What's the difference between H4 and H8 electrodes?

H4, H8, and H16 are diffusible hydrogen designators per AWS A5.1/A5.5. H4 means ≤4 mL of diffusible hydrogen per 100 g of deposited weld metal; H8 means ≤8 mL/100g; H16 means ≤16 mL/100g. Lower numbers require stricter packaging and shorter atmospheric-exposure limits. For crack-sensitive applications — A514, A517, high-restraint joints — H4 or H8 is standard practice.

Does AWS D1.1 require electrode conditioning to be documented on the WPS?

D1.1 requires the WPS to identify the filler metal by classification. Baking and storage requirements are governed by AWS A5.1/A5.5 and manufacturer data; they are typically captured on the WPS as supplementary information or in a project electrode-control document that the WPS cross-references. Some owners require explicit baking parameters on the WPS face; others accept a reference to the manufacturer's data sheet by revision number.

At what temperature do you bake E7018 electrodes?

Per AWS A5.1 and most manufacturer data sheets, E7018 electrodes are reconditioned at 500–800°F (260–430°C) for 1–2 hours. The exact range is on the manufacturer's data sheet — always follow the manufacturer's maximum baking temperature, as exceeding it damages the flux coating. After baking, transfer immediately to a holding oven at 250–300°F (120–150°C).

How long can E7018-H4 electrodes be out of the oven?

Per AWS A5.1 Appendix and most manufacturer data, E7018-H4 electrodes from opened cans are typically limited to 4 hours at relative humidity ≤50% before reconditioning or disposal. E7018 without an H suffix may be allowed up to 9 hours in mild conditions. Your project specification or owner requirement may be stricter than the standard. The clock starts when you open or unseal the container.

May 29, 20266 min read

Low-hydrogen electrode conditioning: H4, H8, H16 on a WPS

Moisture in SMAW electrodes causes hydrogen cracking. What H4, H8, H16 designators mean and how to document baking and storage requirements on the WPS.

SMAW AWS D1.1 low hydrogen electrodes

Hydrogen-assisted cracking (HAC), also called hydrogen-induced cracking (HIC) or cold cracking, can occur hours or even days after a weld is completed and visually accepted. It is one of the most common causes of structural weld failure — and one of the most preventable.

The mechanism: atomic hydrogen enters the weld pool at the arc, diffuses into the heat-affected zone (HAZ) during cooling, and causes brittle cracking under residual stress. The three conditions required for HAC are a susceptible microstructure, sufficient hydrogen, and tensile stress. Remove any one of them and the crack doesn't form. For SMAW, hydrogen control starts with the electrode.

The H-designator system

AWS A5.1 (carbon steel SMAW electrodes) and AWS A5.5 (low-alloy steel SMAW electrodes) introduced the optional diffusible-hydrogen designator as a classified suffix. An electrode carrying an H designation has been tested and certified to produce weld metal with diffusible hydrogen at or below the stated limit when the electrode is used within its atmospheric-exposure limit:

H4 — ≤4 mL diffusible hydrogen per 100 g of deposited weld metal
H8 — ≤8 mL/100g
H16 — ≤16 mL/100g

An electrode without an H suffix has not been certified to a hydrogen ceiling. The base classification (E7018) still identifies a low-hydrogen flux formulation — but there is no tested upper bound. For general structural work on A36 and A572, E7018 without an H suffix is widely used. For crack-sensitive applications, the H suffix closes the loop.

Use H4 or H8 whenever you are welding:

Quenched-and-tempered high-strength steels: A514, A517, A710
High-carbon or high-carbon-equivalent base metals
High-restraint joints where residual stresses will be elevated
Joints subject to CVN toughness requirements where hydrogen-flake cracking in the weld metal is a concern

Why moisture is the problem

The flux coating on a low-hydrogen electrode is hygroscopic — it absorbs atmospheric moisture readily. An E7018 rod left on a bench overnight in a humid shop can absorb enough moisture to push its diffusible hydrogen output well above the H8 threshold, regardless of how it left the manufacturer's packaging.

The physics: at the arc, coating moisture becomes steam. At the extreme temperatures of the arc column, steam dissociates into atomic hydrogen and oxygen. Atomic hydrogen dissolves in the molten weld metal with high solubility, then becomes trapped in the solidifying HAZ. As the weld cools and hydrogen solubility drops, diffusion into stressed microstructural sites causes cracking.

The key is that the damage happens after the arc is out — sometimes hours or days later. A weld that passes visual and passes RT on the day of welding can crack in the field.

Reconditioning baking

Reconditioning restores moisture-exposed electrodes. For E7018 and similar low-hydrogen iron-powder coatings, the reconditioning cycle per AWS A5.1 Appendix and most manufacturers is:

Temperature: 500–800°F (260–430°C)
Hold time: 1–2 hours
Oven loading: spread on trays, not piled — heat must reach all electrodes

Always follow the manufacturer's maximum temperature limit. Exceeding it damages or destroys the flux coating, changing the arc characteristics and mechanical properties of the deposited weld metal. A burned coating is not salvageable.

Reconditioning is not an infinite loop. Most manufacturers limit electrodes to one or two reconditioning cycles. If electrodes have been wet (exposed to condensation, rain, or standing water), do not recondition — scrap them.

Holding ovens and quivers

After baking, electrodes go into a holding oven at 250–300°F (120–150°C). A holding oven maintains moisture-free conditions; it does not recondition. Electrodes should move from the reconditioning oven to the holding oven immediately — they should not cool to room temperature between cycles.

Portable rod ovens (quivers) operate at the same 250–300°F range and travel to the weld station. For field work where welders are remote from the shop, quivers keep the current shift's electrode supply within exposure limits. If your WPS or project specification requires "continuous holding," the welder needs a quiver.

Some project specs require quivers for all E7018 work regardless of H designation. That is a contract requirement above the code minimum — it should appear in the project-level welding specification or on the WPS.

Atmospheric-exposure limits

Atmospheric-exposure limits define how long electrodes removed from an oven (or opened packaging) can remain unprotected before moisture absorption exceeds the H-level certification threshold. Limits are specified in AWS A5.1 Appendix A and vary by H designation and ambient relative humidity (RH):

E7018-H4: approximately 4 hours at ≤50% RH
E7018-H8: somewhat longer — check the manufacturer's data sheet
E7018 (no H suffix): up to 9 hours in mild conditions per A5.1 guidance

The clock starts when you unseal the can or remove electrodes from the holding oven, not when you start welding. A rod that has been on a bench for 5 hours in a 70% RH shop environment is suspect for H4 certification regardless of how it was stored before that.

On humid days, shorten the exposure window conservatively — the limits are derived from typical ambient conditions. A monsoon afternoon or a winter shutdown with condensation is not typical.

Documenting on the WPS

The WPS must identify the filler metal by AWS classification — for example, E7018-H4 per AWS A5.1. For electrode conditioning, you have three acceptable documentation approaches:

1. Explicit parameters on the WPS face — list baking temperature range, hold time, atmospheric-exposure limit, and holding oven temperature directly in the WPS supplementary fields. Best practice for A514, high-restraint joints, or any joint where HAC is an identified risk.

2. Reference to the manufacturer's data sheet — note "electrode conditioning per [Manufacturer] data sheet, Rev. [X], dated [date]" on the WPS. The referenced data sheet must be filed in the quality records and retrievable on request.

3. Cross-reference to a project-level electrode-control procedure — some shops maintain a separate controlled document covering all electrode types, baking parameters, holding requirements, and exposure limits. The WPS references the document number and revision. This works well for shops that weld multiple processes and want electrode control centralized.

Whichever approach you use, there must be an auditable chain: an inspector or auditor reviewing the package can trace from the WPS to the specific conditioning requirements, and from the production records to confirmation those requirements were followed.

For a process-level WPS walkthrough using E7018, see SMAW E7018 low-hydrogen WPS. For how hydrogen control interacts with preheat selection, see preheat and interpass temperature on a WPS and carbon equivalent and preheat under AWS D1.1.

Field-control failures to avoid

Opening multiple cans to have a full supply — once open, all electrodes in those cans are on the atmospheric-exposure clock. Open what you can reasonably use in the shift.

Reusing rods from the previous shift without checking time — if they sat overnight on a bench, they need reconditioning before use. Documenting the reconditioning is not optional.

Ignoring humidity — at 80% RH, moisture absorption is rapid and the published exposure limits are conservative baselines, not generous targets.

No oven log — if a third-party audit asks when electrodes were baked and at what temperature, you need a written log. A verbal assertion from the welder does not satisfy the documentation requirement.

Electrode control is a short procedure to write and a simple habit to enforce. The cost of a hydrogen crack in a primary structural member — non-destructive re-examination, weld removal, re-welding, potential structural delay — is not.

Ready to build SMAW procedure documents with correct filler classifications and conditioning notes built in? See WPS generation for D1.1 SMAW procedures.

Rule library based on AWS D1.1:2025; verify against your governing edition.

FAQ

Frequently asked.

What's the difference between H4 and H8 electrodes?: H4, H8, and H16 are diffusible hydrogen designators per AWS A5.1/A5.5. H4 means ≤4 mL of diffusible hydrogen per 100 g of deposited weld metal; H8 means ≤8 mL/100g; H16 means ≤16 mL/100g. Lower numbers require stricter packaging and shorter atmospheric-exposure limits. For crack-sensitive applications — A514, A517, high-restraint joints — H4 or H8 is standard practice.
Does AWS D1.1 require electrode conditioning to be documented on the WPS?: D1.1 requires the WPS to identify the filler metal by classification. Baking and storage requirements are governed by AWS A5.1/A5.5 and manufacturer data; they are typically captured on the WPS as supplementary information or in a project electrode-control document that the WPS cross-references. Some owners require explicit baking parameters on the WPS face; others accept a reference to the manufacturer's data sheet by revision number.
At what temperature do you bake E7018 electrodes?: Per AWS A5.1 and most manufacturer data sheets, E7018 electrodes are reconditioned at 500–800°F (260–430°C) for 1–2 hours. The exact range is on the manufacturer's data sheet — always follow the manufacturer's maximum baking temperature, as exceeding it damages the flux coating. After baking, transfer immediately to a holding oven at 250–300°F (120–150°C).
How long can E7018-H4 electrodes be out of the oven?: Per AWS A5.1 Appendix and most manufacturer data, E7018-H4 electrodes from opened cans are typically limited to 4 hours at relative humidity ≤50% before reconditioning or disposal. E7018 without an H suffix may be allowed up to 9 hours in mild conditions. Your project specification or owner requirement may be stricter than the standard. The clock starts when you open or unseal the container.