quality bulletin _december 6, 2013

8/13/2019 Quality Bulletin _December 6, 2013

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QUALITY BULLETIN

Friday, December 6th

, 2013

Hygienic Design and Construction

Throughout the guideline the following colours and icons are used :

1. JointsWelding is the preferred method of joining, provided that it is done correctly, to ensure a

smooth and continuous weld.

Where detachable joints are unavoidable, they must be hygienically sealed.

Requirement for detachable joints include :

- oa!ial alignment of the mating bores,

- "n a!ial stop for controlled compression of the seal,

- Room for thermal e!pansion of the seal,

- "voidance of sharp edges such that seals are not damaged,

- #ree from crevices.


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PT. Tetra Pak Stainless Equipment Jl. Raya Pulo Gebang Km.3 Cakung Jakarta 13950, IndonesiaTelp. +62-21 48700967 (Hunting)Tetra Pak Internal

The connections shown on the left allow misalignment and do not control the compression of

the seal.

"s below is metal to metal joints must not be used in hygienic plant pipelines.


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2. Seal design

$uring heating the seal will e!pand to cover an increasingly larger surface of steel %#ig.&',

(rotecting micro-organisms trapped between the seal and the steel surface against contact with

hot water, chemical solution or steam. "fter cooling down and shrin)age of the seal, the

surviving micro-organisms may be released and will multiply and contaminate the product.

#ig. & : "n *-ring seal made from an elastomer may, as a result of the difference in thermal

e!pansion between metals and elastomers, draw micro-organisms into its groove. There they

may be protected from contact with hot water or steam during later cleaning processes.

#ig. &.& shows an *-ring e!panded by heating, and

#ig. &.+ shows it after cooling again %e!aggerated to illustrate principle'


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*-ring can be acceptable from a hygienic point of view if mounted in a way that ensures that the

area of steel covered by the product side is not influenced by thermal e!pansion. *ften this

leads to large forces inside the *-ring and as a result the lifetime of the *-ring may be reduced

significantly. "cceptable applications are shown in #ig. +.

%+.' hows an e!ample of an e!pectable sensor fitting

%+.' /ecause of the virtually complete entrapment of the seal and the differences in thermal

e!pansion between elastomer and steel, forces inside the seal may accelerate ageing, so that

more frequent replacement may be required compression of seals.

orrect $esign for #lange onnection with rectangular eal as below :

%0.' *ver ompression 1 eal protruding into product area.

%0.' 2nsufficient ompression 1 revice between the two flanges and possibility of lea)age.

%0.&' "cceptable $esign


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3aterial that have insufficient resilience and which e!pand significantly more than stainless

steel, such as polytetrafluoroethylene %(T#4, e!pansion coefficient appro!. 55!5-6

75,

compared to appro!. 6!5-6

75 for stainless steel' may change shape as a result of heating. 2n a

design as shown in #ig.6, the material will not provide a tight seal anymore after cooling down.

3. Dynamic Sealsare must be ta)en that dynamic seals can be cleaned. The narrow annular space which is

usually found at the product side in the pro!imity of the seal must be avoided %#ig.8.'. The

space around the seal should be as wide as possible %#ig.8.'.


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. Drainabilityorrect $esign of Transition pipe for draining as below :


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!. Dead "reas2ncorrect mounting of sensors in process lines will result in large dead areas which are

unacceptable %#ig.'. 2f a dead area is unavoidable, its length must be as short as possible and

tis cleanability must be demonstrated. #or all pipe diameters the length of the up stand should

be smaller than its diameter %2 9 d'.


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hort dead legs %&., &.' will be cleanable, long ones not %&.&, &.+'. $ead leg position in

%&.+' is better than in %&.&' due to the direction of the flow.

2n all cases the temperature of the surfaces in the dead area may be lower than required %#ig.+

below'.

%+.' and %+.' decontamination with liquids

%+.&' decontamination with steam.

"lternatively, a welded poc)et may be used. "ttention should be given to the quality of the

weld, which must be smooth and continuous. #urthermore, to avoid shadow areas, the direction

of the flow must be as indicated %#ig.0'.


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6. #nternal "ngles and Cornersharp corners must be avoided. "ll internal angles and corners should be well radiused to

facilitate cleaning. #ig.;. shows how to weld without sharp corners and #ig.


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The weld shown in %;.' results in a sharp corner which may accumulate soil and become

difficult to clean.

The weld in %;.' avoids such a problem, provided it is ground flush with the surrounding

surfaces.

%


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'. &hermal #nsulationThe same principles apply to the insulation of process vessels which should also be enclosed, as

shown in #ig.. $epending on the duty of the tan), it may be necessary to provide a filtered

vent hole to prevent unacceptable pressures between the inner and the outer walls %e.g. during

sterilisation' and maintain the hygienic integrity of the insulation.

quality bulletin _december 6, 2013

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