Oil and gas piping is not one product but four, chosen by where the pipe sits in the chain: casing and tubing inside the well, line pipe for gathering and transmission, fittings, flanges and the artificial lift string at the surface. Each is bought to a different specification, and the grade follows the pressure, the temperature and whether the wellstream is sweet or sour.
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The three segments, and what each one buys
Upstream covers the well itself. Steel pipe here is API 5CT casing to line the borehole and tubing to carry the produced fluid to surface, with couplings, centralisers, pup joints and thread protectors making up the string. Where the well is completed for artificial lift, the sucker rod string and its surface hardware are part of the same package.
Midstream is where the fluid leaves the field: gathering lines and then transmission pipelines. This is API 5L line pipe territory, welded or seamless depending on diameter, with coating for burial and corrosion protection, and the fittings and flanges that join one length to the next.
Downstream and process piping runs to the ASME codes rather than to API 5L. ASTM A106 seamless pipe, ASTM A335 chrome moly for hot service and ASTM A312 stainless for corrosive streams, with matching alloy and stainless fittings.
Choosing the grade
Three questions decide the grade in most enquiries. What pressure and diameter does the line carry, which sets the wall thickness and the grade from B up to X70. What temperature, which decides whether ordinary carbon steel is acceptable or whether a low-temperature or alloy grade is needed. And is the service sweet or sour — if hydrogen sulphide is present, the hardness of the steel has to be controlled and the choice of grade narrows sharply, which is covered on the sour service page.
What is normally called out
| Service need | Product | Standard and grade |
|---|---|---|
| Wellbore casing | API 5CT Casing Pipe | API 5CT, grades J55 to Q125, STC / LTC / BTC |
| Production tubing | API 5CT Tubing Pipe | API 5CT, grades J55, N80, L80, P110, EUE / NUE |
| High-pressure or gas-tight wells | Premium Connection Casing and Tubing | API 5CT with metal-to-metal seal connections |
| Artificial lift | API 11B Sucker Rod | API 11B, grades C, D, K, KD, HL, HY |
| Transmission and gathering | API 5L Seamless Steel Pipe | API 5L PSL1 / PSL2, grades B to X70 |
| Large diameter pipelines | API 5L LSAW Welded Steel Pipe | API 5L PSL2, grades B to X70 |
| Buried and offshore lines | Anti-Corrosion Coated Steel Pipe | 3LPE, 3LPP or FBE to the project coating specification |
| Process and high-temperature piping | ASTM A106 Seamless Carbon Steel Pipe | ASTM A106 grades A, B, C |
| Hot and corrosive process service | ASTM A335 Alloy Steel Pipe | ASTM A335 P5, P9, P11, P22, P91 |
| Connections and branch take-offs | Butt Weld Elbow | ASME B16.9, ASTM A234 WPB / WP11 / WP22 / WP91 |
| Flanged joints | Pipe Flanges | ASME B16.5 and B16.47, ASTM A105, A182 F316 |
How a package is specified
An OCTG enquiry is usually written as: outside diameter and weight per foot, grade, connection type, and the range length. A line pipe enquiry is written as: outside diameter, wall thickness or schedule, grade and product specification level, coating, and the line standard — API 5L for transmission, or ASME B31.3 and B31.8 for the design. Both need a destination port and a quantity before a price means anything, and both are usually supplied against an inspection regime agreed in advance.
- State the product specification level. API 5L PSL2 carries mandatory impact testing and tighter chemistry than PSL1, and the price difference is real.
- Name the connection, not just the grade. STC, LTC, BTC, EUE, NUE and premium connections are not interchangeable and change the delivered price.
- Say whether the service is sour. If H2S is present, grades and hardness limits change before the quote is written, not after.
- Confirm the length range. Range 2 and Range 3 change the tonnage per piece and the shipping configuration.
- Decide the documentation before ordering. EN 10204 3.1 or 3.2, third-party inspection, and any additional testing all have to be priced in.
- Give the destination port. Freight and coating availability both depend on it, and inland destinations add a leg that must be quoted.
Frequently asked questions
What is the difference between casing and tubing?
Casing lines the borehole and is cemented in place for the life of the well; tubing is run inside the casing to carry the produced fluid to surface and is pulled for workovers. Casing is the larger diameter and the permanent structure; tubing is the smaller, replaceable production conduit.
Which steel pipe standard applies to oil and gas pipelines?
API 5L covers the pipe itself for both gathering and transmission. The pipeline design is governed by ASME B31.8 for gas transmission and ASME B31.4 for liquid pipelines, and those codes determine the wall thickness and grade the design requires.
When is premium connection casing needed instead of API buttress thread?
When the joint must seal gas-tight under high pressure, when the well is deviated or the string sees cyclic loading, or when the connection has to carry combined tension and bending. A metal-to-metal seal is used because an API threaded and coupled joint relies on thread compound to seal.
Do you supply the full string or individual items?
Either. A complete OCTG package can be supplied with casing, tubing, couplings, centralisers, pup joints and thread protectors together, or individual items can be quoted against their own specification when the rest of the string has been sourced elsewhere.
Where to go next
- Steel pipe weight calculator – work out the weight of any size and wall thickness
- Pipe schedule chart – wall thickness for every schedule, carbon and stainless
- Request a quotation – send the specification, quantity and destination port
- Casing and tubing (OCTG) – API 5CT well casing and tubing, J55 through P110 and Q125
- Line pipe and steel pipe – seamless, ERW, LSAW and SSAW to API 5L and ASTM
- Sour service – what hydrogen sulphide does to the choice of grade
Ready to price your enquiry? Tell us the specification, the dimensions, how much you need and where it is going. We reply with what is available and what it costs.
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