Technical knowledge
ASME B16.5 pressure temperature ratings: how to read the tables
How ASME B16.5 pressure class, material group and temperature interact, what the rating actually means, how to interpolate, and the mistakes that cause an under rated flange to be ordered.
How the rating system works
ASME B16.5 groups materials by their mechanical behaviour and assigns each group a table of maximum allowable working pressure at a series of temperatures. The class number, such as 150, 300 or 600, identifies the table set rather than a fixed pressure. For a given class, the rating depends on both the material group and the temperature.
A worked comparison
| Temperature | Carbon steel group | Stainless group | Nickel alloy group |
|---|---|---|---|
| Ambient | Highest rating | Slightly lower | Comparable with stainless |
| 200 C | Reduced | Reduced less | Holds well |
| 400 C | Substantially reduced | Moderately reduced | Least reduction |
| 500 C and above | Limited or not permitted | Reduced further | Often the only viable option |
Tip The table above is illustrative of the trend only. Always take the actual rating from the ASME B16.5 table for your material group, class and design temperature.
Errors that cause under rated orders
- Ordering on class alone. Class 300 does not mean 300 psi, 300 bar or any other fixed value.
- Using fluid temperature instead of metal temperature. Insulated, steam traced or sun heated piping can be significantly hotter than the fluid.
- Ignoring the gasket and bolting. The joint is only as capable as its weakest component.
- Assuming the flange rating covers the pipe. The pipe wall and the fitting rating must be checked separately.
- Forgetting hydrostatic test conditions. Test pressure can exceed the design pressure at low temperature.
Above NPS 24
ASME B16.5 covers NPS 1/2 to NPS 24. Larger sizes fall under ASME B16.47, which has two series: series A, derived from the MSS SP-44 practice, and series B, derived from API 605. The two are not interchangeable dimensionally, and the choice must be made on the order and matched to the mating equipment.
Questions about this topic
Does a Class 300 flange handle 300 psi?
Not necessarily. Class 300 identifies a rating table. The actual maximum allowable working pressure depends on the material group and the temperature, and it may be higher or lower than 300 psi at your conditions.
What temperature should I use for the rating?
The design metal temperature of the flange, not the fluid temperature. Account for insulation, solar gain, steam tracing and upset conditions.
Which series should I choose for large diameter flanges?
ASME B16.47 series A and series B differ in bolt circle, thickness and number of bolts. Choose based on the mating equipment and the piping specification, and state the series explicitly on the order.
Questions about our products
What products does Hangbo Alloy supply?
Four product families, all available in nickel-based alloys, titanium, duplex and special stainless steel: flanges, butt weld pipe fittings, elbows, and seamless tube and pipe. Flanges cover weld neck, long weld neck, slip-on, blind, socket weld, threaded and lap joint patterns. Fittings and elbows cover concentric and eccentric reducers, equal and reducing tees, caps, stub ends, and 45°, 90° and 180° returns in both long and short radius, plus 3D and 5D bends for piggable lines. Seamless tube and pipe is supplied cold drawn or hot finished from 6 mm to 630 mm outside diameter.
Which alloy grades are available for these products?
More than 90 grades are published in our grade library. The most requested are Inconel 625, 718, 600 and X-750, Hastelloy C-276, C-22 and B-2, Monel 400 and K-500, Incoloy 800H, 825 and 925, duplex 2205 and super duplex 2507, 316L, 904L and 254SMO stainless steel, and titanium Grade 2 and Grade 5. Nickel-based grades can also be supplied with VIM plus ESR double melting where cleanliness or fatigue life is critical.
What sizes, wall thicknesses and pressure classes can you supply?
Flanges run from NPS ½ to NPS 24 to ASME B16.5 and from NPS 26 to NPS 60 to ASME B16.47 Series A or B, in pressure classes 150 through 2500. Butt weld fittings and elbows run from NPS ½ to NPS 48 (DN 15 to DN 1200) in wall thickness Schedule 5S through XXS. Seamless tube and pipe covers 6 mm to 630 mm outside diameter, in random lengths of about 5 to 7 metres or fixed lengths up to 12 metres. Non-standard and intermediate sizes are quoted on request.
Which material and dimensional standards do you work to?
Forged flanges to ASTM B564, B381 and A182 with dimensions to ASME B16.5 and ASME B16.47. Butt weld fittings and elbows to ASTM B366 and A403 with dimensions to ASME B16.9 and MSS SP-43. Seamless tube and pipe to ASTM B444, B423, B622, B163, B167, B861, A312, A213 and A790. Marking follows MSS SP-25 and the applicable product standard. If your project is governed by EN, DIN, JIS or a company specification, send the document and we will confirm equivalence before quoting.
Is there a minimum order quantity?
There is no minimum for standard sizes and grades held in stock, and prototypes, spares and small trial batches are accepted. Made-to-order melts and special forgings carry a minimum weight that depends on the alloy and the route, typically from about 500 kg for special grades.
What inspection and certification is issued with the goods?
Every shipment carries an EN 10204 3.1 mill test certificate quoting the actual chemical and mechanical results for the specific heat lot, together with dimensional records and heat treatment data where applicable. Testing is carried out in house by optical emission spectrometry, tensile, impact and hardness testing, plus ultrasonic and eddy current examination, with hydrostatic pressure and intergranular corrosion testing to ASTM G28 or A262 Practice E where the specification requires it. Third party inspection by SGS or another recognised agency can be arranged, and their report is issued alongside the shipment.
What are typical lead times?
Standard stock items ship within days. Common production grades such as Inconel 625 or duplex 2205 are typically a few weeks. Special chemistries, larger forgings and items that require third party inspection take longer and are quoted individually against the requirement.
How are the products packed for export?
Flanges and fittings receive a rust preventive coating, are individually wrapped and are packed in plywood cases secured with steel banding. Tube ends are capped and bundles are strapped. Packing lists quote heat numbers so every case can be cross-checked against the mill certificate on arrival. We quote EXW, FOB, CFR, CIF and DAP, and mixed-alloy orders can be consolidated into one shipment with a single documentation package.
How do I request a quotation or a sample?
Send the grade or UNS number, the dimensions including schedule or wall thickness, the governing material and dimensional standards, quantity, any heat treatment or NDT scope and the certificate type you need; a drawing is ideal for special flanges and fittings. Email [email protected] or message us on WhatsApp +86 15618279078 and we normally issue a formal quotation within 24 hours on working days. Samples and previous test reports can be arranged before the first order.
Talk to an engineer
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