Pressure Vessels Specification

1. Introduction

This specification governs pressure vessels provided in accordance with the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1; Pressure Vessels, referred to as the ASME Code. Carbon steel vessels are generally limited to wall thickness of 1-1/2" (38 mm) or less and design temperatures of 65000F (3430C) or less.

This specification may be supplemented with other requirements such as vessel data sheets, Project Technical Requirements, Standard Drawings and/or other supplementary specifications (for vessels in specific services, such as three-phase separators).

The combined documents mentioned in this specification define the minimum acceptable requirements for the design, fabrication, inspection and testing of unfired pressure vessels suitable for installation on an offshore platform.

Buyer reserves the right to procure pressure vessels in accordance with the ASME Code even though they may be outside the formal scope of ASME Code, for instance due to size or pressure rating. Such pressure vessels should conform to all ASME Code requirements, except for application of the ASME Code Stamp and National Board Registration.

The most recent issue of the standards, specifications and codes (using the latest addenda issued through the date of this agreement) should be considered as a part of this Specification.

In addition to project technical requirements, pressure vessels should meet all requirements of the governmental authorities having jurisdiction at the location where the pressure vessel is to be installed, as stated in the Agreement, Contract, or Purchase Order, as applicable.

Vessels should be designed to meet the operating and design conditions listed on Vessel Data Sheets. Shell diameter, length and nozzle sizes shown are considered as minimum unless defined otherwise.

Vessels should be equipped with all attachments such as nozzles, manways, tray support rings, and insulation clips.

1.1 Responsibilities

Supplier should be solely responsible for providing complete and operable pressure vessels in full accordance with all applicable industry codes and standards, government regulations and project technical requirements.

Written permission must be obtained before any work is subcontracted.

1.2 Conflicts and Exceptions

All conflicts between this specification or other technical requirements and the applicable codes and standards should be submitted in writing for approval.

2. References

The following documents are considered part of this specification. Use the edition of each referenced document in effect on the date of the publication of this specification.

Industry Standards

American Institute of Steel Construction (AISC)
Manual of Steel Construction


American Society of Civil Engineers (ASCE)
7 Building Code Requirements for Minimum Design Loads in Buildings and Other Structures


American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code

Section II - Materials
Note: SFA requirements for welding consumables may be located in Part C of Section II

Section VIII - Rules for Construction of Pressure Vessels, Division 1

Section VIII - Rules for Construction of Pressure Vessels, Division 2, Alternative Rules

Section IX - Qualification Standard for Welding and Brazing Procedures, Welders, Brazers, and Welding and Brazing Operators
B1.1 Unified Inch Screw Threads
B16.5 Pipe Flanges and Flanged Fittings
B16.47 Large Diameter Steel Flanges, NPS 26 Through NPS 60
B31.3 Process Piping
SFA-5.4 Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding
SFA-5.9 Specification for Bare Stainless Steel Welding Electrodes and Rods


American Society for Testing and Materials (ASTM)
SA-36 Carbon Structural Steel
SA-234 Pipe Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service
SA-263 Specification for Corrosion-Resisting Chromium Steel-Clad Plate, Sheet, or Strip
SA-264 Specification for Corrosion-Resisting Chromium-Nickel Steel-Clad Plate, Sheet, or Strip
SA-285 Pressure Vessel Plates, Carbon Steel, Low and Intermediate Tensile Strength
SA-325 High-Strength Bolts for Structural Steel Joints
SA-435 Specification for Straight-Beam Ultrasonic Examination of Steel Plates
SA-578 Specification for Straight-Beam Ultrasonic Examination of Plain and Clad Steel Plates for Special Applications


American Welding Society (AWS)
D1.1 Structural Welding Code - Steel
A4.2 Standard Procedures for Calibrating Magnetic Instruments to Measure the Delta Ferrite Content of Austenitic and Duplex Ferritic-Austenitic Stainless Steel Weld Metal
A4.3 Standard Method for Determination of the Diffusible Hydrogen Content of Martensitic, Bainitic and Ferritic Steel Weld Metal Produced by Arc Welding


Code of Federal Regulations
46 CFR Part 50 General Provisions
46 CFR Part 54 Pressure Vessels
46 CFR Part 57 Welding and Brazing


National Association of Corrosion Engineers (NACE)
MR-01-75 Sulfide Stress Cracking Resistant Metallic Material for Oil Field Equipment


Process Industry Practices (Drawings) (PIP)
PIP VEFV1103 Vessel Grounding Lug
PIP VESV1003 Fabrication of Welded Vessels and Tanks to be Lined


Steel Structures Pointing Council
SSPC SP-5 White Metal Blast Cleaning
SSPC SP-10 Near-White Blast Cleaning


Welding Research Council
WRC 107/297 Local Stresses in Cylindrical Shells Due to External Loadings on Nozzles


Welding Journal Research Supplement
Stresses in Large Horizontal Cylindrical Pressure Vessels on Two Saddle Supports, by L.P. Zick,Last Modified 2015.

3. General Requirements

The design, materials, fabrication, inspection, testing and documentation of pressure vessels should be in full accordance with the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 or Division 2; Pressure Vessels, and project technical requirements. All Addenda issued through the date of the Agreement, Contract, or Purchase Order should apply in full.

Unless specified otherwise, Supplier should be solely responsible for detailed process design.

  • Any vessel sizing or design criteria provided, including diameter, length, nozzle sizing, internal configurations, etc., should be considered preliminary and confirmed by Supplier.
  • Reduction of specified sizing or design criteria should not be acceptable without prior approval, in writing.

Unless specified otherwise, pressure vessels should have a minimum service life of 20 years, and internals that are readily replaceable should have a minimum service life of 10 years.

Pressure vessels specified for “sour service” should be in accordance with NACE MR-01-75.

All flanges should be in accordance with the latest edition of ASME B16.5, or ASME B16.47.

Piping outside the limits of the ASME Code, if included, should conform to ASME B31.3.

4.0 Materials

Materials and construction for pressure vessels should conform to the ASME Code and with the requirements of this Specification, including the applicable Appendices, unless otherwise indicated on the Buyer-approved vessel drawings.

Any recommended material substitutions that do not meet the above requirements should be submitted to the Buyer for review and approval. For example, Supplier may, with Buyer approval, upgrade material in lieu of impact testing.

Castings should be prohibited, unless agreed to by the Buyer in writing.

All materials should be new and free from mill scale.

Impact test exemption per Division 1, Paragraph UG-20 (f), is not allowed except for P1, Group 1 material up to 1/2" (13 mm) thick.

5.0 Engineering

5.1 General Engineering

Supplier should be responsible for the detailed mechanical design of pressure vessels in accordance with the ASME Code and other Technical Requirements.

The minimum acceptable internal corrosion allowance should be 1/8" (3 mm) for all “wetted” components, including but not limited to the vessel shell, heads, nozzles, internals, etc., unless specified otherwise.

  • If the vessel is to be clad, no corrosion allowance is necessary.
  • Internals that are fabricated from stainless steel or corrosion resistant high alloy steels should be exempt from this corrosion allowance requirement.
  • Internal rings, supports, baffles, vortex breakers, miscellaneous plates and structural shapes, piping supports, etc., should have a minimum thickness of 1/4" (6 mm) exclusive of corrosion allowance.

For internals "wetted" or exposed on both sides, the corrosion allowance should be at least 50% greater than the single side corrosion allowance specified for the shell.

Internals that are bolted and easily removable from the vessel should be exempt from the 150% corrosion allowance requirement, i.e., they should be provided with the same corrosion allowance as the shell.

The minimum thickness of all pressure containing components, including shells, heads, nozzle necks, piping, etc., should be 1/4" (6 mm), including corrosion allowance. The minimum thickness of internals should be 1/4" (6 mm), including corrosion allowance.

A corrosion allowance of 1/8" (3 mm) should be added to the calculated thickness of skirts or support legs attached to vertical vessels and to saddles that support horizontal tanks or drums.

If provided, General Arrangement Drawing should be considered preliminary and Buyer will finalize arrangement details during the approval process. Buyer reserves the right to revise nozzle locations, at no additional cost, up to the point of actual fabrication, i.e., until the shell or head penetrations are cut.

Pressure vessels should be designed and fabricated to facilitate maintenance, repairs and alterations, in particular on adjustable or removable internals.

When specified on the vessel data sheet, vessels designed for internal pressure should be stamped for external pressure, as noted.

The design pressure of equipment in vacuum service or which may be subjected to vacuum during reasonable start-up, operating, shutdown or upset conditions, should be full vacuum except where the Supplier can demonstrate that an economical alternative design will not allow full vacuum to occur.

The following Minimum Design Metal Temperatures (MDMT) and coincident pressures should be indicated on both the vessel nameplate and the Manufacturer's Data Report.

  • MDMT at Maximum Allowable Working Pressure (MAWP).
  • Lowest allowable MDMT and coincident maximum pressure

Vessels subject to steam-out should be designed to withstand the steam-out pressure/temperature condition and external pressure of 7.5 psi (0.5 bar) at 450°F (2320C).

5.2 Design Requirements

Supplier's design should accommodate all of the following requirements, as applicable.

  • Fabrication/Handling Loads
  • Internal Design Pressure
  • External Design Pressure
  • Ocean Transportation Accelerations
  • Wind Pressure Loads
  • External Nozzle Loads
  • Support Clip Point Loads
  • Thermal Expansion
  • Hydrostatic Test
  • In-Service Flooded Condition
  • Sand Loadings

Static head pressures should be included in the design pressure.

The MAWP should be based on the actual metal thickness less corrosion allowance.

The maximum allowable pressure should be limited by the shell or heads, not by minor parts such as flanges, nozzle necks, reinforcing pads, piping, fittings, or manways. The design report should clearly identify the limiting component.

Vessels in vacuum service should be designed for a minimum internal pressure of 50 psig (3.45 bar).

MDMT should be as shown in vessel datasheet, which should apply to both pressure containing and vessel support components. MDMT should not be warmer than 500F (100C).

The shells of larger diameter horizontal vessels should have sufficient thickness and/or adequate stiffness to be structurally stable when full of water at atmospheric pressure.

Temporary and permanent stiffening should be provided to prevent distortion of the vessel during manufacture and transport.

Vessel supports should be designed for wind, seismic and transportation loads.

5.3 Shell

Pressure vessel shells should be fabricated from rolled and welded plate.

For vessels 24" (610 mm) and smaller in outside diameter, seamless pipe in accordance with ASME Code may be utilized.

Vessels made from pipe should have wall thicknesses that account for the mill under thickness tolerance allowed by the piping Code and ASTM specifications.

Longitudinal seams on horizontal vessels should be located a minimum of 30 degrees above the horizontal plane through the centerline of the vessel. Long seams should be staggered about the vessel vertical centerline between adjacent shell cans.

5.4 Heads and Transitions

Unless specified otherwise, all vessel heads should be 2:1 ellipsoidal type with straight flanges a minimum of 1-1/2" (38 mm) long.

For vessels 24" (610 mm) and smaller in outside diameter, weld caps in accordance with the ASME Code may be utilized.

Tori-conical transition sections are preferred. Conical transitions are permitted only when agreed to by the Buyer.

When conical transitions are used:

  • Joint efficiency of 1 is not permitted, due to difficulty in examining the joints.
  • Stiffening rings should not be located closer than 6" (150 mm) from the weld seam of conical transitions.

5.5 Nozzles, Manways, Bosses and Other Openings

Unless specified otherwise by Buyer, all vessel nozzles should be flanged, with a minimum size of 1-1/2" NPS (DN 40).

Flanged nozzles smaller than 1-1/2" NPS (DN 40) should not be allowed unless specifically approved in writing by Buyer, and should never be smaller than 3/4" NPS (DN 20).

Threaded connections should not be allowed unless specified or specifically approved in writing, by Buyer.

  • If approved, threaded connections should be 6000# forged steel full couplings as a minimum.
  • Threaded connections should be limited to either 1/2" or 3/4" NPS (DN 15 or 20).
  • Threaded connections should have their threads chased after installation or postweld heat treatment.
  • Threaded connections should not be acceptable for use on internally coated or clad vessels or stainless steel vessels.

Weld-o-lets, Thread-o-lets, and Sock-o-lets should not be acceptable for vessel connections.

“Set-on" nozzle designs are not acceptable.

All shell and head attachments, including nozzle necks, manway necks, threaded couplings, reinforcing pads and clips should be located a minimum of 2" (50 mm) from vessel longitudinal and circumferential seams.

  • When unavoidable and approved in writing by the Buyer, attachments may cover a welded joint.
  • However, prior to covering the joint, the seam weld should be ground flush and 100% radiographed to a minimum of 6" (150 mm) beyond each side of the attachments.

Nozzles should be either long weld neck flanges, or of built-up construction from pipe nozzle necks and flanges.

  • Long weld neck flanges are preferred by Buyer for all nozzles 3" (DN 80) and smaller.
  • Flanges used in built-up construction should be forged steel weld neck type, bored to match the inside diameter of the pipe nozzle neck.
  • Socket welded or slip-on flanges should not be acceptable, except on manways.
  • Studded pad-type nozzles should not be permitted

Unless specified otherwise, ANSI Class 150 through Class 600 series flanges should be raised face (RF) type, and Class 900 and above should be ring type joint (RTJ) flanges.

On nozzles and manways having tongue and groove facing, the groove should be on the vessel unless the flange face is directed downward, in which case the tongue should be on the vessel.

Vessel nozzle neck thickness should be in accordance with the ASME Code, but with the following minimum thickness requirements:

Nominal Diameter (DN) Nom. Pipe Size: Min. Schedule:
40 1-1/2" XXS
50 to 80 2" to 3" 160
100 4" 120
150 to 250 6" to 10" 80
300 to 400 12" to 16" 60
450 to 500 18" to 20" 30
600 24" 40

Nozzle outside projections should be sufficient for the removal of a properly sized stud from the back side of all flange bolt holes, i.e., between the back of the flange and the vessel shell, head or reinforcing pad. As a minimum, all nozzles should project at least 6" from the vessel outside diameter to the flange face.

Nozzle Design Details and Reinforcement

  • Nozzle design details and reinforcement calculation per current Code is acceptable, provided the design conforms to all the other requirements listed in this specification.

Nozzles with Inside Projections

  • Vessel drains and liquid outlets should be flush with the inside surface of the vessel and should be provided with vortex breakers, unless otherwise shown on the vessel drawings. Flush designs may be required to remove internals.
  • The projection of process connection nozzles should be established with due consideration of sand or scale accumulation.
  • Buyer approval of nozzle projections should be required.
  • Inner edges of nozzles, manway necks, and other pressure vessel penetrations should be ground smooth to 1/8" (3 mm) minimum radius.

Reinforcing Pads and Saddles

  • All reinforcing pads and saddles should be drilled and tapped for a 1/4" NPT (DN 8) telltale hole.
  • Telltale holes should be located on the low axis of the reinforcing pad.
  • Two (2) telltale holes should be provided on all nozzles greater than 24" NPS (DN 600), and on all split or segmental reinforcing pads.
  • A preliminary compressed-air and soap-suds test should be made in accordance with Paragraph UW-15(d) of the ASME Code.

Manways and Manholes

  • Manways should be provided to access each vessel section that requires cleaning or maintenance, and to permit the removal of internal components.
  • Designs should comply with Standard Drawing GF-C87280.
  • Unless specified otherwise, manway size should be 20" NPS (DN 500) for vessels with inside diameters of 4'-0" (1220 mm) and less, and 24" NPS (DN 600) for vessels with inside diameters greater than 4'-0" (1220 mm).
  • A grab bar should be provided inside the vessel above the manway to facilitate vessel entry, as well as individual rung ladders below.
  • All manways and handholes, as well as nozzles designated as "spare", should be provided with blinds, including studs, nuts and gaskets.
  • Handhole blinds should be provided with two (2) handles.
  • All nuts, bolts and washers should be carbon steel coated with Type II Class 8 chromated/cadmium plating.
  • Manway blinds should be hinged or davited, complete with a handle.
  • Nozzle, manway and handhole flange bolt holes should straddle vessel normal centerlines unless noted otherwise.
  • Handholes should be circular with an 8-inch (203 mm) minimum interior diameter.


  • Davits should be designed such that no adjustments are necessary to align the blind flange with its mating flange.
  • Davits should not sag.
  • Davits should be fitted with grease fittings in the swivel.
  • Davit arms fabricated from pipe should be capped to prevent intrusion of moisture.

Nozzles, manways, handholes and couplings should be attached to the vessel with full penetration welds, including reinforcing pad to nozzle neck welds.

The orientations of critical nozzles should be shown on the Vessel Data Sheet.

The Supplier should be responsible for ensuring that nozzle locations will allow for easy access to various control instruments and valves.

The use of gooseneck nozzles (nozzles with elbows, tees, or any other weld fitting) should be subject to Buyer approval.

Vessel Nozzle Loads

  • Vessel/Nozzle connections should be capable of withstanding reasonable piping loads.
  • Buyer reserves the right to supply actual piping loads as they become available.
  • Local stress at the nozzle connection should be calculated using WRC 107/297 when applicable, or ASME Section VIII, Div 2, Appendix 4. Extrapolation of geometric parameter curves in WRC 107/297 should not be permitted.

5.6 Internals

Internal non-pressure-containing parts, such as trays and catalyst support beams, internal equipment, such as cyclones and grids, and attachments welds to vessel, should be designed using allowable stress for material and temperature specified in ASME Section II, Part D, as applicable.

Supplier should provide all internals in accordance with the following requirements.

  • Internals furnished by others should be installed by the Supplier.
  • Baffles, partitions, and other parts should be designed to accommodate differential thermal expansion between vessel shell and internal parts.
  • Baffles, partitions, and other parts should be designed to avoid trapping water or flammable liquids that cannot be drained or purged.

An inlet diverter should be provided on the inlet nozzles of vessels that handle multi-phase fluids, e.g., separators, scrubbers, knockout drums, etc. In addition, inlet diverters should be provided for erosive fluids and for high velocity fluids such as those downstream of high pressure let-down valves.

  • Inlet diverter design should utilize either box or pipe type construction.
  • Three-phase vessels should be equipped with inlet compartmental boxes or baffles with downcomer pipes, to pipe fluid to the interface level.
  • Compartmental boxes should be adequately sized for gas/liquid separation.
  • The inlet diverter should be designed such that no "reflection" of the inlet stream impinges or erodes the vessel shell.
  • A wear plate should be provided on the vessel shell or head if diverter construction directs the inlet fluid against the vessel shell or head.
  • Wear plates should be a minimum of 3/8" (10 mm) thick.
  • Wear plate size should be a minimum of five times the cross sectional area of the inlet nozzle or 12" (305 mm) greater in radius than the nominal pipe size of the inlet nozzle, whichever is greater.

Mist extractors should be provided to remove entrained liquids from gas streams to a minimum level of 0.1 gallon per million standard cubic feet (MMSCF) at 10 microns and larger, and should be sized to maximize turndown capacity.

  • The design should base the open area on the Manufacturer's maximum allowable velocity and the governing combination of pressure and flow.
  • Materials of construction and all mounting hardware should be 316L stainless steel.

Mist extractors should be either parallel plate (vane) type or wire mesh mist pad types as specified. If not specified, mist extractors should be parallel plate (vane) types.

Parallel plate (vane) type mist extractors should be provided with a liquid collection pan, including a liquid seal, to allow proper drainage to the liquid section.

Wire mesh mist pad extractors should have a mist pad density of 11 pounds per cubic foot (lb/ft3) (176 kg/m3) minimum, and mesh thickness of 6" (150 mm) minimum.

Contact the Buyer for additional requirements on vapor/liquid separators and scrubbers.

  • Mist pads should be of 316L stainless steel construction, including mesh, support grid, distribution plates and all mounting hardware.
  • Mist pad assemblies should be accessible for inspection and maintenance, and easily removable for cleaning or replacement.

Vortex breakers should be provided on all liquid outlets that feed process equipment, in particular pumps and hydrocyclones.

  • The design of vortex breakers should comply with Industry Standard.
  • Nozzle inside projection should be flush with the bottom of the vessel.

Vessel drains should be flush with the bottom of the vessel and should be provided with vortex beakers unless shown otherwise on vessel drawings.

If specified in the vessel data sheet, Supplier should provide a jetting system for sand removal.

  • The system should consist of a loop-type manifold with Vee-Jet Model H3/8U6550 steel jet nozzles, or Buyer approved equal, directed at the vessel drains from both sides.
  • Minimum inlet nozzle and header size should be 2" NPS (DN 50).
  • All piping should be schedule 80 thickness as a minimum and should be adequately supported with stand-offs that are seal welded to the vessel shell.
  • All drains should be covered with a removable sand pan a minimum of 18" in length.
  • Jetting system piping should use flanged spools of such length that they may be readily inserted and removed through the vessel manway(s).

Internal stiffener rings should be seal welded.

  • Seal welding details should be indicated on the Supplier's approved detailed fabrication drawings.
  • Provide a 1-inch (25 mm) skip in the weld at the bottom of an internal pad for a vent.
  • Avoid welding over vessel shell welds.

Unless specified otherwise, all internal bolting should be 316 stainless steel, and should be double-nut.

Vessels installed on a Floating Production Facility (FPF).

  • Due to the motions of the FPF, Supplier should design all vessels to maintain performance comparable to similar vessels installed on a fixed foundation. This will require Supplier to pay close attention to the design of vessel internals and may require the installation of additional baffle plates or other motion suppression internals to maintain acceptable performance.
  • Motions for which the equipment should be designed should follow Basis of Design.

Mole Sieve Vessels

  • Fatigue analysis is typically required for these vessels.
  • Structural support beams for mole sieve vessels should be designed on the basis of a 20 psi (1.4 bar) (minimum) pressure drop from gas flow across the bed. This differential pressure should be added to the design live and dead loads from other internals.

5.7 External Attachments

Supplier should provide all external attachments in accordance with the project requirements or vessel data sheet.

External attachments should be shop-welded prior to any stress relief.

External attachments should not cover vessel weld seams without prior Buyer approval.

Lifting Lugs

  • Lifting lugs should be provided to facilitate handling and installation.
  • Horizontal vessels should be provided with two (2) lugs installed on the top centerline of the shell.
  • Vertical vessels should be provided with two (2) lugs installed on the top.
  • Vertical vessels should be provided with one tailing lug installed at the skirt base plate to facilitate laydown and uprighting of the vessel.
  • Lifting lug design should incorporate a safety factor of 2.0 applied to the vessel total dry weight, including all internals.
  • Unless specified otherwise, the lug design load should include the weight of external attachments such as ladders and platforms.
  • Lug design should be based on a maximum sling angle of 30 degrees from the vertical.
  • For vertical vessels, the lug design should account for shipment of the vessel in the horizontal position and uprighting of the vessel.


  • All vertical vessels 6'0" (1.8 m) or more in overall height should be equipped with clips on the shell and top head to permit the addition of a ladder and platform.
  • Pairs of ladder clips should be provided below the top head seam, above the skirt baseplate and at intervals not exceeding a 12'0" (3.7 m) spacing.

Insulation Support

  • Unless specified otherwise, Supplier should furnish shop-welded insulation supports in accordance with the project requirements or vessel data sheet.
  • Support rings should be provided on approximately 12'0" (3.7 m) centers projecting to within ½" (13 mm) of the thickness of the insulation.

Grounding Lug

  • A grounding lug should be supplied with the vessel.

5.8 Vessel Supports

5.8.1 General

Vessel supports should be designed in accordance with the AISC Manual of Steel Construction.

  • Support bolting design (size, number, minimum spacing, etc.) should be based on use of ASTM SA-325 bolting.
  • Designs based on other bolting should require Buyer approval.

Wind, seismic and transportation loads should be in accordance with ASCE 7.

  • Basic wind speed should be per project requirements.
    • As a minimum, the design wind velocity should be 100 miles per hour (3-second gust) (160 km/hr).
    • Unless otherwise stated, Exposure Category D (wind from open body of water) should be assumed.
    • Unless otherwise stated, importance factor for wind load should be 1.15.
  • Seismic coefficients should be as stated in the project requirements.
  • Unless otherwise specified by Buyer, transportation design loads should be based on a lateral acceleration of 0.65g acting along both the longitudinal axis and the transverse axis, and a vertical acceleration of 1.5g as a minimum. The allowable stress may be increased by 33% for the transportation design condition.

Vessels should be provided with integral self-supporting supports designed to accommodate the following loads and load combinations, without additional support.

  • Erect Load with Full Wind. Dead load should include installed weight of the vessel, including internals, platforms, insulation and other permanent attachments.
  • Operating Load with Full Wind or Seismic Loads
    • Operating load should include all dead and live loads, full and zero process liquid levels, full and zero pressures and thrust loads from attached piping.
    • Full and zero liquid level and pressure combinations are required to determine the maximum longitudinal tensile and compressive stresses.
  • Field Hydrostatic Pressure Test Load with Partial Wind

When a field hydrostatic pressure test is required, the vessel should be assumed to be full of water and support should be designed for 50% of the design wind speed (or 25% of the wind load).

When specified by Buyer, vessel supports should be designed to support the vessel completely filled with sand at 3000 pounds per cubic yard (lb/yd3)(1800 kg/m3), and simultaneously subjected to the maximum wind load. As a minimum, production separators and test separators should be designed to meet this requirement.

Base plates and rings should be designed such that the support bearing pressure should not exceed 750 psi (51.7 MPa).

Support steel should be a minimum of 1/4" (6.4 mm) thick including corrosion allowance.

  • A corrosion allowance of 1/8" (3 mm) should be added to the calculated thickness of skirts, saddles and support legs.
  • All support welding should utilize continuous seal-welded construction, both inside and outside.

5.8.2 Horizontal Vessels

Horizontal pressure vessels should be provided with two (2) structural steel saddles welded to the vessel shell.

Additional supports should not be acceptable without prior written agreement by Buyer.

Saddle design should include a web plate, base plate, end flanges and stiffening webs as a minimum.

  • The contact angle between the saddle and vessel shell should be between 120 and 150 degrees.
  • A reinforcing plate should be provided between the vessel shell and the saddle, if needed to reduce local concentrated stresses in the vessel wall.
  • All saddle reinforcing plate corners should have a radius of five times the plate thickness, as a minimum.

Unless specified otherwise, saddles should be provided with bolt holes to allow bolted connection to platform steel.

  • Saddle bolt holes should be slotted at one end of the vessel for thermal expansion if the temperature difference between maximum operating condition and minimum ambient condition is greater than 1000F (380C).
  • If thermal growth between the saddles exceeds 3/8" (10 mm), a slide bearing plate should be provided between the saddle base plate and the supporting structural member on the platform.
  • The slide plate design should include Teflon slide plates and pipe sleeve-type guides.

Horizontal vessel shells should be analyzed in accordance with L. P. Zick's "Stresses in Large Horizontal Cylindrical Pressure Vessels on Two Saddle Supports."

In no case should the distance between the head tangent line and the saddle centerline be greater than 20% of the tangent to tangent length of the vessel.

Internal stiffener rings should not be accepted as a means of stiffening horizontal vessels.

5.8.3 Vertical Vessels

Vertical vessels should be provided with a circular skirt-type support.

  • Support skirts should be the same outside diameter as the vessel supported.
  • The skirt should be butt-welded to the knuckle portion of the bottom head, and the weld should be contoured to blend smoothly into the head.
  • The allowable stress value for skirt thickness should be calculated in accordance with the ASME Code using a weld joint efficiency of 0.55.

Unless specified otherwise, skirts should be provided with bolt holes to allow bolted connection to platform steel.

Skirt design should include a base ring, access openings, high point vents and pipe openings, as follows:

  • Skirts should be provided with a base ring with a minimum thickness of 1/2" (13 mm) and a maximum thickness of 2" (50 mm).
    • If necessary, gusset plates should be provided to limit the base ring to 2" maximum thickness.
    • Gusset spacing should be 18" (457 mm) minimum.
  • Skirts should be provided with one (1) access opening.
    • The opening should be 18" (457 mm) minimum in diameter.
    • Skirt access openings should be reinforced with a pipe or rolled collar-type sleeve along the perimeter of the opening.
    • The access opening may be oblong on tall skirts, to provide better access.
    • Provisions should be made so that the skirt will not hold water.
  • Skirts should be provided with a minimum of two (2) vent holes located as close to the bottom head of the vessel as possible. Vent holes should be 2" (50 mm) in size, evenly spaced around the vessel circumference, and reinforced with pipe sleeves.
  • All pipe openings should be reinforced with pipe sleeves approximately 1" (25 mm) larger in diameter than the largest pipe spool flange, as applicable.
  • All reinforcing sleeves should project 2" (50 mm) beyond the skirt (both internally and externally) or should be equal in length to the thickness of any fireproofing or insulation to be applied to the vessel, whichever is greater.
  • The number of anchor bolts should be in multiples of four and there should be a minimum of four.
  • The minimum size of anchor bolts for towers should be 1 inch (25 mm) diameter.
  • The minimum size anchor bolts permitted for vessels other than towers should be 3/4" (19 mm) diameter.
  • Fillet welds attaching skirts to heads should have a minimum fillet size of the thickness of the skirt.
  • If base rings are fabricated from segments, these should be joined with full penetration double butt welds.

Vessels with outside diameters less than or equal to 24" (610 mm) and not exceeding 10'-0" (3.05 m) in overall height may be provided with leg type supports, subject to Buyer approval.

Wind Requirements for Vertical Vessels

  • Vertical vessels or columns with H/D ratios exceeding 15 (where H is the length of the vessel from the point of support to the top tangent line and D is the average diameter in the top third of the vessel column) should be checked for vortex shedding vibrations.
  • Critical wind velocity of the vessel should be greater than 3 times the maximum 10-minute sustained wind velocity corrected at the top of the vessel.

Unless otherwise specified, deflection at the top of vertical vessels or columns should be limited to 6 inches per 100 ft (5 mm per meter) of vessel height.

6.0 Fabrication

6.1 General

All Code Category A and B weld joints, including longitudinal and circumferential joints in vessel shells, heads, and nozzles should be full penetration, double butt welds (Type 1).

Where access limitations require the use of single-welded butt joints, the weld detail should ensure a full penetration weld with a smooth internal surface contour, to obtain radiographs equivalent in quality to double butt welded joints.

An acceptable equivalent for Category A and B joints in nozzles, elbows, and single-sided closure seams, is a single welded butt joint with a gas tungsten arc (GTAW) root bead.

Vessels with a wall thickness of 1/2" (13 mm) and less may utilize single butt-welded joints, with prior Buyer approval.

  • The weld detail employed should ensure a full penetration weld utilizing a single "V" or "U" type weld bevel.
  • Joints in vessels to be internally coated should utilize double butt welds regardless of thickness, to assure good coating application.

All Code Category C and D weld joints, including attachment welds on nozzles, couplings, and manways, should be full penetration welds through the vessel wall, including reinforcing pads where used, and should be welded from both sides.

Where access limitations require the use of single-welded joints, the weld detail should ensure a full penetration weld with a smooth inside surface contour.

Back-up strips should not be used.

Vertical downhill welding should not be permitted.

All semi-automatic or fully-automatic welds should be made utilizing a multi-pass technique.

All non-pressure containing welds, both internal and external, should be full, continuous seal welds.

  • Skip or stitch welding should not be acceptable.
  • Internal and external attachments to vessels shell or head should be continuously seal welded.

Welding wire used in submerged arc or metallic inert gas processes should be stored in such a manner as to avoid contamination by the formation of oxides on the wire surface.

Electrodes, wires and fluxes should be selected to produce welds with mechanical properties not less than that of the base metal.

Low hydrogen consumables should be certified by the electrode manufacturer, or tested by Supplier to comply with AWS A4.3 H8 or better.

An internal gas purge should be provided for the root pass and the second layer of stainless steel welds for any gas shielded process.

Welding should not be permitted in inclement weather (wind and/or rain) unless both the welder and the work are well protected from the elements.

Welding should not be permitted when the wind velocity exceeds 5 miles per hour (8 km/hr) for gas shielded processes and 10 miles per hour (16 km/hr) for flux shielded processes unless appropriate wind screens are used.

Welding (without preheat) should not be permitted if the relative humidity is above 50%.

The minimum required preheat for carbon steel should be as follows:

  • 50°F (100C) if either the ambient temperature or the metal surface temperature is less than 50°F (100C), for thicknesses up to 1.25 inches (32mm).
  • 200°F (930C) for thicknesses greater than 1.25 inches (32mm).

All welding equipment should be in good condition and subject to inspection by Buyer. Any equipment found in need of repair should be removed from fabrication work until said repair is completed.

For pressure vessels that are to be internally lined, fabrication details should comply with PIP VESV1003.

6.2 Qualification of Welding Procedures and Welders

All Weld Procedure Specifications (WPS) and Procedure Qualification Records (PQR) should be submitted to and approved by the Buyer prior to any welding. All welding procedures should be in writing and should contain the minimum information according to ASME Section IX Forms QW-482 and 483.

Pre qualified procedures will not be accepted for processes other than automatic submerged arc and manual shielded metal arc.

The essential variables must be defined in the procedure specification and must be adhered to in production welding.

For P1 materials, each WPS should include a statement indicating the Minimum Design Metal Temperature (MDMT) for which the WPS is qualified. Qualification may be either by Charpy impact testing or by exemption, as provided by paragraph UCS-66 of the ASME Code.

Vessels in sour service are subject to the requirements of NACE MR-01-75. All welding procedures must be supported by Procedure Qualification Records that show compliance with the hardness limitations listed in MR-01-75 for weld metal, HAZ, and parent metal.

Supplier should submit a weld map that identifies the proposed welding process for all welds, or types of weld configurations, prior to the start of welding.

  • The map must identify the Welding Procedure Specification (WPS) for each weld and must show that the WPS assignments are consistent with the Minimum Design Metal Temperature for each weld.
  • If requested by Buyer, Supplier should provide a welding sequence for critical joints or welds.

6.2.1 Welder and Welding Operator Qualification

All welder qualifications and certificates with picture identification should be submitted to Buyer for approval prior to any fabrication.

6.2.2 Weld Repair Procedures

Supplier should prepare weld repair procedures that outline the steps necessary to make cap, through-wall, and partial penetration repairs. All weld repair procedures should be submitted to Buyer for approval prior to start of repair work.

6.3 Welding Processes

Acceptable weld processes for welding of the pressure envelope and supports should include the following:

  • Gas Shielded Flux Core-Arc Welding (FCAW-G)
  • Gas Metal-Arc Welding (GMAW)
  • Gas Tungsten-Arc Welding (GTAW)
  • Shielded Metal-Arc Welding (SMAW)
  • Submerged-Arc Welding (SAW)

6.3.1 Gas Shielded Flux Core-Arc Welding (FCAW-G)

  • For carbon steel, the maximum wire diameter for FCAW consumable should be limited to 1/16" (1.6 mm) for out of position welding and 3/32" (2.4 mm) for flat position welding.
  • Electrode diameter should not exceed 3/32" (2.4 mm) for austenitic stainless steel.
  • 100% ultrasonic inspection is required for all nozzle attachment welds made using FCAW.

6.3.2 Shielded Metal-Arc Welding (SMAW)

  • Low hydrogen electrodes (e.g., E7018) should be required, except cellulosic SMAW electrodes may be used for the root and hot pass on single-sided butt welds.
  • Coated electrodes should be stored in dry heated storage bins or cabinets.
  • Cellulosic electrodes should not be permitted for welds on API flanges.
  • The following electrode classifications should NOT be accepted:
    • E6012
    • E6013
    • E7014
    • E7020
    • E7024
    • E8013-B2

6.3.3 Submerged-Arc Welding (SAW)

  • Semi-automatic equipment is not permitted.
  • Weld passes should not be greater than 3/8" (10 mm) thick.
  • SAW procedure qualification test records should show the name of the manufacturer and the trade name of the wire and flux used to qualify the procedure. Flux manufacturer's trade name should be an essential variable.
  • Addition of alloy agents through the flux should not be acceptable.
  • SAW is not permitted for austenitic stainless steel.

6.4 Production Welding

GMAW and TIG welding processes should be limited to root passes unless specifically approved otherwise by Buyer in writing.

  • All GMAW root welds should be back gouged to remove all deposited metal prior to the start of welding of the remaining passes.
  • The interrupted-arc (short-circuit transfer) GMAW process should not be used except for the following applications.
    • Root passes on circumferential, longitudinal, or nozzle-to-shell welds only if backgouged and backwelded.
    • Root passes on circumferential piping welds for fabricated nozzles or internal piping.
    • Root passes on nonpressure-containing vessel internals.

Nozzles, couplings, and manways should be attached to the vessel with full penetration welds through the vessel wall, including any reinforcing pads or plate which may be used.

All long seams should clear nozzles, clips, and other external parts by a minimum of 2.0 inches (50 mm).

Long seams of trayed vessels should not be located behind downcomers.

Long seams for horizontal vessels should be located a minimum of 30 degrees above the horizontal plane through the centerline of the vessel.

Long seams should be located such that internal visual inspection can be made with as much of vessel internals in place as possible.

Welds are to be chipped or ground flush with the plate on the inside of the vessels where necessary for the passage of trays and baffles. Melting out of the reverse side of the weld should not be permitted.

Internal and external attachments to vessel shell or head should be continuously seal welded (unless prohibited by the ASME Code), except that a 1" (25 mm) skip in the bottom of an internal pad should be made for a vent. Supplier should include weld details on approved detailed fabrication drawings.

Jigs should be utilized on direct connected instrument nozzle pairs to accurately set dimensions and ensure that flange faces are parallel.

All welds should be thoroughly cleaned after each pass by power wire brushing to remove all slag, splatter, coatings and dirt.

  • All joints welded from both sides should be back chipped or back gouged to sound metal before continuing welding on the second side of the joint.
  • The use of needle guns to remove slag from finished welds should be prohibited.

Tack welding should be removed.

Welds should not be started or stopped within 12 inches (300 mm) of a weld junction.

Welding leads should not be clamped so as to cause arc strikes inside RTJ grooves.

Grounds may be clamped to hubs, etc. Bolt-on or swivel grounds should be used whenever possible.

ASME B31.3 should be the authority for welding piping outside the limits of the ASME Pressure Vessel Code.

All structural welding should conform to sizes of welds as noted on drawings or, if not specified, should conform to the requirements of AWS D1.1.

For vessels in cyclic service, as specified in the data sheet, e.g., molecular sieve dehydrators, all attachment welds to pressure parts should be ground to a smooth radius.

6.5 Heat Treatment and Stress Relieving

Postweld heat treatment (stress-relief) should be provided in accordance with ASME Code, and as specified in the Technical Requirements or vessel data sheet. Vessels subject to sulfide stress cracking should be postweld heat treated.

When heat treatment is required, the whole vessel should be heat treated at one heating.

Flange faces should be protected against oxidation during heat treatment.

Welding should not be allowed on pressure vessels after stress relieving, unless specifically authorized in writing by Buyer and in accordance with ASME Code requirements.

When heat treatment is required on vessels and equipment where access to the internal surfaces is impossible after the final weld closure, the Supplier should state in the proposal the method to be used to control scale formation or to remove scale.

During postweld heat treatment, vessels should be blocked and supported as necessary to avoid any deformation or damage.

If internal parts are installed in the vessel prior to postweld heat treatment, all parts should be realigned after postweld heat treatment to comply with the vessel drawing.

After postweld heat treatment, warpage should be corrected and all bolts should be retightened.

7.0 Inspection and Testing

7.1 General

Buyer reserves the right to inspect, or for an authorized representative to inspect, vessels at any time during fabrication and to have access to all test records and results.

Supplier should afford Buyer, free of cost, all necessary and reasonable information and use of facilities needed for determining that vessels are being furnished in accordance with the Technical Requirements and vessel data sheets.

Buyer inspection should not relieve Supplier of responsibility for all examinations necessary to assure compliance with the ASME Code and the requirements of this specification and the vessel data sheet.

Prior to the final inspection, all slag, loose scale, dirt, grit, weld splatter, paint, oil, test medium and other foreign matter should be removed from inside and outside the vessel.

For vessels in cyclic service, for which attachment welds to pressure parts have been ground to a smooth radius, the ground welds should be checked by magnetic particle or dye Penetrant examination.

7.2 Non Destructive Examination

Supplier should provide ultrasonic or magnetic particle inspection of all welds utilizing the Flux Core Arc Welding (FCAW) process.

For nozzle attachment welds using FCAW, 100% ultrasonic inspection is required.

Note: Supplemental inspection requirements may be adopted to monitor in-service H2S-induced cracking.

Ultrasonic inspection in accordance with ASME Code, Appendix 12 should be required for all Code Category C and D welds.

7.3 Radiographic Inspection

As a minimum, all butt welds (including butt welds for flange-to-pipe nozzles and nozzles constructed of rolled plate) should be spot radiographed in accordance with ASME Code.

  • One radiograph should be taken showing not less than 14" (350 mm) of weld for each longitudinal and each circumferential joint in the shell and heads.
  • One spot radiograph (14") (350 mm) should be taken of each butt weld in the skirt of a vertical vessel.

When 100% radiography is specified, all butt welds should be included.

  • Spot radiography per Section 7.3 first item is also mandatory for all Category B welds, including nozzles, only when full radiography is required
  • Category C and D welds should receive the following inspections:
    • Backgouged surfaces of all Category C and D welds should be liquid penetrant or magnetic particle tested per Appendix 8 or Appendix 6 of the ASME Code, as applicable.
    • All surfaces of completed Category C and D welds should be magnetic particle inspected per Appendix 6 of ASME Code.
    • Unless otherwise specified, NDE in above items will be randomly inspected by a Buyer inspector or representative.
  • When specified in the vessel data sheet as an alternative to previous bullet point, ultrasonic testing (UT) is required for Category C and D welds in accordance with Code Appendix 12. This option is required only when full radiography is mandated in the vessel data sheet or Project Technical Requirements.

When full (100%) radiography is specified for solely Code Category A weld joints, spot radiography should be required for all Code Category B welds, including nozzles.

Welds subjected to forming operations, as might occur in a welded head, should be fully (100%) radiographed after forming, but before attachment to the vessel.

Buyer should be notified five (5) working days in advance of final spot radiography, so that Buyer may designate the locations of the random radiographs.

  • For any rejectable weld defects that, in the opinion of Buyer, do not appear to be random in nature, the entire length of that weld should be radiographed.
  • Should additional repairs be required, then Supplier should repair all defects in accordance with ASME Code, and Supplier should bear all costs for the additional radiographs and repairs.
  • Should repairs not be required, Buyer will reimburse Supplier for the costs of the additional radiographs.
  • Any vessel that becomes fully (100%) radiographed should be given ASME Code status and stamped as a fully radiographed vessel.

For carbon steel vessels, radiographs should not be taken within 24 hours of completion of the weld being examined.

Radiographic film should be retained by Supplier for at least a year after the date that the Authorized Inspector approves the Manufacturer's Code Data Report.

All welds in piping outside the limits of the ASME Code should be inspected radiographically and interpreted in accordance with ASME B31.3.

Piping requiring stress relieving should be radiographed before and after stress relieving.

7.4 Hydrostatic Pressure Testing

After completion of all fabrication, welding, visual inspection, NDE, radiography, stress relieving and telltale-hole air tests, Supplier should perform a hydrostatic test in accordance with the ASME Code.

  • Hydrostatic tests should be performed in the presence of, and with the approval of, Supplier's Authorized Inspector and/or Buyer.
  • Vessels should not have been previously hydrotested by Supplier without Buyer authorization.
  • Hydrostatic testing of piping outside the limits of the ASME Code should be as prescribed in ASME B31.3.

Supplier should furnish all test facilities, equipment and materials, including chart recorder, gages, blinds, studs, nuts, gaskets, etc. necessary for the test.

The vessel should be cleaned internally and externally of all dirt, debris, weld slag, weld spatter, etc. before hydrostatic testing.

The hydrostatic test should be performed with the "in service" type of gaskets, and should not utilize any gasket sealing compounds.

Vessels should not have been primed, painted, or internally coated prior to hydrostatic testing.

Supplier should provide ten (10) days advance notification so that the hydrostatic test may be witnessed by Buyer.

Fresh potable water should be utilized for hydrostatic testing. The minimum water and metal temperature for the test should be 600F (150C) or 300F (170C) above MDMT at MAWP, whichever is warmer.

Hydrostatic Test Pressure should be determined as follows:

  • The hydrostatic test pressure should be the pressure calculated to stress the full thickness, including corrosion allowance and cladding, if any, of the strongest Category A weld to a minimum of the appropriate Code test factor (i.e., 1.3 for Division 1 vessels or 1.25 for Division 2 vessels) times the allowable stress for the material at the test temperature.
  • This pressure is based on the Code test factor times the Maximum Allowable Pressure New and Cold (MAP).
  • No component of the vessel should be stressed above 90% of its specified minimum yield strength.
  • If the hydrostatic test pressure so calculated will stress components of the vessel above 90% of the specified minimum yield strength, the test pressure should be reduced by the least amount necessary to avoid overstressing weaker components.

The minimum test time should be one (1) hour after stabilization of pressure and temperature.

  • Test pressure and temperature should be chart recorded.
  • Ambient air temperature should be recorded at the start and end of testing.

After the final hydrostatic test, the vessel should be drained completely and dried thoroughly.

  • Draining and drying should be completed within one week of filling the vessel with hydrostatic test water.
  • If the vessel cannot be visually inspected to ensure complete drying, the Supplier should use a dehumidified air dryer to show that the outlet relative humidity is the same as the inlet relative humidity.

Horizontal vessels should be hydrostatically tested with the permanent support saddles. Additional temporary supports should not be allowed.

Vertical vessels should be properly supported if hydrostatically tested in the horizontal position.

Blinded nozzles, handholes and manways should be provided with new gaskets after completion of hydrostatic testing and painting.

7.5 Pneumatic Pressure Testing

Pneumatic pressure testing should not be accepted in lieu of hydrostatic testing on vessels.

All reinforcing, saddle and wear pads should be pneumatically tested with air and soapsuds at 15 psig (1 bar) prior to hydrostatic testing.

8.0 Protective Coatings

Supplier should provide external and internal coatings as specified.

Coating procedures, including pre-cleaning, surface preparation, application and products to be used should be reviewed and approved by Buyer prior to the start of the coating process.

The proposed procedures should be in accordance with the requirements listed in vessel data sheet and the (coating) product data sheets.

All coating work should be performed after completion of all fabrication and testing, including hydrostatic pressure testing and reinforcing pad air testing.

The entire vessel (including the inside of the skirt, outside of the bottom head, entire base ring, and all skirt attachments) should be coated.

  • Nozzles should be painted on the flange edges, inside bolt holes, and up to the gasket surface.
  • RTJ flange grooves should be protected during blasting and greased during painting operations.

Couplings should be tightly plugged with hex-head plugs during blasting and painting.

Bolt holes in vessel supports and attachments should be blasted and fully primed before assembly.

Ladders, cages, platforms and handrails should be hot-dip galvanized and/or coated.

9.0 Identification and Markings

Vessels should be provided with a stainless steel nameplate in accordance with the ASME Code.

The nameplate should include the following data as a minimum, which should be engraved or stamped into the nameplate:

  • ASME Code Stamp (indicating degree of radiography and stress relief)
  • National Board Registration Number
  • Manufacturer's Name
  • Manufacturer's Serial Number
  • Year Built
  • Maximum Allowable Working Pressure - Hot and Corroded (MAWP)
  • Maximum Allowable Pressure - New and Cold (MAP)
  • Corrosion Allowance
  • Shell Material and Thickness
  • Head Material, Thickness and Type
  • Vessel Name (Service) and Tag Number
  • Purchase Order Number
  • Vessel Weights - Dry, Operating and Hydrostatic Test
  • MDMT at MAWP.
  • Lowest allowable MDMT and coincident maximum pressure.

Nameplates should be located so that they are easily accessible after installation.

On insulated vessels, the nameplate should be installed on a "T" or "U" bracket so as not to be covered or obstructed by insulation.

Nameplates should be securely attached to pressure vessels using one of the following methods:

  • Seal-welding to shell or head prior to stress relief or hydrostatic testing.
  • Riveted (stainless steel) to a “T” or “U” bracket.
  • Bolted (stainless steel) to a “T” or “U” bracket with the nuts tack welded.

The vessel name (service) and tag number should be painted or stenciled the on opposite sides of the vessel.

  • Lettering should be black, 6" (150 mm) high capital block letters, and located on the shell horizontal centerline for horizontal vessels, and about 6'-0" (1.85 m) above the base plate for vertical vessels.
  • Horizontal vessels longer than 20'-0" (6 m) T/T, or greater than 8'-0" (2.5 m) in outside diameter should also include identification lettering on both heads.
  • Tall vertical vessels should include additional identification lettering at each operating level as specified by Buyer.

Supplier should mark actual vessel dry weight on the shell and heads with paint sticks before shipping.

For vessels with internal coating or postweld heat treating, a warning should be painted on the outside of the vessel after completion stating: “This vessel is internally coated – depressure with care” and/or “This vessel has been postweld heat treated - no welding to this vessel is allowed.”

10.0 Preparation for Shipment and Storage

Supplier should be responsible for preparing vessels for shipment and storage in accordance with the Commercial Terms and Conditions.

After fabrication, ladders, platforms, and other removable items supplied by vessel Supplier should be completely installed on the vessel in the shop to ensure proper fit-up, then disassembled and shipped separately.

  • Each platform and ladder section should be identified with a metal tag, loosely wired to each section.
  • Loose shipped items should be properly tagged with the item name, the vessel name, and the tag number.

All unpainted finished surfaces, e.g., flange gasket faces, threads, etc., should be coated with suitable rust preventive or grease.

  • All bolting should be lubricated with thread lubricant prior to final installation.
  • Telltale holes in reinforcing and saddle pads should be plugged with heavy grease.

All flanged openings should be protected with a flange cover, plastic sheet, and gasket.

  • Flange covers should be constructed from exterior grade plywood, 1/2" (13 mm) minimum thickness, and secured with a minimum of 50%, or four (4) bolts, whichever is greater.
  • A plastic sheet should be inserted between the flange face and the wooden cover.
  • Threaded openings and couplings, except telltale holes in reinforcing pads and saddles, should be protected with a forged steel hex head pipe plug rated for the maximum allowable working pressure of the vessel.
  • Plugs should be either chromated/cadmium plated carbon steel or 316 stainless steel.

Supplier should provide suitable supports for internal parts, which might be damaged during shipment.

  • Temporary internal supports should be painted yellow, and the vessel should be clearly identified or tagged as having temporary internal supports.
  • If removal of the supports is required prior to putting the vessel into service, the Buyer should be notified in writing, with a drawing showing the supports to be removed.

Supplier will submit for review and approval by Buyer, a written storage procedure for storage up to twelve (12) months.

All gage glasses and cocks should be tagged, packed in clearly marked waterproof crates suitable for twelve (12) months outdoor storage, and shipped separately.

Supplier should be responsible for loading and securing vessels on transport truck/vessel at Supplier's manufacturing facility.

  • The Supplier should provide the vessel with wood skids or crates to ensure protection against damage during shipment.
  • Supplier should provide Buyer at least one (1) week advance notice of vessel completion and delivery availability.

If vessel is specified to be stored, Supplier should provide suitable type and quantity of desiccant for the stated storage period.

Desiccant should be placed in bags and tagged for ease of identification, removal and replacement.

Supplier should notify Buyer in writing of any special handling procedures, such as:

  • Limitations on lifting or sling angles.
  • Restrictions on laying vertical vessels in the horizontal position.
  • Internal supports necessary for shipment.
  • Height restrictions, e.g., bridges, power lines, etc. along land transportation routes of the completed vessel(s).

Each removable piece of equipment that will be shipped separately from the vessel should be identified with a stainless steel tag.

  • The tag should be securely wired to the equipment.
  • The identification tag should be die-stamped with the item number, platform number, piece number, and the total number of pieces.

The identification tag should include the vessel tag name and number, to which each piece corresponds.

One full-sized copy of the approved vessel as-built drawings should be sealed in plastic and shipped with the vessel.

Supplier should clearly mark, in 2-inch (50 mm) letters, the proper information required to identify the items inside crates.

A “bill of lading” placed into a waterproof container should be attached to both the inside and outside of each crate.

If Supplier is responsible for shipping, Buyer should be notified at least one week in advance of the intended vessel delivery.

11.0 Documentation Requirements

Supplier should provide documentation in accordance with ASME Code and the vessel data sheet or Technical Requirements.

The following approval documentation should be submitted to Buyer for review and approval prior to the start of fabrication:

  • ASME Code Calculations
  • Buyer Required Calculations - Process and Sizing, Wind, Transportation, Lift, Center of Gravity, etc.
  • Weld Map with WPS Identification (including MDMT identifications and welding sequences for critical joints, if requested by Buyer)
  • Weld Procedure Specifications and Procedure Qualification Records
  • General Arrangement and Elevation Drawing
  • Fabrication Sections and Details
  • General Design, Fabrication and Painting Procedures and/or Notes

Supplier approval submittals should include copies or prints per Buyer’s requirements.

Buyer reserves the right to relocate the vessel connections, clips, lugs, etc., before fabrication is begun.

Supplier should allow two (2) weeks for Buyer review and return of approval drawings.

Supplier's general arrangement and fabrication drawings should include the following information as a minimum:

  • Plan, Elevation and End Views - fully dimensioned and drawn to scale
  • Shell Thickness and Head Thickness and Type
  • Details of all Vessel Internals and External Attachments
  • Bill of Materials - component, material specs, quantities, ratings, and thickness
  • Nozzle Schedule - mark, quantity, description, sizes, rating, type, thickness
  • Flange ratings
  • Nameplate Details - including dimensions and mounting details
  • Vessel Weights - shipping, dry, hydrotest, operating normal and operating flooded (or 100% sand-filled, if applicable)
  • Hydrostatic Test Pressure
  • Radiography and NDE Requirements
  • Weld details
  • Surface preparation for coatings: external and internal
  • Coating requirements: external and internal
  • Clearance from main seams for attachments and penetrations
  • Bill of materials

After completion of the vessel, Supplier should provide “Record Data Books” to Buyer. The Record Data Books should include the following documentation, as a minimum:

  • ASME Code Data Report
  • Drawings, Sections and Details (“As-Built”)
  • Calculations (ASME Code and Buyer Required)
  • Weld Procedure Specifications, Procedure Qualification Records and Weld/Welder Identification Maps
  • Mill Test Certificates
  • Fabrication and Inspection Records
  • Hydrostatic Test Chart and Certificate
  • Stress Relief Chart and Certificate (if applicable)
  • Nameplate Rubbing or Photograph
  • Operating and Maintenance Manual (if applicable)

Supplier should utilize industry standard drawing practices, as a minimum, in executing the work.

  • For instance, all drawings should utilize title blocks and revision blocks for drawing identification and control.
  • All drawings should be dated and signed by appropriate Supplier representatives.
  • When revised, Supplier should identify revisions on drawings with clouds and revision triangles and the title and revision blocks should be appropriately completed with descriptions, dates, and signatures.

Supplier should furnish final as-built drawings and data sheets in both hard copy and editable electronic formats.



Tags: Pressure Vessel Offshore