What is road crossing calculation as per API PR 1102?

There are two road crossing procedures in accordance with API PR 1102 which are for rig load and highway load. The calculation consists of 8 major steps.

Step A – Design Input Parameters:

There are three categories for input.

Category 1 – Pipe and Operational Data:

  1. Nominal Diameter, ND
  2. Outside Diameter, D
  3. Operating Pressure, p
  4. Steel Grade
    • API 5L Grade A25 to Grade X70
    • ISO 3183 GR L245 to Gr L485
  5. Specified Minimum Yield Strength, SMYS
  6. Design Factor (for hoop stress – Barlow), F
  7. Design Factor (Effective stress), F’
  8. Design Factor (for fatigue stresses), F”
  9. Longitudinal Joint Factor, E
  10. Installation Temperature, T1
  11. Maximum/Minimum Operating Temperature, T2
  12. Temperature Derating Factor, T
  13. Corrosion Allowance
  14. Wall Thickness, t
  15. Corroded Wall Thickness, tw
    • Corroded Wall Thickness = Wall thickness – Corrosion Allowance
  16. Transported Product

Category 2 – Installation and Site Data:

  1. Depth, H/C
  2. Bored Diameter, Bd
  3. Soil Type
    • Soft to medium clay sand with high plasticities
    • Soft to medium clay sand silts with low to medium plasticities, loose sands & gravels
    • Stiff to very stiff clays and silts; medium dense sands
    • Dense to very dense sands and gravels
  4. Modulus of Soil Reaction, E’
  5. Resilient Modulus, Er
  6. Unit Weight, y
  7. Unit Weight
  8. Type of Longitudinal Weld
    • Seamless
    • SAW
  9. Wheel Load Design
    • Design wheel load from single axle, ps
    • Design wheel load from tandem axle, pt
  10. Pavement Type
    • Flexible pavement
    • No pavement
    • Rigid pavement

Category 3 – Misc. Pipe Steel Properties:

  1. Young’s Modulus, Es
  2. Poisson’s Ratio, ns
  3. Coefficient of Thermal Expansion, aT

Step B – Check Allowable Hoop Stress

  1. Calculate the Hoop Stress as follow:
    • SHi (Barlow) = Design Pressure * Outside Diameter / 2* Corroded Wall Thickness
  2. Check if SHi (Barlow) <= F (Design Factor) * E (Longitudinal joint factor) * T (Temperature Derating Factor) * SMYS (Specified Minimum Yield Stress)

Step C – Circumferential Stress Due to Earth Load

  1. Wall thickness to diameter ratio, tw / D
  2. Stiffness factor for earth load circumferential stress, KHe in accordance to figure 3, API 1102
  3. Depth to bored diameter ratio, H/Bd
  4. Burial factor for earth load circumferential stress, Be in accordance to figure 4, API 1102
  5. Bored diameter to outside diameter ratio, Bd/ D
  6. Excavation factor for earth load circumferential stress Ee in accordance to figure 5, API 1102
  7. Circumferential stress due to earth load, She
    • SHe = KHe * Be * Ee * y * D

Step D – Impact Factor, Fi and Applied Design Surfaces Pressure, w

  1. Impact factor, Fi
    • In accordance with figure 7, API 1102
  2. Applied design surfaces pressure, w
    • Contact area over applied wheel load, Ap
    • W = pt/ Ap or w= ps/ Ap

Step E – Cyclic Stresses, DSHh and DSlh

  1. Cyclic circumferential stress, DSHh
    • Highway stiffness factor for cyclic circumferential stress, KHh in accordance with figure 14, API 1102
    • Highway stiffness factor for cyclic circumferential stress, GHh in accordance with figure 15, API 1102
    • Highway pavement type factor, R in accordance with table 2, API 1102
    • Highway axle configuration factor, L in accordance with table 2, API 1102
      • DSHh = KHh * GHh * R * L * Fi * w
  2. Cyclic longitudinal stress, DSLh
    • Highway stiffness factor for longitudinal stress, KLh in accordance with figure 16, API 1102
    • Highway stiffness factor for longitudinal stress, GLh in accordance with figure 17, API 1102
    • Highway pavement type factor, R in accordance with table 2, API 1102
    • Highway axle configuration factor, L in accordance with table 2, API 1102
      • DSLh = KLh * GLh * R * L * Fi * w

Step F – Circumferential Stress Due To Internal Pressurization, Shi

  1. SHi = p * (D – tw ) / ( 2 * tw )

Step G – Principal Stresses, S1, S2, S3

  1. S1 = SHe + DSH + Shi
  2. S2 = DSLh – Es * aT * (T2 – T1) + ns * (SHe + SHi)
  3. S3 = -p
  4. Seff = ( 0.5 * [ (S1 – S2)2 + (S2 – S3)2 + (S3 – S1)2 ] )0.5
  5. Seff < SMYS * F’ ?

Step H – Check Fatigue

  1. Girth Welds
    • Fatigue endurance limit of girth weld, SFG
    • SFG * F’’
    • Check DSLh < SFG * F”?
  2. Longitudinal Welds
    • Fatigue endurance limit of longitudinal weld, SFL
    • SFL * F’’
    • Check DSHh < SFL * F”

Leave a Reply

Your email address will not be published. Required fields are marked *