870\u00b0C<\/span><\/td>\n<\/tr>\n
Typical Applications<\/span><\/td>\nHeat exchangers, chemical process lines<\/span><\/td>\nSuper heaters, reheater, furnace tubing<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Two differences carry real engineering weight. TP347H holds a carbon floor of 0.04% that TP347 never guarantees, and it calls for solution annealing near 1095\u00b0C against 1040\u00b0C for the standard grade. Grain size, creep rupture life, and code allowable stress follow from those two requirements. Mills supplying <\/span>Stainless Steel TP347 Seamless Tubes<\/b> often dual certify one heat when chemistry and grain size satisfy both designations.<\/span><\/p>\n

Chemical Composition Compared<\/b><\/h2>\n

Carbon is the major difference between the grades. TP347 caps carbon at 0.08% with no minimum, so a mill can ship material at 0.02% and stay fully compliant. TP347H requires a carbon level between 0.04% and 0.10%. This ensures there is enough carbon to form niobium carbides, which keep the metal strong at extremely high temperatures. Chromium and nickel stay identical across both grades, which explains why aqueous corrosion behavior barely shifts between them. Niobium stabilization differs slightly. TP347 demands niobium at ten times the carbon content, TP347H at eight times, with both capped at 1.00%.<\/span><\/p>\n\n\n\n\n\n\n\n\n\n
Element<\/b><\/td>\nTP347<\/b><\/td>\nTP347H<\/b><\/td>\n<\/tr>\n
Carbon<\/span><\/td>\n0.08 max<\/span><\/td>\n0.04 to 0.10<\/span><\/td>\n<\/tr>\n
Chromium<\/span><\/td>\n17.0 to 20.0<\/span><\/td>\n17.0 to 20.0<\/span><\/td>\n<\/tr>\n
Nickel<\/span><\/td>\n9.0 to 13.0<\/span><\/td>\n9.0 to 13.0<\/span><\/td>\n<\/tr>\n
Niobium<\/span><\/td>\n10 x C min, 1.00 max<\/span><\/td>\n8 x C min, 1.00 max<\/span><\/td>\n<\/tr>\n
Manganese<\/span><\/td>\n2.00 max<\/span><\/td>\n2.00 max<\/span><\/td>\n<\/tr>\n
Silicon<\/span><\/td>\n0.75 max<\/span><\/td>\n0.75 max<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Procurement teams ordering <\/span>Stainless Steel 347 Pipe<\/b> alongside tubing will find ASTM A312 mirrors these limits closely, so one mill heat can cover both product forms.<\/span><\/p>\n

Comparing Mechanical Properties and High-Temperature Performance<\/b><\/h2>\n

Room temperature minimums match across both grades. Differences surface once metal temperature climbs past 538\u00b0C, where creep governs the design calculation rather than yield strength.<\/span><\/p>\n

Tensile Strength<\/b><\/h3>\n

Both grades meet 515 MPa minimum tensile strength in the solution annealed condition. Mill certificates commonly report 590 MPa to 620 MPa, with no consistent gap between the two.<\/span><\/p>\n

Yield Strength<\/b><\/h3>\n

ASTM sets 205 MPa minimum yield for each grade. Coarser grain in TP347H can pull measured yield slightly lower, though both clear the specification without difficulty.<\/span><\/p>\n

Creep Resistance<\/b><\/h3>\n

TP347H resists creep better. Its carbon floor and the ASTM grain size 7 or coarser requirement produce a structure that deforms slowly under sustained load above 550\u00b0C.<\/span><\/p>\n

Stress Rupture Performance<\/b><\/h3>\n

Rupture life at 650\u00b0C favors TP347H by a wide margin. ASME allowable stresses reflect that advantage, permitting thinner walls at the same design pressure in creep range service.<\/span><\/p>\n

Oxidation Resistance<\/b><\/h3>\n

Both grades resist scaling in air to roughly 870\u00b0C continuous and 925\u00b0C intermittent. Chromium drives this behavior, and chromium content stays identical in each specification.<\/span><\/p>\n

Intergranular Corrosion Resistance<\/b><\/h3>\n

Niobium locks carbon into NbC and starves chromium carbide formation across the 425\u00b0C to 815\u00b0C sensitization band. Both grades pass ASTM A262 Practice E after welding.<\/span><\/p>\n

Long Term Thermal Exposure<\/b><\/h3>\n

TP347 loses ductility slowly through thousands of hours near 600\u00b0C. TP347H holds its structure better, which is why boiler codes list it for sustained high-temperature duty.<\/span><\/p>\n

TP347 vs TP347H Seamless Tubes for Different Industrial Applications<\/b><\/h2>\n

Grade selection follows service temperature more than industry label. Each application below names the better-suited grade and gives the reasoning behind that match.<\/span><\/p>\n

Heat Exchangers<\/b><\/h3>\n

TP347 suits most shell and tube service. Metal temperature in condensers and process coolers stays below 538\u00b0C, so the guaranteed carbon floor of TP347H returns nothing measurable.<\/span><\/p>\n

Super Heaters<\/b><\/h3>\n

TP347H governs here. Metal temperature reaches 600\u00b0C to 650\u00b0C, creep rupture strength sets the wall thickness, and the coarse grain of the H grade extends element life.<\/span><\/p>\n

Petrochemical Plants<\/b><\/h3>\n

Both grades appear on one site. Reformer and cracking furnace tubes take TP347H for creep duty, while cooler process and transfer lines run on TP347 without penalty.<\/span><\/p>\n

Power Generation<\/b><\/h3>\n

TP347H carries the load in boiler circuits. ASME assigns it higher allowable stresses above 538\u00b0C, letting designers trim wall thickness on reheater and header tubing at equal pressure.<\/span><\/p>\n

Chemical Processing<\/b><\/h3>\n

TP347 covers reactor and transfer lines. Corrosion performance outweighs creep strength at these temperatures, and chromium and nickel stay identical.<\/span><\/p>\n

High-Temperature Process Piping<\/b><\/h3>\n

TP347H handles sustained exposure above 550\u00b0C. Its coarse grain resists slow deformation across thousands of operating hours, which standard TP347 cannot promise from one heat to the next.<\/span><\/p>\n

Fabrication route matters as much as temperature. Tight U-bends and heavy welding can still favour TP347 near the crossover point.<\/span><\/p>\n

Specification and Fabrication Considerations Compared<\/b><\/h2>\n

ASTM A213 covers seamless tubes for boiler, super heater, and heat exchanger duty, while ASTM A312 covers pipe. Both list 347 and 347H, and mills routinely dual certify. <\/span>Stainless steel seamless tube sizes<\/b> run from 3.2 mm to 127 mm outside diameter with walls between 0.4 mm and 12.7 mm, covering most exchanger and boiler layouts.<\/span><\/p>\n

Welding needs attention either way. Niobium raises the risk of weld metal fissuring, so welders keep heat input low and hold interpass temperature under 150\u00b0C. TP347H allows less latitude here because of its carbon floor. Solution annealing separates the two once more, 1040\u00b0C minimum for TP347 against 1095\u00b0C for TP347H, and that gap affects mill lead time.<\/span><\/p>\n

Key Factors to Consider Before Choosing Between TP347 and TP347H<\/b><\/h2>\n

These considerations resolve most specification requirements. Evaluating them against operational service data ensures an optimal selection rather than simply relying on previously ordered grades.<\/span><\/p>\n