I NSTRUM ENTS & C ONTROLS :
2.9 Piping Materials for Specific Fluid Services
Types of Services: As per ANSI B 31.3, the fluid services have been classified in five different categories for sake of safe operation based on design conditions, design criteria, design consideration
& design limitations. However, practically, the different fluid services are as mentioned below:
(I) UTI LI TI ES SERVI CE: COMMERCIAL CARBON ST EEL PIPE SUCH AS IS 1239 IS COMMONLY USED IN
UT ILIT Y SERVICE. THE ST EEL PIPE WHICH IS OF A T YPE OR GRADE NOT ACCEPTABLE FOR HYDROCARBON SERVICE, SOME DEFINIT E MARKING SYST EM SHOULD BE ESTABLISHED TO PREVENT SUCH PIPE FROM ACCIDENTALLY BEING USED IN HYDROCARBON SERVICE. ONE WAY TO ACCOMPLISH T HIS WOULD BE TO HAVE ALL SUCH PIPE GALVANIZED OR PAINT ED IN ST RIP TO FULL LENGT H OF PIPE.
(ii) Category-D fluid: The fluid which design pressure is 150 psi or less with design temperature between –29ºC and 166ºC and do not damage to the human tissue or otherwise on exposure.
Category-D Fluid is non-toxic and non-flammable. Piping is designed as per ANSI B 31.3, chapter I to VI for metallic and chapter vii for non-metallic and lined piping. The following carbon steel pipe can be used. ASTM A 53 GR F, ASTM A734 made from other than ASTM A 215 plate, API 5L GR B (Furnace Butt-welded), ASTM A 211 and ASTM A134 made from other than ASTM A285 plate.
(iii) Category-M Fluid: The fluid service which operating pressure is not high. It is flammable or non-flammable, but toxic. It causes, by leakage to a very small quantity of the fluid, irreversible harm to the human on a single exposure. It cannot be designed under code or under chapter VII sufficiently to protect personnel from exposure to a very small quantity of the fluid in environment. Category-M fluid service piping is designed by chapter VIII rules of ANSI B 31.3. Sufficient safeguarding shall be provided to the piping for category-M fluid service. Category-M fluid service piping shall not be designed or used under severe cyclic conditions and high-pressure piping. Category-M fluid service piping shall be avoided with dynamic effects such as impact caused by external or internal conditions (e.g., change in flow rate, hydraulic shock, and liquid or solid slugging, flushing and geysering) and also vibrations, which may arise from pressure pulsation, resonance in compressor or wind loads.
ASTM A 134 and ASTM A 139 pipe shall not be used. Fittings confirming to MSS SP-43 and proprietary “Type C” lap-joint stub end butt-welding fittings shall not be used in category-M fluid service. Creased or corrugated bends shall not be used. Threaded or sockets welding outlet branch connections are not permitted to be used. Flat closures (blanks) shall not be used. Valves having threaded bonnet joints shall not be used. Valve bonnet or cover plate closures shall be flanged, secured by at least four bolts with proper gaskets to stop the stem leakage to the environment. Single-welded slip-on flanges, Expanded joint flanges, Lap joint flanges and threaded flanges shall not be used. Socket welded joints greater than 1 ½” size shall not be used. Expansion joints shall not be used.
(iv) Normal fluid service:This is a fluid, which is not at high pressure but whose design pressure or design temperature is not limited to 150 psi or between –29 C to 166 C respectively. This is toxic or non-toxic, flammable and damage to the human tissue on exposure or irreversible damage on single exposure. It is designed and constructed per chapter I to VI for metallic piping, per chapter VII for non-metallic and lined piping to sufficiently protect personnel from exposure to very small quantities of the fluid in the environment. Any pipe and piping components listed in codes &
specifications may be used in “Normal Fluid Service”. Unlisted piping component material may be used only after qualifying the design conditions and criteria and other design parameters.
(v) Severe Cyclic Condition Fluid service: The fluids, which do not have very high pressure but toxic, non-flammable and produce a serious irreversible harm on a single and very small quantity exposure. Fluid comes under “Category-M fluid” but can be designed and constructed in severe cyclic conditions to prevent occurrence of it as per Chapter VIII rule, is called severe cyclic condition fluids. This fluid service cannot be designed on experience, service conditions & location involved, as per base code or chapter VII sufficiently to protect personnel from exposure to very small quantities of the fluid in the environment. The following pipe may be used under severe cyclic condition fluid service.
(vi) High Pressure Fluid service: High pressure is considered to be pressure in excess of that allowed by the ASME B16.5 PN 20 (class 2500) rating for the specified design temperature and material group. Non-metallic or metallic lined piping components are not permitted for use in high pressure piping category. There is no provision for category-M fluid service in high-pressure piping.
The design of High Pressure piping should be done as per following considerations:
Mitre bend shall not be used in high-pressure piping.
Pipe to pipe cut & welded branch connections shall not be used in high-pressure piping.
All welded pipes or cast-forged fittings shall have joint quality or cast quality factor not less than 1.0.
(vii) Steam Tracing (NIBR): Certain process lines, tanks, vessels, are required to be heated up constantly to prevent the fluid passing through the lines, stored tank or vessel from freezing. Heating keeps the temperature high enough for free flows of fluid and proper pumping ability. Heating is done with the help of steam tracing or electrical tracing. Steam tracing is done by running one, two, or three lines parallel along the process line at equal distance on periphery of the lines and touching the line or inside the tank or vessels to be heated up. Process lines shall be indicated to be traced in the line list system. Steam supplies for tracing are obtained from process steam lines or independent steam supplies line, exhaust bleed steam or from other continuous source of steam supply lines. Steam supply shall be always available even if other unit or steam lines are under shutdown or out of operation. Minimum steam pressure for tracing shall be 1.5 kg / cm2 and maximum steam pressure shall be 3.5 kg / cm2. The minimum steam temperature shall be the saturation temperature at the given pressure. The size of steam supply header shall be 3” Dia. (80 mm) Maximum for header and ½” Dia.
for steam tracing line, running along the process line. The number of tracers along the process lines for heating shall be as per design calculation by the designer. However, under normal condition of heating the number of tracers lines shall be mentioned below:
Tracer line size Number of ½” Dia. Tracers
4” NB and smaller 1
6” NB to 16” NB 2
18” NB and larger 3
The useful length of tracer line in a single run at a steam pressure of 3.5 Kg /cm2 shall be maximum as mentioned below:
1. Open system of tracing - 40 meter max. (With no recovery).
2. Closed system of tracing - 25 meter max (With condensate recovery).
The tracer loops shall start at the highest point and terminate at lowest point in the system, in general.
But sometimes there is an unavoidable pocket in the tracers. The sum of all pockets in a loop of tracer shall be proportionate to the differential steam pressure in the tracer (i.e., maximum 3.5 Kg /cm2) to max total sum of vertical depth of pocket (i.e., max. 3000 mm). Example: The total depth of pockets in above diagram is A + B + C. Every tracer shall be provided with a separate steam trap at the end at lowest point.
(viii) Non-Corrosive Hydrocarbon Service: The most commonly used types of pipe are ASTM A106, Grade B, and API 5 L, Grade B. ASTM A106 is only manufactured in Seamless while API 5 L is available in Seamless, Electric Resistance Welded (ERW) and Submerged Arc Welded (SAW).
When API 5L, Grade B, pipe requires excessive wall thickness, higher strength pipe such as API 5LX, Grade X52, may be used. However, special welding procedures and close supervision are necessary when using API 5LX, Grade X46 or higher. ANSI B 31.3 specifically excludes the following types or grades of pipe from hydrocarbon service:
All grades of ASTM A 120.
Furnace lap weld and furnace butt weld.
Fusion welds per ASTM A 134 and A 139.
Spiral weld, except API 5LS.
(ix) Corrosive Hydrocarbon Service: Design for corrosive hydrocarbon service should provide for one or more of the following corrosion mitigating practices: 1) Chemical treatment; 2) Corrosion resistant alloys; 3) Protective coatings. Chemical treatment of the fluid in contact with carbon steels is by far the most common practice and is generally adopted. Corrosion resistant alloys, which have proven successful, may be used. If such alloys are used, careful consideration should be given to welding procedures and the possibility of sulphide and chloride stress cracking. Adequate provisions should be made for corrosion monitoring (coupons, probes, spools etc.,) and chemical treating. API 5L GR B, A106 GR B, A312 GR TP 304, TP 316, TP 316L are recommended.
(x) Sulphide Stress Cracking Service: The following guidelines should be used when selecting pipe if sulphide stress corrosion cracking is anticipated;
Only seamless pipe should be used.
Cold expanded pipe should be used only after normalizing, quenching and tempering, or heat treatment.
Carbon steels, alloy steels and other materials which meet the property, hardness, heat treatment and other requirement of NACE: MR- 01-75 is acceptable for use in sulphide stress cracking service.
The most commonly used pipe grades which will meet the above guidelines are: ASTM A106, Grade B; ASTM A333, Grade 6 and API 5L, Grade B, seamless and API 5LX is also acceptable. Welding of this grade material presents special problems. To enhance toughness and reduce brittle fracture tendencies, API 5L and 5LX should be normalized for service temperatures below 30 F. ASTM A333, Grade 6, is a cold service piping material and should have adequate notch toughness in the temperature range (- 20 to 650 F).
(xi) Steam (IBR) Service: Central Boiler Board in India exercises the material, design and construction of a boiler steam pipe, economizers, or super heaters. The representative of Central Boiler Board is the Chief Inspector of Boiler in the state of India. To exercise the power to supervise the job, the Central Boiler Board has made Regulations, which control the materials, design, construction, and inspection of the work. This Regulation is called “Indian Boiler Regulation-1950”
or “IBR”.
The chief inspector will register the work under boiler regulation, subject to the following conditions:
(i) Boilers: When a closed vessel, exceeding 22.75 litres (five gallons) in capacity, and which
is used expressly for generating steam under pressure and include any mountings and fittings is called Boiler and comes under Indian Boiler Regulation.
(ii) Economizer: When a feed pipe, wholly or partly exposed to the action of flue gases for the purpose of recovery of waste heat is called Economizer and comes under Indian Boiler Regulation.
(iii)Steam Pipe: When a pipe through which steam passes from boiler to a prime mover or other
users or both, and, if, satisfy the following conditions, (a) the pressure at which steam passes through such pipe, exceeds 3.5 kg/cm2 above atmospheric pressure, or (b) the internal diameter of the steam pipe exceeds 254 mm, it is called a Steam Pipe and comes under Indian Boiler Regulation.
In any industry, if there is a boiler, economizer, and steam pipe or all of them, then the design, materials, fabrication, the Chief Inspector of Boiler does erection and hydrostatic testing. The total package of above nature of work has to be offered to the Chief inspector of Boiler for approval of the package including materials, fabrication, and erection and testing. A completion certificate has to be obtained by the manufacturer from the office of the Chief Inspector of Boiler as per IBR code requirements.
Limitations on selection of IBR materials: IBR Inspector of the Central Boiler Board of India should certify all IBR piping materials in the form III before use.
Carbon Equivalent (CE): The Carbon Steel IBR piping materials should have Carbon Equivalent Maximum 0.25%.
(xii) Sour Service: Sour service is the hydrocarbon service containing hydrogen sulphide. The presence of Hydrogen sulphides causes Sulphide Stress Cracking (SSC) of metallic material in wet conditions. The standard NACE MR-01-75 defines the sour service and recommends materials, which will not fail in wet sour service fluid conditions. The following recommended materials minimize SSC but also HIC (Hydrogen Induced Cracking), Step-Wise cracking or Hydrogen Blistering. All materials should be quenched & tempered or normalized condition or normalized &
tempered condition.
Pipes: API 5L Grade B (seamless) & SAW (Longitudinal); A 106 Grade B (seamless), A 333 Grade 6 (seamless); A 671 Grade CC 70 CL 32- SAW (Longitudinal); A672 Grade CC 70 CL 32- SAW (Longitudinal); API 5L Gr. X 52, X60, SAW (Longitudinal);
Studs/Nuts: A 193 Gr. B7M; A 194 Gr. 2HM; A 320 Gr. L7M; A 194 Gr. 7M; Studs should be fully threaded with two nuts. HIC test and SSC test are not required for studs and nuts.
Castings: A216 Gr. WCB; A217 Gr. WC6; A351 Gr. CF3M Fittings: A 234 Gr. WPB (SMLS); A420 Gr. WPL6 (SMLS); A105 (Forged); SS-SP-75 Gr. WPH452 (Welded); A 234 Gr. WPBW / WPCW (Welded); A350 Gr. LF2 (Forged); MSS-SP-75 Gr. WPH460 (Welded).
Gaskets: Spiral wound gaskets of SS 316 L with Compressed Asbestos (CA) filler should be used. In case of RTJ type, the gasket should be Soft Iron with maximum hardness 90 BHN. HIC & SSC tests are not required.
Flanges: A694 Gr. F52; MSS-SP-44 Gr. F60; A105; ASTM 350 Gr.
LF2;
Valves: Valve body should be cast or forged steel. Other component and TRIM materials should be SS 316 with maximum hardness RC 22 and hard faced with Stellite hardness up to maximum RC 43. All part of the valve should be stress relieved. A105 (Forged); A216 Gr. WCB (Casting); A352 Gr. LF2 (Forged); A352 Gr.
LCB (Casting)
Limitation for Material Metallurgy Sour Service:
All steel should be fully killed and fine-grained and should have high resistance to hydrogen sulphide attack such as “HIC” & “SSC”.
All steels should be produced either by basic oxygen or Electric Furnace process only.
All steels should have following treatment during steel making process:
Steel should be treated to have low sulphur and low Phosphorus and should be vacuum degassed.
Steels should be calcium treated for morphology control. Steels should be treated to avoid inclusions like metallic oxide clusters, silicates, magnesium sulphide etc.
Steels should be rolled and heat treatment should do so as to eliminate “low temperature transformation of microstructures associated with segregation”, such as binate Band or Islets or Martensite in order to reduce the propagation of HIC.
Carbon Equivalent (C.E): Carbon Equivalent (C.E) and Pcm should be as per Table indicated below and should be computed by following formulas:
If c = < 0.12;
The weld ability based on a range of CE values can be defined as follows:
Carbon equivalent (CE) Weld ability
Up to 0.35 Excellent
0.36–0.40 Very good
0.41–0.45 Good
0.46–0.50 Fair
Over 0.50 Poor
Material Test Requirement Sour Service: The manufacturer should carry out all the following test duly witnessed by Third party inspection agency and shall conform to the requirement given in following table:
Chemical compositions as given in table below.
Mechanical properties such as UTS & ratio of Yield to Tensile Strength and following should be acceptable.
UTS = 77000 PSI (max.)
Ratio of Yield to Tensile Strength should not exceed 0.8.
Hardness should be maximum RC 22 or 248 HVs or 237 BHN for each heat.
Longitudinal weld seam should be 100% radiographic. Repair welds should not be permitted of any size. All valves casting should be 100% radiograph and acceptance limit should be as per B16.34, Annexure-B.
Seamless pipe for Sour Service: Maximum sulphur and phosphorus content should be 0.01% and 0.02% respectively. If the sulphur and Phosphorus content is more than the above limit specified, the HIC testing should be carried out on pipe where the content exceeds the above value.
Welded pipe for Sour Service: HIC should be compulsorily carried out for each welded pipe irrespective of sulphur and phosphorus content value. The acceptance criteria should be as follows:
i. CSR =< 0.00%
ii. CLR =< 10.00%
SSC Test for Sour Service: SSC test is not required, but when the sulphur and phosphorous contents exceeds 0.020% and 0.010 % (for seamless) or 0.003% (for welded) respectively then SSC test should be compulsorily carried out for acceptance of the pipe for every heat. Similarly, when UTS is greater than 77000 psi (54 Kg/mm2), SSC test is compulsorily for acceptance of the pipe for every heat. The acceptance criteria should be as follows:
AT 72% of SMYS,” Time to failure”, should not be less than 720 hrs.
Corrosion Tests for Sour Service: The corrosion tests should be carried out compulsorily for the
-(xiii) Cryogenic Service: The Cryogenic Service has been defined for proper piping design handling the material at cold temperature. The temperature level, for a cryogenic fluid service, starts at –100 0 F to absolute zero, i.e. –459.7 0 F. There are many factors being encountered while handling the cryogenic fluid because they are cold. The cryogenic fluids include the liquefied gases like oxygen, nitrogen, helium, methane, and carbon dioxide, Argon and to make certain metals super conductive.
Cryogenic fluids are used to cool any product to produce physical changes i.e. to liquefy gases and to manufacture gases such as Oxygen, Nitrogen, Helium and Methane and to make certain metal super conductive. Cryogenic system handles following fluids at low temperature. It absorbs heat from outside source and tends to vaporize or saturated vapour gets superheated. This increases the pressure in the vessel. Cryogenic fluids are very limited, such as, Acetylene; Air and Argon. In general, the following table shows the materials commonly used in low temperature Cryogenic service:
Temperature Range, 0F Material
0 to –20 Carbon Steel ASTM A333 Gr.3, Gr. 6, API 5L Gr.B -20 to –50 Carbon Steel (Aluminium Killed), ASTM A333 Gr.6 -50 to –150 Alloy Steels, ASTM A333 Gr.3
-150 to –320 Alloy Steels or Non-Ferrous, ASTM A312 Gr.TP304 Below –320 Non-Ferrous, ASTM A312 Gr.TP304