Weld reinforcement for cryogenic vessels

Definition of Cryogenic Temperature

According to SH/T3525-2015 Petrochemical Welding Code for Low-Temperature Steel, the definition of cryogenic temperature varies depending on the standard. Several references define cryogenic steel temperature as -10°C, -20°C, or -29°C, with a broader range from -20°C to -269°C. For example, the Japanese standard sets -10°C as cryogenic, while the West German DIN standard defines cryogenic steel working temperatures between -20°C and -269°C. Some sources even consider -40°C as cryogenic. In the U.S., the ASME code does not explicitly define cryogenic temperature but uses -20°F (-29°C) as a control indicator, applying consistently to both vessels and pipelines.

Weld reinforcement for cryogenic vessels

According to GB150, cryogenic pressure vessels are defined as those operating at temperatures of -20°C or lower. Meanwhile, GB50517 Construction Quality Acceptance Specification for Petrochemical Metal Pipeline Engineering classifies cryogenic pipelines as those designed for temperatures below -29°C. Therefore, in SH/T3525-2015, cryogenic vessels are defined as those operating at temperatures of -20°C or lower, while cryogenic pipelines are defined as those operating at temperatures of -29°C or lower.

Weld Reinforcement for Cryogenic Vessels

SH/T3525-2015 outlines specific requirements for weld reinforcement in cryogenic steel vessels under section 9.1.3:

1.Butt Joint Welds for Cryogenic Steel Vessels:

The weld reinforcement should not exceed 10% of the wall thickness or 3mm, whichever is smaller.

2.Butt Joint Welds for Piping:

If the thinner wall thickness in the joint is 6mm or less, the external weld reinforcement should not exceed 1.5mm.

If the thinner wall thickness in the joint is greater than 6mm, the external weld reinforcement should not exceed 2.5mm.

3.Internal Surface of Butt Joints:

The weld should be flush with the inner wall of the vessel or pipeline.

4.Fillet Welds:

The welds should have a smooth transition. If not, they should be ground to achieve a smooth surface.

Related article: Type testing of cryogenic valves in pressure piping components