Pipe Thickness Calculation Under External Design Pressure or Vacuum Condition | EveryEng

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Pipe Thickness Calculation Under External Design Pressure or Vacuum Condition

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1 enrolled

1487 views

₹ 999

118 min

Anytime

English

1487 views

Anup Kumar DeyOwner of https://whatispiping.com/

Energy & Utilities

Pharmaceutical & Healthcare

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Lifetime access
Certificate of completion

Volume pricing for groups of 5+

Why enroll

Participants choose this course because it helps them:

✅ Gain Specialized Knowledge – Learn concepts of external pressure and vacuum design rarely covered in detail during general piping courses.
✅ Apply International Standards – Understand how to use ASME codes and charts for real-world thickness calculations.
✅ Enhance Career Opportunities – Stand out as a piping professional with expertise in a critical and specialized design area.
✅ Avoid Costly Design Errors – Prevent failures like buckling and collapse by applying correct design methodologies.
✅ Work on Case Studies – Practice hands-on calculations and problem-solving based on industry scenarios.
✅ Build Confidence – Be able to independently verify, review, and optimize pipe thickness designs under external loads.

Your instructor

Anup Kumar Dey

Senior Piping Engineer

Owner of https://whatispiping.com/

20+ yrs experience·Oman

Is this course for you?

You should take this if

You work in Energy & Utilities or Pharmaceutical & Healthcare
You're a Mechanical Engineering / Piping & Layout Engineering professional
You want to build skills in Engineering & Design
You prefer self-paced learning you can revisit

You should skip if

You need a different specialisation outside Mechanical Engineering
You need live interaction with an instructor

Course details

Pipe thickness calculation under external design pressure or vacuum conditions is primarily concerned with preventing collapse or buckling rather than failure due to internal pressure. When a pipe is subjected to external pressure (such as vacuum, submerged conditions, or buried installation), the pipe wall must be thick enough to resist instability caused by compressive forces. Unlike internal pressure design, which is governed by material strength, external pressure design depends heavily on the pipe’s geometry (diameter-to-thickness ratio), material stiffness, and support conditions.

The design is typically based on standards such as ASME Boiler and Pressure Vessel Code, specifically the external pressure charts provided in UG-28. The procedure involves calculating the allowable external pressure using parameters such as outside diameter (Do), wall thickness (t), and unsupported length (L). A key parameter is the ratio ( \frac{Do}{t} ), which indicates the pipe’s susceptibility to buckling—the higher the ratio, the more कमजोर (prone) the pipe is to collapse. Another important factor is the length parameter ( \frac{L}{Do} ), which accounts for the effect of supports; longer unsupported lengths reduce resistance to external pressure.

The process generally includes assuming a trial thickness, calculating geometric ratios, and then using design charts (or equations derived from them) to determine the allowable external pressure. This value must be greater than the design external pressure (including full vacuum if applicable). If not, the thickness is increased and the process is repeated. In some cases, instead of increasing thickness, engineers may add stiffening rings or reduce the unsupported span to improve resistance.

For practical design, it is important to also consider ovality (out-of-roundness), corrosion allowance, fabrication tolerances, and material properties at operating temperature, as these can significantly affect buckling resistance. Proper evaluation ensures that the pipe will not deform or collapse under vacuum or external pressure, maintaining structural integrity and safe operation.

Course suitable for

Key topics covered

- Rules for Pipe Thickness Calculation under External Pressure/ Vacuum Condition

- Steps for External Pipe Thickness Verification

- Example of Pipe Thickness Calculation under Vacuum Condition/External design pressure condition

- Examples when pipe thickness calculation under external pressure is required

Course content

The course is readily available, allowing learners to start and complete it at their own pace.

2 modules8 lectures1 hr 58 min

Opportunities that await you!

Skills & tools you'll gain

Engineering & Design

Career opportunities

✎ Where this fits — what comes before, what comes next

₹999

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Questions and Answers

Q: You're reviewing a brownfield line where the subcontractor claims vacuum protection is provided by a PSV. While checking notes titled 'external pressure vacuum pipe wall thickness ASME UG-28', you pause. During steam-out with closed vents, the PSV lifts as designed. What physical failure does this safeguard NOT prevent?

A: Governing principle: external pressure failure is controlled by shell instability, not internal overpressure limits. In steam-out or nitrogen purge, the PSV only relieves positive internal pressure; once pressure drops below atmospheric, the pipe still sees full vacuum and can buckle elastically. Option B catches engineers thinking in pressure–temperature space, but brittle fracture isn't the dominant mode under near-ambient vacuum conditions.

Q: A DN250 carbon steel drain line has been in intermittent wet service for 15 years and is now reassessed for full vacuum per a query titled 'carbon steel pipe vacuum collapse corrosion allowance'. UT shows general thinning but no pitting. Which degradation mechanism most directly affects external pressure capacity?

A: Governing principle: collapse pressure scales strongly with D/t, so any loss of wall is critical. General corrosion directly reduces the effective thickness before applying UG-28 charts, shifting the pipe into an unstable regime under vacuum. Option D tempts those thinking about geometry, but ovality here is fabrication-driven, not caused by low-velocity drains.

Q: You're under time pressure: supports are being welded today. The line is NPS 12, long straight run, full vacuum design case flagged in an email titled 'UG-28 external pressure pipe support spacing'. Which design change most reliably increases allowable external pressure without changing pipe grade?

A: Governing principle: elastic buckling pressure rises as effective length decreases. External pressure charts explicitly include L/D terms, so adding supports or shoes is a direct lever when thickness is fixed. Option B traps engineers used to internal pressure logic, where yield strength dominates, but it barely moves elastic buckling limits.

Q: During a walkdown, someone argues the flooded buried line can't see much load. You sanity-check using a note titled 'hydrostatic external pressure buried pipe vacuum equivalent'. Roughly what external pressure does 10 m of water impose?

A: Governing principle: hydrostatic pressure equals ρgh. For water, 10 m head gives ~100 kPa, which is comparable to full vacuum and fully relevant for collapse checks. Option D appeals to geotechnical intuition, but soil arching doesn't remove hydrostatic load when the trench is flooded.