How To – Fabrication of DNV Certified Skids 2.7-1

Increased demand for fabricated DNV skids is being driven by quality and safety concerns for equipment being installed on any DNV classed vessel, including any offshore platform, marine vessel, FPSO, drill ship, or other marine installation. These concerns are at an all-time high as a result of the Macondo blowout in the Gulf of Mexico in 2010.

dnv classed vessel skid fabrication 2.7-1

Operating these complex systems and facilities requires complex fabrication. Our principal’s DNV certification procedures assure owners, authorities, and other stakeholders that the DNV classed facility has certified equipment aboard and complies with DNV classification rules and requirements – independent of location.

Classing Societies and the IMO

IMO is the International Maritime Organization and it is the United Nations agency responsible for the safety and security of shipping and the prevention of pollution by ships. The IMO is the standard-setting authority for the safety, security, and environmental aspects of international shipping. It creates a regulatory framework for the shipping industry that is universally adopted.

The IMO has adopted standards for other “recognized organizations” like the DNV which are called classification societies.

At Ocean Fab, safety, quality, the environment, and compliance with DNV standards are our number one concern. In order to gain DNV emblems for any skidded equipment, a number of approval and certification procedures must be followed. Our principals have many years’ experience with complex fabrications, including subsea and offshore / topside fabrication.

DNV has traditionally been more popular in European waters, but since it has become the number one classing society in the world, more and more super major oil companies and operators are requiring that any equipment going on a DNV Classed Offshore Installation going anywhere in the world become certified by DNV. Whether it’s a temporary or a permanent installation – fixed or floating offshore installations, ships, drill rigs, production rigs, or offshore vessels, including floating platforms. This equipment can include rental equipment, skidded equipment, shipping containers, seacans, frames, structural steel, twistlocks, sea fastening clips, deck fastening, waste skips, tanks – the list goes on and on.

*Disclaimer: Ocean Fab nor its principals are in any way affiliated with DNV GL. DNV regulates all of the processes listed below for DNV certification. These are only historical examples of the processes that we have gone through with DNV. DNV will be the final authority for any process, including new ones that Ocean Fab’s principals have to certify for our clients. The rules change frequently – Please consult your local DNV office for more details. Ocean Fab is not an engineering company – however, our principals can provide engineering services.

Quality Control – Ocean Fab principal’s Quality Management System ensures the quality of procedures and facilities by implementing a QMS in accordance with ISO 9001. QMS audits and approval by the DNV classification society verify that our QMS meets the high standards and are qualified to manufacture skids according to those DNV standards.

Witnessing is a large part of the certification process for DNV. A DNV surveyor will need to witness numerous aspects in the process of certification including the weld procedure approval, welder qualification, the weld startup of each specific project, and during various milestones in the project – according to the Quality Inspection & Test Plan. DNV Surveyors will come and inspect / witness at defined inspection points.
1. Coupon witnessing – once our written weld procedure has been approved, a DNV surveyor must come to our facility and witness the welding of test coupons.
2. Welder Qualifying
3. Start Up
4. Millstone audits according the Quality Inspection & Test Plan.
5. Inspection of the prototype and the prototype is also tested

Three Most Common DNV Standards for DNV Classed Offshore Equipment

The three most common standards relate to a portable offshore unit, and usually involve some type of “Lifting Operation” either from the dock to the vessel or lifting on the open seas. The standards apply to any fabricated enclosure or skid for offshore vessels and marine applications. They include:

DNV Standard 2.7-1 *Offshore Containers (applies to skids, frames, enclosures, etc.) – standard for certifying offshore container transport units and produced by a privately-held company. As defined by the International Maritime Organization, an offshore container is a “portable unit, specially designed for repeated use in the transport of goods or equipment to, from or between fixed and/or floating offshore installations and ships.”
Offshore containers are also commonly called “skids” in the offshore oil and gas community, as they are often used to transport large components to drilling and production rigs. These can be as simple as frames that hold the contents. The skid, along with its contents, is sometimes referred to as a “skid package.” The three typical phases of transport are: shoreside (e.g. by fork lift truck), by supply vessel and lifting to and from offshore installations. The Standard for Certification includes design requirements related to all three phases.The requirements for design, testing and production of offshore containers in EN 12079 are directly based on DNV Standard for Certification 2.7-1

dnv skid fabrication-2.7-1

DNV Standard 2.7-2 Offshore Service Modules – Offshore service modules are often designed to perform temporary services on installations/vessels and therefore may be moved among different offshore installations/units and into different national waters.

DNV Standard 2.7-3 Portable Offshore Units – covers all other types of portable offshore units, other than offshore containers. The standard is built on the 2.7-1 DNV Standard and usually involves lifting operations while on the open seas – versus simply loading and unloading from the dock.
Note: It’s important to note, that while DNV 2.7-1 most commonly refers to the term “shipping container” This standard also covers Skidded Equipment, DNV Baskets, Mud Skips, Cutting Boxes, Waste Skips, Enclosures, and Tanks. These can be as simple as frames that hold the contents. The skid, along with its contents, is sometimes referred to as a “skid package.”

DNV Project Timeline and Scheduling

Because of the large amount of paperwork, scheduling, and witnessing involved for final DNV certification, it is paramount that we work within our client’s expectations for scheduling. Ocean Fab’s principals have years of experience with this process and have developed relationships with local DNV surveyors and other DNV administration to facilitate this process and keep everything on schedule.

For DNV approval and certification, there are five basic steps:
1. Certification of our (or our client specified) written Weld Procedure, Lab Tests, and Welder Qualification
2. Appraisal and approval of our principals equipment / skid / frame design
3. Audit / survey during the initial welding Start Up
4. Production – Audit / survey during the manufacturing of the equipment
5. Testing of the prototype – For “Type” Approval (Type approval means there are a series of the same units being manufactured over a period of time)

Note: It’s important to note that DNV certification is project specific. In other words, each new fabrication order we get from our client has to go through a new DNV approval and certification process. Even if it is a repeat order for the same exact product. In some circumstances it is advisable to get a series of the same manufactured product approved by DNV – For repeat products which fall under a more manufacturing mode of construction we can get DNV surveyors to approve a “Type Approval”.

Step #1 – DNV Weld Procedure Approval
The Survey – Submit Our Written Weld Procedure WPS, PQR, and lab test specifications / plan for Review & Compliance – Qualify the welders.

The very first step of the survey process is to submit our written WPS (Weld Procedure Specification) and PQR (Procedure Qualification Record) for DNV approval for an in house welding procedure. This paperwork outlines the details of what needs to be accomplished, the purpose, the inspection test program, and what is required from DNV.

We submit WPS, PQR’s, and Lab Testing Specs to a DNV Welding Engineer for review. Once the Welding Engineer gives approval, we schedule a DNV Surveyor to be at our facility to witness the welding of the coupons.

The inspection test program includes: – Verification and testing of materials – Welder Qualification – Acceptance of weld procedures – Acceptance of NDE procedures – Witness and acceptance of prototype testing – Verification of identification and marking.

Variables / Parameters: Welding Processes, Joint Design, Positions, Filler Material, Electrical Characteristics, Heat (Amps x Volts x 60 / Travel Speed), Technique, Pre-heat interpass and Post weld heat treatment, Shielding, Initial and Interpass cleaning / grinding

Lab Testing Outline – Coupon Testing Specifications
Visual Testing
Ultrasonic Testing
Magnetic Particle Testing
Side Bends
Reduced Section Tension Tests
All Weld Metal Tensile
CVN Tests (Charpy V-Notch tests) Specimens with various notches
Hardness Test – Vickers Hv10
Macros (photographs included)

We then weld the coupons and record the information. All test welds are witnessed, prepared, welded, and tested in conformance with the requirements of the specified Structural Welding Code.
Upon completion of the weld coupons we ship the coupons to the testing lab to be tested. Lab Testing must be witnessed by DNV.

After the lab tests have been witnessed and approved, we the write the lab results/parameters in to the WPS/PQR’s, then submit those documents back to DNV for the final approval stamping. The updated PQR’s and WPS will be based on the supporting data and lab results. DNV will then do a final review and either provide DNV approval or any suggested changes.

Once lab testing results are received back at our facility, we finish filling out the WPS paperwork with the information provided by the PQR’s. Finally, we submit the completed WPS, PQR’s and lab testing results to DNV Welding Engineer for weld procedure approval.

When finally approved, we give a DNV Surveyor the opportunity to come out to witness the qualification of our welders to the new weld procedure.

This approval is specific to our company and witnessed by DNV. Ocean Fab’s principals have been approved for numerous welding procedure by many of the classing societies, including ABS and DNV. Often times we can submit one of our existing welding procedures which has already been approved by another classing society and DNV will allow us to use it. However, any existing welding procedure still has to go through the proper certification with DNV for approval and certification.

dnv fabrication skid equipment

Step #2 Engineering and Design – of the DNV Equipment / Structure
Our principals submit the structural design of the offshore skidded equipment which must be reviewed and approved by DNV. The design approval process assures that the design of the equipment which is to be installed on a DNV classed vessel complies with the DNV rules. This is the beginning of the process to assure that the fabricated equipment satisfies DNV’s requirements.

The Design approval includes an initial review, the issue of comments, and a review of next document revisions to confirm incorporation of DNV comments. During the design approval process, our principals can provide approved engineered drawings. This process can take 6 to 8 weeks.

Design Review Options:

Case Approval – for one off pieces of equipment or small production runs.
Case by case approval tends to be job specific for a known batch (customer purchase order) and only valid for that batch.

Type Approval
If our client needs to manufacture several units over a period of time a Type Approval is requested from DNV. This is only valid for certain time frames and must be renewed periodically.

Our principals submit the following documentation for Design Review:

The container’s structural drawings are reviewed according to the standards referenced in IMO MSC/Circ. 860. Details of the materials and strength of the cargo containment structure, as well as the lifting and securing arrangements are appraised. Drawings must show: – Dimensions and load ratings – Material specifications – Details of welding methods and weld sizes – Details of any other fastening methods – Details of any special treatment for materials – Details of sealant materials – Details of corner fittings and closure mechanisms, together with name(s) of the manufacturer(s) of these parts – Mandatory marking.

The design must also consider all of the various components and forces subjected to the equipment skid:
For example, the steel, stability against tipping, Design Temperature, Allowable Stresses, Lifting with the “lifting set”, Design of lifting sets, Lifting with forklift truck, Horizontal Impact, Vertical Impact, Container walls, Minimum material thickness, Welding (some welds are full penetration welds and others are fillet welds), Floor (drainage), Doors and hatches, Intermediate cargo decks, Internal securing points, Fork lift pockets, Pad eyes, Prototype Testing, Coating and corrosion protection, Dimensions and strength of lifting sets, weights, and sling angle calculations.

Step #3 The Start Up for a Specific Unit of DNV Certified Equipment
Once DNV approves our Design and WPS, the next step, before we begin welding, is to schedule DNV to witness a weld start-up. This needs to be done on each new series (purchase order), even if it’s the same repeat items that was made before.

At this time DNV can also qualify additional welders and begin layout for DNV witness / audit of the start-up. Only after final approved certification and individual welder qualification are we ready to fabricate and schedule a DNV surveyor for a weld start/audit.

For multiple items where our clients need to manufacture several units over a period of time a “Type Approval” is requested from DNV . For “Type Approval” The DNV surveyor will usually audit more often in the beginning until they’re comfortable with our QMS for the project, then it will diminish and become random.

We communicate schedule milestones to all parties as we go along with the project.

During fabrication, welder ID stamps are stamped on each weld. We provide a Weld Map or written record of which welder welded what part of the assembly.

Step #4 Production of the DNV Equipment
During the production phase, DNV will periodically visit our facility and audit the process during manufacture. The frequency of the audits depends on how comfortable they are with our quality processes, procedures and adherence to the design and the Quality Inspection & Test Plan.

Production Inspection – The DNV surveyor typically uses the following criteria when inspecting during the production phase.
— Dimensional control
— Visual inspection of weld preparation, welding, alignment, material marking etc.
— Review of material certificates
— Review of WPS/WPQ, Welders Qualification Tests, welding consumables
— Review of equipment documentation as necessary
— Review of NDE documentation and report
— Review of the marking

Production Documentation – General Production is performed according to approved drawings, specifications and procedures. We must submit our quality plan for acceptance before production starts. The certification of each container is based on the following documentation, which we retain for the time period specified by DNV.
— Approved drawings, including a general arrangement drawing
— Structural calculations
— Type approval certificate (where relevant – only for multiple repeat units)
— Material documentation
— Welding procedure qualifications (WPQ)
— Welding procedure specifications (WPS)
— Welder’s qualification certificates
— Weld Map – (written record of which welder welded what part of the assembly)
— Report on traceability of materials in the primary structure
— Report from manufacturing inspection
— Report from dimensional control
— Report from non-destructive examination (NDE).
— Report from prototype testing
— Report from production testing
— Report from final inspection.

Markings – During production, and on the finished product, we identify the materials used for the primary structure with the corresponding documentation. When markings are not visible on the finished product, we provide a log of the components to identify and ensure traceability of the materials.

Inspection of Welds – Inspection of Welds Welds are subject to visual inspection and NDE. All welds are 100% visually inspected unless otherwise agreed in an MSA.

Step #5 – Testing of the DNV Equipment
“Type” approval of the equipment first involves the construction and testing of the first article or prototype, built according to the approved drawings. It must also use the same materials as proposed for normal production. Tests include: – Four-point lift using all padeyes – Two-point lift test using opposed padeyes – A vertical impact test – A tilt test – Tanks for dangerous cargoes shall in addition be tested with all the requirements of the IMDG code.

DNV Emblem – Once the DNV surveyor has completed the manufacturing inspection, witnessed testing and reviewed the production documentation a “Certificate for Offshore Container” (Form No. 49.07a) will be issued. The numbered DNV emblem for offshore containers (or skid / frame) will be affixed to the container (or skid / frame). The authorized DNV surveyor will hard stamp and the certificate number into the bottom frame below the emblem or in other suitable location on the primary structure near the emblem.

Certified Weld Procedures – Qualified Welders – Certified Design

Procedure – A procedure is the description of the technique (method) adopted to preform quality welding as required by the applicable code. The procedure must be qualified against the certain standards (Codes)
• AWS D1.1
• DNV, Standard for Certification No.2.22 ‘Lifting Appliances’ ,
• DNV, Standard for Certification No.2.7-1 ‘Offshore Containers’,
• DNV, Standard for Certification No.2.7-3 ‘Portable Offshore Units’,

Welder – The contractor (the fabrication shop) is the entity qualifying the weld procedure itself, the individual welder is not certifying the procedure – they are only being qualified to weld according to the procedure.
We must certify that any of our welders welding to the previously qualified (in-house) specification have been tested and are qualified to preform that weld procedure. The welder’s Qualification Test Sheets and Welder Qualification Test Record must be available, attesting to their ability to weld in accordance to our Welding Procedure Specification.

Design – The structural design of the offshore skidded equipment is provided by either our clients or principals. Whoever is responsible for the design, the design must be reviewed and approved by DNV. The design approval process assures that the design of the equipment which is to be DNV classified complies with the DNV rules. This is the beginning of the process to assure that the fabricated equipment satisfies DNV’s requirements.

Special Thanks to – T-Rex Graphics and Animations

Graphic image source – T-REX Graphics and animations. As an added value service, T-REX 3D designs allow clients the ability to utilize T-REX scale models of a DNV equipment placement to more easily navigate complex DNV vessel layouts, effectively allowing operators the capability to safely place the equipment (virtually) before actual equipment had been installed.

T-REX work has been featured in E&P Magazine as well as numerous other industry publications.

T-REX’s render farm facilitates the massive amounts of parallel processing required to generate 3D animations. Currently, 150 CPU Cores have been created and are continuously being added to shorten render times.

Whether we create graphics for the fabricated equipment we construct for you, or your in-house fabricated equipment – the animations effectively illustrate to clients how structures are installed and maintained. We also have a wide range of structural and piping models, developed into a fully produced 3D artistic rendition–ready for computer simulation.

Our clients can also benefit from having their conceptual ideas illustrated and printed as large-format graphic posters and interactive PDFs as projects are being developed.

Our 3D models can provide full functionality of moving parts and assemblies, exact bill of materials, weights, center of gravity of components and assemblies, and 2D + 3D cad drawings.

3D models can also be used in the development of FAT and SIT layout, procedures, equipment accessibility, transportation load out, testing and training.Design packages include: Still Images | Animations | Video

*Disclaimer: Ocean Fab nor its principals are in any way affiliated with DNV GL. DNV regulates all of the processes listed above for DNV certification. These are only historical examples of the processes that we have gone through with DNV. DNV will be the final authority for any process, including new ones that Ocean Fab’s principals have to certify for our clients. The rules change frequently – Please consult your local DNV office for more details. Ocean Fab is not an engineering company – however, our principals can provide engineering services.


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