The stream writes the order, not the grade

Refinery and petrochemical work is where a stock catalogue gets stress-tested, because the same plant can hold carbon pipe, 9-chrome furnace runs and nickel-alloy valve trims within twenty metres of each other. The A106 seamless pressure pipe page opens with the honest version of the market: this material is used in the development of gas or oil refineries, petrochemical plants, ships, boilers and power plants. That sentence sells nothing on its own. It only becomes an order once somebody has decided what the stream is doing, because a grade stencilled on a drawing tells you the chemistry, while the fluid tells you whether that chemistry will survive the year.

The carbon spine still carries most of the volume

Strip away the exotic units and most petrochemical volume is still carbon steel moving hydrocarbons, steam and utilities. A106 is the high-temperature service branch of that spine, in grades A, B and C with tensile minimums of 48,000, 60,000 and 70,000 psi, supplied cold drawn at 15 to 100 mm outside diameter with 2 to 10 mm wall, or hot rolled at 25 to 700 mm with 3 to 50 mm wall, every length hydrostatically tested or, as an alternative, examined over the full body by nondestructive electric test. The utility side belongs to A53 pipe, written for steam, water, gas and air lines with mill test certificates to EN 10204/3.1B, and the A53 building structure listing carries grades A and B across schedules from SCH 40 to XXS. Where the duty crosses the fence line into transmission, the API 5L line pipe page states its application as pipeline transportation in the petroleum and natural gas industries, in PSL1 and PSL2, grades A and B through X80, stocked 2 to 26 inch outside diameter with fixed lengths of 5.8, 6, 11.8 and 12 metres in SRL and DRL. The wider X42 to X70 listing extends the range to DN6 through DN1200 with 1 to 60 mm wall, and a buyer who knows whether the line is a process line or a transmission line already knows which of these pages to quote.

Above roughly 400 C the chromium count starts to matter

Heater outlets, transfer lines and reformer-adjacent circuits leave plain carbon behind, and the alloy pipe pages document the step. A335 P22 carries 1.90 to 2.60 per cent chromium and 0.87 to 1.13 per cent molybdenum, tensile minimum 415 MPa with 205 MPa yield and 30 per cent elongation, in outside diameters from 19.05 to 114.3 mm with 2.0 to 14 mm wall and lengths to 16,000 mm, every length hydrostatically tested and each pipe also examined by a non-destructive method. The heat treatment condition is part of the specification on that page, listed as A, N+T and Q+T, and sampling follows the furnace route, five per cent of each treated lot for batch work and never fewer than two pipes on continuous lines. P91 is the ferritic step above it, with molybdenum and chromium raising the tensile to 415 MPa and yield to 205 MPa on the page figures, Schedule 20 through XXS, and SA335 P91 supplied with IBR test certificate. A buyer quoting either grade should read the condition code as part of the price, because the same casting in a different heat treatment state is a different pipe.

Stabilised austenitics hold the cycling duty

Where a circuit heats and cools often enough that sensitisation becomes the failure mode, the stabilised austenitic grades take over. The 321/321H plate page describes titanium-stabilised material intended for temperatures up to 1,650 degrees Fahrenheit with higher creep and stress rupture properties than its unstabilised relatives, and names gas processing, petrochemicals and off-shore oil drilling refineries among its users. 347 does the same work with columbium and tantalum, recommended for intermittent heating between 427 and 899 degrees Celsius and for welds that will never see a post-weld anneal, with 515 MPa tensile, 205 MPa yield and 40 per cent elongation on the page. At the hot face of the plant, 310S holds continuous service to 2,000 degrees Fahrenheit, with one caveat the page prints in its own sentence: the rating holds provided reducing sulphur gases are not present, which is exactly the condition a heater flue can violate. 310S pipe covers the tubular form of the same argument.

When the stream, not the temperature, sets the limit

Acidic and chloride-bearing streams push the choice past any ferritic grade. The 904L page lists chemical plant, oil refinery and petrochemical plants among its applications, alongside sulphuric and phosphoric acid duty, and its low carbon content keeps intergranular corrosion resistance in the welded condition. 825 goes further in both directions, resisting oxidizing and reducing environments, with petroleum refining named in its stocked applications, but the same page warns that exposure above 1,000 degrees Fahrenheit, about 540 Celsius, changes the microstructure and cuts ductility, so it is not a creep-design alloy. Pure reducing acid is B2 territory, indifferent to hydrochloric acid at any strength and any temperature, while mixed streams with oxidizing salts belong to C-276. The Monel 400 page reads like a petrochemical inventory in one paragraph: crude petroleum stills, process vessels and piping, boiler feed water heaters and deaerating heaters.

The water side of the plant climbs a familiar ladder

Cooling water, wash water and brackish process water follow the corrosion logic rather than the creep one. 316 and 316L are the baseline, 317LMN carries more molybdenum and nitrogen and outranks 316L and 317L on pitting and crevice performance, and 254 SMO is written for high chloride streams with strength nearly twice the 300 series. The duplex tier buys that resistance with yield strength, the 2205 page quoting roughly twice the austenitic figure, available as S31803, S32205 and 2205 seamless pipe, while 2507 carries a 316 degree Celsius service ceiling printed on its own page and LDX 2101 holds the economical end of the ladder.

What the enquiry should carry

A petrochemical enquiry that quotes the stream gets a quotable answer: the fluid and its contaminants, the normal and upset temperature band, any hydrogen in service, the heat treatment condition required, the non-destructive method to be witnessed, and the certificate level. It also pays to say where the order ends, because the surrounding plant is ordinary catalogue work: Q235 plate and the steel structure programme build the racks, Z275 galvanized coil clads them, and the cutting, bending and welding services take the lot to site-ready. The alloy page decides the stream; the rest decides whether the project ships on time.