Welding Inspection of Cryogenic Pressure Vessel and Points for Attention

1. Selection of welding materials

Welding Inspection of Cryogenic Pressure Vessel – The selection of welding materials for low temperature pressure vessel steel must ensure that the welding joints contain the least harmful impurities such as sulfur, phosphorus, oxygen and nitrogen, will obviously reduce the toughness of the welded joint.

When the load is large at low temperature, the same requirement should be applied to the non-pressurized accessory welding joint welded with the low-temperature pressurized component, and the welding material should be selected according to the welding requirement when the load is small.

Low hydrogen basic electrodes for welding pressurized or pressurized components to non-pressurized components of cryogenic pressure vessels should be selected from the shielded metal arc welding of GHT5117“Carbon steel electrodes” and GBT5118“Low alloy electrodes”. Submerged arc welding flux should choose basic or neutral flux.

2. Product welding test plate

The low temperature impact test of ferrite steel product welding test plate is as follows: Ferrite type welding material (except 9% ni steel) should generally be used for welding between ferrite steels. The low-temperature impact test temperature of the welded joint and the requirements of the low-temperature impact energy of the welded joint metal, fusion line and heat-affected zone shall comply with the requirements of the drawings or relevant technical documents and shall not be less than 27J.

The welding material for dissimilar steel welding between ferritic steels is generally selected according to the base material with higher toughness requirement. The impact test temperature of the weld metal shall not be higher than the lower of the base metal on both sides. The welding procedure qualification of dissimilar steel and the heat treatment state of the product welding test plate shall be the same as the final use state of the vessel. Performance tests shall meet the following requirements:

The tensile and bending test requirements of the welded joint are lower than those of the base metal on both sides;
The requirements of low-temperature impact energy shall be in accordance with the drawings or relevant technical documents and shall not be less than 27J. If strictly specified, the fusion line on the lower side of the weld metal and the impact energy of the heat-affected zone shall be the base metal on the lower side of the weld metal, the impact energy of the fusion line and heat affected zone of the higher strength side is required according to the requirements of the higher strength side base material.

3. Points for attention in selection of welding materials for austenitic steels

The selection of welding materials between austenitic steels shall meet the following requirements:

The carbon content of welding joint is less than or equal to 0.01% ;
The chemical composition of the welded joint metal shall meet the requirements of E0-19-10, E00-19-10, E00-23-13 in the GB T983“Stainless steel electrode” and H0CR21NI10, H00cr21ni10, H0cr26ni21 in the GB T4242“Stainless steel wire for welding” in the GB T983“Stainless steel rod and wire for inert Gas metal arc welding”;
When the design temperature is lower than -100 ° C, the low temperature Charpy v-notch impact test should be carried out according to JB 4708< Welding Procedure Evaluation of steel pressure vessel > , and it should meet the requirements of table 4-5 in the standard.

4. Points for attention in welding between ferrite steel and austenitic steel

In general, CR23NI13 or CR26NI21 type high chromium-nickel or nickel-based welding materials should be used in the dissimilar welding between ferrite steel and austenitic steel, and stress relief heat treatment should not be carried out after welding. The welding procedure qualification and product welding test plate of this kind of dissimilar steel shall meet the following requirements:

The tensile strength of the welded joint is not less than the minimum value of the minimum tensile strength of the base metal on both sides;
The impact energy of fusion line and heat-affected zone on the side of ferrite steel should be in accordance with the tensile strength of ferrite steel and meet the requirements of Table 4 -5. The impact energy of welded joint metal should also meet the requirements of Table 4 -5;
The joint shall be subjected to a lateral bending test. The test method shall be in accordance with GB150, D = 4A, and no crack defect exceeding 1.5 mm shall be detected in any direction on the tensile surface after the 180 ° bending test, and no crack defect exceeding 3 mm shall be found at the fusion line.

5. On-site bad connection quality monitoring and control points

Field welding of cryogenic pressure vessels must be conducted in strict accordance with the approved welding procedure. First of all, the control of welding line energy, welding line energy will lead to increase in the toughness of the weld and Haz decline. Therefore to minimize overheating, the use of small welding line energy. The supervision of welding line energy can be carried out by controlling the current, voltage, welding speed and stipulating the welding length of each electrode.

In multi-pass welding should be as far as possible to reduce the temperature between the welds (interlayer temperature) , that is, as far as possible not continuous welding. Rapid multi-pass welding is beneficial to grain refinement and improve the toughness of Weld, but this effect can not be achieved if the interlayer temperature is too high.

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