Welding and Steel Repair

Shop welding on steel parts, frames, racks and equipment, and both shops take walk-in repair work. The first question on any broken part is whether it is worth welding at all, and the answer depends on the steel, the crack and what the part does.

Why it broke comes before how to fix it. A clean break from one overload is a different problem from a crack that grew slowly under repeated loading. A crack that is simply filled in often comes back beside the weld, so the repair sometimes needs a plate added or the joint changed so the load goes somewhere else.

A crack also has to be stopped before it is welded. Peterbilt's 2024 Heavy Duty Body Builder Manual describes the preparation plainly: drill a hole of 1/4 to 3/8 inch at the end of the crack to prevent it spreading, bevel the crack to allow a better weld, and get full weld penetration along its entire length.

The same manual draws a hard line on what that weld can be trusted for. Peterbilt's frame rails are heat treated and should not be welded, because welding heat nullifies the heat treatment and greatly reduces the rail's tensile strength. The manual gives the crack procedure only as a temporary emergency repair, and says the only permanent repair for a cracked frame member is replacing it. If a cracked truck frame comes in, that is the conversation we start with.

Hardened wear plate brings a specific risk, hydrogen cracking. SSAB, which makes Hardox plate, says its grades resist hydrogen cracking better than other wear resistant steels because of a relatively low carbon equivalent, and still sets out the controls. Preheat the weld area to the recommended minimum temperature. Use processes and consumables that give no more than 5 ml of hydrogen per 100 g of weld metal. Keep the joint clear of rust, grease, oil and frost.

SSAB's other rules are about geometry and heat. Weld starts and stops go at least 50 to 100 mm, about 2 to 4 inches, from a corner, to avoid excess stress there. The root opening should not exceed 3 mm. Tack welds should be at least 50 mm long, with shorter tacks allowed on plate up to 8 mm. For Hardox 400 and 500 the maximum recommended interpass temperature is 225°C, so heat has to be managed on a long repair.

Mixed joints follow a simple rule in SSAB's guidance. When two plates of the same grade but different thickness are welded together, the thicker plate sets the preheat and interpass temperatures. When two different steels meet, the plate needing the higher preheat sets them. A patch on the side of a dump body is exactly that kind of joint.

Bring it to either shop during opening hours: Division Street in Lancaster or Penrose Street in Sun Valley. A photo of the break sent ahead helps settle whether it is worth the trip, and larger jobs on truck bodies are covered on our general repairs and modifications page.