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EN 10253 Type B Specialists
EN 1.7338 10CrMo5-5 ASTM WP11 equivalent ≤540°C

P11 (1.7338) — 10CrMo5-5 Pipe Fittings

1¼Cr-½Mo-Si alloy steel buttweld fittings to EN 10253-2 Type B. The elevated silicon content (0.50–1.00%) distinguishes P11 from P12 (1.7335) and improves oxidation resistance and creep rupture strength at temperatures approaching 540°C. ASTM A234 WP11 / ASME P-No.4 equivalent.

EN Designation
10CrMo5-5
EN 10216-2 / EN 10222-2
Werkstoffnummer
1.7338
W.Nr. per DIN EN system
ASTM Equivalent
A234 WP11
ASME P-No. 4 · UNS K11597

Chemical Composition — EN 10CrMo5-5 (1.7338)

ElementRange %Note
Carbon (C)0.08–0.15Controls hardness
Silicon (Si)0.50–1.00Key differentiator vs P12
Manganese (Mn)0.40–0.70
Chromium (Cr)1.00–1.50Oxidation + creep
Molybdenum (Mo)0.45–0.65Creep strength
Phosphorus (P)≤0.025
Sulphur (S)≤0.010

Silicon 0.50–1.00% is the defining characteristic of P11 (1.7338) vs P12 (1.7335, Si ≤0.35%). The higher Si raises the protective oxide scale quality and improves resistance to steam oxidation and inter-crystalline corrosion.

Mechanical Properties — EN 10253-2 Type B

PropertyValue
Tensile Strength (Rm)410–560 MPa
Yield Strength (Rp0.2, min)275 MPa
Elongation (A, min)22%
Charpy KV (min, long.)40 J at +20°C
Hardness (max)197 HBW
Delivery conditionNormalised + Tempered
PWHT requirement690–750°C (mandatory)

P11 (1.7338) vs P12 (1.7335) — Key Differences

PropertyP12 (1.7335)P11 (1.7338)
EN designation13CrMo4-510CrMo5-5
Werkstoffnummer1.73351.7338
Si content≤0.35%0.50–1.00%
Cr range1.00–1.50%1.00–1.50%
Mo range0.45–0.65%0.45–0.65%
ASTM equivalentWP12WP11
Max service temp540°C540°C
Oxidation resistanceGoodBetter (Si effect)
PMI distinctionXRF/OES needed to confirm Si content — visually identical

Applications & PWHT

  • ›Boiler headers and steam drums — coal-fired and gas-fired power boilers where oxidising flue gas contacts the outer pipe surface
  • ›Superheater and reheater piping — elevated Si gives better protective oxide scale than P12 at the same temperature
  • ›Refinery fired heater coils — where oxidation rate at operating temperature is the selection constraint
  • ›Heat recovery steam generators (HRSG) — intermediate and high-pressure sections
PWHT mandatory: 690–750°C for all P11 welds. Soak time minimum 1 hour per 25 mm wall thickness. Hardness after PWHT ≤197 HBW. Confirm Si content by PMI (XRF or OES) before using P11 filler wire — Si-matched filler required to prevent dilution mismatch.

International Equivalent Grades — 1.7338 / P11

StandardGrade DesignationComposition
EN10CrMo5-5 (W.Nr. 1.7338)1¼Cr-½Mo-Si, Si 0.50–1.00%
ASTMA234 WP11 / A335 P11UNS K11597
ASMESA-234 WP11P-No. 4, Group No. 1
BS/BS EN1A (BS 3602)1CrMoSi steel
DINNo direct DIN 17175 grade (13 CrMo 4 4 is P12, 1.7335)Previously DIN 17175
Related alloy steel grades: P12 (1.7335) · P22 (1.7380) · P5 (1.7362) · P91 (1.4903) | ASTM equivalent: ASTM A234 WP11

Quote P11 (1.7338) Fittings

EN 10253-2 Type B. PWHT time-temperature chart and hardness results on EN 10204 3.1 certificate. PMI (XRF) for Si content confirmation available on request.

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Testing & Inspection

  • ✓ Chemical analysis against EN 10216-2 / EN 10253-2
  • ✓ Tensile test, with impact test where the standard or your order requires it
  • ✓ Hardness check after PWHT
  • ✓ PMI (positive material identification) on every order
  • ✓ Visual and dimensional inspection to EN 10253
  • ✓ NDT (UT, RT, MT or PT) when your order or code calls for it
  • ✓ EN 10204 3.1 certificate as standard; 3.2 with TÜV, Lloyd's Register, Bureau Veritas, DNV or your own inspector

Size Range

DN15–DN600 and larger. Outside diameters follow the EN 10220 / EN ISO 1127 pipe series; wall thickness is matched to your connecting pipe.

SizeOD (mm)
DN 1521.3
DN 2026.9
DN 2533.7
DN 3242.4
DN 4048.3
DN 5060.3
DN 6576.1
DN 8088.9
DN 100114.3
DN 125139.7
DN 150168.3
DN 200219.1
DN 250273.0
DN 300323.9
DN 350355.6
DN 400406.4
DN 450457.0
DN 500508.0
DN 600610.0

Export Documents & Packing

  • ✓ Commercial invoice, packing list and certificate of origin
  • ✓ EN 10204 certificates with heat-number traceability
  • ✓ PED 2014/68/EU and AD 2000-Merkblatt W0 documentation for European projects
  • ✓ Seaworthy wooden cases or pallets, bevel ends protected, marked to your instructions
  • ✓ FOB, CFR or CIF delivery terms
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Frequently Asked Questions: P11 (1.7338) Fittings

How does P11 (1.7338) differ from 13CrMo4-5 (1.7335)?

P11 has a higher silicon content (0.50–1.00%), which improves oxidation resistance and creep rupture strength at temperatures approaching 540°C.

What is the ASTM equivalent of 1.7338?

ASTM A234 WP11, ASME P-No. 4.

Which certificates come with P11 fittings?

EN 10204 3.1 as standard, or 3.2 with third-party inspection, plus PED documentation for European projects.

Supplying an Indian boiler or ASME B16.9 project? The equivalent grade is listed on our group site ibrfittings.com: ASTM A234 WP11 fittings.

Further reading