A tank cover is a stainless steel access cover welded or fitted to an opening on a process vessel, providing a closeable entry point for inspection, cleaning or physical access to the tank interior. The tank cover category is specified by process engineers, vessel fabricators and maintenance teams wherever hygienic repeatable access is required — from dairy balance tanks and brewery fermenters to pharmaceutical process vessels subject to PED 2014/68/EU requirements.

Alfa Laval's product documentation describes circular, oval and rectangular access covers in a range of configurations and pressure classes. Product-wetted components are typically AISI 316L (1.4404) and material traceability is supplied via EN10204 3.1 certificates in the standard documentation. Seal choices include EPDM, NBR, FPM (Viton) and silicone (Q), with FDA and USP Class VI declarations recorded for several seal options where documented.

Choosing the right tank cover starts with four linked decisions: is the vessel a classified pressure vessel or an atmospheric/low-pressure tank; what opening geometry and clear opening are required for personnel or equipment; what cleaning regime (CIP/SIP) and surface finish level are required; and which seal material is compatible with the product and temperature range. The Alfa Laval range spans non-pressurised LKDS covers for dairy balance and CIP holding tanks to HLSD-2 covers intended for pressure-vessel service where EC unit verification (module G) under PED 2014/68/EU is required. The sections below summarise the main families and give selection guidance based on the published Alfa Laval technical data.

Alfa Laval organises tank covers by opening geometry and intended service. Circular covers are the most common for tank-top access. Oval covers are side-mounted and provide larger personnel access. Rectangular covers fit side openings commonly used for product removal or machine interfaces in wine and juice production.

Circular tank covers

The HLSD-2 family is Alfa Laval's pressure-capable circular cover. Its lid is secured by swing bolts and retained on a rigid hinge that stops the open cover at 20–30° past vertical. Sizes are published from 200 mm to 600 mm; allowable pressure and test pressure are tabulated per size, lid thickness and bolt count. For example, the 200 mm HLSD-2 with an 8 mm lid and four bolts is rated at 14.7 bar at 50 °C and has a Ptest value of 21.1 bar in the selection table. HLSD-2 documentation records EC unit verification module G per PED 2014/68/EU for installations in pressure vessels, and product-wetted parts are AISI 316L (1.4404) with a typical internal finish of Ra 0.8 µm.

LKDC covers are intended for top-mounted non-pressurised openings. They use a replaceable self-sealing double lip seal to prevent fluid spray during CIP and transport. LKDC product documentation lists sizes from Ø202 to Ø620 and shows acid-pickled Ra 0.8 µm as the standard finish; a 3-A approved finish of Ra 0.4 µm is offered where required. Wire and laser-cut safety grids in 316L are available for non-3-A models.

LKDC-LPB and LKDC-LP variants are engineered for vacuum and low-pressure conditions up to 1 bar (working pressure −1 to 1 bar) but are explicitly not PED-approved and therefore not substitute pressure-vessel covers. The LP variant adds springs and a safety pin on the handles for safer manual handling under residual pressures. EPDM is the standard seal; NBR, FPM and silicone (Q) are documented optional seals.

Types C, CG and CG-LP provide flexibility for static tanks and road tankers. CG includes a tempered sodalime glass lid for inspection of non-pressure tanks; CG-LP extends the glass-lid concept to 1 bar overpressure and full vacuum. The glass component is specified with a maximum temperature of 120 °C in the Alfa Laval data.

The LKDS is a non-watertight circular cover supplied with a splash guard and intended for dairy balance tanks and CIP holding tanks where a watertight seal is not required. LKDS documentation notes that covers are delivered unassembled and that product-wetted surfaces are acid-pickled with Ra values appropriate for hygienic process quality.

Oval tank covers

Oval Type O and LKD families are side-mounted access covers sized for personnel entry or larger inspection openings. Type O uses an electropolished lid and brushed frame and can open inwards, outwards or sideways depending on the variant. Several Type O variants are published with below-liquid-level static pressure ratings ranging from 1.3 bar to 4.0 bar.

The LKD family includes models with distinct pressure ratings and frame profiles. The LKD 532 × 432 is documented with a maximum static pressure of 4.8 bar and a test pressure of 3.75 bar in the product data. A flat-lid variant of that footprint is listed at 35.4 kg and is suitable for bottom or side installation with a published static rating of 2.3 bar for that flat configuration. The LKD 542 × 446 is specified with an angled frame to reduce spray shadows and ease cleaning; its published static rating is 2.8 bar with a test pressure of 4.2 bar. The LKD 440 × 320 is available in standard and pressure models and is documented as complying with FDA and EU 1935/2004/EC declarations where noted.

Rectangular tank covers

Rectangular Type R covers fit side-mounted rectangular openings. Alfa Laval data lists five Type R models with calculated maximum pressures for below-liquid-level installations from 0.5 bar to 1.0 bar, depending on the model. Clamps provide perimeter compression of the seal. The manufacturer emphasises correct frame welding and post-weld verification that the seal contacts the full seating surface to achieve rated performance and avoid leak paths under static head.

Tank covers are used wherever vessels require periodic access for inspection, cleaning, sampling or manual intervention. The cover family and specification vary by industry because surface finish, regulatory traceability, pressure class and cleaning regimes all differ. Alfa Laval product documentation maps the families to common industry requirements so that fabricators and process engineers can choose covers that meet hygienic, mechanical and regulatory constraints.

Dairy processing

Dairy balance tanks are typically atmospheric and need covers that prevent spray during CIP rather than watertight closures. LKDS is documented specifically for this use and is supplied with a splash guard. Where vacuum forms during cleaning recirculation, LKDC-LPB or LKDC-LP models are published to withstand operating conditions between −1 and 1 bar. LKDC's self-sealing double lip design is shown in Alfa Laval documentation as a way to prevent fluid ejection during CIP and during transport on mobile tanks where applicable.

Food and beverage production

Process tanks in food production often combine requirements: product-wetted surfaces at Ra 0.8 µm or better, material traceability, and seals compatible with process fluids. LKDC covers meet many of these needs for top-entry openings; oval LKD covers are used where side access or larger openings are required. CG/CG-LP glass-lid variants allow visual inspection without opening the vessel and are documented with a 120 °C glass temperature limit; CG-LP extends that to 1 bar overpressure and full vacuum in the product literature.

Brewery fermenters and conditioning tanks

Brewery vessels need full wetting during CIP; spray shadows at the frame-to-wall junction are a common cleaning challenge. Alfa Laval documents the LKD 542×446 as having an angled shaped frame designed to reduce these spray shadows and to simplify external cleaning. Its static pressure rating and lip seal arrangement mean the seal remains effective under normal positive or negative pressure swings in fermenters and conditioning tanks.

Wine and juice production

Wine and juice processes often use side-wall access for bulk removal or inspection. The LKD 440×320 and Type R rectangular covers are documented options for such use cases: LKD provides rounded access shapes and electropolished 3-A-capable finishes in some variants, while Type R rectangular covers are used where rectangular geometry matches vessel fabrication or machine interfaces. Alfa Laval data lists Type R models with calculated below-liquid pressure ratings to support selection for these operations.

Pharmaceutical and biopharma

Pharmaceutical process vessels require traceability and, when applicable, pressure-equipment conformity. Alfa Laval lists the HLSD-2 as meeting PED 2014/68/EU requirements with EC unit verification module G and as suitable for fluid groups 1 and 2 in hazard category IV where that certification is required. Where vessels are outside PED scope, 3-A approved LKDC variants and electropolished LKD options provide the documented surface finishes (Ra 0.4 µm) and seal material declarations (FDA / USP Class VI) sought in biopharma cleanability and material-compatibility specifications.

Core components

Every tank cover assembly consists of the lid, the frame (zarge), the seal and the fastening system. The lid closes the opening. The frame is welded into the vessel and defines how the lid seats. The seal sits between lid and frame; its material determines compatibility with process fluids and temperatures. The fastening system — swing bolts on HLSD-2, clamps on Type R, or handles and pins on LKDC/LKD variants — provides the clamping force that compresses the seal to achieve the required tightness.

Alfa Laval documentation consistently lists product-wetted components in 1.4404 (AISI 316L). Other structural parts such as hinges and external supports are commonly 1.4301 (AISI 304). Plastic components such as handles and hinge inserts are Nylon in the published physical data.

Surface finish on product-wetted areas is controlled by Ra specification. Standard acid-pickled or semi-bright finishes appear at Ra 0.8 µm in the Alfa Laval data. 3-A approved variants use electropolishing to reach Ra 0.4 µm on product-wetted surfaces where documented. The HLSD-2 data specifies outside Ra 1.6 µm and inside Ra 0.8 µm as standard for that family.

Pressure rating and operating principle

Pressure rating is a primary selection factor. HLSD-2 is the Alfa Laval circular cover family intended for installation in classified pressure vessels. Allowable pressure values are published in selection tables that reference cover size, lid thickness (SL) and bolt count. For example, the selection table entry for Size 200 with SL 8 mm and 4 bolts lists PS 50 °C as 14.7 bar and Ptest as 21.1 bar. For Size 600, SL 14 mm with five bolts the table lists PS 50 °C as 7.0 bar with Ptest 10.0 bar. These tabulated figures must be used when specifying HLSD-2 for a pressure vessel application.

Most other circular covers are intended for atmospheric or low-pressure service. LKDC models are documented as non-pressurised except the 202 variant (0.4 bar). LKDC-LPB and LKDC-LP are published with a working pressure range of −1 to 1 bar: they are designed to withstand vacuum and low-pressure conditions arising in CIP or production but are explicitly not PED-approved and therefore are not substitutes for certified pressure-vessel components.

Oval LKD covers are rated by model for static pressure. For instance, the LKD 532 × 432 is documented with a maximum static pressure of 4.8 bar and a test pressure of 3.75 bar. The LKD 542 × 446 is published with a static rating of 2.8 bar and a test pressure of 4.2 bar. The LKD 440 × 320 appears in the Alfa Laval technical data with a static rating of 1.5 bar and a negative working pressure capability of 0.5 bar for the pressure variant.

Seal material selection

Seal material choice balances temperature, chemical compatibility and regional regulatory constraints. Alfa Laval documentation summarises standard seal materials and operating temperatures as follows:

HLSD-2 O-ring documentation expands options: FEP-covered silicone (−60 °C to +200 °C) and PFA-covered silicone (−60 °C to +230 °C) are listed with FDA and USP Class VI compliance where noted. EPDM is a common choice for ambient-to-moderate CIP temperatures. Where CIP or SIP temperatures exceed EPDM limits, NBR or FPM (Viton) are the documented alternatives. For pharmaceutical SIP above 121 °C, Alfa Laval data indicates FPM or coated silicone options for compatibility and biocompatibility where specified.

CIP compatibility and cleaning design

Alfa Laval documents emphasise seal positioning and frame geometry to maintain CIP effectiveness. The LKDC double lip seal is described as self-sealing so that CIP spray presses the lip into its seat rather than dislodging it. The LKDS solution is published as non-watertight but supplied with a splash guard to redirect cleaning fluid back into the tank. Frame geometry differences, such as the angled frame on LKD 542×446, are documented as measures that reduce spray shadows and improve the full wetting of the frame interior during CIP.

Installation quality is essential for below-liquid covers: Type R documentation instructs that frames must be welded carefully and that after welding the seal must be checked to ensure full contact around the seating face. Any discontinuity under static head can become a leak path.

Certification requirements

Alfa Laval product literature indicates that lid and frame material certificates EN10204 3.1 are supplied as standard for the models documented. HLSD-2 documentation additionally references EC unit verification module G under PED 2014/68/EU for pressure-vessel installations. FDA §177.2600 declarations and USP Class VI notes appear in the Alfa Laval data for specific seal materials and are recorded in the product literature where applicable. ASME BPE certification is shown as an optional project-level certification for HLSD-2 in the technical data.