ASTM A608 High Alloy Heat Resistant Radiant Pipe Centrifugal Casting Tube
Centrifugal Casting Stainless Alloy Reformer tube Radiant Tubes manufacturer
ASTM A608/A608M
Standard Specification for Centrifugally Cast Iron-Chromium-Nickel High-Alloy Tubing for Pressure Application at High Temperatures
ASTM A608 covers centrifugally cast (not wrought) austenitic and ferritic alloy steel pipes that are designed for high-temperature and corrosion-resistant service, such as:
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reformer tubes
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furnace rolls
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petrochemical furnace piping
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heater tubes and manifolds
Pipes produced under A608 are typically used in pressure or structural applications where elevated temperature strength and oxidation resistance are critical.
Manufacturing Process
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Casting method: Centrifugal casting (spun casting)
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Type: Usually austenitic or ferritic-austenitic alloys
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Heat treatment: Solution annealed or as specified by the purchaser
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Condition of supply: Machined to nominal dimensions, or as-cast with machining allowance
Typical grade of ASTM A608 casting pipe
HK 40 is a high-temperature stainless steel alloy specifically engineered for demanding applications where both strength and corrosion resistance are crucial. This alloy exhibits enhanced strength compared to other high-temperature materials, making it suitable for highly stressed components in elevated temperature environments. HK 40 offers good resistance to both oxidizing and reducing process flows, ensuring its suitability for a variety of challenging conditions. Furthermore, it provides good general corrosion resistance, protecting it from degradation in harsh environments. With a service limit of 1875 degrees Fahrenheit (1025 degrees Celsius), HK 40 maintains its structural integrity and resists degradation even under prolonged exposure to heat. Its good weldability and castability further enhance its versatility, making it suitable for complex fabrication and integration into various systems.
ASTM A608 Chemical Requirements
The material shall conform to the requirements as to chemical composition as prescribed in Table 1.
| Grade | Composition, % | |||||||
| Carbon | Manganese | Silicon | Chromium | Nickel | Phosphorus | Sulfur | Molybdenum | |
| HC30 | 0.25–0.35 | 0.5–1.0 | 0.50–2.00 | 26–30 | 4.0 max | 0.04 max | 0.04 max | 0.50 max |
| HD50 | 0.45–0.55 | 1.50 max | 0.50–2.00 | 26–30 | 4–7 | 0.04 max | 0.04 max | 0.50 max |
| HE35 | 0.30–0.40 | 1.50 max | 0.50–2.00 | 26–30 | 8–11 | 0.04 max | 0.04 max | 0.50 max |
| HF30 | 0.25–0.35 | 1.50 max | 0.50–2.00 | 19–23 | 9–12 | 0.04 max | 0.04 max | 0.50 max |
| HH30 | 0.25–0.35 | 1.50 max | 0.50–2.00 | 24–28 | 11–14 | 0.04 max | 0.04 max | 0.50 max |
| HH33 A | 0.28–0.38 | 1.50 max | 0.50–2.00 | 24–26 | 12–14 | 0.04 max | 0.04 max | 0.50 max |
| HI35 | 0.30–0.40 | 1.50 max | 0.50–2.00 | 26–30 | 14–18 | 0.04 max | 0.04 max | 0.50 max |
| HK30 | 0.25–0.35 | 1.50 max | 0.50–2.00 | 23–27 | 19–22 | 0.04 max | 0.04 max | 0.50 max |
| HK40 | 0.35–0.45 | 1.50 max | 0.50–2.00 | 23–27 | 19–22 | 0.04 max | 0.04 max | 0.50 max |
| HL30 | 0.25–0.35 | 1.50 max | 0.50–2.00 | 28–32 | 18–22 | 0.04 max | 0.04 max | 0.50 max |
| HL40 | 0.35–0.45 | 1.50 max | 0.50–2.00 | 28–32 | 18–22 | 0.04 max | 0.04 max | 0.50 max |
| HN40 | 0.35–0.45 | 1.50 max | 0.50–2.00 | 19–23 | 23–27 | 0.04 max | 0.04 max | 0.50 max |
| HT50 | 0.40–0.60 | 1.50 max | 0.50–2.00 | 15–19 | 33–37 | 0.04 max | 0.04 max | 0.50 max |
| HU50 | 0.40–0.60 | 1.50 max | 0.50–2.00 | 17–21 | 37–41 | 0.04 max | 0.04 max | 0.50 max |
| HW50 | 0.40–0.60 | 1.50 max | 0.50–2.00 | 10–14 | 58–62 | 0.04 max | 0.04 max | 0.50 max |
| HX50 | 0.40–0.60 | 1.50 max | 0.50–2.00 | 15–19 | 64–68 | 0.04 max | 0.04 max | 0.50 max |
ASTM A608 Tensile Properties
Tension tests at room temperature are not recommended as acceptance criteria under this specification since the alloys are intended for elevated-temperature service, and room-temperature tests do not have a dependable relationship to elevated-temperature properties. (Where the design of the tubing is based on an assumption of certain minimum creep-rupture properties, one of the supplementary requirements of this specification may be stipulated on the order to ascertain the ability of the material to meet the design properties.)
ASTM A608 Permissible Variation in Dimensions
Machined Tubing (Tubing Machined on Inside and Outside):
8.1.1 The tolerances given in Specification A 999/A 999M shall govern, except that the wall thickness shall not vary over the specified minimum wall thickness by more than 10 % or 1 ⁄ 16 in. [1.6 mm], whichever is greater. There shall be no variation under the specified minimum wall thickness.
8.2 As-Cast Tubing (No Machining or Machined on Inside or Outside):
8.2.1 Outside Diameter (For Tubes Ordered to Outside Diameter):
8.2.1.1 Tubes machined on the outside shall meet the requirements of Specification A 999/A 999M.
8.2.1.2 Tubes not machined on the outside shall meet the permissible variations of Table 2.
| Specified Outside Diameter of Tubing | Permissible Plus or Minus Variations from Specified Outside Diameter | ||
| in. | mm | in. | mm |
| From 2 to 4 | 50 to 100 | 0.08 | 2.0 |
| Over 4 to 12 | 100 to 300 | 0.10 | 2.5 |
| Over 12 to 24 | 300 to 600 | 0.12 | 3.0 |
| Over 24 to 36 | 600 to 900 | 0.16 | 4.1 |
| Over 36 to 54 | 900 to 1350 | 0.25 | 6.4 |
8.2.2 Inside Diameter (For Tubes Ordered to Inside Diameter):
8.2.2.1 Tubes machined on the inside shall meet the requirements of Specification A 999/A 999M.
8.2.2.2 Tubes not machined on the inside shall have permissible variations as agreed upon by the purchaser and the manufacturer.
8.2.3 Wall Thickness—The wall thickness shall not exceed the calculated minimum as cast wall thickness by more than the limits shown in Table 3. The calculated minimum wall thickness shall be equal to the specified minimum wall thickness plus the manufacturer’s allowance for “inside surface feed metal” and outside surface roughness. Upon request, the manufacturer’s allowance shall be furnished to the purchaser.There shall be no variation under the calculated minimum as cast wall thickness. For tubes over 24 up to and including 54 in.[600 to 1350 mm] in diameter the “permissible variations over specified minimum as cast wall thickness” shall be agreed upon by the manufacturer and the purchaser.
| Specified Outside Diameter of Tubing | Permissible Plus or Minus Variations from Specified Outside Diameter | ||
| in. | mm | in. | mm |
| From 2 to 4 | 50 to 150 | 0.08 | 2.0 |
| Over 4 to 12 | 150 to 300 | 0.10 | 2.5 |
| Over 12 to 24 | 300 to 600 | 0.13 | 3.3 |
8.2.4 Length—If definite lengths are ordered, no length of tubing shall be under the length specified and not longer than the tolerance shown in Table 4.
| Outside Diameter of Tube | Permissible Excess Length | ||
| in. | mm | in. | mm |
| From 2 to 12 | 50 to 300 | 1 ⁄ 4 | 6.4 |
| Over 12 to 24 | 300 to 600 | 1 ⁄ 2 | 13 |
| Over 24 to 54 | 600 to 1350 | 1 | 25 |
9. Finish
9.1 Machined Tubing—All tubes shall be reasonably straight and free of rejectable indications. All visual irregularities shall be explored for depths. When the depth encroaches on the specified minimum wall thickness, such irregularities shall be considered rejectable indications.
9.2 As-Cast Tubing:
9.2.1 The outside surface shall be adequately cleaned (such as by shotblasting, sandblasting, wire brushing, grinding, or machining). The metal surface so revealed shall be visually inspected and shall be free of linear discontinuities or other imperfections that encroach on the specified minimum wall of the tube.
9.2.2 Various degrees of surface roughness occur on unmachined tubing. If a specific surface finish is required, it shall be a matter of agreement between the manufacturer and the purchaser.
9.3 Surface Irregularities Not Classified as Rejectable—Visual surface defects that have been explored and that do not encroach on the minimum sound wall thickness shall be blended either by machining or grinding the surface into the surrounding unaffected surface area of the tubing.
9.4 Repair by Welding—Repair of injurious defects by welding shall be permitted and major weld repairs shall be permitted only subject to the approval of the purchaser. Weld repairs shall be considered major if the depth of the cavity prepared for welding exceeds 20 % of the required minimum wall thickness or if the total surface area exceeds 10 in. 2 [65cm 2 ]. Defects shall be completely removed before welding. If defects are linear, complete removal shall be checked by liquid penetrant inspection (Practice E 165). Only qualified operators and procedures in accordance with Practice A 488/A 488M shall be used. All weld repairs shall be subjected to the same inspection standard as the tubing.
10. Pressure Test
10.1 All tubing shall be subjected to an internal air pressure of at least 75 psi [515 kPa] for at least 1 min either while submerged in clear water or with the entire outer surface coated with sulfur-free soap suds at the discretion of the manufacturer.In the usable portion of the tube, leaks are not permitted. If the Hydrostatic Test, Supplementary Requirement S6, is invoked,the exact details of the test and testing procedure shall be clearly defined and made a part of the Ordering Information(3.1.8).
10.2 Leaks may be repaired by welding only if such repair is approved by the purchaser.
Equivalent grades heat resistant steel centrifugal casting tube chart:
| Grade | Corresponding grade | ||||
| HG/T | DIN/EN | ASTM | JIS | ||
| NH25-20 | ZG40CR25NIZ0SI2 | GX40CRNISI25-20 | 1.4848 | HK40 | SCH22 |
| NH20-32NB | ZG14NI32CR20NB | GX10NICRSINB32-30 | 1.4859 | CT15C | SCH34 |
| NH25-35NB | ZG50NI35CR25NB | GX40NICRSINB35-26 | 1.4852 | HP50+NB | SCH24XNB |
| NH25-35MIC | ZG50NI35CR25NB | GX45NICRNB35-25 | 1.4856 | HP50+NB(MA) | |
| NH25-35W | Z50NI35CR25EW4 | HP50+W | |||
| NH28-48-5W | ZG45NI48CR28W5SI2 | G-NICR28W | 2.4879 | NA22H | SCH42 |
| NH30-40-5AL | |||||
| NH35-45MIC | ZG50NI45CR35NBM | GX45NICRSINB45-35 | 1.4889 | ||
| NU25-35-15CO | ZG50NI35CR25CO15W5 | ||||
| NH33-48-15W | |||||
ASTM A608 Centrifugal Casting Tube
Common Applications
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Furnace tubes & radiant coils
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Petrochemical reformer tubes
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Ethylene cracking furnace manifolds
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Waste incinerator piping
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Reheater and superheater tubes
Equivalent / Related Standards
| Standard | Description | Related Grade |
|---|---|---|
| ASTM A297 | Heat-resistant steel castings (static) | HK, HP, HF, etc. |
| ASTM A351 | Austenitic stainless steel castings for pressure service | CF8M, CF3M, etc. |
| ASTM A744 | Corrosion-resistant castings for chemical industry | Similar chemistry |
| EN 10295 | Heat-resistant steel castings | GX40NiCr26-20 (≈ HK40) |
| DIN 17445 | Centrifugally cast steel tubes | Equivalent high-temp grades |
