DESIGN METHOD FOR SUBSEA EQUIPMENT SUBJECT TO HYDROGEN INDUCED
STRESS CRACKING
TECHNICAL FIELD
[0001] The present invention relates generally to subsea equipment piping design
and, more specifically, to designing subsea piping systems subject to Hydrogen Induced Stress
Cracking (HTSC).
BACKGROUND
[0002] The world's use of fossil fuels has grown exponentially over the past several
decades. With this growth, the oil and gas industry has broadened the search for new oil and gas
reserves to meet the ever growing consumer demand. The search for new oil and gas reserves
now includes areas previously unimaginable for exploration. The need to produce oil and gas
from these new regions has presented a new set of problems related to the design and validation
of equipment used in the production of the newly discovered oil and gas reserves.
[0003] Some of the new areas which are producing substantial oil and gas reserves are
located beneath the ocean. In the subsea environment, new problems associated with flow line
and production equipment have produced a new class of equipment design problems which are
sometimes referred to as "Hydrogen Induced Stress Cracking" (HISC). In general, HISC
problems are created by two environmental factors, specifically the availability of ionic
hydrogen at the surface of chromium alloyed steel constructed subsea equipment due to such
equipments' immersion in an aqueous solution.
[0004] The result of such HISC related problems is manifested by a weakening of the
alloyed steel components and structures. Subsequent component and/or structural failure can
occur leading to safety issues, environmental damage by contamination to the surrounding
subsea location and high repair costs based on equipment location. Analysis of failed subsea
systems has indicated that consideration of HISC factors should be included in the overall design
process associated with subsea systems which are made of certain materials (e.g. Duplex and
Super Duplex Stainless Steel) used in the acquisition and recovery of subsea reserves of oil and
gas.
[0005] Current methods for analyzing and designing subsea oil and gas production
systems, while capable of allowing for HISC considerations, require many hours of computer
computational time to complete an analysis of one set of conditions. For example, in a first
design/evaluation step, a one-dimensional frame model is developed with center lines
representing the axis of the piping system. After the frame model is complete, the axial lines are
replaced by finite pipe elements. The pipe elements are able to simulate all various types of
operating and non-operating conditions and allow the assessment of ASME requirements (i.e.
ASME B31.8).
[0006] In a second step, the pipe elements are partially or fully replaced by shell
elements. The number of elements replaced is dependent on the sections of the design under
review. Like the pipe elements, the shell elements are able to simulate both operating and nonoperating
conditions. However a significant feature of shell elements in the design process is
that the shell elements allow for the prediction of local stresses and therefore the assessment of
linear HISC (i.e. DNV RP-F1 12). However the many sets of load conditions and the associated
sets of computational runs associated with processing the shell elements in this second step can
be prohibitively expensive both in terms of time and computing requirements.
[0007] In a third step, elements identified as not compliant with required conditions
based on the linear analysis of step two are replaced with three-dimensional sub-models. An
analysis is performed with elasto-plastic material properties allowing the assessment of non
linear HISC conditions. The result of the three-dimensional sub-model analysis allows for the
prediction of local strains on the analyzed elements.
[0008] Accordingly, market pressure is demanding a method for designing subsea oil and
gas equipment capable of withstanding the rigors of the subsea environment without the
prohibitively expensive costs, in terms of analysis time and computational requirements, of
existing techniques.
SUMMARY
[0009] Exemplary embodiments relate to systems and methods for analyzing and
designing subsea components and systems for oil and gas recovery capable of withstanding the
subsea environment and the problems associated with HISC. The methodology includes the
development of Transfer Functions (TF) for each type of pipe element. For example, transfer
functions can be developed for bends, tees, couplings, welds and the like which are associated
with subsea piping.
[0010] According to an exemplary embodiment, the data collected from the first step of
the current methodology is provided to the appropriate TF. The appropriate transfer function is
based on the pipe element under investigation. The TF transforms the collected pipe data into
local stresses associated with the pipe element for the user specified conditions of the analysis.
However, it will be appreciated by those skilled in the art that such advantages are not to be
construed as limitations of the present invention except to the extent that they are explicitly
recited in one or more of the appended claims.
[001 1] According to another exemplary embodiment, a series of simulations can be
performed on the subject pipe element using different conditions without developing a new
transfer function for each set of conditions. The results of the series of simulations creates a
profile of the local stresses, based on the different conditions, allowing a more accurate and
reliable design of the associated pipe element. Any pipe element determined to be noncompliant
with the linear HISC analysis provided by the TF can then be analyzed by the
previously described third step of the existing HISC analysis. The elimination of the time and
resource intensive second step of the existing HISC analysis provides for designing a subsea oil
and gas system capable of withstanding the conditions of the subsea environment while
providing an economical and timely analysis and design phase as demanded by current industry
and market requirements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings illustrate exemplary embodiments, wherein:
[0013] Figure depicts system models representing the three different simulations
associated with the background art;
[0014] Figure 2 depicts a pipe with a ninety degree bend to illustrate the amount of FEM
elements required in the three different types of simulations;
[0015] Figure 3 depicts a method of making a HISC assessment based on a pipe model,
transfer functions and a three dimensional sub-model according to an exemplary embodiment;
[0016] Figure 4 depicts a method of generating transfer functions and making a HISC
assessment based on a series of user defined conditions according to an exemplary embodiment;
[0017] Figure 5 depicts a general computing environment for performing the calculations
associated with generating transfer functions and making a FfJSC assessment according to an
exemplary embodiment;
[0018] Figure 6 depicts a transfer function component comprising a transfer function
generator, a transfer function engine and transfer function storage according to an exemplary
embodiment;
[0019] Figure 7 depicts a bend pipe element illustrating representative independent
variables associated with deriving a transfer function according to an exemplary embodiment;
[0020] Figure 8 depicts a bend pipe element illustrating forces and moments acting on
the bend pipe element according to an exemplary embodiment; and
[0021] Figure 9 depicts a bend pipe element illustrating predicted locations of maximum
stress on the bend pipe element according to an exemplary embodiment.
DETAILED DESCRIPTION
[0022] The following detailed description of the exemplary embodiments refers to the
accompanying drawings. The same reference numbers in different drawings identify the same or
similar elements. Also, the following detailed description does not limit the invention. Instead,
the scope of the invention is defined by the appended claims.
[0023] To provide context for the subsequent discussion relating to transfer function
generation and the use of the generated transfer functions in HISC assessment systems according
to these exemplary embodiments, Figure 1 schematically illustrates piping models associated
with the current method of system design. As discussed previously, the method uses three
modeling systems illustrated by system 100 and is comprised of three steps. In a first step, a
frame model of the piping system is constructed with piping lines 108 coinciding with the axis of
the three-dimensional pipes. After constructing the frame model, the lines are replaced with pipe
elements 104 representing the piping system and providing data (area, inertia, etc.) associated
with the desired piping system. The result of the first step is the production of a pipe model 102.
[0024] Next, in a second step, the pipe model produced by the first step is fully or
partially replaced by shell elements 110. The resultant shell model 106 can simulate operating,
incidental and stroke conditions allowing the assessment of linear HISC conditions. The driving
force behind this model is the prediction of local stresses of the pipe elements.
[0025] Proceeding to the third step, a determination is made for each pipe element to
determine if the linear HISC assessment is compliant. If it is determined that a particular pipe
element is non-compliant with the linear HISC assessment then a three-dimensional sub-model
112 is generated for the pipe element 114. The three dimensional sub-model 112 is then run with
elasto-plastic material properties, developing a non-liner HISC assessment. After running the
three-dimensional sub-model 112, a determination is made regarding the acceptability of the pipe
element based on its current design.
[0026] Looking now to FIG. 2 and another exemplary embodiment 200 of the current
method of piping system design, representations of a bend pipe element for the three different
models depicts the relative complexity of the different models. The bend with a uni-axial
element 202 is the model used for the first step 102 previously described. This model requires
the least amount of input data and the least amount of computational time. For example, the
representative bend uni-axial element 202 has twelve degrees of freedom, six for each element
end.
[0027] The bend pipe element 204 with a shell elements 206 is a more complex model
with each shell element 206 having twenty-four degrees of freedom. The shell elements 206 are
pieced together to represent the surface of the bend pipe element 204 and require many more
calculations per shell element 206 in addition to the many shell elements 206 required to
represent the surface of the bend pipe element 204. The three-dimensional sub-model 208 with
solid elements 210 is the most complex model because it models the entire structure of the bend.
The solid elements 210 and the shell elements 206 have similar degrees of freedom and therefore
computational complexities but the three-dimensional sub-model 208 requires many more solid
elements to define the structure. Accordingly, the computational times required for a solid
element modeled bend is much greater than the computational time required for a shell element
modeled bend. However, in the current design method the second step 106 shell modeling is
conducted over the entire piping system whereas the third step 112 three-dimensional submodeling
is applied to only pipe elements viewed as linear HISC non-compliant based on the
shell model analysis.
[0028] Referring now to FIG. 3, a method 300 of making a HISC assessment based on a
pipe model, transfer functions and three-dimensional sub-model according to an exemplary
embodiment is illustrated. Beginning at step 302, a pipe model is generated representing the
piping system. A frame model is first constructed of lines representing the axis of the pipes in
the system. Next, the frame lines are replaced by their corresponding pipe elements. Each pipe
element provides the associated real data such as area, inertia and the like representing the actual
piping system configuration.
[0029] Next at step 304, the pipe model results for each pipe element are collected and
presented to the transfer function associated with the pipe element. The transfer function
calculates predictions for the local stresses of the elements by post-processing forces and
moments of the pipe model. The manner in which such transfer functions can be determined
according to exemplary embodiments is described below. Next at step 306, the calculated local
stress values are evaluated for linear HISC compliance. Compliance is determined by comparing
the calculated local stress values to standard engineering tolerances. In particular, the linear
compliance is assessed by listing, for each component: 1) the maximum membrane stress in the
principal directions, 2) the maximum membrane plus bending stresses in the principal directions
and 3) Von Mises [eqv.] with just membrane plus bending stresses.
[0030] Continuing to step 308, a determination is made of whether the pipe element is
linear stress compliant. If the pipe element is not linear stress compliant then the method 300
proceeds to step 310. At step 310 the method simulates the pipe element with a threedimensional
sub-model. The three-dimensional sub-model performs a non-linear HISC
assessment by predicting local strains on the pipe element. If the pipe element is non-compliant
with the non-linear HISC assessment then a redesign of the pipe element is required. If the pipe
element is compliant with the non-linear HISC assessment then the method 300 continues to step
312 and a determination is made as to whether any other pipe elements require evaluation. If
additional pipe elements require evaluation then the method 300 returns to step 306 and repeats
with the next pipe element. For example, the non-linear HISC compliance is assessed in a course
and, if required, fine evaluation. According to an exemplary embodiment, the previously
described evaluation is performed just for those pipe elements for which predicted strains are not
sufficiently below HISC limits. The method according to this exemplary embodiment provides
results inside and outside of five percent of wall thickness and generates strain plots versus wall
thickness, however those skilled in the art will appreciate that other limits may be used. The
plots are automatically generated for any sections where stress concentrates. In another aspect of
this exemplary embodiment, plots are also generated at regularly spaced sections from the bend
end section.
[0031] Looking now to FIG. 4, a method 400 of generating transfer functions and using
the transfer functions for repetitive calculations using different user defined conditions without
generating new transfer functions according to an exemplary embodiment is illustrated.
Beginning at step 402, the method generates transfer functions by running a set of combinations
of the pipe element dimensions for each type of load applicable to the pipe element. Next, at
step 404, user defined conditions are provided to the transfer function as inputs. Continuing to
step 406, the transfer functions are exercised and the local pipe element stresses calculated by the
transfer functions are collected.
[0032] Next at step 408, a determination is made regarding additional calculations with a
different set of user defined conditions. If additional transformations are required using another
set of user defined conditions then the method returns to step 404 and repeats the transformation
without generating new transfer functions based on the updated user defined conditions. It
should be noted that an optimization point of the method according to this exemplary
embodiment is the ability to calculate local pipe element stresses for different user defined
conditions without the need to generate new transfer functions based on the new user defined
conditions.
[0033] Referring now to FIG. 5, illustrated therein is an example of a suitable computing
system environment 500 in which the claimed subject matter can be implemented. It should be
noted that the computing system environment 500 is only one example of a suitable computing
environment for a mobile device and is not intended to suggest any limitation as to the scope of
use or functionality of the claimed subject matter. Further, the computing environment 500 is not
intended to suggest any dependency or requirement relating to the claimed subject matter with
respect to any one, or any combination, of the components illustrated in the exemplary operating
environment 500.
[0034] With reference to FIG. 5, an example of a remote device for implementing the
various aspects described herein includes a general purpose computing device in the form of a
computer 510. Components of computer 510 can include, but are not limited to, a processing unit
520, a system memory 530, and a system bus 521 that couples various system components
including the system memory 530 to the processing unit 520. The system bus 521 can be any of
several types of bus structures including a memory bus or memory controller, a peripheral bus,
and a local bus using any of a variety of bus architectures.
[0035] Computer 510 can include a variety of computer readable media. Computer
readable media can be any available media that can be accessed by computer 510. By way of
example, and not limitation, computer readable media can comprise computer storage media and
communication media. Computer storage media includes volatile and nonvolatile as well as
removable and non-removable media implemented in any method or technology for storage of
information such as computer readable instructions, data structures, program modules or other
data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash
memory or other memory technology, CDROM, digital versatile disks (DVD) or other optical
disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage
devices, or any other medium which can be used to store the desired information and which can
be accessed by computer 510. Communication media can embody computer readable
instructions, data structures, program modules or other data in a modulated data signal such as a
carrier wave or other transport mechanism and can include any suitable information delivery
media.
[0036] The system memory 530 can include computer storage media in the form of
volatile and/or nonvolatile memory such as read only memory (ROM) and/or random access
memory (RAM). A basic input/output system (BIOS), containing the basic routines that help to
transfer information between elements within computer 510, such as during start-up, can be
stored in memory 530. Memory 530 can also contain data and/or program modules that are
immediately accessible to and/or presently being operated on by processing unit 520. By way of
non-limiting example, memory 530 can also include an operating system, application programs,
other program modules, and program data.
[0037] The computer 510 can also include other removable/non-removable,
volatile/nonvolatile computer storage media. For example, computer 510 can include a hard disk
drive that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk
drive that reads from or writes to a removable, nonvolatile magnetic disk, and/or an optical disk
drive that reads from or writes to a removable, nonvolatile optical disk, such as a CD-ROM or
other optical media. Other removable/non-removable, volatile/nonvolatile computer storage
media that can be used in the exemplary operating environment include, but are not limited to,
magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state
RAM, solid state ROM and the like. A hard disk drive can be connected to the system bus 521
through a non-removable memory interface such as an interface, and a magnetic disk drive or
optical disk drive can be connected to the system bus 521 by a removable memory interface,
such as an interface.
[0038] A user can enter commands and information into the computer 510 through input
devices such as a keyboard or a pointing device such as a mouse, trackball, touch pad, and/or
other pointing device. Other input devices can include a microphone, joystick, game pad,
satellite dish, scanner, or the like. These and/or other input devices can be connected to the
processing unit 520 through user input 540 and associated interface(s) that are coupled to the
system bus 521, but can be connected by other interface and bus structures, such as a parallel
port, game port or a universal serial bus (USB). A graphics subsystem can also be connected to
the system bus 521. In addition, a monitor or other type of display device can be connected to the
system bus 521 via an interface, such as output interface 550, which can in turn communicate
with video memory. In addition to a monitor, computers can also include other peripheral output
devices, such as speakers and/or a printer, which can also be connected through output interface
550.
[0039] The computer 510 can operate in a networked or distributed environment using
logical connections to one or more other remote computers, such as remote server 570, which
can in turn have media capabilities different from device 510. The remote server 570 can be a
personal computer, a server, a router, a network PC, a peer device or other common network
node, and/or any other remote media consumption or transmission device, and can include any or
all of the elements described above relative to the computer 510. The logical connections
depicted in FIG. 5 include a network 571, such local area network (LAN) or a wide area network
(WAN), but can also include other networks/buses. Such networking environments are
commonplace in homes, offices, enterprise-wide computer networks, intranets and the Internet.
[0040] When used in a LAN networking environment, the computer 510 is connected to
the LAN 571 through a network interface or adapter. When used in a WAN networking
environment, the computer 5 0 can include a communications component, such as a modem, or
other means for establishing communications over the WAN, such as the Internet. A
communications component, such as a modem, which can be internal or external, can be
connected to the system bus 521 via the user input interface at input 540 and/or other appropriate
mechanism. In a networked environment, program modules depicted relative to the computer
510, or portions thereof, can be stored in a remote memory storage device. It should be
appreciated that the network connections shown and described are exemplary and other means of
establishing a communications link between the computers can be used.
[0041] Looking now to FIG. 6, a transfer function component 602 according to an
exemplary embodiment comprises a transfer function generator 604, a transfer function engine
606 and transfer function storage 608. It should be noted that the transfer function component is,
in this exemplary embodiment, stored in the system memory 530 of the computing environment
510 and executed by the processing unit 520 of the computing environment 510. The transfer
function generator provides for the creation of transfer functions associated with pipe elements
that correlate local stresses on a pipe element with loads applied to the pipe element. A second
order transfer function equation for a unitary load in a specific location (node), would appear as:
S i = c + (a * Ro) + (a2 * Ri) + (a3 * Rb) + (a4 * Ab) +
(a5 * Ro * Ri) + (a7 * Ro * Rb) + (a8 * Ro * Ab) + (a * Ri * Rb) + . .. +
(a + * Ro2) + (an+2 * Rb2) + . .. + (an+5 * Ab2) eq. 1
where S = Stress (S) generated by a specific force or moment (F, M) in a direction (i);
c = constant; a a = coefficients, Ro = outer radius; Ri = inner radius; Ab = bend angle;
and
Rb = bend radius, see also the variables 700 as illustrated in FIG. 7 .
Based on the fact that stress distribution is linearly dependent on the load, transfer functions are
generated for non-unitary loads as the product of the non-unitary load at the node and the stress
at the node (S i 0de = Li * S @ ode) s evaluated by eq. 1. For example, transfer functions are
created for each stress component (e.g. radial stress, axial stress, hoop stress, etc.) and for each
type of load with the total component stress evaluated as
Sradial@node - LI * S i di ode + L2 * SF2_radial@node + L4 * SMl radial@node · · · +
L6 * SM3_radial@node
where S = stress; L = load; F = force and M = moment, see forces/moments 800 as illustrated in
FIG. 8. It should be noted that similar equations are derived for hoop stress axial stress etc. It
should also be noted that according to exemplary embodiments, a transfer function is generated
for each load type and, therefore, the total local stress is calculated by summing the stress values
for each load type. The summation is valid because the stresses are component stresses such as
hoop stress, radial stress, etc.
[0042] According to one exemplary embodiment, transfer functions are generated only
for nodes where stress concentrates. For example, in a bend, stress concentrates at one of the
three stress locations 900 in a system under design as indicated in FIG. 9. In FIG. 9, the
illustrated sections indicate the typical locations where stresses concentrate. Based on the load
combination, one section will develop more stress than the others. For example, pressure
stresses the 1/2 of ANG section while out of plane movement stresses the 1/3 of ANG section.
Further, the angular position can vary based on the load combination. For the elaborated
reasons, transfer functions are generated at twenty-four different angular locations. The
maximum may fall between any two consecutive locations therefore a final evaluation is
performed by interpolation. In total, analysis of the bend in this exemplary embodiment employs
four hundred thirty-two transfer functions based on locations, force components and force types.
[0043] The transfer function engine 606 provides for executing the appropriate transfer
function with the data necessary from the previously constructed pipe model to transform the
structural input data into local pipe element stress values. In another exemplary embodiment, the
transfer function engine 606 can loop through a series of input data collections and transform the
input data to a corresponding series of pipe element local stress values. Alternatively, the local
transfer function engine 606 can transmit the data collected from the pipe model to a remote
transfer function engine 606, located on another computer communicatively connected to the
local transfer engine function 606, for processing the input data into the pipe element local stress
values. In this manner, the data processing can be accomplished on either (or both) the local
computer and a remote computer.
[0044] The transfer function storage component 608 provides for storing generated
transfer functions so that the transfer functions can be reused to run another simulation at a later
time. In one non-limiting example, new user defined conditions can appear as a result of a
change in the piping configuration and the applicable transfer functions can be recalled without
the need for generating a new set of transfer functions. In another non-limiting example, the
stored transfer functions can be transmitted to another computer system and stored or executed at
the remote location.
[0045] As used in this application, terms such as ''component", "display", "interface" and
the like are intended to refer to a computer-related entity, either hardware, a combination of
hardware and software, software, or software in execution as applied to a system for verification
of subsea equipment subject to HISC. For example, a component may be, but is not limited to
being, a process running on a processor, a processor, an object, an executable, a thread of
execution, a program and a computer. By way of illustration, both an application running on a
server and the server can be components. One or more components may reside within a process
and/or thread of execution and a component may be localized on one computer and/or distributed
between two or more computers, industrial controllers, and/or modules communicating
therewith. Additionally, it is noted that as used in this application, terms such as "system user",
"user", "operator" and the like are intended to refer to the person operating the computer-related
entity referenced above.
[0046] The above-described exemplary embodiments are intended to be illustrative in all
respects, rather than restrictive, of the present invention. Thus the present invention is capable of
many variations in detailed implementation that can be derived from the description contained
herein by a person skilled in the art. All such variations and modifications are considered to be
within the scope and spirit of the present invention as defined by the following claims. No
element, act, or instruction used in the description of the present application should be construed
as critical or essential to the invention unless explicitly described as such. Also, as used herein,
the article "a" is intended to include one or more items.

CLAIMS :
1. A method for assessing hydrogen induced stress cracking associated with a subsea piping
system comprising:
(a) determining a one-dimensional model for an element of said subsea piping system;
(b) performing a one-dimensional analysis for said element using said one-dimensional
model and a plurality of operating conditions to identify at least one point associated with
hydrogen induced stress cracking for said element;
(c) applying at least one transfer function to said at least one point to transform said at
least one point from a one-dimensional representation to a local stress assessment; and
(d) outputting said local stress assessment.
2. The method of claim 1, further comprising:
(a) analyzing said local stress assessment for a first predetermined compliance; and
(b) if said local stress assessment is non-compliant then determining and running a threedimensional
sub-model for said element and analyzing output from said three-dimensional sub
model for a second predetermined compliance.
3. The method of claim 2, wherein said first predetermined compliance is a linear hydrogen
induced stress cracking compliance.
4. The method of claim 2 or claim 3, wherein said output from said three-dimensional sub
model is a local strain assessment.
5. The method of any of claims 2 to 4, wherein said second predetermined compliance is a
non-linear hydrogen induced stress cracking compliance.
6 . The method of any preceding claim, wherein said element comprises, bends, tees,
manifolds, couplings, welds and hubs.
7. The method of any preceding claim, wherein said plurality of operating conditions
comprises said element area and inertia.
8. A method for generating a transfer function for predicting local stresses on a subsea
piping system element, the method comprising:
(a) determining a three-dimensional model for said subsea piping system element;
(b) iteratively running said three-dimensional model with a plurality of pipe geometric
dimensions and loads and generating a series of component transfer functions describing local
stress associated with said subsea piping system element; and
(c) summing said series of component transfer functions to generate said transfer
function.
9. The method of claim 8, wherein said pipe loads comprise moments and forces.
10. The method of claim 8 or claim 9, wherein said geometric dimensions comprise said
subsea piping system element inner radius and outer radius.
11. The method of any of claims 8 to 10, wherein said local stress comprises hoop stress and
radial stress.
12. A computer-executable system stored in a memory and executing on a processor for
verifying subsea piping systems are compliant with hydrogen induced stress cracking
assessments, the system comprising:
(a) a transfer function generator component for creating transfer functions;
(b) a transfer function engine component for executing said transfer functions; and
(c) a transfer function storage component for archiving said transfer functions.
13. The system of claim 12 wherein said transfer function engine component and said
transfer function storage component are located on different computers.
14. The system of claim 12 or claim 13, wherein said transfer function engine component
transmits input data to a second transfer function engine component, located on a separate
computer system, for transforming said input data into pipe element local stress values.
15. The system of any of claims 12 to 14, wherein said computer-executable system further
includes program instructions stored in said memory which, when executed on said processor,
operate to assess hydrogen induced stress cracking associated with a subsea piping system by
performing the steps:
(a) determining a one-dimensional model for an element of said subsea piping system;
(b) performing a one-dimensional analysis for said element using said one-dimensional
model and a plurality of operating conditions to identify at least one point associated with
hydrogen induced stress cracking for said element;
(c) applying at least one transfer function to said at least one point to transform said at
least one point from a one-dimensional representation to a local stress assessment; and
(d) outputting said local stress assessment.
16. The system of claim 15, further comprising:
(a) analyzing said local stress assessment for a first predetermined compliance; and
(b) if said local stress assessment is non-compliant then determining and running a threedimensional
sub-model for said element and analyzing output from said three-dimensional sub
model for a second predetermined compliance.
17. The system of claim 16, wherein said first predetermined compliance is a linear hydrogen
induced stress cracking compliance.
18. The systems of claim 16 or claim 17, wherein said output from said three-dimensional
sub-model is a local strain assessment.
19. The system of any of claims 16 to 18, wherein said second predetermined compliance is a
non-linear hydrogen induced stress cracking compliance.
20. The system of any of claims 15 to 19, wherein said element comprises, bends, tees,
manifolds, couplings, welds and hubs.