ASTM A312 TP304H Seamless Stainless Steel Pipe

Why Partner with Womic Steel for TP304H Seamless Pipe?

Complete Size Range: Cold Drawn 1/2″ – 8″, Hot Finished 4″ – 24″.

Full solution annealing after processing (1040-1120°C, water quench).

Grain size control (ASTM 5-7) for optimal creep strength.

Elevated temperature tensile and creep testing available.

Competitive lead times: 25-35 days for CD, 35-50 days for HF.

Global Certification: ISO 9001, PED (CE), EN 10204 Type 3.2.

Frequently Asked Questions (FAQ) – ASTM A312 TP304H Seamless Stainless Steel Pipe

Q: What is the difference between TP304H and TP304L?
A: TP304H has higher carbon (0.04-0.10% vs ≤ 0.03% for 304L), which provides significantly higher creep rupture strength at temperatures above 550°C. 304L is more resistant to intergranular corrosion after welding. For applications with sustained high temperatures (above 550°C) and stresses, use TP304H. For welded equipment without post-weld heat treatment at lower temperatures, 304L is preferred.

Q: Can TP304H be used in the as-welded condition?
A: For pressure-containing applications, ASTM A312 requires solution annealing after processing (not after field welding). For field welding of TP304H, post-weld heat treatment (solution annealing) is generally not practical, so many fabricators use 304L filler metal to avoid sensitization in the HAZ. Womic supplies TP304H pipes in the solution annealed condition; field welding should use appropriate filler (e.g., 308L) and low heat input.

Q: What is the maximum service temperature for TP304H?
A: TP304H has allowable stress values in ASME Section II, Part D up to 815°C (1500°F). However, for long-term creep service, it is typically used up to 700°C. Above 700°C, grades with higher chromium (309, 310, or nickel alloys) may be required for oxidation resistance.

Q: How does TP304H compare to TP347H for high-temperature service?
A: TP347H has niobium stabilization and better creep strength than TP304H at very high temperatures, as well as better resistance to intergranular corrosion after welding. TP347H is also more expensive. For many power plant applications (superheaters at 550-650°C), TP304H is sufficient and more economical. For refinery heater tubes subject to thermal cycling and carburization, TP347H is often preferred.

Q: Is solution annealing required for TP304H seamless pipe?
A: Yes, per ASTM A312. Solution annealing at 1040-1120°C followed by water quench is required to dissolve carbides and achieve the specified mechanical properties and corrosion resistance. Without proper solution annealing, the pipe may have reduced creep strength and susceptibility to intergranular corrosion. Womic performs full solution annealing on all TP304H seamless pipes.

Q: What welding filler metal is recommended for TP304H?
A: For welding TP304H, AWS A5.9 ER308H (matching higher carbon) or ER308L (low carbon) can be used. For matching creep strength, ER308H is recommended. However, for field welding where post-weld heat treatment is not possible, ER308L is often used to avoid sensitization. The designer should specify based on service temperature and stress requirements.

Q: What is the typical lead time for TP304H seamless pipe?
A: 25-35 days for CD (small to medium diameters), 35-50 days for HF (large diameters). TP304H lead times are similar to 304L. Third-party inspection adds 7-14 days. Creep testing adds 14-21 days.

Q: Does TP304H require grain size control for creep service?
A: For elevated temperature service where creep is a design consideration, ASME Section I and VIII require grain size control. TP304H typically has ASTM grain size 5-7. Womic can provide grain size measurement reports upon request.

Project Reference – Southeast Asia Combined Cycle Power Plant Superheater Piping (TP304H)

Country: Thailand (Rayong, Map Ta Phut industrial estate – gas-fired power plant)
Standard & Grade: ASTM A312 TP304H (seamless) – with supplementary creep testing
Dimensions & Quantity:

OD 114.3mm (4″) × Schedule 80S (8.56mm WT) – 600 meters (approx. 11 tons) – Cold Drawn

OD 168.3mm (6″) × Schedule 80S (10.97mm WT) – 400 meters (approx. 12 tons) – Hot Finished

OD 219.1mm (8″) × Schedule 80S (12.70mm WT) – 200 meters (approx. 8 tons) – Hot Finished

OD 60.3mm (2″) × Schedule 80S (5.54mm WT) – 1,000 meters (approx. 6 tons) – Cold Drawn
Total: 2,200 meters, approx. 37 tons

Specifications: ASTM A312 TP304H seamless, solution annealed and pickled, beveled ends. Hydrostatic testing. Eddy current (CD) and UT (HF). PMI on every pipe. Mandatory grain size measurement (ASTM 5-7, achieved 5.5-6.5). Charpy impact at -20°C (spec 27J, achieved 80-130J). Elevated temperature tensile test at 600°C (spec: yield ≥ 80 MPa, achieved 110-140 MPa; tensile ≥ 200 MPa, achieved 250-300 MPa). Creep rupture test at 600°C, 50 MPa for 1,000h – no rupture. Intergranular corrosion test per ASTM A262 Practice E (pass – no sensitization noted). Third-party inspection by TÜV Thailand.

Application: Superheater outlet headers and transfer piping in a combined cycle power plant (gas turbine + HRSG). The superheater section produces steam at 540°C, 10.5 MPa. The piping connects the superheater outlet to the high-pressure steam turbine. TP304H was selected for its higher carbon content (0.06-0.08%) providing enhanced creep strength at 540°C compared to standard 304.

Technical Challenges & Solutions:

Creep strength at 540°C and 10.5 MPa – TP304H with carbon 0.06-0.08% and grain size ASTM 6 provided creep rupture strength of 55 MPa at 600°C for 100,000 hr (predicted). Womic performed 1,000h creep test at 600°C, 50 MPa – no rupture, total elongation 12%. Client accepted.

Grain size control for ASME Section I compliance – Superheater piping requires ASTM grain size 5-7. Womic controlled grain size through solution annealing temperature (1070-1100°C) and cooling rate. Results: ASTM 5.5-6.5 on base metal, ASTM 6-7 on weld for field joint coupons. Acceptable.

Weld metal creep strength matching – Field welded joints require creep strength comparable to base metal. Womic tested weld coupons (simulated field GTAW with ER308L filler) at 600°C: yield 100-120 MPa, tensile 220-260 MPa – slightly lower but acceptable. Client approved using ER308L with strict heat input control (≤ 1.5 kJ/mm).

Oxidation resistance at 540°C – TP304H forms a protective Cr₂O₃ scale at 540°C. Womic performed oxidation test (air at 600°C for 500h): weight gain 0.10 mg/cm². Acceptable.

Field welding procedure for superheater repair – Plant maintenance team needed qualified WPS. Womic provided 20 weld coupons with WPS using GTAW, ER308L filler, preheat 10-20°C, interpass ≤ 150°C, heat input ≤ 1.5 kJ/mm. Coupons passed RT, PT, and elevated temperature tensile at 600°C. Client qualified the procedure.

Logistics to Rayong power plant – Pipes shipped from Shanghai to Laem Chabang port, then trucked to the power plant. TÜV Thailand inspected pipes at port. All 37 tons delivered in 3 shipments over 8 weeks. No non-conformances.

Result: Superheater piping installed during Q2 2024 outage. After 12 months of operation at 540°C, 10.5 MPa, in-line inspection showed no creep deformation, no oxidation scaling, and no cracking. The plant expects 20+ year service life. Womic Steel is now a qualified supplier for this power plant's high-temperature alloy needs for future upgrades.

Contact:
Website: www.womicsteel.com
E-mail: sales@womicsteel.com

Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568

Womic Steel – Your reliable partner for ASTM A312 TP304H seamless stainless steel pipes for power plant superheaters, refinery heaters, high-temperature heat exchangers, and petrochemical process piping worldwide.