What are the most common piping mistakes in oil and gas?

The most common piping mistakes include confusing NPS with OD, using wrong pressure classes, throttling ball valves, mating RF with FF flanges, reusing gaskets, and specifying wrong material grades for sour service. These errors cause leaks, failures, and costly rework.

How can I avoid costly piping specification errors?

Review all specifications against the applicable ASME, API, and EN standards. Cross-check pressure-temperature ratings, verify material compatibility with the service fluid, and ensure dimensional consistency (NPS, schedule, class) across all connected components.

What happens if you mix ASME and EN flanges?

ASME B16.5 and EN 1092-1 flanges have different bolt hole patterns, face finishes, and pressure ratings. Mixing them causes bolt misalignment, gasket sealing failure, and potential leaks. Always use flanges from the same standard in a flanged joint.

Why shouldn't you throttle a ball valve?

Ball valves are designed for on/off service. Throttling causes the ball seat to erode from high-velocity flow, leading to seat damage, leakage, and premature failure. Use globe or control valves for flow regulation instead.

Common Mistakes in Piping

Technical and commercial piping errors that cause leaks, failures, rework, and cost overruns — with quick fixes and links to detailed guides.

Pipes

12 mistakes

NPS vs OD, schedule errors, seamless vs welded, sour service

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Valves

15 mistakes

Throttling ball valves, class mixing, check valve orientation, FAT

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Flanges

15 mistakes

Class ≠ PSI, RF vs FF mating, ASME/EN mixing, bolt length

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Pipe Fittings

10 mistakes

Schedule matching, socket weld gap, end prep, wrong standard

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Gaskets & Bolts

10 mistakes

Reusing gaskets, torque sequence, PTFE limits, stud vs machine bolt

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Materials

10 mistakes

A106 vs A333, duplex confusion, NACE compliance, grade mixing

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Procurement

12 mistakes

MTC 3.1 vs 3.2, Incoterms, equivalent materials, TPI scope

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Why This Section Exists

Piping engineering involves thousands of specifications, standards, and material grades. Even experienced engineers make mistakes — ordering the wrong flange class, confusing NPS with OD, or specifying A106 for low-temperature service.

Each page lists 10-15 common errors (both technical and commercial), explains the risk, and provides a one-line fix with a link to the relevant in-depth article. No fluff, no repetition — just the mistakes and how to avoid them.