Pressure Vessel Component Cases: Head & Flange Component Protection

In the logistics chain of pressure vessel fabrication and maintenance, heads and flanges are the two component families that suffer most from impact damage. Once the curved surface of a head develops a dent or local plastic deformation, it directly affects subsequent fit-up and weld quality. Once the sealing face of a flange is scratched or indented, even a defect of a few tenths of a millimetre can become a leak path at hydrostatic test or in service. The conclusion is clear: a pressure vessel component case must be designed around contoured form-fitting support, sealing-face isolation, graded zoned inserts, and verifiable sealing and test evidence - not simply around putting components into a strong box. JUNZHJIA supplies this class of case with custom inserts, OEM/ODM programmes and volume production to pressure vessel fabricators, chemical equipment suppliers and export traders.

The transport difficulty of pressure vessel spares differs from that of general machinery spares. It is not fear of a fall; it is fear of invisible damage. A slight depression in a head surface is hard to see after painting. A fine scratch on a flange sealing face only shows up under blueing or angled lighting. Both types of defect typically reveal themselves at the next process step - fit-up, welding or hydrostatic test - when rework is extremely expensive. This article gives protection grades, restraint methods, insert materials, sealing levels and verification references by component category, with comparison tables, an acceptance method and a FAQ section that process, quality and procurement staff can quote directly.

Table of Contents

• 1. A Risk Map for Pressure Vessel Component Transport
• 2. Component Families and Protection Grade Logic
• 3. Head Cases: Elliptical, Spherical and Torispherical Heads
• 4. Flange Cases: Weld-Neck Flanges and Sealing-Face Protection
• 5. Tubesheets and Heat-Exchanger Tube Bundles
• 6. Shell Courses and Nozzles: Thin-Walled Long Parts
• 7. Gaskets, Bolts and Fasteners
• 8. Heavy-Duty Structure and Lifting: Large-Diameter Heads
• 9. Rust Prevention, Machined Faces and Heat-Treatment State
• 10. Insert Materials and Restraint Methods Compared
• 11. Sealing, IP Ratings and Pressure Equalisation
• 12. Test References and Regulatory Boundaries for Pressure Parts
• 13. Acceptance, AQL and the OEM/ODM Flow

1. A Risk Map for Pressure Vessel Component Transport

A risk map is more useful for decisions than a list. Transport risk for pressure vessel components arrives along four routes.

The first is point load. A head is a thin-walled surface of revolution whose resistance to local load is far lower than its resistance to uniform load. A steel strap pulled directly across a head surface, or a timber batten braced against a spherical face, creates a point load. As a rule, direct steel-strap lashing against a thin-walled head should be avoided entirely; the load must be distributed over a sufficiently large contact area through a curved saddle or soft pad.

The second is impact on edges and bosses. Flange sealing faces, nozzle end faces, bolt holes and weld bevels are all high-value, small-area features. Once struck, they must be dressed, and dressing may destroy the bevel angle or the sealing-face roughness.

The third is cumulative deformation. Thin-walled long parts such as shell courses and nozzles progressively ovalise or bow through repeated handling. A single event is invisible; the accumulation exceeds tolerance.

The fourth is corrosion and contamination. Machined faces, bevels and sealing faces corrode readily in humid conditions, and the corrosion products are themselves a contaminant that affects subsequent weld quality.

These four routes map to four countermeasures: distribute the load, isolate the contact, control the restraint points, and isolate the environment. Miss any one and the case is a container rather than a protection system. For projects assessing a supplier from scratch, see how to choose a protective case OEM factory.

2. Component Families and Protection Grade Logic

Grading by surface sensitivity, stiffness, weight and downstream process dependency is the first step in case configuration. Pressure vessel components are especially sensitive to the last dimension: a flange is not an expensive part, but the bevel on it determines the quality of an entire weld.

In real projects one batch of pressure vessel spares frequently spans V1 to V4. Split the cases by grade rather than packing everything together, and provide a case-splitting list with drawing-number identification. The benefits are that each case weight stays controllable, the carrier can allocate cases individually, and unpacking acceptance can use a different method per grade - visual and blueing for V1, curved templates for V2, dimensional measurement for V3 and V4.

For critical V1 and V2 components, contoured custom inserts are the core measure. Capture the actual surface by 3D scanning and then mill the cavity; how closely the cavity follows the component determines the magnitude of point load. Cavity depth is normally 1/2 to 2/3 of component height so that nothing falls out when the case is turned over. For the complete workflow from scan to finished insert, see the custom foam insert guide.

3. Head Cases: Elliptical, Spherical and Torispherical Heads

The head is the archetypal thin-walled curved shell among pressure vessel components. Common forms include elliptical, torispherical, spherical, conical and flat heads, ranging from 300 mm to over 4000 mm in diameter.

The core risk is local denting. Under a concentrated force, the local curvature of a thin-walled head changes, producing a depression that may or may not be visible. The consequences are twofold: fit-up gaps become uneven and weld quality suffers, and as a pressure part the depression introduces additional bending stress. The first principle of head transport is therefore no point contact of any kind.

Practical measures:

• Form-fitting curved saddles: saddle curvature should be as close as possible to the head outer surface, with 8 to 15 mm of soft padding at the contact face. For large heads, use at least three saddles evenly distributed around the circumference.
• Rigid support at the rim: the rim, which is the circumferential edge that will be welded to the shell course, is the relatively stiffer region and can serve as the principal load-bearing zone. Placing the head rim-down on an annular saddle is the most robust arrangement.
• Edge protection rings: the bevel at the rim is a critical feature and should have a removable protective ring so that it cannot be struck during turning and lifting.
• No direct steel-strap lashing: if strapping is unavoidable, insert a full curved pad between strap and head to spread the load over a large area.
• No stacking: two heads must never be stacked directly on each other; a form-fitting separator is mandatory, and heads of different sizes must not be nested for transport.

Spherical heads have one extra consideration: a spherical surface offers no natural anti-rotation feature, so it can roll in transit. Provide anti-rotation blocks or grooves in the saddle, with multiple location points where necessary. Conical heads tend to deform circumferentially under load, so saddles should be placed at the stiffer end rims and at mid-cone.

Alignment with downstream process also matters. If the bevel has already been machined, the protective ring should be designed for removal at unpacking. If the head is awaiting fit-up, avoid chlorine-bearing or sulphur-bearing materials inside the case, which can cause pitting in humid conditions.

4. Flange Cases: Weld-Neck Flanges and Sealing-Face Protection

The value of a flange is concentrated in its sealing face. There are three common failure modes: scratching (score marks, galling), indentation (localised dents) and corrosion (pitting). All three reduce the effectiveness of the sealing contact stress.

The design rule for flange cases is: sealing face free, outer diameter load-bearing, bolt holes protected.

• Sealing face free: cavity depth should be less than flange thickness, so that the sealing face touches no hard object and carries no load beyond its own weight.
• Outer diameter load-bearing: use the outer diameter or the raised back boss as the primary contact face, with soft padding at the contact.
• Bolt-hole protection: where holes are threaded or have fit requirements, fit protective plugs to keep out debris and prevent impact.
• Item separation: flanges must be separated by soft dividers; never let metal faces rub directly against each other.

For weld-neck flanges, the neck is a slender transition that deforms easily under side load. The cavity should restrain both the flange disc and the neck; supporting only the disc and leaving the neck unsupported is a common mistake.

For large-diameter flanges above DN500, single-item weight can reach several hundred kilograms, and standing on edge in an annular saddle is preferable to laying flat. Laying flat with the sealing face down risks indentation from trapped debris. Standing on edge leaves the sealing face facing sideways, where a simple cap prevents contact, and it also simplifies lifting and visual inspection.

Sealing-face caps should be removable and the case exterior should be marked with the sealing-face orientation and a note that caps are removed first at unpacking. For flanges going into long-term storage, apply a peelable rust-preventive film rather than ordinary machine oil.

Where a case carries flanges together with gaskets and bolts, a removable divider system (removable divider system design) keeps small items in their own compartments and prevents them from drifting into the sealing-face zone and causing scratches.

5. Tubesheets and Heat-Exchanger Tube Bundles

A tubesheet is a key component of a shell-and-tube heat exchanger: large diameter, moderate thickness, densely drilled with tube holes. Its dominant failure modes are impact damage to tube-hole edges and loss of tubesheet flatness. Once a tube-hole edge is burred or rolled over, tube insertion and expansion are obstructed.

Tubesheets are normally stood on edge or leaned at a slight angle, supported at two or three points on the outer diameter. The drilled tube-hole field must never be used as a support face. Where holes are already machined, the hole field should be covered with an overall protective plate, either soft or rigid with a compliant liner.

A heat-exchanger tube bundle is a classic V4 long slender component with requirements similar to boiler heating surfaces: multiple cradles, end caps and capped tube ends. The differences are that exchanger tubes are smaller in diameter, more numerous, and often already expanded or welded, which makes them more sensitive to vibration. Wrap the bundle as a whole in a soft wrap plus outer sleeve so that the bundle is restrained as a unit rather than tube by tube.

For bundles that have already been expanded, there is an additional risk of tube-end displacement. Vibration in transit can cause micro-movement of the tube ends relative to the tubesheet, and over time the expanded joints can loosen. A rigid overall frame restraint that minimises relative movement is the recommended answer.

6. Shell Courses and Nozzles: Thin-Walled Long Parts

Shell courses and long nozzles are the components most often casually stacked during handling, and they are also the most easily damaged by that stacking.

The dominant failure of a shell course is ovalisation. A thin-walled cylinder has low radial stiffness, and after stacking or side loading its cross-section becomes elliptical, producing misalignment when it is later fitted to a head or flange. Protection points: support in a half-round cradle matched to the shell diameter, with at least two support positions distributed slightly inboard of the two ends; never place hard objects inside the shell where they can score the bore.

The dominant failure of a long nozzle is bending. A nozzle is slender and bows under side load, and nozzle perpendicularity directly affects later installation. Use multiple cradles plus end caps, and fit a plug or protective cap at the end.

Where the bevel has already been machined, bevel protection is the priority: removable protective rings or soft wrapping to keep the bevel away from other components.

If a shell course or nozzle has already been heat treated, no restraint that could cause plastic deformation may be applied (see section 9). For long-term storage of shell courses, protect the bore against corrosion, and include desiccant and a humidity indicator card in the case.

7. Gaskets, Bolts and Fasteners

These small items are the most commonly underestimated, and on site they are the most common cause of a work stoppage due to a missing or damaged item.

Gaskets: the sealing faces of spiral-wound, serrated and corrugated metal gaskets are extremely sensitive; a scratch or a bend means scrap. Non-metallic gaskets fear compressive deformation and moisture. Bag each item separately and lay it flat in a shallow cavity; never bend or compress heavily. For spiral-wound gaskets, cavity depth should be less than gasket thickness so the sealing faces are free.

Bolts and nuts: the threads and the head bearing face of high-strength bolts are critical; impact creates stress concentration. Store by size in separate compartments and fit thread protectors. For bolts that have been pre-tensioned or marked, keep the set together and label the intended location.

The shared requirement for gaskets and bolts is set integrity. The connecting items for one flange - gasket, bolts, nuts and washers - should be stored and identified as one set to prevent mixing on site. This is the core advantage of compartmented inserts over bulk packing.

For fasteners intended for clean service, such as stainless bolts in a corrosive medium, avoid timber inserts inside the case. Wood chips and tannins can cause both contamination and corrosion.

8. Heavy-Duty Structure and Lifting: Large-Diameter Heads

Large-diameter heads above 2000 mm and large tubesheets can weigh 500 to 2000 kg per item, at which point the case itself must be designed as a load-bearing structure.

• Integral floor and pallet: pallet height 80 to 120 mm, connected to the case with through-bolts, for forklift handling.
• Reinforcement: longitudinal ribs and corner blocks on the side walls; add transverse ribs where a wall exceeds 1.5 m.
• Lifting points: corner ring seats with single-point capacity designed at 2 to 2.5 times case gross weight to cover dynamic factors. Lifting points must align with the internal saddle frame.
• Form-fitting restraint: the saddles for large heads should be replaceable form-fitting blocks so that different sizes can be accommodated.
• Stacking declaration: state the maximum number of layers. Large head cases are generally not recommended for stacking; if stacking is unavoidable, the internal frame must carry the load directly.

To repeat the boundary: the component case described here is an outer transport packaging container. It does not participate in the pressure vessel pressure boundary, is not a pressure part, and does not replace the design, manufacture and inspection of the pressure vessel itself. Heads, flanges and shell courses as pressure parts must follow the applicable regulations and standards, including GB/T 150 for pressure vessel design, GB/T 25198 for pressure vessel heads, and TSG 21, the regulation for safety technology supervision of fixed pressure vessels. The case is responsible only for mechanical and environmental protection during transport and storage. This boundary should be written into the technical agreement to avoid any confusion of responsibility.

9. Rust Prevention, Machined Faces and Heat-Treatment State

Corrosion of pressure vessel components is most acute in ocean freight and rainy-season storage. Prevention must address material, coating and environment simultaneously.

Material line: stainless and carbon steel parts must be separated to avoid galvanic corrosion; stainless parts must not touch galvanised parts directly, because zinc accelerates pitting of stainless steel in humid conditions; aluminium and copper must not touch stainless steel directly.

Coating line: machined faces such as flange sealing faces, bevels, threads and tube ends should receive a peelable rust-preventive film or an environmentally acceptable rust-preventive grease. Ordinary machine oil is not suitable as a long-term rust-preventive layer: it runs off under hot humid conditions and readily captures dust, creating an abrasive paste effect. After coating, mark the case exterior as requiring cleaning before installation.

Environment line: sealing plus desiccant plus a humidity indicator card is the standard combination. Ocean freight projects are normally designed with a 60 to 90 day desiccant margin; the higher the case sealing level, the slower the desiccant is consumed.

Protection of heat-treatment state is repeatedly underestimated. Once a component that has been normalised, tempered, solution treated or stress relieved suffers plastic deformation in transit, its state marking no longer matches its actual state, and appearance inspection cannot detect the difference. Therefore:

• never press rigid clamp bars directly onto heat-treated parts;
• never force a heat-treated part into position inside the case;
• place load-bearing points on stiffer regions away from welds and heat-affected zones;
• for austenitic stainless parts that have been solution treated, avoid contact with carbon steel, because iron contamination becomes a corrosion initiation site.

For long-term case care and inspection cycles, see protective case service life assessment.

10. Insert Materials and Restraint Methods Compared

Choosing an insert material is a balance between cushioning, support, oil resistance, cleanliness and cost. One special requirement for pressure vessel components is that no corrosive medium may be introduced, so the chemistry of the material and its outgassing behaviour deserve attention.

A three-layer structure is recommended: a rigid outer support layer (pallet or steel frame), an energy-absorbing middle layer (PU or EVA), and a surface-protection inner layer (felt or soft pad). This layering attenuates shock energy progressively along the transmission path and outperforms simply increasing the thickness of a single foam layer. For a detailed comparison between materials, see case foam material comparison.

On restraint method, prefer hard stops plus elastic support over clamping. The hard stop controls the direction of displacement while the elastic support absorbs vibration energy; together they give reliable restraint without high clamping pressure, which is especially important for thin-walled parts.

11. Sealing, IP Ratings and Pressure Equalisation

Case protection levels are defined by IEC 60529, and the identical Chinese standard is GB/T 4208. Three levels are typical for pressure vessel component cases.

The three critical parameters of seal design are gasket material and hardness, compression ratio, and uniformity of clamping after closure. Gaskets are commonly silicone or EPDM with compression at 20 to 30 percent. The longer the case, the harder it is to guarantee mid-span clamping force, which is when more latches or a reinforcing beam are needed. For the combined design of latch and seal, see toolbox hinge and latch sealing structure.

Pressure vessel components are often large, so the internal volume of a sealed case is large and the pressure differential problem on multi-climate routes is more pronounced. When a case moves from a hot environment to a cold one, or the reverse, the differential can reach several kPa, enough to force the gasket into the case or bulge the shell. The answer is a pressure equalisation valve: it allows gas to exchange slowly and equalise the differential while blocking liquid water and dust. For principles and selection, see pressure equalisation valve configuration.

For large-volume sealed cases going into long-term storage, include a humidity indicator card and provide a quickly replaceable desiccant compartment so that every opening does not introduce fresh moisture.

12. Test References and Regulatory Boundaries for Pressure Parts

Whether a case is strong enough should be supported by test evidence. Three families of reference are commonly used for pressure vessel component cases.

• The GB/T 4857 series covers vibration, impact, stacking and drop test methods.
• The ISTA series organises test sequences around the distribution environment and suits export orders.
• ASTM D4169 uses a distribution cycle plus assurance level approach and suits high-value large items.

For cargo like pressure vessel components - heavy, high precision, strongly dependent on downstream process - at least vibration, impact and stacking should be completed. Add a specific check for V2 curved components, re-verifying head curvature with a template after testing, and a bending verification for V4 long parts. For methods and criteria see GB/T 4857 transport packaging testing and ISTA transport testing procedures.

Where a project needs an environmental test reference, MIL-STD-810H may be used as a reference for environmental test methods such as temperature and humidity, vibration and shock. It is not itself a military certification and does not constitute product certification. External documents must state this precisely to avoid any misreading as a military-grade certification.

On regulatory awareness, one boundary must be clear: the design, manufacture and testing of a component case fall within transport packaging and are not governed by the standard system for pressure vessel pressure parts. The design and manufacture of pressure parts themselves must follow GB/T 150, GB/T 25198, TSG 21 and other applicable standards and regulations; the case only has to guarantee mechanical and environmental protection during transport and storage. Where components involve special media or service conditions, the protection requirements and responsibility boundary should be defined in the technical agreement.

13. Acceptance, AQL and the OEM/ODM Flow

Acceptance should follow a three-check, one-measure flow.

Start with the outer case: examine the corners and base for rupture or distortion, and look specifically for water staining on the cell that carries the head rim and flange sealing faces, since ingress there can spot the bevel and sealing face. Verify that the seals are intact and match the document, then read the humidity indicator card; a colour change means the head bevel and flange sealing face must be checked for damp staining before fit-up.

Check the appearance: verify drawing numbers and quantities against the case-splitting list; inspect head surfaces for dents using a curvature template or angled lighting; inspect flange sealing faces for scratches and indentation; inspect bevels for impact damage; inspect bolt holes for damage.

Check the state: verify heat-treatment markings and state certificates; verify iron-contamination inspection records for stainless parts where required.

Measure critical dimensions: head curvature with a template, flange sealing-face flatness with a straight edge and feeler gauge, shell-course roundness measured in two directions 90 degrees apart, nozzle straightness with a taut line.

For volume orders, incoming inspection of cases and inserts can follow an AQL sampling plan (see custom case acceptance and AQL sampling): control appearance defects at general inspection level II with AQL 2.5, and treat defects affecting protective performance - missing gasket, misaligned cavity, incorrect saddle curvature, failed latch - at AQL 0.65 or under tightened inspection.

The OEM/ODM flow typically runs: requirement clarification (component list, dimensions, weights, materials, heat-treatment state, transport mode, destination climate), grading and case-splitting plan, insert design with form-fitting curvature, sample case trial fit, test verification, volume production, and delivery with identification. The sample stage should be aligned with component availability and pulled forward in project scheduling. JUNZHJIA supports the sample stage with insert drawings and trial-fit feedback, supplies seals and hardware configured to each head and flange size, and returns trial-fit records plus packing documents that map every component to its drawing number.

For cases intended for reuse across projects, use a standard shell plus changeable form-fitting saddles strategy: the shell and hardware are common while saddles are customised to head sizes. Later projects then only need new saddles, which measurably reduces lead time and cost. Where tooling is involved, evaluate mould amortisation first (see protective case mould cost analysis).

FAQ

Q: Why must a pressure vessel head be supported on form-fitting saddles instead of ordinary timber battens?

A: Ordinary timber battens are not recommended. A head is a thin-walled surface of revolution whose resistance to local load is far lower than its resistance to uniform load. Between a batten and a curved surface the contact is a line or even a point, producing very high contact stress. Under the combination of transport vibration and inertial load this readily creates a local depression. Such a depression has two consequences: first, fit-up gaps become uneven and weld quality and misalignment tolerance suffer; second, as a pressure part the dented region carries additional bending stress, which is a latent hazard. A depression is also often invisible after painting and typically only shows up at fit-up or hydrostatic test, when rework is very expensive. The correct approach is a saddle whose curvature closely follows the head outer surface, with 8 to 15 mm of soft padding at the contact face to spread the load over a large area; at least three saddles evenly distributed around the circumference, with the principal load-bearing points preferably at the stiffer rim. If strapping is unavoidable, insert a curved pad between strap and head to distribute the load.

Q: How can flange sealing faces be protected from scratching and indentation in transit?

A: The core principle is sealing face free, outer diameter load-bearing. Four practices follow. First, cavity depth must be less than flange thickness so the sealing face touches no hard object and carries no load beyond its own weight. Second, use the outer diameter or the raised back boss as the primary contact face with soft padding at the contact. Third, flanges must be separated by soft dividers; never let metal faces touch and rub. For large-diameter flanges, standing on edge in an annular saddle with the sealing face facing sideways under a removable cap is safer than laying flat and also simplifies lifting. Fourth, fit protective plugs or rings to bolt holes and bevels. In addition, keep the packing area away from cutting and grinding stations so metal chips cannot fall into the case, and apply a peelable rust-preventive film rather than machine oil to sealing faces. At unpacking, remove the caps first and then the dividers, so that the act of unpacking does not create new scratches.

Q: How should IP65, IP66 and IP67 be chosen for these cases?

A: Choose by actual exposure, and do not default to the highest rating. IP65 is dust tight and protected against water jets, suitable for in-plant movement, indoor storage and covered road transport. IP66 is dust tight and protected against powerful water jets, suitable for washdown environments or heavy rainfall exposure. IP67 is dust tight and protected against temporary immersion, typically 1 m for 30 minutes, suitable for ocean freight, open storage yards and rainy-season long-haul transport. Three cautions apply. First, an IP rating describes only protection against solids and water, not impact resistance, which depends on structural design and test evidence. Second, the achieved level depends on gasket compression and condition, normally 20 to 30 percent compression; too little leaks and too much causes permanent set. Third, large-volume cases crossing climate zones face a more pronounced pressure differential and should be fitted with a pressure equalisation valve. Also note that open-cell foam, felt and wood in a sealed case absorb moisture and then act as an internal water source; prefer closed-cell materials.

Q: Why do small items such as gaskets and bolts need dedicated insert design?

A: Because they are the most common cause of a site work stoppage through absence or damage. The sealing faces of spiral-wound, serrated and corrugated metal gaskets are extremely sensitive; one scratch or bend means scrap. Non-metallic gaskets deform under compression and suffer from moisture. Impact on the threads or head bearing face of a high-strength bolt creates stress concentration. More important is set integrity: the connecting items for one flange comprise gasket, bolts, nuts and washers, and if these are shipped loose, items are easily mixed up or lost, halting assembly. The recommendation is to compartmentalise by flange size, with each compartment holding one set and labelled with its intended location. Keep spiral-wound gaskets in a cavity shallower than the gasket thickness so the sealing faces are free, and fit thread protectors to bolts. This is the core value of a compartmented insert over bulk packing, and on petrochemical projects with tight maintenance windows it measurably reduces waiting time on site.

Q: What has to be observed in transit for a head or shell course that has already been heat treated?

A: The core requirement is to avoid plastic deformation, because once heat-treatment state is altered by plastic deformation, appearance inspection cannot detect it and the consequence is early failure in service. Four points apply. First, never press rigid clamp bars or steel straps directly onto heat-treated parts; use elastic support. Second, never force a heat-treated part into position in the case; packing should place and locate the part, not compress and wedge it. Third, place load-bearing points on stiffer regions well away from welds and heat-affected zones so that concentrated stress does not form near a weld. Fourth, for austenitic stainless parts that have been solution treated, avoid direct contact with carbon steel, which causes iron contamination that becomes a corrosion initiation site; use isolating pads and keep carbon steel dust out of the packing area. Mark the heat-treatment state on the case exterior and supply the state certificate with the shipment so that it can be verified on arrival.

Q: Can large-diameter head cases be stacked, and how should lifting points be designed?

A: Large-diameter head cases are generally not recommended for stacking, because large thin-walled heads are sensitive to load from above and the cases themselves are already heavy. If a project must stack, the internal frame should carry the load directly, and the technical agreement should state the maximum number of layers and the load-bearing locations; stacking must be squarely aligned, case on case, with no bridging. Lifting point design has three requirements. First, corner ring seats with single-point capacity at 2 to 2.5 times case gross weight to cover dynamic factors. Second, lifting points must align with the internal saddle frame so that force passes directly into the frame rather than into the walls. Third, lifting point positions should not conflict with the sealing-face orientation, and a lifting diagram should be marked on the case exterior where necessary. The pallet should also be integrated with the floor, 80 to 120 mm high, connected by through-bolts rather than clips alone, for reliable forklift handling under heavy load.

Q: Does a pressure vessel component case need to reference pressure vessel standards?

A: The boundary must be distinguished. The design, manufacture and testing of a case fall within transport packaging and are not governed by the standard system for pressure vessel pressure parts; the case is not a pressure part and does not participate in the pressure boundary. However, referencing related standards as background and awareness in project documentation is reasonable. GB/T 150 addresses pressure vessel design, GB/T 25198 addresses pressure vessel heads, and TSG 21 is the regulation for safety technology supervision of fixed pressure vessels. The purpose of such references is to align packaging design with the accuracy and machined-face requirements of the components themselves, not to bring the case within the scope of special equipment supervision. The recommendation is to include one sentence in the technical agreement: this component case provides mechanical and environmental protection during transport and storage only and does not replace the design and manufacturing requirements of the component itself. That avoids any confusion of responsibility.

Q: When should a batch of pressure vessel spares be split across multiple cases?

A: Split whenever the batch spans more than one protection grade. Typical situations include V1 precision items such as sealing-face flanges, gaskets and instrument connections travelling with V2 curved items such as heads, and with V4 long slender items such as long nozzles or tube bundles. Mixed loading has three risks: the weight range is wide and heavy items press on light ones in transit; the stiffness range is wide and hard items abrade soft surfaces under vibration; and acceptance methods differ, since V1 needs visual and blueing checks, V2 needs a curvature template, and V3 or V4 need dimensional measurement, which is difficult to zone in a mixed case. After splitting, supply a case-splitting list with drawing-number identification and mark the grade on each case exterior so the carrier can allocate cases properly. The number of cases increases, but the probability of damage and the difficulty of acceptance both fall, and total cost is usually lower.

Q: Which insert materials should be avoided around stainless steel components?

A: Avoid anything that introduces carbon steel contact, chlorides or moisture-retaining organics. Untreated timber support blocks are the main offender: they hold moisture, they can transfer iron contamination to stainless surfaces, and wood extracts can promote corrosion in humid conditions, so timber blocks must never touch stainless parts directly. Ordinary open-cell foam and felt absorb moisture and then release it into the case when the temperature falls, raising local humidity against the component surface. Soft PVC materials are also best avoided because plasticisers can migrate onto rubber or coating surfaces, leaving them tacky or reducing coating adhesion. For stainless components, use closed-cell EVA or PE for the inner layer, add a clean barrier film at contact faces, keep carbon steel tools and dust out of the packing area, and where the project requires it, apply a chloride-free rust-preventive film rather than a generic greasy product. Include desiccant and a humidity indicator card so that any moisture uptake is visible before corrosion begins.

Conclusion & Related Reading

The design logic of a pressure vessel component case can be summarised in four lines: turn point loads into distributed loads with form-fitting support; reduce scratch risk to a minimum by isolating contact; control long-part deformation with hard stops plus elastic support; and isolate environmental attack with sealing plus desiccant. Add graded case splitting, test verification and unpacking acceptance, and the arrival condition of pressure vessel spares moves from experience-based to record-based.

The boundary bears repeating: the component case is an outer transport packaging container. It does not participate in the pressure vessel pressure boundary, is not a pressure part, and does not replace the design and manufacture of the pressure vessel. Pressure parts themselves must follow GB/T 150, GB/T 25198, TSG 21 and applicable regulations, and MIL-STD-810H may serve only as an environmental test method reference, not as a military certification.

JUNZHJIA (Kexin New Materials (Guangdong) Co., Ltd.) supplies head and flange component cases with custom inserts, form-fitting saddles, OEM/ODM programmes and volume production to pressure vessel fabricators, chemical equipment suppliers and exporters, and can issue case-splitting plans, fabrication-batch packing specifications with head and flange cavity layouts, seal lists and hydrostatic-test-ready inspection records that map each item to its drawing number.

Related Reading

• Case Foam Material Comparison
• Pressure Equalisation Valve Configuration
• GB/T 4857 Transport Packaging Testing Essentials