Stainless Steel Strip Electrode Overlay Welding on Plunger Surfaces

Technical Background and Application Context

This 1998 publication by Jiao Jianguo from Jilin Chemical Industry Company Chemical Equipment Plant describes the application of strip electrode welding (SEW) for stainless steel overlay on plunger surfaces. Plungers are critical components in reciprocating pumps used in chemical processing, where they operate in aggressive media (acids, caustics, chlorides) and experience high cyclic contact stresses from valve seats. The base plunger material is typically carbon steel or low-alloy steel, which provides adequate mechanical strength but insufficient corrosion resistance for chemical service.

Strip electrode welding is a specialized overlay technique that uses a solid metal strip as the filler material, fed continuously alongside a welding electrode (typically a carbon or copper rod). This technique offers several advantages over conventional wire electrode methods for overlay applications, including higher deposition rates, lower dilution, and better compositional control.

Process Description and Parameters

Strip Electrode Welding Fundamentals

In strip electrode welding, the strip serves as the primary filler metal while a consumable electrode (carbon rod, copper rod, or stainless steel rod) provides the arc energy. The strip is fed at a controlled angle (typically 45–60° to the weld line) and melts progressively into the weld pool. The key process variables are:

Parameter	Typical Range	Notes
Strip thickness	3–6 mm	Determines bead height per pass
Strip width	20–50 mm	Determines bead width
Arc voltage	20–35 V	Depends on electrode type
Current density	80–120 A/cm²	Higher than SMAW
Travel speed	100–300 mm/min	Depends on desired bead size
Strip feed angle	45–60°	From the welding direction
Preheat temperature	100–200 °C	For carbon steel substrate
Interpass temperature	≤250 °C	To limit grain growth

Material Selection for Plunger Overlay

The authors selected 304 or 316 stainless steel strip for the overlay, depending on the specific service chemistry:

304 stainless steel – for general acid service without chlorides.
316 stainless steel – for service containing chlorides or where pitting resistance is required.
Transition layer – E309L stainless steel wire or strip to minimize dilution effects.

The dilution rate in strip electrode welding is typically 15–30%, lower than the 30–50% dilution in conventional SMAW overlay. This is because the strip is a solid, continuous source of filler metal rather than a discrete wire that melts into an existing weld pool.

Welding Sequence for Plunger Geometry

Plungers typically have cylindrical surfaces with threaded sections and hardened valve seat areas. The welding sequence must accommodate these geometric features:

Machining preparation – Remove existing hardened layers and threads from the overlay area; machine to a uniform cylindrical surface.
Transition layer – Apply 1–2 passes of E309L wire electrode to create a metallurgically compatible interface.
Overlay passes – Apply 2–4 passes of stainless steel strip to achieve the required thickness (typically 3–5 mm).
Post-weld machining – Machine the overlay to final dimensions and surface finish (Ra ≤ 1.6 μm).

Quality Control and Characterization

Chemical Composition Verification

A critical quality parameter is the chemical composition of the overlay, particularly at the interface where dilution occurs. The authors emphasized sampling from multiple depths to characterize the dilution gradient:

Depth from Surface	Expected Ni (%)	Expected Cr (%)	Phase Structure
0 mm (surface)	8–10	18–20	Austenite + 5–10% δ-ferrite
1 mm	6–8	16–18	Austenite + ferrite
2 mm	4–6	14–16	Mixed austenite-ferrite
3 mm (interface)	2–4	10–14	Ferrite-dominant
Base material	<0.5	<1	Pearlite + ferrite

Mechanical Properties

The overlay must maintain adequate hardness and toughness for plunger service:

Surface hardness – HB 180–230 (annealed condition)
Bond strength – ≥250 MPa (per NB/T 47014 test method)
Corrosion resistance – Intergranular corrosion test per GB/T 4334 (no intergranular attack)
Cyclic fatigue – Minimum 10⁶ cycles at design contact stress

Advantages of Strip Electrode Welding for Plunger Applications

The study highlights several advantages of SEW over alternative overlay methods for plunger applications:

Lower dilution – The continuous solid strip provides a larger volume of filler metal per unit arc energy, resulting in lower base metal dilution and better compositional retention.
Higher deposition rate – 2–3 kg/h compared to 0.5–1 kg/h for SMAW, reducing production time.
Better surface quality – The wide, flat strip produces uniform, smooth beads that require less post-weld machining.
Reduced hydrogen pickup – The strip is typically low-hydrogen, and the process is less susceptible to hydrogen-induced cracking than wire electrode methods.
Good geometric adaptability – The strip can be fed at various angles to accommodate complex plunger geometries.

Defects and Countermeasures

Defect	Cause	Countermeasure
Cracking at interface	High dilution, CTE mismatch	Use transition layer, increase preheat
Excessive dilution	Too thin strip, too high travel speed	Increase strip thickness, reduce travel speed
Surface porosity	Contamination on strip surface	Clean strip, use proper shielding
Uneven bead profile	Inconsistent strip feed	Calibrate feed mechanism, maintain constant angle
Hardness variation	Inconsistent heat input	Monitor voltage and current continuously

Study Insights and Engineering Implications

This work demonstrates the practical applicability of strip electrode welding for precision overlay applications where compositional control and surface quality are critical. The plunger application is representative of many chemical equipment components where stainless steel overlay is required on carbon steel substrates. The relatively low dilution achieved with SEW means that fewer overlay passes are needed to achieve the required surface composition, reducing production costs.

The work also implicitly addresses an important economic consideration: plungers are relatively small components, but they are used in large quantities in chemical plants. The productivity advantages of SEW (higher deposition rate, less post-weld machining) translate directly into cost savings at scale. Engineers working on similar applications should consider SEW as a viable alternative to conventional SMAW or SAW overlay, particularly when compositional purity of the overlay is critical. The technique is well-suited for in-house fabrication shops where the capital investment in specialized SEW equipment is justified by volume production.