Industries / Oil and gas
Large Part Machining for Oil and Gas Equipment
Pressure boundary parts, sour service materials, and a paper trail that starts before the first cut.
A wellhead housing or a manifold block is not machined for looks or even mainly for fit. It is machined to hold a pressure boundary, which means the bores, the flange faces and the thread forms all carry a consequence that most heavy parts do not. A missed dimension on a bracket is a rework. A missed dimension on a pressure part is a safety incident.
The second defining feature of this sector is the material. Wells that produce hydrogen sulphide need materials and hardness limits chosen to resist sulphide stress cracking, which rules out some grades and some heat treatments a shop might otherwise reach for. Between the pressure rating and the service condition, the material and the paperwork are usually decided before the machining sequence is, not after.
Parts that come through this route
Not an exhaustive list. It is here so you can tell whether your part behaves like these, which is what decides the machine and the sequence.
- Wellhead housings and spoolsBores and flange faces machined to a pressure class, usually on a vertical turning lathe with a live milling head for bolt patterns.
- Valve bodies and bonnetsInternal bores, seat pockets and flanged connections in low alloy or corrosion resistant grades.
- Manifold blocksMultiple intersecting bores on several faces that have to line up, the same problem a gearbox housing poses but at a higher pressure class.
- Blowout preventer componentsHeavy forged bodies and rams with bore and seal groove tolerances that leave little room for a second attempt.
- Flanged connections to a pressure classFace flatness, bolt circle accuracy and ring groove finish machined to the class rather than to a general tolerance.
- Skid frames and structural supportsWelded structures carrying the pressure equipment, with machined mounting pads and levelling faces.
Where this work usually goes
Machine classes that suit the sector. Full typical envelopes and part weights are on the machine class reference.
Vertical turning lathe
Wellhead housings, spools and anything essentially round, with a live milling head so bolt patterns happen in the same setup as the bore.
Horizontal boring mill
Manifold blocks and valve bodies with bores on several faces that must line up on a calibrated rotary table.
Heavy horizontal lathe
Long forged bodies and tubulars where length exceeds diameter.
Materials
Low alloy steels such as 4130 and 4140 for standard service, duplex and super duplex stainless where corrosion or chloride exposure rules out carbon steel, and nickel alloys for the highest pressure and temperature connections. Sour service work follows NACE MR0175 material and hardness limits rather than a general specification.
Paperwork this sector expects
- API monogram or equivalentSome pressure equipment is only accepted from a shop holding the relevant API license. State this requirement up front so shops without it can rule themselves out honestly.
- Material certificatesFull traceability to EN 10204 3.1 or 3.2, checked against the sour service limits if the application calls for them.
- Positive material identificationConfirmation that the alloy in hand matches the certificate, standard practice on pressure boundary parts.
- Non-destructive testingUltrasonic and magnetic particle or dye penetrant on forgings and welds, specified and witnessed before the part is closed up by machining.
What to put in the RFQ
On top of the envelope, finished weight, material and tolerance that every heavy part needs, this sector wants these as well.
- The pressure class or rating the part is designed to
- Whether the service is sour, and which NACE limits apply
- Whether an API monogram or a specific license is required of the shop
- Material grade and the certification level, 3.1 or 3.2
- Positive material identification and which non-destructive tests are required
- Thread form and gauge requirements on connections, if any
Have a part like these?
Send the envelope, the finished weight and the sector. We match it with shops that already work to this paperwork. Reply within 24 business hours.