Table 3.2 vs Table 5.11 — What Changed?
When D1.1 was reorganized in the 2015 edition, preheat متطلبات moved from Clause 3 to Clause 5. The old Table 3.2 became Table 5.11. The preheat values and four-category structure (A through D) carried over intact. The 2025 edition then expanded the table from 4 categories to 7, adding Categories E, F, and G for hydrogen designators H8 and H4.
If you learned D1.1 from the 2010 or earlier editions, you may still think of this as "Table 3.2." It is the same table with the same logic — just renumbered and expanded. Any WPS that still references Table 3.2 was written to a pre-2015 edition and should be reviewed against the current الكود to confirm the preheat values still match. In most cases they will, but the new Categories E, F, and G may allow reduced preheat if you are using H8 or H4 filler metals.
The 7 Preheat Categories (A Through G)
Table 5.11 assigns each اللحام process and معدن الحشو combination to one of seven categories. The category determines the column you read in the table. Within each column, preheat increases with material السماكة.
| Category | Process / Hydrogen Level | Typical Filler Metals |
|---|---|---|
| A | SMAW with غير منخفض الهيدروجين electrodes | E6010, E6013, E7014, E7024 |
| B | SMAW-LH, GMAW, FCAW, SAW (no H designator) | E7018, ER70S-6, E71T-1 |
| C | Same as B for high-المتانة steels (Group III/IV) | E7018, ER70S-6 on A572 Gr.65 |
| D | H8 designator (Group I/II steels) | E7018-H8, E71T-1-H8 |
| E | H8 designator (Group III steels) | E8018-C1-H8 |
| F | H8 designator (Group IV steels) | E9018-G-H8 |
| G | H4 designator (all steel groups) | E7018-H4, ER70S-6-H4 |
Categories A and B apply to the vast majority of structural fabrication. Category A carries the highest preheat requirements because non-منخفض الهيدروجين electrodes deposit more الهيدروجين القابل للانتشار, increasing cracking risk. Category B covers every other common process. Categories D through G reward tighter hydrogen control with reduced preheat — this is new in D1.1:2025.
How to Read Table 5.11
Reading the table is a three-step process: identify the category from the process and filler metal, select the column for that category, then read across to the thickness band for your material.
Once you have the category, read down that column to the thickness band matching your material. The intersection gives the الحد الأدنى preheat and درجة حرارة بين الممرات in °F and °C.
Understanding Thickness Bands
Categories A through C use four المعيار thickness bands: up to 3/4 in (20 mm), over 3/4 in through 1-1/2 in (20–40 mm), over 1-1/2 in through 2-1/2 in (40–65 mm), and over 2-1/2 in (65 mm). Thicker material requires higher preheat because the greater mass acts as a larger heat sink, pulling heat away from the لحام faster and increasing the معدل التبريد in the المنطقة المتأثرة بالحرارة.
For example, A36 with E7018 (Category B) requires no preheat for material up to 3/4 in thick, 50°F for 3/4–1-1/2 in, 150°F for 1-1/2–2-1/2 in, and 225°F for material over 2-1/2 in. The same steel with E6010 (Category A) would require higher preheat at each thickness band because of the higher hydrogen content.
Categories D through G use variable thickness bands that change depending on the specific steel المواصفة. The preheat values in these categories are generally lower than Categories A through C at the same thickness, rewarding the tighter hydrogen control.
Hydrogen Designators (H4, H8, H16)
The hydrogen designator is the key differentiator between categories. It indicates the الحد الأقصى diffusible hydrogen in the deposited معدن اللحام, measured in milliliters per 100 grams of deposited metal.
H16: 16 mL/100g maximum. This is the baseline low-hydrogen level. SMAW electrodes with an H16 suffix and most standard GMAW/FCAW wires qualify here (Category C for high-strength steels).
H8: 8 mL/100g maximum. Tighter control. Electrodes must be tested and classified to this level. Qualifies for Categories D, E, or F depending on the steel group. In practice, E7018-H8 electrodes are widely available and cost only slightly more than standard E7018.
H4: 4 mL/100g maximum. The tightest hydrogen control available in filler metals. Qualifies for Category G, which offers the lowest preheat requirements. Achieving H4 typically requires careful قطب كهربائي storage and handling — any moisture absorption can push hydrogen above this threshold.
In practice, this means: If your shop is already using E7018-H8 electrodes (many do for quality reasons), you may be able to reduce preheat by switching from Category B to Category D for common structural steels. This saves time and propane on thick-plate work. Check with the engineer — the WPS must specify the hydrogen designator to take the reduced preheat.
Which Category Applies to Your Weld?
The most common question fabricators have is: "I have A992 steel, E7018 electrodes, and 1 in plate — what category?" The answer: Category B, which requires 50°F minimum preheat for 3/4–1-1/2 in thickness. If you switch to E7018-H8, you move to Category D and may get reduced or zero preheat for the same steel and thickness.
For a quick lookup of any steel, process, and thickness combination, use the preheat calculator. It covers all 464 combinations in Table 5.11 and shows the category, minimum preheat, and applicable footnotes.
CWI Exam Tip
CWI Part C question pattern: A question may ask "What is the minimum preheat for A572 Gr.50, 2 in thick, welded with E7018?" The key steps: A572 Gr.50 is a Group II steel. E7018 is SMAW low-hydrogen with no H suffix = Category B. The thickness band is 1-1/2 to 2-1/2 in. Read the Category B column at that thickness band. A common trap: the question may reference "Table 3.2" in the stem — the answer is the same value from Table 5.11, just renumbered.