Chrome Moly Pipe

What is Chrome-Moly Pipe?

A chrome-moly pipe (short for chromium-molybdenum pipe) is a steel alloy pipe that contains chromium (Cr) and molybdenum (Mo) as the main alloying elements. These pipes are widely used in high-temperature and high-pressure service because of their strength, toughness, and resistance to corrosion and oxidation.

Here’s a breakdown:

Composition

• Chromium improves hardness, tensile strength, and corrosion resistance.

• Molybdenum enhances strength at high temperatures, creep resistance (ability to withstand long-term stress at high heat), and resistance to hydrogen attack.

• Common grades: ASTM A335 (for seamless ferritic alloy-steel pipe) such as P11, P22, P91, etc., where the number indicates different Cr-Mo content and mechanical properties.

Properties

• Withstands high operating temperatures (up to 1000°F+ depending on grade).

• High tensile and yield strength compared to carbon steel.

• Good weldability (though some grades require post-weld heat treatment).

• Excellent resistance to oxidation and wear.

Applications

• Power generation: boiler tubes, steam lines, headers, superheaters.

• Petrochemical & refinery: catalytic reforming units, hydrocrackers, HF alkylation, and hydrogen service.

• Industrial plants: high-temperature service piping, pressure vessels.

Standards

• Seamless pipes: ASTM A335

• Welded pipes: ASTM A691

• Related fittings: ASTM A234 WP11, WP22, WP91

Chrome moly pipes are the backbone of high-temperature, high-pressure piping systems in energy and refinery industries, chosen over plain carbon steel when strength and durability at elevated temperatures are critical.

Chromium and Molybdenum in Pipe Materials

Role of Chromium (Cr)

1. Corrosion & oxidation resistance

• Chromium forms a thin, stable oxide film that protects steel from scaling at high temperatures.

• That’s why Cr-Mo steels can handle steam, flue gases, and refinery environments better than plain carbon steel.

2. Hardness & wear resistance

• Chromium increases hardness, making the pipe more resistant to abrasion and mechanical wear.

3. Strength contribution

• Enhances tensile strength, especially important in pressure piping.

Role of Molybdenum (Mo)

1. High-temperature strength & creep resistance

• Molybdenum is excellent at resisting creep (slow deformation under long-term stress at high heat).

• This is why Cr-Mo pipes are used in boilers, power plants, and refineries running 800–1200°F.

2. Hydrogen resistance

• Mo reduces susceptibility to hydrogen attack and embrittlement - critical in refining and petrochemical plants.

3. Toughness & weldability

• Moly improves impact strength and helps the material stay tough even after welding and heat treatment.

Together (Cr-Mo synergy)

• Cr + Mo provide a balance of:
  Oxidation & corrosion resistance
  High-temperature strength and creep resistance
  Durability under cyclic loading and thermal stress

That’s why chrome-moly pipes (like ASTM A335 P11, P22, P91) are the industry standard for high-pressure, high-temperature piping systems.

What is ASTM A335 Spec?

ASTM A335 is one of the most important specifications for alloy steel pipes in high-temperature and high-pressure service.

Here’s a clear breakdown:

What ASTM A335 Covers

• Title: Standard Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service

• Governs seamless pipes only (not welded).

• Material: Ferritic alloy steels, typically chromium-molybdenum (Cr-Mo) steels.

• Use: High-temperature applications such as boilers, superheaters, heat exchangers, steam lines, and refinery service.

Key Features

1. Seamless only → made without welding, giving higher integrity and pressure capability.

2. High temperature resistance → due to chromium and molybdenum alloying.

3. High creep strength → resists deformation under stress at elevated temperatures.

4. Hydrogen resistance → some grades resist hydrogen attack, critical in refineries.

Common Grades in ASTM A335

Each grade has different Cr and Mo content, tuned for specific service:

Applications

• Power plants: superheaters, reheaters, headers, steam piping.

• Refineries: catalytic reforming, hydrocracking, hydrogen service.

• Petrochem: high-temperature fluid service.

ASTM A335 is the global spec for seamless Cr-Mo alloy steel pipes in high-temperature service, and each grade (P11, P22, P91, etc.) is tailored for different temperature, pressure, and corrosion demands.

ASTM A335 Grade Equivalents

How to Read This

• ASTM A335 = US spec (ASTM/ASME standards).

• ASME SA-335 = Boiler & Pressure Vessel Code adoption of ASTM A335.

• EN 10216-2 / DIN 17175 = European seamless alloy steel pipe standards.

• Grades align closely but may have slight chemistry/mechanical differences, so MTC (Mill Test Certificates) must always be checked for project approvals.

Comparison of ASTM A335 P-Grades

Key Differences

• Cr % and Mo % rise with grade → improving high-temp strength, oxidation resistance, and creep life.

• P11 & P22 are the most widely used in refineries & power generation.

• P91 & P92 are modern “creep-strength enhanced ferritic (CSEF)” steels - designed for 650 °C+ service and long operating life.

• P1 & P5 are older/lower-alloy grades - still used, but less common today in new builds.

ASTM A335 Mills around the world

chrome-moly pipes (ASTM A335 / ASME SA335 grades like P11, P22, P91, etc.) are specialized seamless alloy steel pipes and only a limited set of global mills produce them reliably.

Here’s a list of major mills (by region) that are known for Cr-Mo production:

Europe

• Vallourec (Germany & France) → Leading producer of A335 P11, P22, P91 seamless pipes for power and petrochemical.

• Tenaris Dalmine (Italy) → Strong in boiler tubes, refinery-grade Cr-Mo piping.

• Voestalpine Böhler (Austria) → Specialty alloys, including P91/P92.

• Salzgitter Mannesmann (Germany) → Alloy steel seamless pipes for power gen and refineries.

Asia

• Sumitomo Metal / NSSMC (Japan) → Premium Cr-Mo, including P91/P92 for critical service.

• JFE Steel (Japan) → High-grade alloy seamless pipes, refinery and boiler service.

• Tianjin Pipe (TPCO, China) → Supplies Cr-Mo pipes (P11, P22), widely used but quality depends on project approvals.

• Baosteel (China) → Produces large range of alloy steel pipes, including Cr-Mo.

India

• Maharashtra Seamless (Maharashtra / Jindal Group) → Produces A335 P-grades up to P91.

• ISMT Limited → Specializes in alloy seamless pipes for oil & gas, power.

• Jindal SAW → Alloy steel seamless pipes, including Cr-Mo grades.

Americas

• U.S. Steel Tubular (USA) → Alloy seamless pipes, though less active in recent years.

• Vallourec USA (Youngstown, OH / Houston finishing) → U.S. branch for Cr-Mo pipes.

• Tenaris Bay City (USA) → Focus on OCTG, but some alloy pipes for power/refinery.

Notes:

• High-grade P91/P92 production is limited to top-tier mills (Vallourec, Sumitomo, JFE, Tenaris, etc.) due to stringent creep strength and heat treatment requirements.

• P11/P22 are more widely produced (even in China and India).

• Project approvals often dictate which mills are acceptable - e.g., major EPCs and refineries often restrict to “approved vendor lists” (AVL).

Major Mills Producing Chrome-Moly (ASTM A335) Pipe

Takeaway:

• P11 & P22 → available from most mills, including China and India.

• P91 & P92 → limited to premium mills (Vallourec, Sumitomo, JFE, Böhler, etc.) due to creep strength and strict heat treatment controls.

• EPC approval lists are critical - many projects won’t accept commodity mills for high-grade alloys.

Chrome-Moly Pipe Mills on Typical AMLs (U.S. Market)

Legend

• ✔ = Commonly on AML

• (✔) = Sometimes approved / conditional

• ✖ = Rarely or never on AML

Takeaway:

• Top 5 universal AML mills → Vallourec, Sumitomo, JFE, Tenaris Dalmine, Salzgitter.

• India mills (Maharashtra, ISMT, Jindal) → appear on AML for lower grades, but not P91/P92.

• China mills (TPCO, Baosteel) → almost never approved for refineries/power.

What are the applications of Chrome-Moly Pipe

Chrome-moly pipe (ASTM A335 / ASME SA335) is used anywhere you need strength + durability at high temperature and pressure. Its chromium (Cr) gives oxidation and corrosion resistance, while molybdenum (Mo) gives creep strength and hydrogen resistance.

Here’s a breakdown of the main applications:

Power Generation

• Boiler tubes, superheaters, reheaters, economizers

• Steam headers and main steam lines

• Ultra-supercritical power plants (P91, P92)
  Handles high-pressure, high-temperature steam cycles.

Refining & Petrochemical

• Hydrocracking and catalytic reforming units

• HF alkylation service (P11, P22 with proper low-RE steels)

• Hydrogen reformers and hydrotreaters
  Resistant to hydrogen attack, creep, and high-temperature corrosion.

Oil & Gas/Midstream

• High-temperature process piping in upstream facilities

• Heater tubes, furnace piping, flare headers

• Steam injection lines (enhanced oil recovery)
  Withstands cyclic heating and thermal stress.

Industrial & Chemical Plants

• Heat exchangers and pressure vessels

• High-temp chemical reactors

• Process piping carrying hot fluids and gases
  Handles corrosive service plus elevated temperature.

Nuclear & Specialty

• Nuclear power plant piping (P91/P92 in superheated steam loops)

• Special chemical synthesis plants needing hydrogen resistance

Why Chrome-Moly Instead of Carbon Steel?

• Carbon steel loses strength above ~400°C (750°F).

• Chrome-moly keeps strength and resists creep up to 650°C+ (1200°F+) depending on grade.

• That makes it the default choice for critical high-temperature service.

Chrome-moly pipes are the backbone of high-pressure, high-temperature piping in power, refining, petrochemical, and industrial plants.

Grade-to-application chart for ASTM A335 chrome-moly pipes

Chrome-Moly Pipe Grades vs. Applications

Quick Mapping

• P11 / P22 → Most common refinery + power plant piping.

• P5 / P9 → Specialized for reformers, hydrogen & furnace service.

• P91 / P92 → High-tech, high-temp, long-life power plants.

• P1 → Older, low-demand service (being phased out).

What is “T-grade” pipe

In ASTM/ASME standards, the “T-grades” are essentially the tubing equivalent of the P-grades (pipe)

What “T” Grade Pipe (Tube) Means:

• P-grades → Defined in ASTM A335 → Seamless ferritic alloy-steel pipe for high-temperature service.

• T-grades → Defined in ASTM A213 → Seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes.

In short:

• P = Pipe (process piping, transmission lines, headers).

• T = Tube (boilers, superheaters, heat exchangers).

Examples of T-Grades

 

Key Differences (P vs T)

• Dimensions:

• P-grades → heavier wall, larger diameters (process piping).

• T-grades → smaller OD, thinner wall (boiler & heat exchanger tubes).

• Application:

• P-grades → pipelines & headers.

• T-grades → inside boilers, heaters, exchangers (where heat transfer is critical).

• Spec:

• P = ASTM A335

• T = ASTM A213

So, T-grades are Cr-Mo alloy steels just like P-grades, but made to boiler/heat-exchanger tubing specs instead of process piping specs.

P-Grade vs. T-Grade Chrome-Moly (ASTM A335 vs ASTM A213)

Rule of thumb:

• If it’s piping outside the boiler, spec will say P-grade (A335).

• If it’s tubing inside the boiler/heat exchanger, spec will say T-grade (A213).

What is A-519 4130/4140?

ASTM A519

• Spec name: Seamless Carbon and Alloy Steel Mechanical Tubing

• Covers seamless tubing for mechanical purposes - not pressure piping like A335.

• Used in machinery, automotive, oilfield tools, aircraft, hydraulic cylinders, etc.

4130 / 4140 Grades (SAE/AISI Designation)

Both are chromium-molybdenum (Cr-Mo) alloy steels, but with different carbon levels:

Applications

• 4130 A-519 tubing:

• Aircraft structures, roll cages, bicycle frames

• Oil & gas - pup joints, downhole tools

• Hydraulic lines, pressure vessels (non-code)

• Chosen when weldability + toughness is more important than maximum hardness.

• 4140 A-519 tubing:

• Drive shafts, crankshafts, tool joints, drill collars

• Mining equipment, heavy machinery parts

• High-strength mechanical parts needing fatigue & wear resistance

• Chosen when strength + hardness are critical.

Key Difference (4130 vs 4140 in A-519)

• 4130: lower carbon → easier to machine & weld, slightly lower strength.

• 4140: higher carbon → stronger, harder, more wear-resistant, but less weld-friendly.

So:
ASTM A519 = the spec (mechanical tubing).
4130 / 4140 = the Cr-Mo steel grades used under that spec, chosen based on whether you need more weldability (4130) or more strength/hardness (4140).

Comparisons Between Major Standards

ASTM A335 vs ASTM A213 vs ASTM A519

Simple takeaway:

• A335 (P-grades) = Pipe for pressure piping.

• A213 (T-grades) = Tube for boilers & exchangers.

• A519 (4130/4140) = Tube for mechanical use (non-code).

ASTM A335 vs ASTM A106

Rule of thumb:

• Use A106 Grade B/C for general carbon steel piping in refineries and petrochemical plants (up to ~800°F).

• Use A335 (P11/P22/P91, etc.) for critical high-temp service where creep strength, oxidation, or hydrogen resistance are required.

What is ASTM A691

ASTM A691 is often mentioned alongside A335, but it’s a different product form.

ASTM A691

• Full Name: Standard Specification for Carbon and Alloy Steel Pipe, Electric-Fusion-Welded, for High-Pressure Service at High Temperatures

• Covers welded pipe (not seamless) - specifically electric-fusion welded (EFW) pipe.

• Made by welding together steel plate (usually alloy steel, Cr-Mo, or carbon steel) into large-diameter pipe.

Key Features

• Form: Electric-fusion welded (E.F.W.) → made from plate, not billet.

• Size Range: Much larger diameters than seamless (A335). Common in 20”–72” OD and heavy wall thicknesses.

• Grades: Uses same alloy designations as A335 (e.g., 1¼Cr-½Mo = 11, 2¼Cr-1Mo = 22, 9Cr-1Mo = 91).

• Heat Treatment: Post weld heat treatment (PWHT) usually required.

• Applications:

• Refineries & petrochemical plants

• Power plants

• High-pressure, high-temperature lines where large diameter alloy pipe is required

ASTM A335 vs ASTM A691

 

In short:

• A335 = seamless chrome-moly pipe for high-temp service (smaller/medium diameters).

• A691 = welded chrome-moly pipe for large diameters, same service conditions.

A106 vs A335 vs A691 Selection Guide

Quick Rule of Thumb

• A106 (carbon seamless): Best for moderate temp pipelines (refinery, petrochem, O&G).

• A335 (alloy seamless): Best for high-temp/high-pressure service (boilers, steam, hydrogen).

• A691 (alloy welded): Best for large-diameter, high-temp piping when seamless isn’t practical.