Equipment shall be designed to operate in one or more of the specified temperature ratings with minimum and maximum temperatures as shown in Table 2, or to minimum and maximum operating temperatures as agreed between the purchaser and manufacturer.
The design shall consider the effects of differential thermal expansion from temperature changes and temperature gradients which the equipment can experience in service. Design for high-temperature rating, e.g. classifications X and Y (see Table G.1), shall take into consideration the effects of temperature on strength levels; see Annex G for guidelines
Equipment shall be designed with materials, including metallics, that meet the requirements set forth in Table 3. Table 3 does not define either the present or the future wellhead environment, but provides material classes for various levels of severity of service conditions and relative corrosivity.
⎯ chloride concentration;
⎯ elemental sulfur.
In making the material selections, it is the responsibility of the purchaser to also consider the various environmental factors and production variables listed in Annex A.
4.2.3.3 Material class ZZ
ISO 15156 (all parts) (NACE MR0175; see Clause 2) includes provisions by means of testing or documented field history for the qualification of materials for
a specific sour-service application that is outside the parameters defined in ISO 15156 (all parts) (NACE MR0175; see Clause 2). This can include the use of materials in fluid conditions
exceeding the limits defined in ISO 15156 (all parts) (NACE MR0175; see Clause 2),
or the use of materials not addressed in ISO 15156 (all parts) (NACE MR0175; see Clause 2). For such sour-service applications, equipment may be described and marked as material class ZZ.
It is the responsibility of the purchaser to evaluate and determine the applicability of the documented data for the intended application. For material class ZZ, the manufacturer shall meet
material specifications supplied or approved by the purchase
r, and shall
maintain traceable records to document the materials of construction, regardless of PSL.
Table 3 — Material requirements
| Material Class |
Minimum material requirements |
Body, bonnet, end and outlet
connections |
Pressure-controlling parts, stems and
mandrel hangers |
| AA |
General Service |
Carbon or Low-alloy steel |
Carbon or Low-alloy steel |
| BB |
General Service |
Carbon or Low-alloy steel |
Stainless steel |
| CC |
General Service |
Stainless steel |
Stainless steel |
| DD |
Sour Service [a] |
Carbon or Low-alloy steel [b] |
Carbon or Low-alloy steel [b] |
| EE |
Sour Service [a] |
Carbon or Low-alloy steel [b] |
Stainless steel [b] |
| FF |
Sour Service [a] |
Stainless steel [b] |
Stainless steel [b] |
| HH |
Sour Service [a] |
CRAs [b,c,d] |
CRAs [b,c,d] |
Note:
[a] As defined by ISO 15156 (all parts) (NACE MR0175; see Clause 2).
[b] In accordance with ISO 15156 (all parts) (NACE MR0175; see Clause 2).
[c] CRA required on retained fluid-wetted surfaces only; CRA cladding of low-alloy or stainless steel is permitted [see 6.5.1.2.2 a)].
[d] CRA as defined in Clause 3; ISO 15156 (all parts) (NACE MR0175; see Clause 2) definition of CRA does not apply.
|
4.3 Design methods
4.3.1 Connections
4.3.1.1 Flanges
Flanges specified in this International Standard have been designed in accordance with design criteria and methods originally developed by API.
4.3.1.2 Clamp hub and outlet end connections
Design of end and outlet clamp hub connections (16B and 16BX) used on equipment specified in this International Standard shall conform to the material and dimensional requirements of ISO 13533.
4.3.1.3 Clamps
Clamps meeting the requirements of ISO 13533 are acceptable for installation on equipment specified in this International Standard with integral clamp hubs meeting the requirements of ISO 13533.
4.3.2 Casing hangers, tubing hangers, back-pressure valves, lock screws and stems
Casing hangers, tubing hangers, back-pressure valves, lock screws and stems shall be designed to satisfy the manufacturer's documented performance characteristics and service conditions in accordance with 4.2. The manufacturer shall specify methods that are consistent with accepted engineering practices for use in design.
4.3.3 Other end connectors, bodies and bonnets
4.3.3.1 General
Other end connectors, bodies and bonnets that utilize
standard materials (in designs other than those specified in this International Standard) shall be designed in accordance with one or more of the methods given in
4.3.3.2 to 4.3.3.5. Standard materials are those materials whose properties meet or exceed the requirements of
Table 6.
Other end connectors, bodies and bonnets that utilize
non-standard materials shall be designed in accordance with the requirements of
4.3.3.6. Non-standard materials are materials with properties that
do not meet all the requirements of Table 6 for a standard material.
In the event that stress levels calculated by the methods in 4.3.3.2 to 4.3.3.6 exceed the allowable stresses, other methods identified by the manufacturer, such as ASME BPVC:2004, with 2005 and 2006 addenda,
Section VIII, Division 3, shall be used to justify these stresses. Fatigue analysis and localized bearing stress values are beyond the scope of this International Standard.
4.3.3.2 ASME method
The design methodology described in ASME BPVC:2004, with 2005 and 2006 addenda,
Section VIII, Division 2, Appendix 4, may be used for design calculations for pressure-containing equipment. Design-allowable stresses, ST, the maximum allowable general primary membrane stress intensity at hydrostatic test pressure, and Sm, the design stress intensity at rated working pressure, shall be limited by the criteria in Equations
(1) and
(2), respectively:
ST = 5 SY / 6 where
SY is the material-specified minimum yield strength
Sm = 2 SY / 3
4.3.3.3 Distortion energy theory
The distortion energy theory, also known as the Von Mises law, may be used for design calculations for pressurecontaining equipment. Rules for the consideration of discontinuities and stress concentrations are beyond the scope of this method. However, the basic pressure-vessel wall thickness may be sized by combining triaxial stresses based on hydrostatic test pressure and limited by the following criterion
(3):
SE = SY
where
SE is the maximum allowable equivalent stress at the most highly stressed distance into the pressure vessel wall, computed by the distortion energy theory method
SY is the material-specified minimum yield strength
4.3.3.4 Experimental stress analysis
Experimental stress analysis as described in ASME BPVC:2004 with 2005 and 2006 addenda,
Section VIII, Division 2, Appendix 6,
may be used as an alternative method to those described in 4.3.3.2 and 4.3.3.3.
4.3.3.5 Design qualification by proof test
4.3.3.5.1 General
As an alternative to the analytical methods above, the pressure rating of equipment may be determined by the use of
a hydrostatic test at elevated pressure. A test vessel, or vessel part, is made from the equipment for which the maximum allowable working pressure is to be established.
It shall not previously have been subjected to a pressure greater than 1,5 times the desired or anticipated maximum allowable working pressure.
4.3.3.5.2 Determination of yield strength
4.3.3.5.2.1 Method
The yield strength of the material in the part tested shall be determined in accordance with the method prescribed in the applicable material specification.
4.3.3.5.2.2 Specimen preparation
Yield strength so determined shall be
the average from three or four specimens cut from the part tested after the test is completed. The specimens shall be cut from a location where the stress during the test has not exceeded the yield strength. The specimens shall not be flame-cut because this might affect the strength of the material.
4.3.3.5.2.3 Alternative specimens
If excess stock from the same piece of material is available and has been given the same heat treatment as the pressure part, the test specimens may be cut from this excess stock. The specimen
shall not be removed by flame cutting or any other method involving sufficient heat to affect the properties of the specimen.
4.3.3.5.2.4 Exemption
If
yield strength is not determined by test specimens, an alternative method is given in
4.3.3.5.3 for evaluation of proof test results to establish the maximum allowable working pressure.
4.3.3.5.3 Test procedure
4.3.3.5.3.1 Instrumentation
Measure strains in the direction of the maximum stress as close as practical to the most highly stressed locations by means of strain gauges of any type capable of
indicating strains to 0,005 % (50 microstrain; 0,000 05 in/in).
The manufacturer shall document the procedure used to determine the location or locations at which strain is to be measured, and the means to compensate for temperature and hydrostatic pressure imposed on the gauges.
4.3.3.5.3.2 Application of pressure
Gradually increase the hydrostatic pressure in the vessel or vessel part, until
approximately one-half the anticipated working pressure is reached. Thereafter, increase the test pressure in steps of approximately
one tenth or less of the rated working pressure until the pressure required by the test procedure is reached.
4.3.3.5.3.3 Observations
After each increment of pressure has been applied, take and record readings of the strain gauges and the hydrostatic pressure. Then, release the pressure and determine any permanent strain at each gauge after any pressure increment that indicates an increase in strain for this increment over the previous equal pressure increment. Only one application of each increment of pressure is required.
4.3.3.5.3.4 Records
Plot two curves of strain against test pressure for each gauge line as the test progresses, one showing the strain under pressure and one showing the permanent strain when the pressure is removed. The test may be discontinued when the test pressure reaches a value, W, of the hydrostatic test pressure that,
calculated from Equations (4) or (5), justifies the desired working pressure, but
shall not exceed the pressure at which the plotted points for the most highly strained gauge line reach 0,2 % strain.
4.3.3.5.3.5 Resulting rating
Compute the maximum allowable working pressure, p, for parts tested under 4.3.3.5 using Equation
(4) if the average yield strength is determined in accordance with 4.3.3.5.2 or Equation
(5) if the actual average yield strength is not determined by test specimens:
p = 0,5W(S
Y/S
R)
p = 0,4W
where
W is the hydrostatic test pressure at which this test was stopped, in accordance with 4.3.3.5.3.2;
S
Y is the material-specified minimum yield strength;
S
R is the actual average yield strength from test specimens.
4.3.3.6 Non-standard materials design requirements
The design methodology described in ASME BPVC:2004 with 2005 and 2006 addenda, Section VIII, Division 2, Appendix 4, shall be used for designs and calculations for pressure-containing equipment utilizing non-standard materials. Design-allowable stresses, ST, the maximum allowable general primary membrane stress intensity at hydrostatic test pressure; Sm, the design stress intensity at rated working pressure; and SS, the maximum combined primary and secondary stress intensity, shall be limited by the criteria in Equations
(6), (7) and
(8), respectively:
S
T = min (5/6 S
Y, 2/3 R
m, min.)
S
m = min (2/3 S
Y , 1/2 R
m, min.)
S
S = min (2 S
Y , R
m, min.)
where
S
Y is as defined as for Equations (4) and (5)
R
m, min. is the material-specified minimum ultimate tensile strength.
| SI |
USC |
| Dimension |
Tolerance (mm) |
Dimension |
Tolerance (in) |
| x.x |
+/- 0.5 |
x.x |
+/- 0.02 |
| x.xx |
+/- 0.13 |
x.xx |
+/- 0.005 |
4.4.3 Bolting
4.4.3.1 End and outlet bolting
4.4.3.1.1 Hole alignment
End and outlet bolt holes for flanges shall be equally spaced and shall straddle common centrelines.
4.4.3.1.2 Stud thread engagement
Stud thread-engagement length into the body for studded flanges shall be a minimum of one times the outside diameter of the stud.
4.4.3.2 Other bolting
The stud thread-anchoring means shall be designed to sustain a tensile load equivalent to the load that can be transferred to the stud through a fully engaged nut.
4.4.4 Test, vent, injection and gauge connections
4.4.4.1 Sealing
All test, vent, injection and gauge connections shall provide a leak-tight seal at the hydrostatic test pressure of the equipment in which they are installed.
4.4.4.2 Test and gauge connection ports
4.4.4.2.1 69,0 MPa (10 000 psi) and below
Test and gauge connection ports for 69,0 MPa (10 000 psi) working pressure and below shall be internally threaded in conformance with the methods specified in 10.2 and shall not be less than 12 mm (1/2 in) nominal size. High-pressure connections as described in 4.4.4.2.2 may also be used.
4.4.4.2.2 103,5 MPa and 138,0 MPa (15 000 psi and 20 000 psi)
Test and gauge connections for 103,5 MPa and 138,0 MPa (15 000 psi and 20 000 psi) working pressure shall be in accordance with 10.11.
4.4.4.3 Vent and injection ports
Vent and injection ports shall meet the requirements of the manufacturer's specifications.
4.5 Design documentation
Documentation of designs shall include methods, assumptions, calculations and design requirements. Design requirements shall include, but not be limited to, those criteria for size, test and operating pressures, material, environmental and other pertinent requirements on which the design is based. Design documentation media shall be clear, legible, reproducible and retrievable. Design documentation shall be retained for five years after the last unit of that model, size and rated working pressure is manufactured.
4.6 Design review
Design documentation shall be reviewed and verified by any qualified individual other than the individual who created the original design.
4.7 Design validation
Manufacturers shall document their design validation procedures and the results of design validation of designs. The design validation procedures, including acceptance criteria for SSVs and USVs, are given in Annex I. Additional validation procedures, including acceptance criteria, are given in Annex F for use if specified by the manufacturer or purchaser.
