Skip to main content

[MW:2385] Re: Diff. bet' n pipe & tube

By Materials & Welding
 Sir,
1)it measns preheating is done to achieve reqd.temp.for welding higher thk(19 mm & above),so as to reduce rate of cooling which leads to cracking in the weld.
2)tube can be treated as a small pipe or pipe below 4" can be used as a tube ina heat exchanger. Pl. reply.
Thanks for valuable responce.
Prashant 

--- On Wed, 10/6/09, tong tong <tong2je@gmail.com> wrote:

From: tong tong <tong2je@gmail.com>
Subject: [MW:2377] Re: Diff. bet' n pipe & tube
To: materials-welding@googlegroups.com
Date: Wednesday, 10 June, 2009, 8:07 AM

Dear Prashant,
Tubing is generally seamless, but may be welded. Its stated size is the actual outside diameter. (ASTM B88 tubing, which is often used for steam tracing, is an exception in that its size designation is 1/8inch (3.2 mm) less than the actual outside diameter.) Tubing is usually made in small diameters and is mainly used for heat exchangers, instrument piping, lubricating oil services, steam tracing, and similar services.
Piping can be made from any material that can be rolled and welded, cast, or drawn through dies to form a tubular section. In all standard sizes, the outside diameter remains nearly constant regardless of the thickness. For nominal pipe sizes of 12 inches (305 mm) and smaller, the size refers to the inside diameter of standard weight pipe; for nominal pipe sizes of 14 inches (356 mm) and larger, the size denotes the actual outside diameter. The pipe diameter is expressed as nominal pipe size (NPS) which is based on these size practices
Preheating is defined as heating of the weld/surrounding base metal to a predetermined temperature prior to the start of welding. The primary purpose for preheating carbon and low-alloy steels is to reduce the tendency for hydrogen induced delayed cracking. It does this by slowing the cooling rate, which helps prevent the formation of martensite in the weld and base metal HAZ. However, preheating may be performed for many reasons, including:

a. Bring temperature up to preheat or interpass temperatures
required by the WPS.
b. Reduce shrinkage stresses in the weld and base metal,
which is especially important in weld joints with high
restraint.
c. Reduce the cooling rate to prevent hardening and a reduction
in ductility of the weld and base metal HAZ.
d. Maintain weld interpass temperatures.
e. Eliminate moisture from the weld area.
f. Meet the requirements of the applicable fabrication code,
such as the ASME Boiler and Pressure Vessel Code, depending
on the chemistry and thickness of the alloy to be welded.

Regards
Tong2je


On Tue, Jun 9, 2009 at 1:22 PM, prashant pansare <prashantpan_99@yahoo.co.in> wrote:
Dear friends,
1) What is the functional diff. in pipe & tube? Why pipe is denoted by NB X Sch. & tube by O.D. X Thk.?
2) Why preheating is done prior to welding?
prashant 

Explore and discover exciting holidays and getaways with Yahoo! India Travel Click here!


Explore and discover exciting holidays and getaways with Yahoo! India Travel Click here! --~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding-unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
-~----------~----~----~----~------~----~------~--~---

Comments

Post a Comment

Popular posts from this blog

Re: [MW:34105] SA266 GR4N 4 Cycle SPWHT

By Materials & Welding
Hi,  You are correct, Minimum refers to the one cycle for which this part will expose until final work shop PWHT. hence mill test certificate shall include this.  Max. SPWHT, refers to additional cycles of heat treatment that are reserved for future repairs during equipment lifetime.  Again, these simulated no. Of cycles shall be specified in MTC.  The idea is we need to make sure that steel mechanical properties are not compromised upon exposure to multiple repairs (i e 4 cycles in your case).  One could say, if steel is subjected to 4 cycles and is ok, then it should by defacto be good for one cycle, yet, this is wrong assumption cause mechanical problems and microstructure of materials varies accordingly based on no. Of cycles for which material will expose. This is apparent in alloy steel and especially for impact test values as an example.  In your case, this forged CS with properties before PWHT can be understood to be " as forged" condition (i.e. Wit...
Post a Comment
Read more

Materails FAQs

By Materials & Welding
Q: What are equivalents for standard Q 235 B (and Q 235 A) for U-channels? (asked by: boris.vielhaber@vait.com) A: DIN Nr. = 2393 T.2, 2394 T.2, EN 10025 W. Nr. DIN 17007 = 1.0038 Design DIN 17006 = RSt 37-2, S235JRG2 (Fe 360 B) Q: What is St DIN 2391 BK material? (asked by: dmcandrews@automaticstamp.com) A: Precision steel tubes, cold-finished/hard. Q: What is C.D.W. Boiler Tube? (asked by: montydude123@yahoo.com) A: Cold Drawn Welded Boiler Tube. Q: WHAT IS W.Nr. 1.4301? PLS TELL US IN EASY LANGUAGUE (asked...
21 comments
Read more

Heat tint (temper) colours on stainless steel surfaces heated in air // Heat tint

By Materials & Welding
Introduction The colour formed when stainless steel is heated, either in a furnace application or in the heat affected zone of welds, is dependent on several factors that are related to the oxidation resistance of the steel. The heat tint or temper colour formed is caused by the progressive thickening of the surface oxide layer and so, as temperature is increased, the colours change.   Oxidation resistance of stainless steels However, there are several factors that affect the degree of colour change and so there is no a single table of colour and temperature that represents all cases. The colours formed can only be used as an indication of the temperature to which the steel has been heated. Factors affecting the heat tint colours formed Steel composition The chromium content is the most important single factor affecting oxidation resistance. The higher the chromium, the more heat resistant the steel and so the development of the heat tint colou...
Post a Comment
Read more