Chemical Composition — EN 13CrMoSi5-5 (1.7337)

Element	Range %	Note
Carbon (C)	0.08–0.15	Controls hardness
Silicon (Si)	0.60–1.00	Key differentiator vs P11
Manganese (Mn)	0.40–0.70
Chromium (Cr)	1.00–1.50	Oxidation + creep
Molybdenum (Mo)	0.45–0.65	Creep strength
Phosphorus (P)	≤0.025
Sulphur (S)	≤0.010

Silicon 0.60–1.00% is the defining characteristic of P12 (1.7337) vs P11 (1.7335, Si ≤0.50%). 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

Property	Value
Tensile Strength (Rm)	440–590 MPa
Yield Strength (Rp0.2, min)	220 MPa
Elongation (A, min)	22%
Charpy KV (min, long.)	40 J at +20°C
Hardness (max)	197 HBW
Delivery condition	Normalised + Tempered
PWHT requirement	690–750°C (mandatory)

P12 (1.7337) vs P11 (1.7335) — Key Differences

Property	P11 (1.7335)	P12 (1.7337)
EN designation	13CrMo4-5	13CrMoSi5-5
Werkstoffnummer	1.7335	1.7337
Si content	≤0.50%	0.60–1.00%
Cr range	1.00–1.50%	1.00–1.50%
Mo range	0.45–0.65%	0.45–0.65%
ASTM equivalent	WP11	WP12
Max service temp	540°C	540°C
Oxidation resistance	Good	Better (Si effect)
PMI distinction	XRF/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 P11 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 P12 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 P12 filler wire — Si-matched filler required to prevent dilution mismatch.

International Equivalent Grades — 1.7337 / P12

Standard	Grade Designation	Composition
EN	13CrMoSi5-5 (W.Nr. 1.7337)	1¼Cr-½Mo-Si, Si 0.60–1.00%
ASTM	A234 WP12 / A335 P12	UNS K11562
ASME	SA-234 WP12	P-No. 4, Group No. 1
BS/BS EN	1A (BS 3602)	1CrMoSi steel
DIN	13 CrMo 4 4 (with Si variant)	Previously DIN 17175

Related alloy steel grades: P11 (1.7335) · P22 (1.7380) · P5 (1.7362) · P91 (1.4903) | ASTM equivalent: ASTM A234 WP12

P12 (1.7337) — 13CrMoSi5-5 Pipe Fittings

Chemical Composition — EN 13CrMoSi5-5 (1.7337)

Mechanical Properties — EN 10253-2 Type B

P12 (1.7337) vs P11 (1.7335) — Key Differences

Applications & PWHT

International Equivalent Grades — 1.7337 / P12

Quote P12 (1.7337) Fittings