ABOUT THIS PRESENTATION

This presentation is about the design theory used by the Australian Piping Code AS 4041-1997. With a focus on facility piping and carbon steel piping which is the most commonly used pipe material in process plants. APIA publications have been referred for this presentation.

It will cover the following design aspects of these codes- Qualifications & Approvals Design, Fabrication & Technical Specification Testing & Examination

The majority of the described aspects have been displayed as lists for better presentation

ABOUT THIS PRESENTATION

This document is the work of Vivek Pandey B.E. (Mech.). Graduate of the University of Auckland.

This document should only be used for self- learning and reference. Always consult the latest AS standard documents. Please do not use this document for commercial purposes. The author is not liable for the usage of this document.

APPLICATION OF AS 4041

AS 4041 sets out minimum requirements for the materials, design, fabrication, testing, inspection, reports and pre-commissioning of piping subject to internal pressure or external pressure or both. Along with specific requirements based on pipe material.

AS 4041 makes use of current American and British Standards such as ANSI/ASME B31.3, Process piping, and BS 806, Specification for the design and construction of ferrous piping installations for and in connection with land boilers, as well as Australian Standards.

AS 4041 classifies piping into classes 1, 2A, 2B and 3 (as per service conditions)

APPLICATION OF AS 4041

Refer section 1 & table 1.4. Class 1 applies with no service limit. Class 2A applies up to 10 Mpag service pressure for any gas and any flammable liquid. Class 2A also applies with no service limit for combustible liquid.

Max. Temp.- no limit for Class1 & 400°C for Class 2A. Min. Temp.- no limit (but >= MDMT)

For Flange Ratings, refer to clause 3.24.4.2 & 3.2. Flange rating as per nominated standard (derating from T>38°C for ASME B16.5 Group 1.1 or 121°C for MSS SP-44).

For control & sampling instrumentation, refer to clauses 3.25.3

Emphasis is placed on Design Approval rather than Designer’s Quals. AS 4041 requires design verification for Hazard Levels A & B

Welding Qualifications

For welding qualifications refer to AS 4458 & AS 3992 (and AS 4037 for NDE). For welder & welding procedure qualification refer to section 5.

Welding supervisor is required for option 2 but not option 1. Welder certification is required for option 1 but not for option 2. Welder qualification is required for both options

Pre- qualified welding procedure is permitted subject to partial re- qualification

Fit- up as per AS 4458 and within close limits for class 1 and medium limits for class 2A

Weld Quality Criteria is very high for class 1 and high for class 2A

Permanent backing ring is permitted for class 2A

Qualification of Materials

Refer to clause 2.2 for qualified materials & clause for 2.2.1 for materials allowed without qualifications

For qualified pipe materials refer to- API 5L and ASTM A53, A106 & A524. Additionally a few AS, ASTM & BS pipes and pipes fabricated to AS 1210. For Class 1piping refer to welded joint efficiency.

For qualified fitting materials refer to- ASME B16.9, B16.11, B16.25, B16.28, A105, A234 & A420. BS 1640.3, 1640.4 & 3799. MSS SP-75. Plus other AS & BS standards.

For qualified flange materials refer to- ASME B16.5 & B16.21. BS 1560.3.1 & 1560.3.2. BS 3293. MSS SP 6 & 44. Also, AS 2129 & AS 4087.

For qualified valve materials refer ASME B31.2, B31.3 or BS 806.

Qualification of Materials

For qualified gasket materials refer to- ASME B16.20 & ASME B16.21

For qualified bolting materials refer to- AS 2528, 1111 & 1112. ASTM A193, A194, A307, A320, A325, A354 & A449. Also, BS 4882.

For qualified pressure gauge materials refer to- AS 1349.

Materials from standards not listed are permitted subject to qualification as equivalent to listed standard. Also, refer to clause 2.2.2.

For materials for which no standards exist, refer to clause 2.2.3. Such materials are only permitted for components other than pipes subject to qualification.

Qualification of Materials

For reclaimed pipes, accessories, valves and fittings, refer to clause 2.2.6. They are permitted subject to qualification.

For material and components not fully identified, refer to clause 2.2.7. They are permitted subject to chemical composition and mechanical properties as specified in a nominated standard.

For component identification, refer to clause 2.5. Also, refer to AS 4458.

For unidentified materials and components, refer to clause 2.2.8. They are not permitted for containing pressurized fluid flows.

For reclaimed corroded, deteriorated or untested components, refer to clause 2.2.9. They are not permitted for containing pressurized fluid flows.

STRAIGHT PIPE WALL THICKNESS

Pipe thickness calculation as per AS 4041, t = PD / (2SaEM + P), where P is internal pressure D is nominal outside diameter SA is allowable stress E is the weld joint efficiency factor M is the piping class factor

Minimum Nominal Wall thickness = Calculated Thickness + Corrosion Allowance + Manufacturing Tolerance

Corrosion allowance should not be less than 1 mm. Apply manufacturing tolerance as specified by manufacturer

ALLOWABLE STRESSES

As per Thin Wall Pipe Theory, Hoop Stress SH = PD / 2t, where P is internal pressure, D is Nominal Diameter and t is thickness

Refer to clause 3.27. AS 4041 applies design margins relative to material permanent deformation (SY or yield stress) and material failure (SU or ultimate stress)- SA = the lessor of SY / 1.5 and SU / 2.35.

The allowable stress equations are similar to ASME B31.3 and the flexibility and stress intensification factors can be sourced from clause 3.27 & table 3.27.5.

For earthquake loading refer to AS 1170.4. For wind loading refer to AS 1170.2.

The following design details are same as for ASME B31.3 except for listed allowable stress value- sustained load stress limit, occasional load stress (including earthquake & wind), expansion stress range limit, expansion stress range limit at temperature close to ambient & low number of temperature cycles and expansion stress- range reduction factor ‘f’.

STRESS ASSESSMENT CRITERIA

The assessment criteria fall under two stress analysis load cases as per clause 3.27.5:

Sustained Load Stress is the sum of longitudinal pipe stresses due to pipe weight, pipe contents, internal pressure and external loads. A stress limit of M*F*SY is specified for normal operation conditions and another limit of 1.33*M*F*SY is specified for inclusion of occasional loads such as wind or earthquake.

Expansion Stress Range is a stress value equivalent to the difference in pipe displacement or flexibility stress within the design temperature extremes from maximum to minimum. The displacement stress is defined as the combination of bending and torsion stresses using equation SE = √(Sb

2 + 4St2)

For piping systems that operate above the installation temperature, the expansion stress range value is calculated as the difference between the value for SE due to all design loads including pipe weight, pipe contents, internal pressure, external loads, displacement & differential temperature and the value for SE due to sustained loads. Otherwise use the method described above.

WELDING AS PER AS 4041 & AS 2885

Welding is to be done as per AS 4458 & AS 3992 (and AS 4037 for NDE).

Butt Welds Full- penetration butt welds are required & throat thickness is less

than thickness of joined thinner part Appendix N - lesser of t/4 and as allowed by AS 4458 Table 8.1 Refer to Appendix N, Figure N1 - limited to wall thickness ratio of 1.5.

Pipe grade not mentioned.

Socket Welds are permitted for pipe size <= DN 65 & Sleeve Welds are not permitted for class 1.

Fillet Welds Not to be used for services with corrosive conditions, cyclic stresses or

thermal gradients that could overstress the attachment welds Size limited to 1.2*tpipe

WELDING AS PER AS 4041 & AS 2885

Stress Corrosion Cracking- Heat treatment to be specified as required

Pre- Welding Heat Treatment (clause 10.1 & table 10.1 of AS 4458) For metal temp. between 0°C & 20°C as follows:

Group A1 (low strength) - 0°C for t<=12 mm, 20°C for 12< t<=25 mm &

40°C for 25<t<=50 Group A2 (medium strength) - 20°C for t<=12 mm, 50°C for 12< t<=25

mm & 80°C for 25<t<=50 Group A3 (high strength >=X52) - 0°C for t<=12 mm, 25°C for 12< t<=25

mm & 50°C for 25<t<=50

Post- Welding Heat Treatment (refer to table 14.1 of AS 4458) Required for t>=32 mm at 580°C to 620°C for steel groups A1, A2 &

A3. The duration varies between groups

Fracture Toughness & Low Temperature Service

Fracture toughness & low temp. service is referred in clause 2.11

Pipe and components used in low temperature service shall satisfy qualifying conditions as specified in Tables 2.11.2 (A) & (B) and Figures 2.11.2 (A) & (B)

A material design minimum temperature (MDMT) is calculated, a test temperature curve is determined based on MDMT & material thickness, fracture toughness test requirements and material limits are determined based on test curve and material grade. Requirement apply for where operating temp. may become lower than 0°C during normal or malfunction conditions.

This code does not consider pipe size and contents as design factors

Design of Bends

Continuous Curved Bends

As per clause 3.15.2.2 use same wall thickness as for straight pipe except where the pipe stress is time dependent then t is calculated using equations 3.15.4.2 or 3.15.4.3 (1) & (2) for all bend angles

Ovality is referred to in clause 3.15.2.3 and usually set as 10% Hot or induction bends are allowed as per clause 3.15.2.1.

Metallurgical properties variation not noted. For elbow wall thickness see clause 3.15.2.1. Temperature-pressure

rating as per elbow material specification of manufacturer. Bends cut from forged bend or elbow are not mentioned Cold bends are permitted as per clause 3.15.2.1.

Design of Bends & Attachments

Mitre Bends

Refer to clause 3.15.4 permitted for any bend angle provided that (a) cut angle <= 15° for

Class 1, and (b) pipe diameter to thickness ratio between 20 to 200 calculate t using equations 3.15.4.2 or 3.15.4.3 (1) & (2) for all bend

angles

Cut & Shut Bends are not permitted

For attachments such as supports, clamps & anchors, refer to clause 3.23.2

Design of Branches

Branch Connections (as per clause 3.19 & table 3.20)

The minimum included angle for Class 1 is 60° (or 45° subject to approval). For Class 2 it is 45°.

Right angle branch followed by a bend is preferred where included angle < 90°

Either run pipe D/t < 100 & Db/Dr <=1, or run pipe D/t > 100 & Db/Dr <=0.5 or design to be qualified

For branch reinforcement & assessment method refer to clause 3.19.8 (ASME B31.3 method of reinforcement replacement equal to pipe area removed in branch opening) or alternatively as per BS 806 method described in Appendix L

The axis of branch & run intersect

Design of Branches

Branch Connections (as per clause 3.19 & table 3.20)

To reinforce branch (a) use of thicker pipe, branch or both, (b) addition of reinforcement pad & (c) other approved, proven and qualified means

For run pipe include weld joint efficiency E if branch intersects seam of welded pipe. For branch pipe E always include E to welded pipe.

For un- reinforced branch, outer diameter distance from run seam or girth weld >= 4 * t run pipe

External non- integral reinforcement method is not permitted without detailed analysis for Class 1

Partial penetration butt or fillet welding requires detailed analysis

Over- Pressure Allowances (refer to clause 3.10.3)

AS 4041 (similar to ASME B31.3) allows an over-pressure of 33% < 10 hrs at any event and < 100 hours total per year 20% < 50 hrs at any event and < 500 hours total per year

Over- Pressure Protection (refer to clause 3.10.3)

Over-pressure protection limit as per AS 4041 is Process pressure limited to 15% or 10% Thermal relief pressure limited to maximum safe working

pressure of weakest component

Pressure & Temperature Variations above the Design Rating or Stress Limit

WELD EXAMINATION

For weld inspection, refer AS 4458 & AS 3992 (and AS 4037 for NDE) AS 4041 requirements:

NDE on 100% of pipeworks

For dye- penetrant test or magnetic particle test of fillet welds Class 1- circumferential welds at nil for t<=20 mm & 20% for t>20 mm. Class 2A- nil. (Refer to AS 4037 Table 7.3)

For radiography test or ultrasonic test of butt welds Class 1- circumferential welds at 10% for t<=20 mm, 20% for 20 mm

<t<=32 mm & 100% for t>32 mm, also longitudinal welds at 100% Class 2A- circumferential welds at 5% and longitudinal welds at 10%.

(Refer to AS 4037 Table 7.3)

For any other considerations refer to clause 1.11.1

HYDROSTATIC TESTING

Test Pressures (refer to Clause 6.7 & Appendix U) Minimum Strength Test Pressure

the lesser of 0.83*SY*P/Sa, 90% of (2t*SY)/D & maximum permitted by component standard

Maximum Strength Test Pressure 90% SY pipe hoop stress (use minimum purchase specification

wall thickness)

Strength Test Hold Period AS 4041 specifies 15 to 25 minutes

Alternative Tests Pneumatic test permitted with test pressure 90% of required

hydrostatic test pressure Initial in- service test generally not permitted

HYDROSTATIC TESTING

Exemptions from hydrostatic testing

Refer to clause 6.8.3

Butt, branch & flange welds including tie-in and cut-in welds subject to materials complying with a listed standard, 100% NDE & initial in-service test

Minor attachment such as temperature and pressure tapings <=DN 40 mm subject to 100% MP or DP and if failure not detrimental to piping in service