NOT YOUR TYPICAL WELDING JOB

Fabricated from ASTM A387 Gr 22 Class 2 Material. This grade of chromium-molybdenum alloy is intended for boilers and pressure vessels used in high temperature service. This material has excellent heat resistance and anti-corrosive/oxidation qualities. The A387 family requires extensive care while welding; more so for grade 22. Appropriate preheat, and sustained elevated temperatures were required during welding to minimize the potential for hydrogen cracking. After welding, a post weld heat treatment (PWHT) was required to minimize the presence of hard zones and stabilize the microstructure of the heat affected zone. To prove the success of our welding practice, a complete Magnetic Particle Inspection was performed both before and after PWHT.

Other uncommon materials used in this fabrication include 253MA – an austenitic, chromium-nickel stainless steel alloyed with nitrogen and reactive elements, used in the region of the hood with highest temperature exposure. Graphalloy bushings – made of self-lubricating, long life material and are custom tailored and press fit which aid in the motion of the hood door. Ceramic Tape with Inconel Threads was used for gasketing between panel sections.

Fabrication was followed by a complete trial assembly in the Lopes shop. Several moving parts on this unit required accurate machining with very tight tolerances. These moving parts were tested through their full range of motion, including a full in-service simulation of the rolling hood door.

The Primary Hood and Door were so much larger/heavier than the area allotted to contain it, reinforcing plates and structural members were designed and installed.

Surface preparation of the final arrangement was completed with a titanium modified inorganic copolymer, a product designed specifically for long term corrosion protection in high temperature atmospheres.