Post - weld Heat Treatment

 

Heat Treatment Necessity Judgment: When the welded structure bears a large stress or when high toughness of the welded joint is required, post - weld heat treatment is needed. For example, after welding the key structural parts of a ship or the offshore engineering structures subjected to alternating loads, post - weld heat treatment can eliminate the welding residual stress and improve the structure and performance of the welded joint.

 

Heat Treatment Parameter Control: For example, tempering treatment can improve the hard and brittle structures in the heat - affected zone of welding and improve the toughness of the joint. Generally, the tempering temperature is between 550 - 650℃. The holding time is determined according to factors such as the thickness of the steel plate. Usually, for every 25mm of thickness, the holding time is 1 - 2 hours. The heating rate and cooling rate also need to be reasonably controlled to avoid the generation of new thermal stresses.

 

Welding Environment Control

 

Humidity Control: The humidity of the welding environment has an impact on the welding quality of E32 - grade steel plates. A high - humidity environment is likely to increase the hydrogen content in the weld, leading to hydrogen - induced cracking. Generally, it is recommended to weld in an environment with a relative humidity lower than 90%. If the humidity is high, dehumidifying equipment can be used to reduce the environmental humidity, or wind - proof and rain - proof measures can be adopted to ensure that the welding area is dry.

 

Temperature Control: Besides considering the pre - heating temperature, the ambient temperature during welding is also very important. If the ambient temperature is too low, it will affect the performance of the welding materials and the heat transfer during the welding process. Generally, the ambient temperature should not be lower than 5℃. If it is lower than this temperature, effective pre - heating measures need to be taken to ensure the welding quality.

 

 

 

NV EH32 high Strength Chemical Composition
Grade	The Element Max (%)
	C	Si	Mn	P	S	Al	N
NV EH32	0.18	0.10-0.50	0.9-1.6	0.035	0.035	0.015-0.08	-
	Nb	V	Ti	Cu	Cr	Ni	Mo
	0.02-0.05	0.05-0.10	0.02	0.35	0.20	0.40	0.08

Crack Sensitivity: Pcm = (C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B)%

 

 

 

Weld Quality Inspection

 

Visual Inspection: After welding, visual inspection should be carried out first. Check whether the weld is well - formed. The surface of the weld should be flat, without obvious defects such as cracks, pores, and slag inclusions. The weld reinforcement should meet the design requirements and generally should not exceed 3mm. The width of the weld should be uniform.

 

Non - destructive Testing: Non - destructive testing methods such as ultrasonic testing (UT) and radiographic testing (RT) are used to check whether there are defects inside the weld. Ultrasonic testing can detect internal pores, slag inclusions, lack of fusion and other defects in the weld. Radiographic testing can more intuitively display the defect situation inside the weld. According to the importance of the welded structure and quality requirements, an appropriate proportion of non - destructive testing and the acceptance criteria are determined.

 

 

 

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