CORROSION RESISTANT OVERLAY WELDING - OPTIONAL REQUIREMENT

Deposit shall comply with UNS N06625 (AWS ERNiCrMo 3) for overlaying of carbon and low alloyed steel. Maximum iron content at the finished surface of the overlay shall not exceed 10 % by weight.

Where overlaying is used to prevent crevice corrosion in seawater systems, alloys with documented crevice corrosion reistance in the as welded overlayed condition shall be used. The deposit shall be accepted by Company.

Overlay of ring type joint grooves shall be in accordance with API 6A.

Heat treatment after overlay welding shall be carried out, as necessary, to meet specified properties. In any case components shall be heat treated as required in the NACE Standard MR0175.

Hardness testing shall be carried out on the qualification test and shall include base material, heat affected zone (HAZ) and fused metal. Vickers hardness HV10 shall be used. The rows of indentations shall be maximum 2 mm below the surface. Examination of HAZ shall be carried out with maximum 0,5 mm distance between the indentations from fusion line, through HAZ into unaffected base material. The hardness for HAZ and unaffected base material shall not exceed the following values:

Metallographic examination shall be carried out on the qualification test for Type 22Cr/25Cr Duplex and Type 6Mo. The testing methods and acceptance criteria shall be as stated in the MDS for the material in question.

The macrosection of the qualification shall show no cracking and complete fusion between base material and overlay weld. The macrosection shall be documented with original photographs.

Corrosion testing shall be carried out on the qualification test for overlay weld of components for sea water bearing services or as agreed. This apply to all materials.

The testing shall be carried out according to ASTM G 48, Method A, and shall show no pitting after 24 hrs exposure

at 40 °C. Maximum weight loss shall be 4,0 g/m2. The sample shall include the crossection from the overlay welded surface into unaffected base material. The test conditions and acceptance criteria shall be as stated on the MDS’ for the material in question.

Thickness of the overlay deposit for corrosion protection after final machinig shall be minimum 3 mm. Normally minimum two layers of weld metal shall be deposited.

Deposit thickness shall be measured. For components with complicated geometry the manufacturer shall establish a procedure for this purpose.

Overlaying shall be carried out to qualified procedures according to ASME IX modified according to this MDS. The qualification shall be carried out on base material of same grade as used in production.

For components with complicated geometry the welding procedure qualification shall be carried out on a representative test piece as agreed with Company.

For Type 22Cr and 25Cr Duplex the component temperature shall not exceed 350 °C. This shall be checked during welding, e.g. with contact pyrometer at the start and end of each string.

The qualification test for these materials shall include Charpy V-notch testing. The test conditions and the acceptance criteria shall be as stated in the applicable MDS’. One set of impact testing shall be carried out with specimens located in the substrate material 2mm below the fusion line between the overlay and the substrate material. The notch shall be perpendicular to the surface

All deposited surfaces shall, after final machining, be 100 % PT examined in accordance ASME VIII, Div.1, App. 8.

No defects are accepted on sealing surfaces.