Where resistance to high temperature and good anti-corrosion characteristics are required, is a carbon alloy steel plate is a material to consider. It is a pressure vessel grade steel which is used commonly by fabricators who supply the oil and gas industry.
Due to the materials excellent corrosion resistant properties, ASTM A387 GRADE 91 Class 1 is also an option for use in sour service environments. The material has good weldability and with its heat resistant qualities, the material is a highly versatile steel which can be used in numerous applications.
Steel type: A387 Grade 91 is a chromium-molybdenum alloy steel (nominally 9% Cr – 1% Mo – V – Nb), not a carbon steel. A387 covers alloy-steel plate for welded boilers and pressure vessels in elevated-temperature service.
Welding Grade 91: Grade 91 is weldable, but it needs strict preheat, interpass-temperature and PWHT control to keep its creep strength.
Sour service: Chromium-molybdenum steels resist oxidation, high-temperature sulfidation and hydrogen attack at elevated temperature. Wet H2S (sour) service is controlled by hardness limits and PWHT under NACE MR0103 / ISO 17945 or NACE MR0175 / ISO 15156, not by chromium content, so state any sour-service requirement on the order.
ASTM A387 GRADE 91 Class 1: Purchasing Specification
| Requirement | What to specify |
|---|---|
| Grade and specification | ASTM A387 Grade 91 ; state the edition, and dual certification to ASME SA-387 if the plate is for ASME code construction. State Type 1 or Type 2 where your edition lists both. |
| Heat treatment | Normalized and tempered (quenched and tempered where the standard permits it); state any simulated PWHT of test coupons. |
| Dimensions | Thickness × width × length in mm or inches, and the number of plates or cut pieces. Sizes are confirmed at quotation. |
| Tolerances | A20 thickness and flatness tolerances, or tighter project limits. |
| Supplementary tests | A20 supplementary requirements as needed: simulated PWHT of test coupons, Charpy impact tests, ultrasonic testing. |
| Documents | Mill test certificate (EN 10204 3.1 or 3.2), marking and any third-party inspection. |
Dimensions, Cutting and Tolerances
Specify thickness × width × length and the number of plates, or send a dimensioned drawing for cut pieces and profiles with the revision, finished-part tolerances and machining allowance. Plates for shells and heads may also need edge preparation for welding.
Equivalents for ASTM A387 Grade 91 Alloy Steel Plates
| BS | EN | ASTM/ASME | DIN |
|---|---|---|---|
| ... | ... | A387-91-1 | ... |
Comparable, not equal: The original table gives no BS, EN or DIN grade for Grade 91. The closest EN 10028-2 plate grade is X10CrMoVNb9-1 (1.4903). Grades in other standards have different chemistry, strength and test requirements, so substitution needs the purchaser’s approval.
Specifications for ASTM A387 Grade 91 Alloy Steel Plates
Chromium & Molybdenum content (according to the ASME specification)
| Designation | Nominal Chromium Content (%) |
Nominal Molybdenum Content (%) |
|---|---|---|
| A387 Grade 91 | 9.00% | 1.00% |
ASME or ASTM: The original line refers to the ASME specification. ASTM A387 and ASME SA-387 give the same chromium and molybdenum ranges for the edition ASME adopts.
Tensile Requirements for ASTM A387 Grade 91 Alloy Steel Plates Class 1 Plates
| Designation: | Requirement: | Grade 91 |
|---|---|---|
| A387 Grade 91 | Tensile strength, ksi [MPA] | 85 to 110 [585 to 760] |
| Yield strength, min, ksi [MPa]/(0.2% offset) | 60 [415] | |
| Elongation in 8 in. [200mm], min % | ... | |
| Elongation in 2 in. [50mm], min, % | 18 | |
| Reduction of area, min % | ... |
Grade 91 strength level: A387 sets one strength level for Grade 91, listed with Class 2: tensile strength 85–110 ksi [585–760 MPa] and minimum yield strength 60 ksi [415 MPa], as shown. Confirm the class designation on the order and certificate against the edition you specify.
Chemical Requirements for ASTM A387 Grade 91 Alloy Steel Plates
| Element | Chemical Composition (%). | |
|---|---|---|
| A387 Grade 91 | ||
| Carbon: | Heat Analysis: | 0.08 - 0.12 |
| Product Analysis: | 0.06 - 0.15 | |
| Manganese: | Heat Analysis: | 0.30 - 0.60 |
| Product Analysis: | 0.25 - 0.66 | |
| Phosphorus: | Heat Analysis: | 0.020 |
| Product Analysis: | 0.025 | |
| Sulphur (max): | Heat Analysis: | 0.010 |
| Product Analysis: | 0.012 | |
| Silicon: | Heat Analysis: | 0.20 - 0.50 |
| Product Analysis: | 0.18 - 0.56 | |
| Chromium: | Heat Analysis: | 8.00 - 9.50 |
| Product Analysis: | 7.90 - 9.60 | |
| Molybdenum: | Heat Analysis: | 0.85 - 1.05 |
| Product Analysis: | 0.80 - 1.10 | |
| Nickel, max: | Heat Analysis: | 0.40 |
| Product Analysis: | 0.43 | |
| Vanadium: | Heat Analysis: | 0.18 - 0.25 |
| Product Analysis: | 0.16 - 0.27 | |
| Columbium: | Heat Analysis: | 0.06 - 0.10 |
| Product Analysis: | 0.05 - 0.11 | |
| Nitrogen: | Heat Analysis: | 0.030 - 0.070 |
| Product Analysis: | 0.025 - 0.080 | |
| Aluminium: | Heat Analysis: | 0.02 |
| Product Analysis: | 0.02 | |
| Titanium: | Heat Analysis: | 0.01 |
| Product Analysis: | 0.01 | |
| Zirconium: | Heat Analysis: | 0.01 |
| Product Analysis: | 0.01 |
Reading the chemistry: Single values for phosphorus and sulfur, and for nickel, aluminium, titanium and zirconium, are maximums. “Heat analysis” is the ladle analysis; “product analysis” is a check analysis on the finished plate. Later editions of A387 have lowered some phosphorus and sulfur limits, so the certificate must meet the edition stated on the order. Columbium is another name for niobium. Recent editions also divide Grade 91 into Type 1 and Type 2, with tighter limits for Type 2; state which type you need.
Grade 91 Strength Level and Grade Choice
A387 sets a single strength level for Grade 91, so both Grade 91 pages cover the same tensile requirements. Grade 91 is chosen for its creep strength at high temperature; allowable stresses come from ASME Section II Part D.
| Strength level | Tensile strength | Yield strength, min | Product page |
|---|---|---|---|
| Grade 91 (single level) | 85–110 ksi [585–760 MPa] | 60 ksi [415 MPa] | This page / ASTM A387 GRADE 91 Class 2 |
Comparing A387 Grades
| Grade | Nominal alloying | Typical reason to choose |
|---|---|---|
| Grade 5 | 5% Cr – 0.5% Mo | More chromium than Grades 11, 12 and 22, for hot, sulfur-bearing refinery service |
| Grade 9 | 9% Cr – 1% Mo | Higher chromium for oxidation and sulfidation resistance at higher temperatures |
| Grade 11 | 1.25% Cr – 0.5% Mo | A widely used 1¼Cr–½Mo grade for refinery and power-plant vessels |
| Grade 12 | 1% Cr – 0.5% Mo | The lowest-alloy chrome moly grade in the range, for moderately elevated temperature |
| Grade 22 | 2.25% Cr – 1% Mo | Higher temperature capability than Grades 11 and 12, and common for hydrogen service |
| Grade 91 (this page) | 9% Cr – 1% Mo – V – Nb | Vanadium and niobium additions give much higher creep strength than plain 9Cr–1Mo |
These grades are not interchangeable; use the grade and class approved in your design.
Applications for A387 Grade 91 Plate
Power-plant steam equipment, headers and process vessels where high creep strength is needed at high temperature. Selection depends on design temperature, pressure, process media, hydrogen partial pressure and design life, so give these with your enquiry.
| Component or duty | Information for selection |
|---|---|
| Pressure-vessel shells and heads | Design code and edition, design temperature and pressure, thickness and PWHT. |
| Reactors and hydrogen service | Hydrogen partial pressure, temperature, toughness and step-cooling requirements. |
| Boiler and heat-exchanger parts | Steam or process temperature, media and corrosion allowance. |
Cutting, Fabrication and Welding
Champak Industries describes full and part plate/profile supply and a plasma-cutting service. Send drawings, piece quantities, tolerances, edge preparation and machining allowances for your Grade 91 requirement.
Welding
Use matching chromium-molybdenum consumables, for example AWS A5.5 E9015-B91 / E9018-B91 (9Cr–1Mo–V–Nb) type, with a procedure qualified to ASME Section IX. Grade 91 needs strict preheat, interpass and PWHT control; incorrect heat treatment can sharply reduce creep strength.
Forming and PWHT
Hot forming, and long or repeated PWHT, can lower the delivered strength. Give the PWHT cycle with your order so test coupons can be given simulated PWHT if your design requires it.
Testing, Inspection Documents and Traceability
Specify the inspection document, heat treatment and supplementary tests when ordering. A management-system certificate is separate from a material inspection document or project approval.
| Requirement | What to identify in the order |
|---|---|
| Mill test certificate | EN 10204 3.1 or 3.2 showing heat and product analysis, heat treatment and tensile results |
| Simulated PWHT | Temperature, holding time and cycles to apply to the test coupons |
| Impact testing | Test temperature and minimum absorbed energy, if required |
| UT and traceability | Ultrasonic testing (for example A435 or A578); heat and plate number transferred to cut pieces |
See the company’s Quality Policy for its published policy.
Source ASTM A387 GRADE 91 Class 1 from Champak Industries
Champak Industries’ company profile records its establishment in Mumbai in 1978 and its stockist, import and export activities. ASTM A387 GRADE 91 Class 1 plate can be requested together with the other ASTM A387 grades or the matching ASME SA 387 GRADE 91 Class 1 page for ASME code orders.
What Determines the Grade 91 Plate Quotation?
Thickness, plate size, quantity, heat treatment, supplementary tests, cutting, inspection and packing all affect the quotation. Include the destination, and say whether pricing is needed per kilogram, per plate or per finished piece.
Packing, Dispatch and Export Requirements
Give the delivery address, required date and unloading constraints; heavy plate may need special handling. For export orders, include the destination port, delivery terms and document list.
ASTM A387 GRADE 91 Class 1: Frequently Asked Questions
01What is ASTM A387 GRADE 91 Class 1?
It is 9% Cr – 1% Mo – V – Nb chromium-molybdenum alloy-steel plate to ASTM A387 Grade 91, used for welded boilers and pressure vessels in elevated-temperature service.
02Is there a difference between Grade 91 Class 1 and Class 2?
A387 sets one strength level for Grade 91, listed with Class 2. Both Grade 91 pages cover the same requirements; confirm the designation against the edition on your order.
03What is the chromium and molybdenum content of A387 Grade 91?
Nominally 9% Cr – 1% Mo – V – Nb. The heat analysis ranges are 8.00–9.50% chromium and 0.85–1.05% molybdenum.
04What tensile and yield strength does ASTM A387 GRADE 91 Class 1 require?
Grade 91 requires a tensile strength of 85–110 ksi [585–760 MPa] and a minimum yield strength of 60 ksi [415 MPa].
05Is ASTM A387 the same as ASTM A387?
ASME SA-387 is the ASME Code adoption of ASTM A387, with the same requirements for the edition adopted. Vessels built to the ASME Code need plate certified to ASME SA-387, so specify dual certification if you need it.
06What is the EN equivalent of A387 Grade 91?
The closest EN 10028-2 plate grade is X10CrMoVNb9-1 (1.4903). It is comparable, not identical, so substitution needs the purchaser’s approval.
07What heat-treatment condition is supplied?
Normalized and tempered (quenched and tempered where the standard permits it); state any simulated PWHT of test coupons.
08Can A387 Grade 91 plate be welded?
Yes, with matching chromium-molybdenum consumables (for example AWS A5.5 E9015-B91 / E9018-B91 (9Cr–1Mo–V–Nb) type) and a qualified procedure. Grade 91 needs strict preheat, interpass and PWHT control; incorrect heat treatment can sharply reduce creep strength.
09Which tests and documents should I request?
A mill test certificate to EN 10204 3.1 (or 3.2 with third-party inspection) showing heat and product analysis and tensile results, plus any A20 supplementary requirements such as simulated PWHT, impact testing or ultrasonic testing.
10How do I get a price and delivery date?
Send the grade and class, thickness, plate size, quantity, cutting, tests, destination and required date through the enquiry form below, by WhatsApp or by phone.