Design of Piping Systems for Food Processing

Guideline no. 5

2006-06-27 Version 1.0 Page 1 of 29 In replacement of New

Design of piping systems for the food processing industry – with focus on hygiene Authors: Folkmar Andersen, Jens; Alfa Laval Kolding A/S

Boye Busk Jensen, Bo; BioCentrum – DTU Boye-Møller, Anne R.; Danish Technological Institute Dahl, Michael; Danish Technological Institute Jepsen, Elisabeth; APV Nordic A/S Jensen, Erik-Ole; Arla Foods amba Nilsson, Bo; Senmatic A/S Olsen, Bjarne; Tuchenhagen GmbH Thomsen, Willy; Royal Unibrew A/S

Prepared by the flow components task group under the auspices of the competence centre of the Danish stainless steel industry.

Guideline no. 5


Den Rustfri Stålindustris Kompetencecenter c/o Teknologisk Institut Holbergsvej 10 DK-6000 Kolding Tel.: +45 72 20 19 00 Fax: +45 72 20 19 19 [email protected] www.staalcentrum.dk This guideline is developed with the support of the Danish Ministry of Science, Technology and Innovation. Published for the Centre by:

Holbergsvej 10 DK-6000 Kolding www.teknologisk.dk © Danish Technological Institute ISBN: 87-7756-750-1

Guideline no. 5


Introduction This guideline provides general advice on the design of piping systems in the food industry. The focus will be on the design and installation of stainless pipes in closed hygienic (CIP cleanable) systems. The guideline is divided into chapters that can be read independently of each other. If read in its entirety, the guideline will contain repetitions, which is a deliberate choice. The guideline is prepared by the flow component task group under the auspices of the competence centre of the Danish steel industry. Guideline no. 1: Cabling and electrical cabinets – with focus on hygiene Guideline no. 2: Check list for the purchase/sale of production equipment – with focus

on hygiene Guideline no. 3: Conveyors – with focus on hygiene Guideline no. 4: Stainless steel in the food industry – an introduction Guideline no. 5: Design of piping systems for the food processing industry – with focus

on hygiene Guideline no. 6: Installation of components in closed processing plants for the food

processing industry – with focus on hygiene Enjoy! Key words Piping systems, pipe runs, food industry, steel quality, hygiene design, requirements, welding, fittings, receiving inspection, mounting, inspection, flow, installation, construction, check list, plant layout

Guideline no. 5


Contents

1. Domain ......................................................................................................................5 1.1. Limitations....................................................................................................................... 5 1.2. Definition and use of guidelines.................................................................................... 5

2. Choice of steel quality..............................................................................................5 2.1. Recommended material selection for the food industry............................................. 6

3. Design of piping systems ........................................................................................8 3.1. Drainability or not? ......................................................................................................... 9

4. Requirements for pipes and fittings .......................................................................9

5. Receiving inspection..............................................................................................10 5.1. Analyses for the inspection of deliveries ................................................................... 10

6. Storage ....................................................................................................................11

7. Welding of stainless steel pipes and fittings .......................................................13 7.1. Choice of material to be welded .................................................................................. 13 7.2. Filler material................................................................................................................. 13 7.3. Welding from a product hygiene perspective ............................................................ 13 7.4. General welding requirements .................................................................................... 14 7.5. Shielding gas................................................................................................................. 15

8. Welding requirements ............................................................................................18 8.1. Equipment ..................................................................................................................... 19 8.2. Welding preparation ..................................................................................................... 19 8.3. Pipe welding .................................................................................................................. 20 8.4. After welding ................................................................................................................. 23

9. Mounting .................................................................................................................24 9.1. Drainability .................................................................................................................... 24 9.2. Pipe dimensions ........................................................................................................... 24 9.3. Pipe layout..................................................................................................................... 24 9.4. Seals at pipe joints ....................................................................................................... 25 9.5. Pipe supports ................................................................................................................ 25 9.6. Production stoppage precautions............................................................................... 25

10. Inspection of completed work ...............................................................................26 10.1. Weld inspection for deliveries ..................................................................................... 26 10.2. Installation inspection .................................................................................................. 27

11. Overview of other guidelines about piping, etc. ..................................................27

12. Applied methods ....................................................................................................29

13. Further information and literature.........................................................................29

14. Change protocol .....................................................................................................29

Guideline no. 5


1. Domain This guideline provides general advice on the design of piping systems in the food industry. Special attention points will be illustrated by drawings/photographs. 1.1. Limitations The focus will be on the design and installation of stainless pipes in closed hygienic (CIP/SIP cleanable) systems for the food industry. 1.2. Definition and use of guidelines The guideline can be used by construction engineers in connection with the design of new and the renovation of old plants. It can also be used by chief installation engineers as a check list to prevent unsuitable installation. Furthermore, the guideline contains knowledge for production supervisors of correct handling and storage of the supplied material. It can also be used by purchasing officers when deciding on the specification of plant layout and parts. Finally, the guideline can be used as a communication tool between purchasing officers and suppliers when coordinating their expectations for the delivery. It is not the purpose of the guideline to recommend certain types of solutions or suppliers. 2. Choice of steel quality Stainless steel of varying quality is the most used material in the food industry for the construction of machines and processing equipment. This is due to the ability of steel of forming a chromium oxide layer on the surface, which will appear smooth and whole, and have good mechanical properties, without the steel corroding. When the chromium oxide layer disintegrates, the steel will corrode. Basically, stainless steel is not a precious metal but a material which is more or less inactive to most environments. Despite the many good properties of stainless steel, it is a complex material in which corrosion problems may arise due to wrong use or treatment. This can lead to the premature replacement of processing equipment or machines. For an introduction to stainless steel, please refer to Guideline no. 4: Stainless steel in the food industry – an introduction.

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2.1. Recommended material selection for the food industry Generally, the quality of steel should be selected according to the environment to which is will be exposed. A change to a more corrosive environment (e.g. changes in the product or detergent/cleaning procedure) may lead to serious corrosion attacks on the plant. In the food industry, stainless steel grades below the following requirements should not be used (see the reason for this limit below and in section 7.1): Carbon content (C) max. 0.05% Molybdenum content (Mo) min. 2.0% When using grades like AISI 304 and AISI 316, special attention should be paid to the carbon content. This can be as high as 0.08%, which is too high if the steel is to be welded. Table 1 shows the most frequently used steel grades in the food industry, including the contents of the most important alloy constituents. When choosing stainless steel for welding operations, a low carbon content is crucial to prevent the formation of chromium carbide. The greater the material thickness, the longer the workpiece will take to heat during welding, and the lower the carbon content has to be.

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Table 1. Stainless steels in various standards, grouped according to grade with a 2004 price index. As prices of stainless steel are very dependent on the alloy constituents, the price index will fluctuate over time. Steel grade C

% Cr %

NI %

Mo %

P %

S %

N %

Price index (relative scale)

AISI 304 min. max.

0.08

18.0 20.0

8.0 10.5

- -

0.045

0.030

AISI 304 L EN 1.4306

min. max.

0.03

18.0 20.0

8.0 10.5

- -

0.045

0.030

SS 2333

min. max.

0.05

17.0 19.0

8.0 11.0

- -

0.045

0.030

C

omm

on s

tain

less

ste

el

(aus

teni

tic)

EN 1.4301 min. max.

0.07

17.0 19.0

8.5 10.5

- -

0.045

0.030

100

AISI 316 min. max.

0.08

16.0 18.0

10.0 14.0

2.0 3.0

0.045

0.030

AISI 316 L EN 1.4404

min. max.

0.03

16.0 18.0

10.0 14.0

2.0 3.0

0.045

0.030

SS 2347 min. max.

0.05

16.5 18.5

10.5 14.0

2.0 2.5

0.045

0.030

SS 2343 min. max.

0.05

16.5 18.5

10.5 14.0

2.5 3.0

0.045

0.030

EN 1.4401 min. max.

0.07

16.5 18.5

10.5 13.5

2.0 2.5

0.045

0.030

EN 1.4436 min. max.

0.07

16.5 18.5

11.0 14.0

2.5 3.0

0.045

0.030

130

AISI 904 L 0.01 20.0 25.0 4.5 - - 300

Aci

d-re

sist

ant s

tain

less

ste

el

(aus

teni

tic s

teel

con

tain

ing

mol

ybde

num

)

AV 254 SMO 0.01 20.0 18.0 6.1 400 SAF 2304 min.

max.

0.03

22.0 23.5

4.0 5.5

0.10 170

SAF 2205 (EN 1.4462)

min. max.

0.03

21.0 23.0

4.5 6.5

2.5 3.5

0.14 190

Dup

lex

stee

l (a

uste

nitic

-ferri

tic

stee

l)

SAF 2507 min. max.

0.03

24.0 26.0

6.0 8.0

3.0 5.0

0.30 400

Please note that although AISI 304 and EN 1.4301 are often regarded as identical, there may be small differences in the carbon content.

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3. Design of piping systems The design of piping systems must ensure a good future-enabled pipe layout by using the fewest possible components, and at the same time ensure optimal functioning of the plant. There are many possible solutions for a pipe run. Often, far more elbows than necessary are used because the designer did not give the layout enough thought. An elbow too much means:

• costs for the purchase of an elbow • costs for the installation • increased energy costs for the entire lifetime of the plant due to

pressure loss It is therefore important to think everything through during the design phase!

Figure 1. Example of more elbows than necessary being used, which leads to increased costs. During replacement of existing piping systems, the existing piping systems are often not dismounted while the new system is being built. The existing piping system will often constitute an obstacle for the new system. Therefore, the existing piping system has to be taken into consideration, and consequently the new system turns out to be less than optimal. The focus should be on optimising the new piping installation. It is better to change the old installation temporarily than to mount new pipes around it, with a poor outcome. When planning the pipe layout, it will be useful to use 3D drawings or perspective drawings to illustrate the pipings. It will be easier for the customer and the supplier to troubleshoot, avoid misunderstandings and find the optimal pipe layout together, before the final mounting is initiated. This will facilitate the mounting process considerably.

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3.1. Drainability or not? Two different operating situations are predominant in the processing industry:

1. The first is that the plant must be emptied every time production has taken place, i.e. it is very important that it can be drained of everything before the plant is left.

2. The second, and most widespread in recent years, is that the plant must be liquid-filled at all times. This means that when a process has ended, a sterile liquid is fed to the plant and left there until the next process is started, when the sterile liquid will be displaced by the process liquids.

Regardless of the chosen solution, the plant must be designed so that it can be drained. This is done by constructing the plant with a highest point and falls on both sides in the process piping system and by incorporating drains to ensure that the plant can be emptied of air, product and CIP-liquids. It is highly unlike that the plant will never have to be emptied at some point. 4. Requirements for pipes and fittings

• The choice of steel quality must match the load and the environment to which it is exposed. A sensible choice might be EN 1.4401, however with a maximum carbon content of 0.05% (see Table 1).

• Pipes must be round, and fittings must have round branch pipes. There must be no oval cross sections at the ends of neither pipes nor fittings. Special attention should be paid to elbows and plungings.

• The inside surface roughness is industry dependent. The typical requirement in the food industry is Ra < 0.8 µm. Please note that according to international norms, there is a difference between specifying a “max. value” and an ”upper value” (and similarly for a ”min. value” and a ”lower value”). If e.g. an "upper Ra value” of 0.8 is specified, it means that 16 per cent of the measurements can be higher than this value. If, on the contrary, a ”max Ra value” of 0.8 is specified, no measurements can be higher than this value. Measurements must 1) be based on sufficient statistical data (a sufficient number of measurements) and 2) be carried out on uniform flawless surfaces that are inside the basis of the estimate.

• The inside surface should be passivated, pickled or electropolished. Special care should be taken when welding electropolished surfaces as a far better gas protection is required for welding of surfaces which have been made “shiny” – e.g. through grinding, electropolishing, etc.

• There must be no scratches, holes, porosity or other surface defects on the product side of the steel.

• Pipes must be delivered free of defects and clean on the inside as well as on the outside. The pipes must be plugged at the ends and wrapped.

• Fittings must be delivered flawless and clean on the outside as well as on the inside, and they must be wrapped, see figure 4.

• All pipes and fittings belonging to the same mounting operation should have identical pipe diameters and material thickness, i.e. be delivered in the same

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standard (DS, DIN, SS and similar). (Later a DIN pipe can, however, be welded onto a DS pipe. It only requires that the pipe with the smallest diameter be milled to the same diameter as the other pipe).

5. Receiving inspection Receiving inspection should ensure:

• That the delivered material contains no visible defects and impurities. This may later on cause problems in the processing equipment where these impurities might accumulate.

• That the material has been delivered in the agreed quality, and that the material comes with certificates verifying this.

• That the supplied pipes are plugged at the ends and dry on the inside. • That the cross section is not oval in the material as this can cause root defects

when welded. Often the case in fittings. • That fittings are delivered in the right degrees/angles that were ordered. • That the inside surface roughness of pipes and fittings complies with the agreed

requirements (often Ra < 0.8 µm). • That pipes as well as fittings are pickled and passivated on the inside. Special

attention should be paid to welds. • That the longitudinal welding in pipes and fittings did not cause discoloration on the

inside, see figure 2. • That fittings and pipes are wrapped. • That surfaces which come into contact with the product are free of scratches, holes,

porosity and other defects that appear as cavities in the surface.

Figure 2. Recently delivered pipes with discoloration in the longitudinal weld. The pipe is a reject. (A mirror is inserted into the pipe. The picture shows the reflection). 5.1. Analyses for the inspection of deliveries The following techniques can be used for the inspection of received material and documentation of surface treatment and finish.

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• Optical emission spectral analyses (OES analyses) to examine the chemical composition stated in the accompanying delivery certificates according to EN 10204/3.1B (identical to prEN 10204/3.1a).

• Light Optical Microscopy (LOM) to inspect the microstructure. • Scanning Electron Microscopy (SEM) for the inspection and photographic

documentation of the surface finish (topography). • Roughness measurements for the documentation of Ra and Rz values and the

recording of surface profiles, cf. ISO 4288, ISO 4287 and ISO 3274. 6. Storage

• Once the receiving inspection is completed, the pipe ends must be sealed. This is to prevent the ingress of impurities and small animals in pipes and fittings.

• All materials (pipes, fittings, valves, etc.) must be stored in dry, dust-free conditions (and not as shown in figure 3).

• All materials (pipes, fittings, valves, etc.) must be stored at a temperature corresponding to that of the mounting site. If this is not possible, the materials must be brought to the mounting site no later than 24 hours prior to the mounting so that they may achieve the temperature of the mounting room. This is to prevent condensation inside the pipes, which may cause welding defects and lead to the rejection of the welds.

• Precautions must be taken to prevent deformation of the stored materials through collision or insufficient support.

• Work in black steel and stainless steel must always be kept separate. This also applies to storage.

Figure 3. Recently delivered pipes incorrectly stored on site.

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Figure 4. Examples of correctly wrapped fittings.

Figure 5. Examples of correctly stored fittings.

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7. Welding of stainless steel pipes and fittings 7.1. Choice of material to be welded Generally, austenitic steels have very high weldability. However, only materials with an 0.05 per cent carbon content or less (dependent on material thickness) should be selected. This is because chromium carbide may easily form in the grain boundaries. The higher the C content in the steel, the easier chromium carbide will form. And when chromium carbide is formed, so are chromium depleted zones. This means that less chromium will be available for the formation of the passive layer, which may easily result in intercrystalline corrosion. 7.2. Filler material When welding stainless steel, never use filler materials with a lower alloy composition than the base metal. A good rule of thumb is always to upgrade the filler material, e.g. to select a filler material that is higher in chromium and molybdenum, when welding AISI 316. The reason is that some of the alloy elements are burnt off in the weld pool. Upgrading the filler material allows for the burn-off of alloy elements, and at best the welding results in a surplus of alloy elements which will improve resistance to weld decay. 7.3. Welding from a product hygiene perspective The design philosophy of equipment is that it should allow the product to flow freely and unhampered through the piping system. It must be possible to clean the system efficiently. Therefore, it is crucial that the welding preparations are thorough. Parts that are to be welded must be thoroughly cleaned and deburred, but appear as sharp-edged (see figure 6, 1+2). Likewise, variations in material thickness, wrong setup, oval pipes or fittings, wrong design or similar will lead to pockets and zones, where CIP becomes insufficient (see figure 6, 3). Incorrect welding may lead to poor hygiene conditions in an otherwise hygienically well-designed plant. Thus, a residual oxygen content of more than 1 per cent in the backing gas will lead to irregularities and burrs in the actual welding surface. Similarly, a beginning corrosion may cause bacterial pockets long before the actual corrosion is detected. Root defects in the welds must be avoided as they can lead to bacterial pockets. The normal roughness of a well-performed weld will be approx. 1.6 to 4 µm. The maximum roughness accepted on the product side is 6 µm. This is accepted as the welded area constitutes a very small part of the total area of the installation, and at the same time the surface topography is very “soft” due to the molten pool.

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Figure 6. 1) The pipe is properly deburred and sharp-edged – ready for welding. 2) Shows the opposite of 1). 3) Shows two pipes with identical diameters that are offset to each other. Welding of offset pipes will lead to shadow zones for the detergent where CIP becomes insufficient. Should it become necessary to weld pipes with slightly different diameters, the smallest of the pipes must be milled to reduce the diameter difference between the pipes to < 20% of the material thickness. Likewise, none of the pipes must be oval or out of flush with each other (eccentric), and the deviation must be < 20% of the material thickness. The distance between workpieces to be welded must be <0.25 mm). (See also figure 8). 7.4. General welding requirements All surfaces – inside as well as outside – must be thoroughly cleaned prior to welding, and all oil and grease-containing material must be removed from the weld zone as it may otherwise lead to impurities during welding, and consequently reduced corrosion stability. Only personnel with a valid certificate for welding stainless steel, and the experience that goes with it, may carry out welding operations on workpieces that are to be used in the food industry. Please note that there are several norms/standards for the certification of welders and welding operators, the design and approval of welding procedure, and for welding requirements (acceptance levels for welding defects). Please refer to the Danish Standard Association for the currently certified welding norms – see www.ds.dk.

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A well-performed weld will not require any form of grinding but, in so far as possible, it should be pickled both on the inside and outside of the pipe. This will increase the corrosion stability. Pickling piping on the inside is difficult, and normally it is not done. This makes it even more important to be meticulous with the gas protection in the pipe welds that cannot be pickled. In general, it should be avoided to mix pipes of different standards (DIN/DS/EN...) as they may vary in terms of diameter as well as material thickness. Should it become necessary to weld pipes with slightly different diameters, the smallest of the pipes must be milled to reduce the diameter difference between the pipes to < 20% of the material thickness. Likewise, none of the pipes must be oval or out of flush with each other (eccentric), and the deviation must be < 20% of the material thickness (see figure 6, 3). All pipes and surfaces that are to be welded must be straight, and to ensure perpendicular cuts, mechanical cutting devices should always be used for cutting pipes. The distance between workpieces to be welded must be <0.25 mm). 7.5. Shielding gas During welding, shielding gas must be used at all times, both on the front and on the backside of the weld zone. The purpose of the shielding gas is to prevent the access of oxygen to the front and backside of the weld pool. Insufficient use of backing gas will lead to oxidation of the heat-affected weld zone. This will weaken the mechanical as well as the anti-corrosive properties. The backing gas must be maintained until the surface temperature is below 250°C. For the gas protection to be full, its residual-oxygen content must be so low that the discoloration in the weld zone is less or equal to level C in the FORCE Institute report no. 94.30 “REFERENCE ATLAS for validating shield gas quality for welding”. See illustration from the report in figure 7.

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[Billedtekster: Level A (oxygen conc. 21 ppm) Level C (oxygen conc. 100 ppm Level E (oxygen conc. 1,000 ppm). From REFERENCE ATLAS for validating shield gas quality for welding] Figure 7. Excerpts from the FORCE Institute report no. 94.30 “REFERENCE ATLAS for validating shield gas quality for welding” showing the discoloration in the weld zone at level A, C and E respectively (from left to right). In pickled dairy pipes, this corresponds to: When using argon gas: max. oxygen concentration 30 ppm When using formier gas: max. oxygen concentration 100 ppm Note: Please note that shining surfaces are much more prone to discoloration than pickled surfaces and thus require a significantly better gas protection (lower oxygen concentration in the shielding gas). Note: Complete gas protection is required for tacking as well as welding! The most frequently used shielding gasses are argon and formier gas. In recent years, Noxal has also gained a footing among “skilful” welders. Often, argon is used in the welding gun and formier gas as gas protection inside pipes. Table 2 shows the properties and possible applications for the three gas types (argon, formier and Noxal). Generally, it is recommended to use argon shielding gas in the welding gun and formier shielding gas as backing gas when welding pipes.

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Table 2. Overview of properties and applications for various backing gasses. Shielding gas Properties Application

Argon Argon is a colourless and odourless noble gas which forms 0.93 vol. % or atmospheric air. Argon is incombustible and nontoxic. Argon is heavier than atmospheric air.

The use of argon is due to its inert nature. Shielding gas for MIG welding of aluminium and copper, and for TIG welding. Flushing gas for cleaning metal smelting installations. Shielding gas for heat treatment of metals. Shielding gas in the electronics industry.

Formier

Formier gas is a reducing gas mixture consisting of nitrogen and a small amount of hydrogen. Formier gas (90% N2/10% H2) is nontoxic and combustible in certain mixing ratios with air. Formier gas is lighter than atmospheric air.

Gas protection with a reducing effect to shield workpieces from atmospheric air during welding, brazing, brazing and tempering. Formier gas is recommended as root shielding (backing gas) in connection with welding of stainless steel, including duplex steel.

Noxal

Noxal is a gas mixture of argon and hydrogen. The mixtures are colourless, odourless and nontoxic. The hydrogen content gives reducing properties to the mixtures. As only mixtures with less than 5% hydrogen are incombustible when mixed with air, Noxal 4 and 6 are categorised as flammable and explosive. Noxal 2 = 97% Ar and 3% H2 Noxal 4 = 93% Ar and 7% H2 Noxal 6 = 80% Ar and 20% H2 Noxal is heavier than atmospheric air.

Noxal 2 and 4: Shielding gasses for TIG, MIG and plasma welding of stainless steel. Noxal 6: Plasma cutting.

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8. Welding requirements Longer operating hours and the use of more aggressive detergents and disinfectants are contributing factors towards increasing the strain on the installations. This increases the requirements for material selection and plant design. In this respect, the quality of the welding is crucial. In connection with new plants or alterations of existing plant, the client (the food manufacturer) selects the steel grade based on the anticipated environmental strains the steel will be exposed to. Once the steel grade is selected, the requirement will be that the welding of the plant does not reduce the quality of the installation. With respect to corrosion, the welds must in principle withstand the same environmental strain as the base material throughout the entire lifetime of the installation. This means that if there is corrosion over time in a weld, but not in the base material, it will be deemed as failure on part of the supplier of the plant. Therefore, the supplier must also provide a warranty for weld stability. Such warranty should not be less than 5 years. Should there be corrosion in the welds (the weld zone), but not in the pipes, the supplier of the plant, who undertook the welding, will be liable in damages. In the event of corrosion of both welds and pipes, the company/the customer is liable. (The weld zone is the area within a 30 mm distance to both sides of the actual weld, as shown in figure 8).

Svejsezone = 2xZ, Z ~ 30 mm

a og b målene skal overholdes såvel udvendigt som indvendigt i rørene

b < 0,15 * t

t, godstykkelse

a < 0,15 * t

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[Billedtekster: Weld zone. A and b measurements must be observed on the inside as well as the outside of the pipes. Material thickness. (Husk at ændre komma i decimal tallet 0,15 til punktum (altså 0.15).] Figure 8. Pipe ends must be cleaned of dirt and grease in a minimum distance of 30 mm from the weld. The concavity/convexity of the weld must be < 0.15 x material thickness. With respect to hygiene, the welds on the product side must be as smooth as possible without burrs, crevices and the like. A well-performed inside weld should have a roughness of the seam of Ra < 3 µm, and the absolute highest acceptable roughness is Ra < 6 µm. The following sections contain guidelines for the process steps. Preparation, execution and inspection of stainless steel welds. 8.1. Equipment The following equipment is expected to be required:

• TIG welding unit with pulse box. • Oxygen meter to check the residual oxygen content in backing gas. • Flow meter to control the gas supply. • Shielding gas (argon or formier gas). (It is recommended to use argon on the

outside and formier gas on the inside of the pipes.) • Pipe cutter.

8.2. Welding preparation For piping installations, observe the following guidelines:

• Pipe ends must be cleaned of both dirt and grease in a minimum distance of 30 mm from the weld.

• Pipes must be shortened in the pipe cutter so as to give the pipes a perpendicular straight cut. Manual shortening with a hacksaw is only acceptable if use of a pipe cutter is not possible, and it has been previously agreed with the customer.

• The shortened pipe ends must be free of burrs. • Pipe ends that are welded must have identical inside and outside diameters. In

case of any difference, the smallest pipe must be milled to the same inside diameter.

• When using fit-up clamps to secure pipe ends, the contact face must be stainless. The directions in figure 8 must be observed.

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8.3. Pipe welding

• Welding of product pipes must only be carried out by certified welders. • During welding, gas protection must be used both inside and outside the pipe. On

the inside of the pipe, the gas protection must be full1 (see section 7.5) • Tacking must always be carried out under full gas protection. • When the weld has been completed, full gas protection must be maintained until the

temperature of the weld is below 250°C. • In so far as possible, all welding operations must be carried out in a vice bench. • When using a filler material, make sure its alloy composition is not lower than that of

the base metal. • The weld must be performed such as to be free of pore defects, root defects,

penetration defects or the like. • To the extent possible, the welder himself must check all welds for correct backing

gas and correct weld root (see figures 9-13). • When welding materials with a thickness of 3 to 40 mm, DS/EN 288, no. 1 to 8 must

be observed. In pickled dairy pipes, this will typically correspond to: When using argon gas: max. oxygen concentration 30 ppm When using formier: max. oxygen concentration 100 ppm (Please note that shining surfaces are much more prone to discoloration than pickled surfaces and thus require a significantly lower oxygen concentration in the backing gas). If sufficient backing gas has been used in accordance with the directions above, there will be no significant discoloration. Therefore, any discolorations that are level C or higher in “REFERENCE ATLAS for validating shield gas quality for welding” will not be accepted (see figure 7). Figures 9-13 show examples of good and poor gas protection with discoloration and weld root.

1 For the gas protection to be full, its residual-oxygen content must be so low that the discoloration in the weld zone is less or equal to level C in the FORCE Institute report no. 94.30 “REFERENCE ATLAS for validating shield gas quality for welding”.

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Figure 9. Tacking without backing gas The blue colour and the formation coke/cinder in the tack root is clear to see.

Figure 10. After all-welding the tack point with the formation of coke in the weld root is clear. (A mirror is inserted into the pipe. The picture shows the reflection).

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Figure 11. Good welds with gas protection: No discoloration and a nice uniform weld root.

Figure 12. Poor weld with insufficient gas protection (blue colour) and with a very poor root.

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Figure 13. Poor weld with an unacceptable gas protection (notice the dark colour), but with a nice uniform root. 8.4. After welding

• After welding, the welder must perform a visual check of the welds on the inside as well as on the outside of the pipe.

• Internal inspection of piping systems is performed by endoscopy. • The inspection of the welds must show no signs of oxidation and weld splatter

around the concavity/convexity of the weld as shown in figure 12. • The weld is pickled on the outside with pickling paste. When possible, it is also

pickled on the inside. • Any subsequent internal inspection of piping systems is performed by endoscopy.

The supplier of the plant must prepare a welding specification describing how the requirements for the welding procedure are met and how compliance with the procedures is checked regularly during the entire construction phase. The client determines the procedure for control and inspection of the finished plant/part of plant. If the delivered plant ”fails” at the inspection, i.e. does not meet the specified quality requirements, the inspection is intensified beyond what was agreed. All defects found must be repaired. The client pays the costs of the established procedure for control and inspection, provided no defects are found. In the event of defects, the supplier of the plant must normally pay for repairs of defects found and bear the costs of the preliminary as well as of the intensified inspection.

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See enclosed example of weld inspection of deliveries in chapter 10. 9. Mounting 9.1. Drainability

• Pipes must be mounted so as to be fully drainable (minimum incline of 3°). • If the location prevents drainability, drain valves must be built in at all low points of

the installation.

9.2. Pipe dimensions

• To avoid undrainable pockets, an eccentric cone must be used to change pipe dimensions in horizontal pipings. For vertical pipes a concentric cone is used.

• There must be no change of pipe dimension without the use of a cone. • Long piping runs must allow pipe expansion in connection with temperature

changes, without this causing unnecessary tension in the pipes. This is ensured by building in a lyre or an expansion joint. Stainless steel expands by more than 1 mm per meter per 100°C heat increase.

• If lyres are built in, these must be large enough to allow for the expansion and contraction without deformation to the pipe.

• If expansion joints are built in, they must be designed to allow cleaning and disinfection.

• The pipes must be dimensioned so that the product is not damaged during the flow. This means that the pipe layout must be such as to minimise any pressure loss, i.e. contain as few elbows etc. as possible (resistance also entails unnecessary waste of energy).

9.3. Pipe layout

• With regard to pumps, it must be ensured that there is a straight piece of pipe immediately before the pump with a diameter of five times that of the pipe. This is to ensure that the liquid flow is sufficiently developed before it hits the impeller as it would otherwise cause vibrations in the pump.

• It must be ensured that changes in pipe direction do not block future expansions of the pipe bridge and the like, which would otherwise lead to poor layout of the expansion and the subsequent risk of cavitation.

• The installation must not contain any dead pockets/blind ends as these would be difficult to clean. In branches where valves are used for the opening/closing of each branch, a valve in the actual branch can be used instead (three-way valves, but not ball valves), to direct the liquid to one branch or the other without causing dead pockets.

• Optimal pipe layout means that the plant is designed to treat the product as carefully as possible with the easiest possible cleaning and the lowest possible energy consumption.

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• The risk of ingress of air must be minimised, as it would mix with the product and possibly create air pockets in the piping system.

9.4. Seals at pipe joints

• No metal-to-metal towards the product stream. • Metal-to-metal stops on the backside of gaskets to avoid overcompression. • No sharp edges where the gasket may expand. This could cause the gasket to be

cut off, e.g. by thermal expansion of the gasket.

9.5. Pipe supports

• Pipe supports must be designed to prevent impurities from settling and subsequent falling into the product, i.e. there must be no horizontal surfaces on the construction. Supports should have a 45° incline.

• Pipe supports on which a profile has been plunged to make the support stronger, may cause pockets where impurities and liquid may settle. This may lead to bacterial growth and corrosion. Pipe supports with smooth flanges are recommended.

• Pipe supports must be mounted in a distance that prevents cavitation in the pipes and at irregular distances so as not to increase the oscillation frequency of the pipes. The distance between pipe supports is selected as needed, typically 1.5-2 m.

• In vertical pipe layouts it must be ensured that pipes are suspended in pipe hangers that fix the pipes and prevent them from sinking and creating a backward slope in the horizontal section of the pipe, so that it is no longer drainable.

• Stainless steel expands by more than 1 mm per meter per 100°C heat increase. As pipe expansions are thermal, it must be ensured that the pipes can move during the expansion, as the pipe supports would otherwise break at the fixing point. Pipe supports must fully encompass the pipe or be cups.

• If pipe cups are used, the pipes should be fixed at regular distances to ensure that they stay in the cup if an accident in the process creates a water-hammer that causes the pipe to lift.

9.6. Production stoppage precautions Pipe systems should not be emptied prior to CIP cleaning, but the product should be displaced by water. In connection with short production stoppages (a few days), the pipes should be liquid-filled (with water or similar). The reason is that it may be difficult to drain piping systems of air. When a piping system is emptied prior to CIP, there is a risk that air is left in the pipes, and air pockets during CIP means that some zones are not cleaned sufficiently.

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10. Inspection of completed work 10.1. Weld inspection for deliveries Much annoyance can be avoided and money saved if the chief installation engineer checks the daily work on the installation. The example below is a suggestion for a weld inspection. Example for weld inspection for deliveries A. Specified requirements for welds on piping installations in stainless steel must be observed. Special

attention is drawn to the requirement that only certified welders carry out welding of stainless installations. Welders who carry out welding operations during installation at a site must take a welding test which is approved by engineer NN or his assistant, before the actual work can commence. The test must be a welding of 2” pipes at a 45° incline.

B. A minimum of 5 per cent of all pipe welds must be endoscopied. Endoscopied welds must subsequently be individually identifiable just as the endoscopy must be videoed, and copies of the video sent to engineer NN or his assistant. The selected welds that are endoscopied must be representative of the welders involved. Engineer NN or his assistant must have the right to select up to 40 per cent of welds for endoscopy.

C. If defects are detected, an extended endoscopy inspection is made on 10 of the welder’s latest welds. If further defects are found, the welder in question must have his certificate renewed. Before the welder can perform welding operations on installations again, he must perform three supervised, error-free welds on setups selected by engineer NN or his assistant.

D. If defects are detected during B, further endoscopy inspection must be carried out on 5 per cent of the other welds that were not referred to under C.

E. Endoscopy must be carried out regularly – e.g. weekly – and video copy hereof must be handed to engineer NN or his assistant, as the inspections are performed.

F. The customer reserves the right to carry out his own endoscopy to an extent chosen by him, and documented defects must be subject to the procedures in B, C and D.

G. The supplier inspects and approves the endoscopied welds mentioned in B, C and D. Engineer NN or his assistant has a two-week right of protest from the receipt of the video. In matters of dispute, an impartial party will be chosen as arbiter. The losing party shall bear the costs for said impartial party.

H. The supplier shall bear the costs for any of the above endoscopies, videos etc. performed by the supplier. The customer shall bear the costs for any of the above endoscopies, videos etc. performed by the customer as control inspections.

Requirements for weld quality and inspection methods should be established during the offer phase.

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10.2. Installation inspection It is inspected whether the layout of the mounted pipe runs is sensible and according to the agreement. Among other things, it is inspected that there are no more elbows than necessary, as they result in pressure loss, i.e. energy loss, throughout the service life of the plant! It is inspected whether the selected pipe dimensions, valves and other equipment are sensible and mounting requirements and guidelines have been observed. If a plant inspection shows inside discolorations from welding, and there is no root defect in the welds, the discolorations can be removed by pickling. If pickling of the inside of pipes is initiated, a pickling procedure must be implemented! The pickling procedure must ensure:

• that rubber gaskets, shaft seals for pumps and similar materials are not damaged • that pickling does not represent any kind of danger or hazard to persons and the

environment • that no equipment is damaged • that essential equipment such as condensers and the like is avoided.

The pickling procedure must be approved by the customer and his safety representative before it can be implemented! 11. Overview of other guidelines about piping, etc. EHEDG Doc. 2, 2004: A method for assessing the in-place cleanability of food processing equipment The test is used to find areas of processing equipment with poor hygienic design where dirt and microbes can be protected from cleaning. The method is based on a comparison between the cleaning effect in a piece of test equipment and a straight pipe piece. The document contains a detailed description of how the test is performed. The test can be bought at EHEDG: http://www.ehedg.org. EHEDG Doc. 2, 2004: A method for assessing the in-place cleanability of food processing equipment The test is used to find areas of processing equipment with poor hygienic design where dirt and microbes can be protected from cleaning. The method is based on a comparison between the cleaning effect in a piece of test equipment and a straight pipe piece. The document contains a detailed description of how the test is performed. The test can be bought at EHEDG: http://www.ehedg.org. The guideline provides basic design principles that should be observed to obtain as satisfactory hygienic design. The document contains general guidelines for hygienic design, requirements for materials, function as regards cleaning, decontamination,

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avoidance of ingress of microorganisms, compatibility with other requirements (e.g. process requirements) and assessment of the hygienic design of equipment. The guideline can be bought at EHEDG: http://www.ehedg.org. EHEDG Doc. 10, 1992: Hygienic design of closed equipment for the processing of liquid food The guideline deals with specific examples of good and poor design of different components and piping systems in closed processing equipment. Some these are: gaskets and couplings, shaft insertions and dead pockets. The guideline can be bought at EHEDG: http://www.ehedg.org. EHEDG Doc. 16, 1997: Hygienic pipe couplings The guidelines describes the design of gaskets and seals that ensure hygienic pipe couplings. The gaskets must be cleanable, disinfectable, impermeable to microorganisms and durable. It includes critical design parameters for gaskets made from elastomers and accurate descriptions of gasket behaviour during heat influence. The guideline can be bought at EHEDG: http://www.ehedg.org. EHEDG Doc. 25, 2002: Design of Mechanical Seals for hygienic and aseptic applications The guideline deals with mechanical seals used in the food production. It provides general criteria for hygienic design and basic requirements for sealing materials. The guideline compares different seals in relation to cleaning, microbial impermeability, disinfectability and pasteurizability. The guideline contains several illustrations. The guideline can be bought at EHEDG: http://www.ehedg.org. Champden & Chorleywood Technical Manual no. 17 (ISBN nr. 0905942078) 2. edition, 1997: Hygienic Design of Liquid Handling Equipment for the Food Industry The guideline is quite comprehensive and contains hygienic design of equipment for the production of liquid products such as milk and other dairy products. It collects advice from the EU directive 89/392/EEC and the Machine Directive, and guidelines from EHEDG publications on equipment for liquids. It touches on subjects such as material selection, including stainless steel, construction, instrumentation of equipment, agitator, piping systems, including taps and pumps, and CIP systems. The guideline can be bought at http://www.campden.co.uk/. 3-A Accepted Practices for Permanently Installed Product and Solution Pipelines and Cleaning Systems Used in Milk and Milk Product Processing Plants, Number 605-04, 1994 The guideline deals with installation and cleaning of fixed pipe lines used in processing equipment for the production of milk and other dairy products. The guideline defines hygienic design, construction, material, manufacture and installation criteria for the fixed pipe lines for cleaning liquids, and the central CIP unit. The guideline does not apply to cleaning systems at the milk producer or piping systems containing dry matter. http://www.techstreet.com/3Agate.html. ASME BPE-2002 Bioprocessing Equipment This standard deals with the requirements of the bioprocessing industry, covering directly or indirectly the subjects of materials, design, fabrications, pressure systems (vessels and piping), examinations, inspections, testing, and certifications. Items or requirements that

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are not specifically addressed in this standard cannot be considered prohibited. Engineering judgements must be consistent with the fundamental principles of this standard. Such judgements shall not be used to override mandatory regulations or specific prohibitions of this standard. http:///www.techstreet.com/. 12. Applied methods Group members’ experience and knowledge was collected and structured from 2004 to 2005. Group meetings and visits to companies were held at the authors’ companies. 13. Further information and literature Furthermore, the www.staalcentrum.dk knowledge portal contains a wide range of relevant links to authorities and organisations, etc. The portal also offers a clear picture of the guidelines, standards, legislation etc. available for specific fields/types of equipment and locations. It is easy to search the material and read a short description of the actual contents. From the relevant links it is possible to order material from the source. FORCE Institute report no. 94.30 REFERENCE ATLAS for validating shield gas quality for welding. 14. Change protocol This is the first edition. Future changes will be listed here.