shielding-mison-gas-30.html
AGA CW Handbook A4_32130-UK
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31 when these
steels
are welded, nitrogen loss occurs in the weld, reducing the weld’s spot corrosion resistance. this can be taken into consideration in tig and mag welding with filler material by using a filler material with a suitable composition. in tig welding without filler material, the nitrogen losses can be com- pensated by using the mison ® n2 shielding gas
, which contains 1.8% nitrogen in addition to argon and helium. 7.2.3. root
protection argon can be used as the root shielding gas of all stainless steels. argon is also used for root protection in the welding of unalloyed and low-alloy steels, aluminium, copper and titanium. high-purity nitrogen can also be used for root protection in the welding of austenitic stainless steels. it can also provide benefits when welding high-alloy austenitic and duplex and superduplex steels, because it prevents nitrogen loss in the weld deposit and helps retain a good resistance to spot corrosion. nitrogen can also be used as the root shielding gas for unalloyed and low-alloy steels. the requirements for the purity of the nitrogen are not as high in this application, however. hydrogen reduces oxide formation on the root side. shielding gases containing hydrogen, formier ® 10 (10% hydrogen in nitrogen) and varigon ® h5 (5% hydrogen in argon) can be used for the root protection of austenitic and high-alloy austenitic steels. however, with titanium-stabilised stainless steels, a shielding gas con- taining nitrogen tends to form titanium nitrides which are visible on the root surface of the weld as yellow areas.formier ® 10 is a flammable gas mixture, and special care should be taken in its use. it should not be used for the root protection of tanks due to the danger of explosion. mison ® ar shielding gas is not recommended for use as the root shielding gas for stainless steels, as it tends to cause discolou- ration of the root. shielding gases for stainless steels the root surface of stainless steels must be protected with a root shielding gas. by limiting the protected volume to the immediate vicinity of the root, the flushing time can be kept short. this reduces gas consumption and often also guarantees the best end result. efficient root protection
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