24 July 2021 Urea Class Stainless Steel
316LMOD Urea Class Stainless Steel
UREA 316L Modified grade has been specially developed for Urea plant applications. It is a 316L modified stainless steel with extra-low silicon content and substantial higher molybdenum contents.
The low carbon content, combined with a well balanced chemistry (low silicon and nickel content close to 14%) makes the alloy fully austenitic, free of intermetallic phase precipitations. The ferrite level is kept under 0.5% in the solution annealing and water quenched conditions.
The alloy is designed for improved corrosion resistance properties in Urea- carbonate environments.
Typical chemistry of filler materials to be used is as follow
Cr Ni Mo Mn N
20% 16% 3% 6.5% 0.2%
EN 10088 / EN 10028 ......... X2 Cr Ni Mo 18-14-3 - 1.4435
AFNOR................................Z3 CND 18.14.03
DIN...................................... W.Nr 1.4435
ASTM. ............................... 316L modified
Alloy CLI UREA Modified is a fully austenitic stainless steel which ferrite content is guaranteed less than 0.5% after solution annealing heat treatment (1120-1180C (2048-2156F) /water quenched). The carbon content is kept low while the steel making is optimised in order to improve the cleanliness properties of the steel. The alloy is designed for urea applications (low carbon and silicon contents).
Typical maximum corrosion results required following different specifications after Huey tests (ASTM A262 C - five periods of 48 h.) are : maximum weight loss lower than 3,3m/48 h (130 mg/dm per 24 h.), with a maximum depth for microcracks of 200 碌m in the long direction and 70 碌m in the transverse direction.
Hot forming
Hot forming should be carried out in a temperature range of 1200-950C (2732- 1742F) after the piece has been uniformely heat treated. Final full annealing tremperature is required to obtain the requested microstructure. It will be performed at 1120-1180C (2048-2156F) followed by water quenching.
Cold forming
Due to its fully austenitic microstructure, the alloy can be cold formed without any problem. The higher molybdenum content and cold hardening behaviour of the steel explains that it may require more powerfull equipments than 304 stainless steel.
Pickling
The UREA Modified grade must be used in the as pickled and passivated conditions. Pickling treatment may be performed with a nitro-hydrofluoric acid bath (10-20 % HN03 - 1.5-5% HF) at room temperature (few hours) or 20 minutes approx. at 60C (140F). 10-20% H2SO4 - 1.5-5% HF pickling bath may also be used.
Alloy UREA Modified can be welded with most of the welding processes : TIG, Plasma, MIG welding, as well as SMAW, SAW or FCAW processes.
The alloy is sensitive to hot cracking phenomenon due to its fully austenitic microstructure.
Weld should be performed in order to obtain extra-low ferrite contents, no carbide or nitrides precipitations, low silicon contents as well as no intermetallic phases precipitations.
Higher manganese content products should be considered.
Use basic coated electrodes or fluxes in order to decrease the hot cracking susceptibility. The heat input should be limited to 1,5 kJ/mm and interpass temperature kept below 150C (302F).
Typical corrosion test results in Huey test solution - ASTM A262-C are as follow :
maxi weight loss 3.3 m/48h - 0,54 g/m虏 h with selective attack lower than 200 m.