Project Overview

In an ethylene production capacity-expansion project of SINOPEC, thick-wall ASTM A335 P11 seamless pipes are required for the high-pressure steam pipeline distributed in several working zones. ASTM A335 P11 is a ferritic low alloy steel grade for high temperature service with deliberate addition of chromium and molybdenum. It has good creep strength at 450°C-550°C. However, there are some major challenges during its welding process including the hardening of heat-affected zone, cold cracks, PWHT, as well as hot cracks in service.

The specification of ASTM A335 P11 seamless pipes covers(O.D x W.T): Φ323 mm x 45 mm, Φ356 mm x 47 mm, Φ406 mm x 54 mm, Φ508 mm x 66 mm and Φ609 mm x 78 mm. The elevation of the main pipeline structure is respectively old device zone[12.5 m], gasoline hydrogenation equipment [10.0 m], cracking zone [12.0 m], quenching zone [10.5 m], compressing zone [10.5 m and 9 m]. When the ethylene-production system starts, the high-pressure steam generated in the cracking furnace is transferred through the pipeline of ASTM A335 P11 seamless pipes to two turbines in old-device zone and other zones. Considering the severe service condition, 100% X-Ray inspection and 10% magnetic-particles inspection on each welding are required.

Chemical Requirements and Properties

ASTM A335 P11 Chemical Composition %
C	Mn	P	S	Si	Cr	Mo
0.05-0.15	0.30-0.60	≤0.025	≤0.025	0.50-1.00	1.00-1.50	0.44-0.65

*Its mechanical properties has been measured by test: yield strength-347 MPa, tensile strength -482MPa, Elongation-22%.
*The carbon equivalent shall be calculated as per CE = C+Mn/6+(Cr+Mo+V)/5+(Si+Ni+Cu)/15 the result of which is 0.586%.
*The cold cracking susceptibility index Pcm = C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10+5B is 0.24%.

Filler Metal Selection for ASTM A335 P11 Pipes

In light of “filler metal matching base metal” principle, welding wire ER80S-B2 and welding electrode E8018-B2 are selected. See the chemical composition and mechanical properties of the two filler metals listed below:

Chemical Composition of ER80S-B2, %
C	Mn	Si	S	P	Ni	Cr	Mo	Cu	Sn
0.09	0.52	0.49	0.008	0.008	0.04	1.04	0.50	0.004	0.004

Mechanical Properties of ER80S-B2
Tensile Strength, [MPa]	Yield Strength, [MPa]	Elongation, [%[	Impact Test @20°C Ave. [J]
629	550	28	281

Chemical Composition of E8018-B2, %
C	Mn	Si	S	P	Cr	Mo	Sn	Sb
0.07	0.74	0.50	0.009	0.009	1.30	0.52	0.003	0.001

Mechanical Properties of E8018-B2
Tensile Strength, [MPa]	Yield Strength, [MPa]	Elongation, [%[	Impact Test @20°C Ave. [J]
660	570	25	160

Typical Beveling End Design

Preheating Before Welding

The ASTM A335 P11 seamless pipes shall be preheated before welding by electromagnetic coils. Its preheating area and positioning are illustrated below. The preheating temperature shall be controlled between 200°C and 250°C and hold for at least 30 minutes before welding.

Welding Process and Welding Parameters

Gas Tungsten Arc Welding(GTAW) is employed to produce the the preliminary welding seam between two ASTM A335 P11 pipes and manual arc welding(SMAW) should be conducted to fully cover the welding area. The flow rate of argon gas during welding is 10 L per minute. The interpass temperature shall be controlled between 200°C and 250°C. When the welding seam is higher than 15 mm or the welding is finished, a 300-350°C post-heating shall be implemented holding for at least 30 minutes. After welding area cools off, a post-welding heat treatment(PWHT) is conducted to relieve the stress by heating to 600-675°C and holding for 2.5 hours.