When a project specification calls for SS 347 347H seamless pipe, buyers generally need more than a price and delivery indication. They need confirmation that the material is suitable for the design temperature, fabrication sequence, code basis, and inspection plan. As an ss 347 347h seamless pipes manufacturer, Stancor Tubulars supplies ASTM A312 TP347 and ASTM A312 TP347H seamless stainless steel pipes for refinery, petrochemical, fertilizer, power generation, heat exchanger, and process piping applications where resistance to sensitization after welding and dependable elevated-temperature performance are required.
Grades 347 and 347H are niobium-stabilized austenitic stainless steels derived from the 18Cr-8Ni family. The niobium addition stabilizes carbon and reduces susceptibility to chromium carbide precipitation during thermal exposure, which helps maintain corrosion resistance in welded systems. The higher-carbon 347H variant is commonly selected where improved creep strength and stress rupture resistance are needed for sustained service at elevated temperature.
ASTM A312 TP347 and TP347H Seamless Pipe Overview
347 seamless pipe is generally chosen where post-weld intergranular corrosion resistance and stabilized austenitic structure are important. 347H seamless pipe is typically specified where the piping system will operate for long periods at elevated temperature and the design basis places greater importance on creep properties. Both grades are widely used in high-temperature process service, but they are not automatically interchangeable in every code-governed application.
Typical end-use sectors include:
- Refinery process piping and transfer lines
- Petrochemical and chemical plant headers
- Boiler, superheater, and steam service systems
- Furnace and heater piping
- Fertilizer and ammonia-related process units
- Power plant balance-of-plant and auxiliary piping
347 vs 347H Seamless Pipe: Practical Selection Criteria
The grade decision should be based on service temperature, design stress basis, expected time at temperature, welding procedure, and governing code requirements. In many procurement situations, TP347 is selected where corrosion resistance after welding is the primary concern. TP347H is more often specified for sustained high-temperature duty because its controlled higher carbon content supports better high-temperature strength characteristics.
In practical terms:
- Choose TP347 where stabilization against sensitization and welded corrosion performance are the main drivers.
- Choose TP347H where creep strength, stress rupture resistance, and continuous elevated-temperature service are more critical.
- Confirm code acceptance against the applicable edition of ASTM, ASME, and project specifications before substitution.
- Review welding procedures and heat treatment requirements for the intended fabrication route.
Superheater lines, hot process headers, steam service, and furnace-related piping frequently move toward 347H seamless stainless steel pipe. Where the service is less creep-driven and more corrosion-focused, standard 347 stainless steel seamless pipe may be the more appropriate choice.
Chemical Composition and Mechanical Property Reference
Project teams often request a quick comparison between the two grades during technical evaluation. The table below summarizes the practical distinction at a high level. Final compliance should always be verified against the latest applicable ASTM/ASME specification and approved mill test certificates.
| Parameter | TP347 | TP347H |
|---|---|---|
| UNS designation | S34700 | S34709 |
| Steel type | Niobium-stabilized austenitic stainless steel | Niobium-stabilized austenitic stainless steel |
| Carbon level | Standard carbon range | Higher controlled carbon for elevated-temperature strength |
| Primary advantage | Resistance to sensitization after welding | Improved creep and stress rupture performance |
| Typical service focus | Corrosion-sensitive welded piping | Sustained high-temperature piping |
| Common supply standard | ASTM A312 / ASME SA312 | ASTM A312 / ASME SA312 |
| Condition | Seamless, solution annealed, pickled/passivated | Seamless, solution annealed, pickled/passivated |
Manufacturing Scope, Dimensions, and Pipe Schedules
A qualified ss 347 347h seamless pipes manufacturer should supply material with dimensional consistency, heat traceability, and testing aligned to the purchase order and project quality plan. Seamless pipe is commonly supplied in standard pipe sizes with dimensions referenced to ASME B36.19M for stainless steel pipe schedules, subject to customer specification.
Common supply parameters may include:
- Standards: ASTM A312 TP347, ASTM A312 TP347H, ASME SA312
- Manufacturing route: seamless
- Size range: NPS-based pipe sizes, subject to mill capability
- Wall thickness: Sch 5S, 10S, 40S, 80S and heavier schedules as specified
- Length: random, double random, or cut length
- Ends: plain end, beveled end, capped as required
- Surface condition: solution annealed, descaled, pickled, passivated
- Marking: grade, size, schedule, heat number, standard, manufacturer identification
For critical piping systems, dimensional compliance is not only a commercial issue but also a fabrication issue. Outside diameter tolerance, wall thickness consistency, straightness, end finish, and ovality can affect fit-up, welding productivity, and field installation.
Testing, Inspection, and Documentation Requirements
For industrial procurement, documentation quality often matters as much as the pipe itself. Buyers typically expect full traceability from raw material to dispatch, supported by inspection and test records. Depending on the project, the supply package may include mandatory standard tests as well as supplementary examinations.
Typical requirements include:
- Mill test certificate to EN 10204 3.1 or as specified
- Heat number traceability on each pipe and bundle
- Chemical analysis and mechanical test results
- Hydrostatic test or non-destructive electric test per ASTM A312
- Flattening and flaring tests where applicable
- Positive Material Identification (PMI) on request
- Intergranular corrosion testing where project-specific
- Hardness verification and grain size checks where required
- Third-party inspection by client-approved agencies
- Visual and dimensional inspection before dispatch
For code-sensitive applications, procurement teams should verify whether supplementary requirements are mandatory under the project specification, especially for high-temperature service, corrosion-critical duty, or owner-approved vendor lists.
Applications of SS 347 347H Seamless Pipes
SS 347 seamless pipe and SS 347H seamless pipe are commonly used where a combination of oxidation resistance, weldability, and elevated-temperature capability is needed. The niobium stabilization makes these grades particularly relevant in systems exposed to thermal cycles or welding-related sensitization concerns.
Representative applications include:
- High-temperature process lines in refineries
- Steam distribution and condensate return systems
- Superheater and reheater related piping
- Thermal oxidizer and furnace piping
- Chemical reactor and transfer piping
- Pressure parts and associated utility lines
Material selection should still be validated against actual process media, chloride exposure, operating pressure, design temperature, and shutdown/startup cycling. Grade selection based solely on a generic stainless steel designation can lead to avoidable service issues.
What Buyers Should Confirm Before Ordering
Before placing an order for ASTM A312 TP347/347H seamless pipe, technical buyers should confirm the following points with the manufacturer or stockholder:
- Exact grade required: TP347 or TP347H
- Applicable standard and edition: ASTM A312 / ASME SA312
- Pipe size, wall schedule, and cut length
- Required testing and supplementary inspection scope
- Documentation level, including MTC and traceability format
- Surface finish and end preparation
- Third-party inspection hold points, if any
- Packing, marking, and dispatch requirements for export or site delivery
This approach reduces the risk of substitution, documentation mismatch, or non-conformance during receipt inspection and project audit.
Supply Considerations from Stancor Tubulars
At Stancor Tubulars, supply of SS 347 347H seamless pipes is aligned to industrial procurement requirements rather than generic retail listing formats. That means emphasis on specification conformity, traceability, inspection readiness, and practical support for project documentation. For buyers comparing multiple sources, the relevant evaluation factors are standard compliance, test coverage, dimensional control, and clarity on whether the offered pipe is suitable for the intended temperature regime.
Where required, material can be reviewed against project-specific requirements for testing, marking, inspection release, and dispatch documentation. This is particularly important for refinery, power, and EPC procurement environments where technical compliance is checked line by line.
FAQ
What is the main difference between SS 347 and SS 347H seamless pipe?
The main difference is carbon content and resulting high-temperature performance. SS 347 is generally selected for stabilized corrosion resistance after welding, while SS 347H is preferred for sustained elevated-temperature service where improved creep strength and stress rupture resistance are required.
Which standard is commonly used for 347 and 347H seamless stainless steel pipe?
The most common supply standard is ASTM A312, with the ASME equivalent SA312 used in code-based applications. Buyers should also verify dimensional requirements against ASME B36.19M and any supplementary project specifications.
What documents should a manufacturer provide with SS 347 347H seamless pipes?
Typical documentation includes a mill test certificate to EN 10204 3.1, heat number traceability, chemical and mechanical test results, hydro or NDT records as applicable, dimensional inspection records, and any requested PMI, third-party inspection, or supplementary test reports.