hi i have a problem with S.S, 316L . As per ASME Sec VIII (elongation> 5% & lethal service ) we must heat treat(stress relive) the head%7Es of my vessels & heat exchanger%60s. 1-heat treat of S.S.316L can damage it? 2-what the temprature & rate & time of heating & cooling? 3-what the specification of furnace?is it special? thanx.

McroEng S.R of S.S. 316 L (if specified and needed from handling lethal service use) can be done. Heads can be separately stress relieved after forming . S.R Temp for Aus S.S 316 L will be at 860-880 deg cent . Heat @ 100 deg cent per hr, hold at 880 deg cent (as a thumb rule: 1 hr at S.R Temp per inch thickness) , slow cool from 880 deg cent or even rapid air cool. For Heat Exchanger : If the entire shell / tube and tube sheets are S.S. 316 L you can keep in a furnace at the above S.R temp (Avoid sulphur bearing (reducing atmosphere) fuel for S.R of Aus S.S 316 L or Nickel bearing materials. S bearing fuel or furnace oil should not be used as fuel in the furnace). If furnace is electrical heating then it is OK. After S.R do a pneumatic test between the tube and tube sheet joints to ensure no leak develop. You may have to ensure leak tight tube to tube sheet joints after S.R. If it is C.S shell and tubes / tube sheets are S.S. 316 L you have to be careful in S.R Temp. What is applicable S.R temp for S.S 316 L may not be applicable for a C.S shell material. This may creat problems if the entire tube bundle / shell is kept in a furnace. You may have to do only site S.R at 880 deg cent for the tube to tube sheet S.S 316 L joints by infra red heater pads to attain S.R temp of 880 deg cent. Trust this help you C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 16, 2006 E-mail: nishi@vsnl.com >hi >i have a problem with S.S, 316L . >As per ASME Sec VIII (elongation> 5% & lethal service ) >we must heat treat(stress relive) the head%7Es of my vessels & >heat exchanger%60s. >1-heat treat of S.S.316L can damage it? >2-what the temprature & rate & time of heating & cooling? >3-what the specification of furnace?is it special? >thanx.

MicroEng / Phong Code does not specify :S.R of Aus S.S is not to done routinely (as per ASME code it is not mandatory also except on specific cases of heavy cold or hot forming or from avoiding problems in specific process service corrosion related problems). In this case, MircoEng has already ordered or about to order formed heads and i believe he would like to know from the forum the temp, the known limitations if any, and approach to do the same . Micro Eng has specified that it will be used for lethal service. So he had asked a view whether S.R is needed and if so what is the best possible approach for S.R?. Before answering, i guess forum members would think about the role of sensitization in S.S materials. Forum members are doubtless aware that : Sensitization occurs for Aus S.S - not at 860-880 deg cent - but at 450-600 deg cent. This cannot be avoided totally, Its effect can be minimized to a large extent by choosing L grade or having stabilizing elements like Ti/Cb/Nb etc and also resort to rapid air or water quench in the temp range of 450-600 deg cent. Not all chromium carbides are harmful for the functioning of SS materials if carbide precitipation is minimum. To avoid this, most heat treaters and clients specify rapid air cool after holding at S.R or Mill anneal or solution anneal temperatures. S.R temp: 860-880 deg cent / Mill Anneal temp: 980-1000 deg cent / Solution Anneal temp : 1100-1140 deg cent. Sensitization will occur even with rapid quenching even from solution heat treated condtiion if enough rapid quenching is not done either in air or in water. You should also remember about the effect of warping on a formed head during quenching or during holding at temp of 1100 deg cent. Question that is to be answered is: Is the sensitized Chromium carbides will add to the problem in service? Not all chromium carbides will affect the material even if it is sensitized (which cannot be avoided either during rapid cooling from S.R Temp (880 deg cent) / Mill anneal temp (980-1000 deg cent) or from Solution annealed temp (1100-1140 deg cent) If forming stress (due to cold work or hot forming) is expected S.R and rapid air cool will be sufficient for most applications of formed heads or for tube to tube sheet joints. There is no need to do solution heat treatment at 1100-1140 deg cent (in my view). You have to take into consideration the effect of warping on a formed head from quenching from solution heat treated temp of 1140 deg cent. From effective way of doing at your country and the facilities available in the place where fabrication of the head is done , one can also choose to go to a well known Heat treating company or engage a consultant etc for doing the job. His basic question : Can S.R is possible? If so what is the limitation? That is answered. There is no need to do solution heat treat as suggesed by Scott or Phong - in my view. Trust this helps you to decide C.V.Srinivasan Nishi Engineers Pvt Ltd India Sept 17, 2006 E-mail: nishi@vsnl.com >You have two responses and two different answers, both of >which are correct. > >The first response is dealing with solution annealing or >reannealing cold worked parts, which I think you may be >talking about regarding your vessel heads. > >The second response to me sounds like stress relieving >austenitic stainless steel welds for service environment, >which there is a big debate on the benefit %E2%80“ stress >relieving vs. sensitization. > >The damage mechanism that you ask about in your question is >sensitization which is caused by stress relieving at the the >sensitizing temperature which is mentioned in the first >response. The second response has you stress relieving >within the senitizing range. > >Sensitizing happens when the carbon in the stainless steel >comes out of solution and ties up the chromium forming >chromium carbide which will reduce your corrosion >resistance. Using low grade stainless steel will help in >preventing the austenitic stainless steel form becoming >sensitized, however not guaranteed. > >Regarding the vessel heads - if you are not forming them >yourself you may want to specify that the heads come in the >annealed condition in your purchase order. Also as stated >earlier you should consult a heat treating company.