Set Value for Filed on Condition in MVC

Question

I have three Tables in SQL with following fileds

1) Order : [OrderID (pk)], [OrderSize], [Thickness], [OD] 

2) PipeAllocation : [PipeNo(PK)], [OrderID (fk)], [Length], [Status]

3) Process: [ProcessID (pk)], [PipeNo(fk)], [Date], [MPP]

 

for adding record in process table I want set value for MPP on criteria of Thickness  so I write following code but I got error of "Object reference not set to an instance of an object.". I dont have any null value in thickness field.

 

my code is 

[HttpPost]
       public ActionResult CreateP3(Process process)
       {
           var tr = process.StageID + process.PIPENO + process.Status;
           var checkme = (from x in db.Processes
                          where x.StageID + x.PIPENO + x.Status == tr && x.Status == "OK"
                          select x).ToList();
           if (checkme.Count > 0)
           {
               ModelState.AddModelError("PIPENO", "You are trying Duplicate Pipe Entry");
           }
           if (ModelState.IsValid)
           {

               if (process.PipeAl.Order.THK > 1)
               {
                   process.MPP = 10;
               }

               process.CuttingSpeed = (process.ActualMeter*1000)/process.CuttingTime;
               db.Processes.Add(process);
               db.SaveChanges();
               return RedirectToAction("IndexP3");
           }

           var EmpAtnList = db.Attens.ToList();
           IEnumerable<SelectListItem> AttnList = from s in EmpAtnList.OrderByDescending(s => s.ATTNDATE)
                                                  select new SelectListItem
                                                  {
                                                      Value = s.ATTNSYSID.ToString(),
                                                      Text = s.ATTNDATE + "--" + s.Emp.EmpName
                                                  };

           ViewBag.ATTNSYSID = new SelectList(AttnList, "Value", "Text");

           //ViewBag.ATTNSYSID = new SelectList(db.Attens, "ATTNSYSID", "EMPCODE", process.ATTNSYSID);
           ViewBag.StageID = new SelectList(db.OMStages, "StageID", "StageName");
           ViewBag.NextStageID = new SelectList(db.OMStages.OrderBy(x => x.StageValue), "StageID", "StageName");
           ViewBag.PIPENO = new SelectList(db.PipeAls, "PIPENO", "PIPENO");
           ViewBag.Status = new SelectList(db.ValueAddLists.Where(x => x.RefName == "PipeStatus"), "RefValue", "Description", process.Status);
           return View(process);
       }